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Front Cover

A giant ejection of matter from the sun (blue color) as observed by the Solar Maximum Mission. Each
eruption ejects about one billion tons of matter into interplanetary space. These clouds of matter travel
at speed s of about three million kilometers per hour and cause global magnetic storms on Earth that
produce intense auroral displays over the poles. A typical aurora viewed from the Dynamics Explorer
satellite is shown in the larger inset to the left. Up to one hundred billion watts is deposited in the
upper atmosphere during such displays. The solar atmosphere is so hot (over a million degrees) that it
blows away from the sun as a steady wind at about a million kilometers per hour past all the known
planets. The presence of this wind was originally inferred from comet tails, which always point away
from the sun. The lower inset shows the first man-made comet, formed recently by a release of barium
from one of the Active Magnetosphere Particle Tracer Explorers spacecraft.

Back Cover

The trajectory of Solar Probe superimposed on a picture of the sun taken during an eclipse. The pearly-
white streamers are shaped by the sun's magnetic field and the solar wind and, in some eclipse
pictures, can be seen to distances of over 7 million kilometers from the sun. The red prominences
visible over the moon's shadow are cool gas condensations suspended in the corona, which is one
hundred times as hot. The Solar Probe spacecraft would explore the sun's vicinity for the first time and
approach to within about 2 million kilometers of the solar "surface." The time marks on the trajectory
show that the near-sun traversal would last for 10 hours, with the spacecraft traveling at a speed of
some 300 kilometers per second (over a million kilometers per hour) at closest approach. The probe
would intersect many of the closed and open magnetic field structures, as is evident in the picture. The
total flight time could be as short as 2.7 years, depending on available propulsion systems.

AN IMPLEMENTATION PLAN
FOR PRIORITIES IN
SOLAR-SYSTEM SPACE PHYSICS

Committee on Solar and Space Physics
Space Science Board

Commission on Physical Sciences, Mathematics,
and Resources

NATIONAL ACADEMY PRESS
Washington, D.C. 1985

NOTICE: The project that is the subject of this document was approved by the Governing Board of
the National Research Council, whose members are drawn from the councils of the National
Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The
members of the committee that cosponsored the workshop were chosen for their special compe-
tences and with regard for appropriate balance.

These proceedings contain papers presented at the workshop, which was arranged and con-
ducted by the sponsoring agency. The subject matter and content of the papers, as well as the
views expressed therein, are the sole responsibility of the authors. In the interest to timely
publication, the papers are presented as received from the authors, with a minimum of editorial
attention.

The National Research Council was established by the National Academy of Sciences in 1916 to
associate the broad community of science and technology with the Academy's purposes of further-
ing knowledge and of advising the federal government. The Council operates in accordance with
general policies determined by the Academy under the authority of its congressional charter of
1863, which establishes the Academy as a private, nonprofit, self governing membership corpora-
tion. The Council has become the principal operating agency of both the National Academy of
Sciences and the National Academy of Engineering in the conduct of their services to the govern-
ment, the public, and the scientific and engineering communities. It is administered jointly by
both Academies and the Institute of Medicine. The National Academy of Engineering and the
Institute of Medicine were established in 1964 and 1970, respectively, under the charter of the
National Academy of Sciences.

SPONSOR: This project was supported by Contract NASW 3482 between the National Academy of
Sciences and the National Aeronautics and Space Administration

Available from:

Space Science Board
National Academy of Sciences
Washington, D.C.

CONTENTS

FOREWORD vii

PREFACE ix

1 INTRODUCTION . 1

2 GUIDING PRINCIPLES 4

3 SCIENCE STATUS AND OBJECTIVES 5

Solar Physics . 5

Physics of the Heliosphere 5

Magnetospheric Physics 7

Upper-Atmospheric Physics 7

Solar-Terrestrial Coupling 10

Comparative Planetary Studies 10

4 IMPLEMENTATION STRATEGY . . . . , 11

Rationale 11

Program Mix in Solar and Space Physics 11

Resource Requirements for Recommended Programs 12

5 SUMMARY OF RECOMMENDED PROGRAMS 14

Introduction 14

Major Missions 16

Explorers 18

Spacelab/Space Station Payload Evolution 18

Suborbital Program 19

Theory and Computer Modeling 19

Mission Operations and Data Analysis 20

Research and Analysis 21

Technology Requirements and Instrument Development 21

6 SCIENCE HIGHLIGHTS AND ACCOMPLISHMENTS 22

Skylab 22

P78-1 22

Solar Maximum Mission 23

Orbiting Solar Observatory-8 23

Heliosphere Missions 23

International Sun-Earth Explorer 24

Dynamics Explorer 24

Shuttle/Spacelab — Space Plasma Physics 25

Planetary Magnetosphere/Atmosphere Missions 25

Atmosphere Explorers 26

Nimbus-7 26

Solar Mesosphere Explorer 27

Pioneer Venus 27

Theory Program ...... 28

7 DETAILED MISSION PLANS— SOLAR AND HELIOSPHERIC PHYSICS 29

Introduction 29

Program Descriptions 29

Priorities 37

iii

8 DETAILED MISSION PLANS— PLASMA PHYSICS 39

Introduction 39

Program Descriptions 39

Priorities 49

9 DETAILED MISSION PLANS— UPPER ATMOSPHERIC PHYSICS 51

Introduction , 51

Program Descriptions 51

Priorities 58

10 PERSPECTIVES 59

Introduction 59

Data Management 59

International Cooperation 59

Mission Costs 59

Facility Management and Operation 60

Computer Facilities and Modeling 60

Space Station 61

Planetary Exploration 61

11 ORGANIZATIONAL STRUCTURE 63

APPENDIX: LEVELS OF INVESTIGATION 65

IV

SPACE SCIENCE BOARD COMMITTEE ON
SOLAR AND SPACE PHYSICS

Stamatios M. Krimigis, Applied Physics Laboratory,

The Johns Hopkins University, Chairman
R. Grant Athay, High Altitude Observatory ^

Daniel Baker, Los Alamos National Laboratory ' '

Lennard A. Fisk, University of New Hampshire
Robert W. Fredricks, TRW —

John W. Harvey, Kitt Peak National Observatory
Jack R. Jokipii, University of Arizona /} X r ’

Margaret Kivelson, University of California, Los Angeles
Michael Mendillo, Boston University
Andrew F. Nagy, University of Michigan — ^ y
Marcia Neugebauer, Jet Propulsion Laboratory
Konstantinos Papadopoulos, University of Maryland
Susan Solomon, Aeronomy Laboratory, NOAA
Darrell F. Strobel, The Johns Hopkins University
George L. Withbroe, Center for Astrophysics

LIAISON REPRESENTATIVES

C.G. Flthammar, Royal Institute of Technology, Stockholm, Sweden
Melvyn L. Goldstein, NASA Goddard Space Flight Center
James Russell, III, NASA, Langley Research Center

EX-OFFICIO

Thomas M. Donahue, University of Michigan

Devrie S. Intriligator, Carmel Research Center

Robert M. MacQueen, National Center for Atmospheric Research

EXECUTIVE SECRETARY

Richard C. Hart

SPACE SCIENCE BOARD

THOMAS M. DONAHUE, University of Michigan, Chairman

DON L. ANDERSON, California Institute of Technology

RAYMOND E. ARVIDSON, Washington University

JACQUES M. BECKERS, University of Arizona

DANIEL B. BOTKIN, University of California

ANDREA K. DUPREE, Center for Astrophysics

FREEMAN J. DYSON, The Institute for Advanced Study

RICCARDO GIACCONI, Space Telescope Science Institute

JAY M. GOLDBERG, University of Chicago

DONALD M. HUNTEN, University of Arizona

STAMATIOS M. KRIMIGIS, The Johns Hopkins University

ROBERT M. MACQUEEN, National Center for Atmospheric Research

HAROLD MASURSKY, Center for Astrogeology

CARL E. McILWAIN, University of California, San Diego

BERNARD M. OLIVER, Hewlett-Packard Company

RONALD G. PRINN, Massachusetts Institute of Technology

J. WILLIAM SCHOPF, University of California, Los Angeles

EDWARD C. STONE, JR., California Institute of Technology

ANTHONY L. TURKEVICH, The University of Chicago

RAINER WEISS, Massachusetts Institute of Technology

GEORGE WETHERILL, Carnegie Institution of Washington

DEAN P. KASTEL, Staff Director

COMMISSION ON PHYSICAL SCIENCES,
MATHEMATICS. AND RESOURCES

HERBERT FRIEDMAN, National Research Council, Chairman

THOMAS BARROW, Standard Oil Company

ELKAN R. BLOUT, Harvard Medical School

BERNARD F. BURKE, Massachusetts Institute of Technology

GEORGE F, CARRIER, Harvard University

HERMAN CHERNOFF, Massachusetts Institute of Technology

CHARLES L. DRAKE, Dartmouth College

MILDRED S. DRESSELHAUS, Massachusetts Institute of Technology
JOSEPH L. FISHER, Office of the Governor, Commonwealth of Virginia
JAMES C. FLETCHER, University of Pittsburgh
WILLIAM A. FOWLER, California Institute of Technology
GERHART FRIEDLANDER, Brookhaven National Laboratory
EDWARD A. FRIEMAN, Science Applications, Inc.

EDWARD D. GOLDBERG, Scripps Institution of Oceanography
MARY L. GOOD, UOP, Inc.

THOMAS F. MALONE, Saint Joseph College
CHARLES J. MANKIN, Oklahoma Geological Survey
WALTER H. MUNK, University of California, San Diego
GEORGE E. PAKE, Xerox Research Center
ROBERT E. SIEVERS, University of Colorado

HOWARD E. SIMMONS, JR., E.I. du Pont de Nemours & Company, Inc.
ISADORE M. SINGER, Massachusetts Institute of Technology
JOHN D. SPENGLER, Harvard School of Public Health
HATTEN S. YODER, JR., Carnegie Institution of Washington

vi RAPHAEL G. KASPER, Executive Director

LAWRENCE E. McCRAY, Associate Executive Director

FOREWORD

For the last several years the Space Science Board has been developing strategies tor guiding
future research programs in the various scientific disciplines involved in space research. This
report, however, has a somewhat different character. While it does specify the scientific
objectives of the field (thereby updating the previous report, Soiar-Sysfem Space Physics in
the 1980's: A Research Strategy , NAS, 1980), it goes further and describes the plan for
implementing the objectives. In this sense, the report more closely follows the methodology of
two recent reports that have received wide acclaim for establishing priorities in related fields
of research. Astronomy and Astrophysics for the 1980's (NAS, 1982) and Planetary Exploration
Through Year 2000 (NASA, 1983),

The Space Science Board (SSB) adopted this different approach for this report for two
reasons. First, with the appearance of the astronomy and planetary priorities reports, a need
was established to do something similar in solar and space physics. Secondly, with NASA
currently involved in preparing a priorities report for the Earth Sciences, it was decided that
the SSB could provide a valuable service for this broad-based effort by undertaking a part of
the subject matter for which the Board was admirably suited through the Committee on Solar
and Space Physics (CSSP). NASA concurred in this decision.

Thus, in November 1983, the Board directed the CSSP to develop a priorities-based study of
solar and space physics, using the 1980 Research Strategy as a basis. The Committee
produced the following report, which was reviewed and approved by the Board in November
1984.

Thomas M. Donahue
Chairman, Space Science Board

PREFACE

In carrying out the charge of the Space Science Board, stated above, the Committee on Solar
and Space Physics (CSSP) proceeded by organizing three separate panels as follows: solar
and heliospheric physics under George L. Withbroe; magnetospheric plasma physics under
Robert W. Fredericks; and upper atmosphere physics under Darrell F. Strobel. Each panel
was asked to solicit inputs from the scientific community in each discipline area on what
constitutes the highest priority science and the optimum means for carrying it out.

The resulting sets of science objectives and programmatic priorities, along with estimated
costs, were organized on a timeline from FY 86 through the year 2000 by each panel. The full
committee examined critically the work of the panels and, after several iterations, a compos-
ite Implementation Plan was agreed upon. This preliminary plan was presented by committee
members to several scientific groups beginning in the spring of 1984; during these sessions
comments and suggestions were solicited. The inputs thus received were considered by the
committee, and a draft version of the report was circulated to over 70 colleagues representing
most institutions active in the field of solar and space physics. Comments and suggestions
were received from about half, and the committee redrafted the document in October 1984 for
presentation to the SSB's November meeting for approval. This extensive interaction with the
community has produced a prioritized Implementation Plan that is supported by most mem-
bers of the scientific disciplines involved.

Our report is published in two parts, the Executive Summary and the main body. The
Executive Summary presents the prioritized program, summaries of the scientific objectives
and recommended missions, near-term budget decisions, and connections to basic physics,
astrophysics, and earth system studies. This part is intended to quickly familiarize the reader
with the substance of the science being addressed and the essential conclusions and recom-
mendations of this study. Although it can stand alone, it should be read in conjunction with
the main body.

The main body of the report describes the detailed science objectives for future research,
the most significant accomplishments of the past research, the way in which the Implementa-
tion Plan was constructed, the detailed mission plans of each of the major sub-disciplines of
solar and space physics research, and some additional thoughts on the general health and
conduct of our science.

An undertaking of this magnitude required the assistance of many individuals and institu-
tions, too numerous to mention. We owe special thanks to Marshall Space Flight Center for
hosting one of our meetings, to Goddard Space Flight Center and the let Propulsion Labora-
tory for assistance on cost estimates for some projects, and, most importantly, NASA Head-
quarters for providing the background information necessary for putting together the Imple-
mentation Plan. We are grateful to Drs. J.D. Bohlin and S.D. Shawhan of NASA who
participated in some of our meetings and provided important information whenever needed.
Dr. T.M. Donahue, Chairman of the SSB, gave us important guidance in the formulation of
this plan. Many of our colleagues commented on several drafts of this document. We are
especially grateful to Dr. DJ. Williams for assistance in the selection and placing of figures
included in this report. The work of Mrs. Carmela Chamberlain and Mrs. Pat Johnson in
typing the innumerable drafts of this report is most appreciated, as is the work of Mrs.
Angelika Peck, who did the design and layout for the Executive Summary. Pinally, we are
grateful to our Executive Secretary, Dr. Richard C. Hart, whose untiring efforts and advice
were invaluable to the completion of this report.

S.M. Krimigis, Chairman
Committee on Solar and Space Physics

preceding page blank not filmed

IX

1 INTRODUCTION

Man's wonder at the manifold phenomena
in the environment and the drive to under-
stand and use them have led to modem sci-
ence. To understand the relationship be-
tween natural events on the Earth and
changes in the Sun has been one of man's
lasting intellectual quests. The scientific
discipline we now know as solar system
space physics is the modern culmination of
efforts to comprehend the relationships
among a broad range of naturally-occurring
physical effects including solar phenomena,
terrestrial magnetism, and the aurora. Un-
derstanding the solutions to these basic
physics problems requires the study of ion-
ized gases (plasmas), magnetohydrodynam-
ics, and particle physics.

Space physics as an identifiable disci-
pline began with the launch of the first
Earth satellites in the late 1950s and the
discovery in 1958 of the Van Allen radiation
belts. The phenomena associated with this
field of study are among the earliest re-
corded observations in many parts of the
world The ancient Greeks were puzzled by
"fire" in the upper atmosphere that we now
call the aurora; there are several possible
references to the aurora in ancient Chinese
writings before 2000 B.C.; there are also
passages in the first chapter of Ezekiel with
vivid descriptions of what we now recognize
as auroral formations.

The observation of sunspots by Galileo in
1610 led to the eighteenth century discovery
of the 11 -year solar sunspot cycle and the
recognition that there was a connection be-
tween sunspot variability and auroral activ-
ity. The large reduction of sunspots during
the second half of the seventeenth century
during a period of unusually cool weather
in Europe suggests a tantalizing connection
between some aspects of solar activity and
climate.

This possible link between solar activity
and terrestrial phenomena could not be
studied in detail until this century. We now
know that, in addition to the atmosphere
that surrounds us, there exists a region, at
higher altitudes, consisting of an electri-

cally conducting plasma permeated by the
Earth's magnetic field. It is called the "mag-
netosphere" because its structure and many
of its processes are controlled by the mag-
netic field. Since the early years of the
space program, we have learned that the
Sun has its own magnetosphere consisting
of a hot (million-degree Kelvin) magnetized
plasma wind (the solar wind) that extends
beyond the orbits of the planets and fills
interplanetary space, forming a distinct cav-
ity in the nearby interstellar medium — the
"heliosphere."

Using knowledge gained over the past 25
years, we can now begin to identify some of
the physical mechanisms linking the Sun to
our near-Earth environment. For example,
motions in the convective layers of the Sun
are believed to generate the solar magnetic
field and solar wind variations; these in
turn affect the Earth's magnetosphere and
regulate the amount of plasma energy inci-
dent on the Earth's polar caps. Associated
magnetospheric activity drives strong winds
in the upper atmosphere and may influence
the dynamical and chemical composition of
the mesosphere and stratosphere as well.
The upper atmosphere, in turn, is the major
source of heavy ions in the magnetosphere.
Further, current research suggests that
small percentage changes (about 0.5 per-
cent) in the total energy output of the Sun
(the solar "constant") may influence short-
term terrestrial climate. These and other
speculative suggestions should be ad-
dressed as part of a comprehensive re-
search program in solar-terrestrial physics
because of their potential importance for the
Earth. Indeed, the Earth and its space envi-
ronment contain coupled phenomena and
need to be studied as a system — from the
Sun and its plasma environment to the
Earth's magnetosphere, atmosphere,
oceans, and biota.

Discoveries in solar and space physics
over the past 25 years have inspired a num-
ber of developments in theoretical plasma
physics. Concepts in charged particle trans-
port theory, developed to describe the be-

1

havior of energetic particles in the solar
wind and magnetosphere, are routinely
used in studying extragalactic radio sources
and laboratory plasmas. Magnetic field re-
connection (involving the explosive conver-
sion of electromagnetic energy into particle
energy), collisionless shock waves, electro-
static shocks, and hydromagnetic turbu-
lence are also among the fundamental
plasma phenomena first studied and eluci-
dated in analysis of solar and space plas-
mas.

Subsequently, these and other concepts
have found application to related branches
of plasma physics, such as nuclear fusion.
The development of space plasma physics
since the 1960s has influenced nuclear fu-
sion research. Pitch-angle scattering and
magnetic reconnection are now tools of lab-
oratory plasma theory, while ideas devel-
oped in fusion work have influenced space
plasma science in important ways. Thus,
the language of plasma physics links two
very important scientific endeav ors: the
search for a limitless supply of clean energy
through thermonuclear fusion and the explo-
ration and understanding of our solar sys-
tem environment, most of which is in the
plasma state.

New concepts developed in studies of so-
lar and space plasmas find important appli-
cations to astrophysical problems as well as
to laboratory plasmas. For example, the
structure of collisionless shock waves can
be resolved only by spacecraft instruments.
Such shocks are invoked in some current
models of star formation. Furthermore, the
study of propagating interplanetary shocks
has contributed to understanding and mod-
eling of acceleration of cosmic rays by
shocks. Particle acceleration via direct elec-
tric fields, observed in the Earth's magne-
tosphere, has been invoked in acceleration
models of pulsar magnetospheres. The sub-
ject of cosmic-ray transport owes much to
detailed in situ studies of the solar wind.
Some stellar winds are thought to be associ-
ated with stars that, like the Sun, have con-
vective outer layers, while winds of more
massive stars are driven by radiation pres-
sure. Explanations of physical phenomena
in astrophysical objects that will remain for-
ever inaccessible to direct observation rest
heavily on insights obtained through stud-
ies of solar system plasmas accessible to in
situ observations.

Even though space plasma physics is a
mature subject, new observations continue
to reveal facets of the physics not recog-
nized previously. For example, observations
of "spokes" in Saturn's rings seemed to
highlight the importance of electromagnetic
forces on charged dust particles. Similarly,
the interaction of dust and plasma in com-
ets is thought to be a central element in
understanding the formation of comet ion
tails. Such observations have given rise to
the study of "gravito-electrodynamics" in
dusty plasmas, which in turn has important
applications to the understanding of the for-
mation and evolution of the solar system, as
pointed out by Alfven some years ago.

The understanding of the near-Earth
space environment is not only a basic re-
search enterprise; it also has extremely im-
portant practical aspects. Space is being
used increasingly for many different scien-
tific, commercial, and national security pur-
poses. Well-known examples include com-
munications and surveillance satellites and
such scientific platforms as the Space Tele-
scope and the Space Station. These space
vehicles must function continuously in the
near-Earth environment, subject to the dy-
namic variations of the heliosphere, the
magnetosphere, and the upper atmosphere.
It is well-established that many spacecraft
systems and subsystems exhibit anomalies,
or even failures, under the influence of
magnetospheric substorms, geomagnetic
storms, and solar flares. Processes such as
spacecraft charging and "single-event up-
sets" (owing to highly ionizing energetic
particles) in processor memories make the
day-to-day operation of space systems diffi-
cult. Finally, these aspects of the near-Earth
environment become particularly important
in view of the planned long-term presence
of man in space. The complement of pro-
grams outlined in this report will allow us
to model the global geospace environment
and will thus allow us to develop a global
predictive capability. This, in turn, should
permit substantial improvements in our
abilities to operate all space-based systems
in the near-Earth region.

We have advanced well beyond the ex-
ploratory stages in solar and space physics,
with some notable exceptions — the solar in-
terior, the environment near the Sun where
the solar wind is accelerated, the atmos-
pheres of some of the planets, and the

boundary of the heliosphere. The phenome-
nological approach appropriate to a young
science still in its discovery phase has pro-
gressed to a more mature approach where
focussed and quantitative investigations are
made, where interactive regimes are stud-
ied, and where theory and modeling play a
central role in advancing understanding.

The future solar and space physics pro-
gram will require tools and techniques sub-
stantially different from those of the past.
Continued progress will require develop-
ment of complex, multifaceted, experimen-
tal and observational projects that will be
technologically challenging. We believe
that the anticipated scientific contributions
fully justify the proposed undertakings.

The purpose of this report is to develop an
overall program of space research that will
address the most significant scientific prob-
lems, that will clearly define the priority of
investigations, and that will be affordable
by NASA.

Several other reports that are related to
this document have appeared in recent
years. The Colgate report ( Space Plasma
Physics: The Study of Solar-System Plasmas ,
NAS, 1978) reviewed the status of the field
and concluded that "space plasma physics

is intrinsically an important branch of sci-
ence." The Kennel report (Solar-System
Space Physics in the 1980's: A Research
Strategy , NAS, 1980) laid out the scientific
goals and objectives for the field. Other re-
ports ( Solar-Terrestrial Research in the
1980's, NAS, 1981; National Solar-Terrestrial
Research Program, NAP, 1984) integrated the
ground-based segment of the field and
stated priorities for its implementation. The
Physics of the Sun (NAP, 1985) reviewed the
scientific content of solar physics and de-
scribed future research directions. A Strat-
egy for the Explorer Program for Solar and
Space Physics (NAP, 1984) emphasized the
need for a revitalized Explorer program for
solar and space physics and outlined sev-
eral specific examples of scientific investi-
gations.

In addition, two other recent reports have
developed prioritized programs in related
sciences: astronomy, Astronomy and Astro-
physics for the 1980's (NAP, 1982); and plane-
tary science, Planetary Exploration Through
Year 2000 (NASA, 1983). Our report is similar
to these in that it is intended to develop the
implementation plan for NASA's solar and
space physics program that will accomplish
the aims of our scientific strategy.

2 GUIDING PRINCIPLES

The scientific goals established by the Ken-
nel report remain the guiding force of this
science. The two principles that served as
the foundation for the design of the strategy
remain extant:

* 'The objectives of solar-system space re-
search are to understand the physics of the
Sun, the heliosphere, and the magnetos-

pheres, ionospheres, and upper atmos-
pheres of the Earth, other planets, and com-
ets.

• Studies of the interactive processes that
generate solar radiation and link it to the
Earth should be emphasized, because they
reveal basic physical mechanisms and have
useful applications . . .

4

3 SCIENCE STATUS AND OBJECTIVES

The following summary of the status of the
subject and the scientific objectives are
adapted from the Kennel report (Solar-Sys-
tem Space Physics in the 1980's: A Research
Strategy , NAS, 1980) with appropriate
changes and updates.

Solar Physics

Major advances in our understanding of the
Sun were made in the 1970s and the early
1980s (see Figure 1). Most, if not all, of the
magnetic flux that emerges from the convec-
tive zone is subsequently compressed into
small regions of strong field (1200-2000 G), a
process that is still not understood theoreti-
cally. Observations confirmed earlier pre-
dictions that the 5-minute photospheric os-
cillation, discovered in the early 1960s, is a
global phenomenon. This discovery has
made "helio-seismology" possible, by which
the depth of the convective zone and the
rotation below the photosphere have been
inferred. In addition, by ruling out the clas-
sical model of coronal heating by acoustic
waves, observations from the ground and
from OSO-8 raised anew the question of
what maintains the corona's high tempera-
ture. Coronal holes were among the major
discoveries of the 1970s. White-light, EUV,
and x-ray observations suggested how co-
ronal holes are related to the convective
zone and to the solar wind. Sky lab observa-
tions unambiguously identified magnetic
arches as the basic structure of coronal
flares. This perception altered our theoreti-
cal picture of solar flares and clarified the
need for a coordinated multi-instrument at-
tack, which was initiated with the Solar
Maximum Mission (SMM).

To better understand all the processes
linking the solar interior to the corona, we
need to study (see Figure IB) the following:

• the Suns global circulation, how it re-
flects interior dynamics, is linked to lumi-
nosity modifications, and is related to the
solar cycle;

* the interactions of solar plasma with
strong magnetic fields — active regions, sun-
spots, and fine-scale magnetic knots — and

how solar-flare energy is released to the he-
liosphere; and

• the energy sources and composition of
the solar atmosphere and corona and the
physics of the Sun s large-scale weak mag-
netic field.

Physics of the Heliosphere

The Sun is the only stellar exosphere where
complex phenomena common to all stars
can be studied in situ. Observations of the
Sun and the heliosphere, the plasma enve-
lope of the Sun extending from the corona to
the interstellar medium, provide the basis
for interpreting a variety of phenomena
ranging from x-ray and gamma-ray radia-
tion to cyclical activity and long-term evolu-
tion, The Sun, together with the heliosphere
and planetary magnetospheres and atmos-
pheres, comprises an immense laboratory
that exhibits complex magnetohydrodynami-
cal (MHD) and plasma physical phenomena
whose study enhances our understanding of
basic physical laws as well as our under-
standing of the influences of the Sun on our
terrestrial environment.

The solar wind has been studied near the
Earth since 1961, At the present time, meas-
urements of the solar wind have been ex-
tended to within Mercury's orbit (0.3 AU) and
past Pluto's orbit but have been confined to
near the ecliptic plane. Quantitative models
of high-speed solar-wind streams and flare-
produced shocks have been developed and
tested against data obtained near the eclip-
tic. The realization that high-speed streams
originate in the rapidly diverging magnetic-
flux tubes of coronal holes has reoriented
much solar wind research. The sector struc-
ture of the solar wind has been unambigu-
ously related to a magnetic neutral sheet of
solar-system scale that connects to the
large-scale magnetic field of the rotating
Sun. Finally, microscopic plasma processes
have been shown to regulate solar wind
thermal conduction and diffusion and, pos-
sibly, local acceleration of particles in solar
wind structures.

To understand better the transport of en-

5

A SOLAR PHYSICS-RECENT ACCOMPLISHMENTS

IMPORTANCE OF
MAGNETIC FIELC

ELEMENTAL AND ISO-
DIFFERENTIATION

IDENTIFICATION OF
SOLAR FLARE GEOMETRY

ORONAL HOLES

CORONAL HEATING

HELIOSEISMOLOGY

B SOLAR PHYSICS-OBJECTIVES

How Do Global Circulation
and Surface Oscillations
Reflect fnter : ~~ ^

What Are th
Corona's En
Sources?

How Does S
Interact witn oirong
Magnetic Fields? How Is
Solar Flare Energy
Released?

How Is Solar
Wind Generated?

: Is the Physics of
the Large Scale Weak
Magnetic Field?

C SOLAR PHYSICS-REQUIRED MEASUREMENTS

HIGH RESU tu I IVIM \U. I f
SHUTTLE OBSERVATIONS
OF ACTIVE REGIONS,
SMALL SCALE FIELDS
AND FLARES

SUREMENTS
. PLASMA
IEAR SOLAR
AL SURFACE

3. SURVEY OBSERVATIONS OF
SURFACE OSCILLATIONS,

LARGE SCALE MAGNETIC
FIELD, LUMINOSITY VARIATION

FIGURE 1 Solar physics: status, objectives, and recommendations. In this series
of sketches of the Sun and its coronal magnetic field we illustrate some recent
accomplishments in solar physics (A), questions that can be fruitfully attacked in
the 1980s and 1990s (B), and the principal research programs needed to answer
these questions (C), Shown here is the Sun and solar corona within 5 solar radii.
The influence of the processes occurring within this region extends throughout
interplanetary space via the solar wind.

6

ergy, momentum, energetic particles,
plasma, and magnetic fields through inter-
planetary space, we need to study the fol-
lowing:

• first and foremost, the solar processes
that govern the generation, structure, and
variability of the solar wind;

• the three-dimensional properties of the
solar wind and heliosphere; and

• the plasma processes that regulate the
transport and acceleration of energetic par-
ticles throughout the heliosphere.

Magnetospheric Physics

New processes regulating Earth's magnetic
interactions with the solar wind were dis-
covered in the 1970s and early 1980s (see
Figure 2A). For example, unsteady plasma
flows that apparently originate deep in the
geomagnetic tail and deposit their energy in
the inner magnetosphere and polar atmos-
phere were observed. Observations of im-
pulsive energetic particle acceleration sug-
gested that the cross-tail electric field is
also highly unsteady. The discovery of ener-
getic ionospheric ions in the near tail and
inner magnetosphere forced a reevaluation
of our ideas concerning the origin and circu-
lation of magnetospheric plasma.

Our understanding of many individual
processes became more quantitative. The
coupling of magnetospheric motions and en-
ergy fluxes to the thermosphere was ob-
served and modeled. Currents flowing
along the Earth's magnetic field and con-
necting the polar ionosphere to the magne-
tosphere were found to create strong local-
ized electric fields at high altitudes. These
fields may accelerate the electrons responsi-
ble for intense terrestrial radio bursts and
auroral arcs. Thus, the problem of auroral
particle acceleration is nearing quantitative
understanding. By contrast, the relationship
between energy circulating in the magne-
tosphere, the energy dissipated in the at-
mosphere, and the concurrent state of the
solar wind has not been unambiguously
quantified even today.

To understand better the time-dependent
interaction between the solar wind and
Earth we need to study the following (see
Figure 2B):

• the transport of energy, momentum,
plasma, and magnetic and electric fields

across the magnetopause, through the mag-
netosphere and ionosphere and into or out
of the upper atmosphere;

• the storage and release of energy in the
earth's magnetic tail;

• the origin and fate of the plasma(s)
within the magnetosphere; and

• how the Earth's magnetosphere, iono-
sphere, and atmosphere interact.

Upper-Atmospheric Physics

The upper atmosphere has traditionally
been divided into the stratosphere, mesos-
phere, thermosphere (and ionosphere), and
exosphere, in order of increasing altitude.
Recent research makes it clear that these
layers and their chemistry, dynamics, and
transport are coupled (see Figure 3A). For
example, downward transport from the ther-
mosphere can provide a source of nitrogen
compounds to the mesosphere and possibly
to the upper stratosphere. The catalytic re-
actions of odd hydrogen, nitrogen, and chlo-
rine compounds destroy ozone, thereby al-
tering the absorption of solar ultraviolet
radiation. Results from three Atmospheric
Explorers (AE), which largely quantified the
photochemistry of the thermosphere and
ionosphere, also illustrated the strength of
the electrodynamic coupling of the thermos-
phere to the magnetosphere. Finally, under-
standing how the upper and lower atmos-
pheres affect each other will be necessary
to complete the description of the chain of
solar-terrestrial interactions. This will re-
quire considerable improvement in our un-
derstanding of the chemistry, dynamics,
and radiation balance of the mesosphere
and stratosphere, as well as of troposphere-
stratosphere exchange processes.

To understand fully the entire upper at-
mosphere and its interaction with the sun
and the magnetosphere, we should study
the following (see Figure 3C):

• the radiant energy balance, chemistry,
and dynamics of the mesosphere and strato-
sphere and their interactions with atmos-
pheric regions above and below;

• the worldwide effects of the magnetos-
phere's interaction with the polar thermos-
phere and mesosphere and the role of elec-
tric fields in the earth's atmosphere and
space environment; and

• the effects of variable photon and ener-

A MAGNETOSPHERIC PHYSICS-RECENT ACCOMPLISHMENTS

ELECTRIC FIELDS
ACCELERATING
AURORAL PARTICLES .
DISCOVERY OF ENERGETIC /

IONS OF IONOSPHERIC ORIGIN
IN MAGNETOSPHERE. ^

magnetopause

Moon ^ '

MODELLING OF
THERMOSPHERIC
WIND GENERATION

3-0 shocked solar wind

UNSTEADY PLASMA FLOWS,

ELECTRIC FIELDS AND '° n/ es s '

PARTICLE ACCELERATION IN
GEOMAGNETIC TAIL

MAGNETOSPHERIC PHYSICS^OBJECTIVES

What is Origin and Fate of ^ -

Magnetospheric Plasmas?

How Does Solar
Wind Couple to
Magnetosphere?

>0

magnetopause

How is Energy Stored
and Released in
Magnetic Tail?

j \ shocked solar wind

How Does Magnetosphere co7/>>

Couple with Atmosphere '° n/ es^-^.

and Ionosphere?

SIX CRITICAL REGIONS OF MAGNETOSPHERIC PHYSICS

ON THE
GROUND

AURORAL FIELD
LINES/

magnetopause

SO LAR
WIND

DEEP IN

GEOMAGNETIC

TAIL

>t> shocked solar wind

MIDMAGNETOSPHERE
EQUATORIAL PLANE

IN THE POLAR °°ck

UPPER ATMOSPHERE

FIGURE 2 Magnetospheric physics: status, objectives, and recommendations. Shown here is the Earth's
magnetosphere — the cavity formed by the interaction of the solar wind with the Earth's magnetic field.

A collisionless bow shock stands upstream of the magnetopause, the boundary separating shocked solar
wind from the magnetosphere proper. The Moon is 60 Earth radii from the Earth; the Earth's magnetic
tail is thought to extend some thousand Earth radii downstream. A illustrates some recent achievements
in magnetospheric physics; B, objectives that can motivate research programs in the 1980s and 1990s. C
illustrates the six critical regions where simultaneous studies are needed to help construct a global
picture of magnetospheric dynamics.

A UPPER ATMOSPHERIC PHYSICS-RECENT ACCOMPLISHMENTS

GENERAL REALIZATION
OF IMPORTANT COUPLINGS
BETWEEN LAYERS AND
THEIR CHEMISTRY,
DYNAMICS AND TRANSPORT

IMPORTANCE OF

ELECTRODYNAMIC

COUPLING

Sola* uK*av<o*ef

pooions Magnetosphere pa*lu . IPs

ATMOSPHERE EXPLORERS
QUANTIFIED THERMOSPHERE
PHOTOCHEMISTRY ABOVE
1 30 km

f *S.

B UPPER ATMOSPHERIC PHYSICS-OBJECTIVES

How Do Variable Photon
and Particle Fluxes
Affect the Thermosphere,
Mesosphere, and Stratosphere?

How Do Energetics, Chemistry,
and Dynamics Interact to
Establish the Structure and
Variability of the Middle
Atmosphere?

Sola* jl'avtota*
pfxrtons

Magnetosphere parities

What Are the World-Wide
Effects of the

Magnetosphere's Interaction
with the Upper Atmosphere?

electric winds

UPPER ATMOSPHERIC PHYSICS-REQUIRED MEASUREMENTS

A SERIES OF SPACE OBSERVATIONS
mesosphere and stratosphere

SELECTED HIGH RESOLUTION
OBSERVATIONS FROM
FREE FLYERS, PLATFORMS,
AND SHUTTLE

Solar utravioM

photons Magnetosphere policies

MONITOR SOLAR LUMINOSITY
AND SPECTRAL IRRADIANCE,

LONG WAVE RADIATION, CHEMICAL
COMPOSITION, DYNAMICS, AND
ENERGETIC PARTICLE INPUT

/ *$, %

FIGURE 3 Upper-atmospheric physics: status, objectives, and recommendations. Sketched in
these figures are the layers into which the atmosphere has traditionally been divided. Our studies
of these layers, and the interacting processes occurring within them, are becoming more inte-
grated. Solar ultraviolet photons deposit their energy largely in the stratosphere and above. The
magnetosphere interacts with the upper atmosphere both through energetic plasma deposition and
through electric fields, which are generated by magnetospheric motions. Plasma heating and
electric fields both couple to upper-atmosphere winds.

getic particle fluxes on the thermosphere
and on chemically active minor constituents
of the mesosphere and stratosphere.

Solar-Terrestrial Coupling

Solar-terrestrial coupling is concerned with
the interaction of the Sun, the solar wind,
the Earth's magnetosphere, ionosphere, and
atmosphere with particular emphasis on the
response of the system to solar variability.
For example, a solar flare produces both a
strong solar-wind shock, which initiates a
magnetic storm when it passes over the
magnetosphere, and energetic protons that
penetrate deep into the polar atmosphere.
Studies of such solar-terrestrial phenomena
can be of considerable practical importance.

To understand better the effects of the so-
lar cycle, solar activity, and solar-wind dis-
turbances upon Earth, we need to

• provide to the extent possible simultane-
ous measurements on many links in the
chain of interactions coupling solar pertur-
bations to their terrestrial response; and

• create and test increasingly comprehen-
sive quantitative models of these processes.

Whereas 10 years ago it was generally
believed that significant effects of solar var-
iability penetrate only as far as the upper
atmosphere, some scientists now believe
that they also reach the lower atmosphere
and so affect weather and climate in ways
not yet completely understood. For example,
it has recently been suggested that the
mean annual temperature in the north tem-
perate zone has followed long-term varia-
tions of solar activity over the past 70 centu-
ries.

To clarify the possible solar-terrestrial in-
fluence on Earth's weather and climate, we
need to

• determine if variations in solar luminos-
ity and spectral irradiance sufficient to mod-
ify weather and climate exist and under-
stand the solar physics that controls these
variations; and

• ascertain whether any processes involv-
ing solar and magnetospheric variability
can cause measurable changes in the
Earth's lower atmosphere.

Comparative Planetary Studies

Comparative studies of the interaction of
the solar wind with planets and comets
highlight the physics pertinent to each and
put solar-terrestrial interactions in a
broader scientific context. The solar system
has a variety of magnetospheres sufficient
to make their comparative study fruitful. Be-
cause the planets and their satellites have
different masses, magnetic fields, rotation
periods, surface properties, and atmos-
pheric chemistry, dynamics, and transport,
comparative atmospheric and magnetos-
pheric studies can help us to understand
these processes in general and possibly to
identify terrestrial processes that might
otherwise be missed.

In the 1970s, Pioneer and Voyager space-
craft made flyby studies of Jupiter's atmos-
phere and magnetosphere, the largest and
most energetic in the solar system. Pioneer
11 and the Voyagers encountered Saturn in
1979, 1980, and 1981. Mariner 10 flybys dis-
covered an unexpected, highly active mag-
netosphere at Mercury. Pioneer Venus re-
sults suggest that the strong interaction
between the solar wind and Venus' upper
atmosphere plays a significant role in the
evolution of its atmosphere.

To understand better the interactions of
the solar wind with solar-system bodies
other than Earth, and to learn from their
diversity about astrophysical magnetos-
pheres in general, we need to

• investigate in situ Mars' solar-wind in-
teraction in order to fill an important gap in
comparative magnetosphere and upper-at-
mosphere studies — previous missions pro-
vided little such information;

• make the first in situ measurements of
the plasma, magnetic fields, and neutral
gases near a comet;

• increase our understanding of rapidly
rotating magnetospheres involving strong
atmospheric and satellite interactions; and

• determine the role of atmospheres in
substorms and other magnetospheric proc-
esses by orbital studies of Mercury — the
only known magnetized planet without an
atmosphere.

4 IMPLEMENTATION STRATEGY

Rationale

The status of solar and space physics, its
science objectives, and the associated
measurement objectives presented in the
previous chapter have remained largely un-
changed since they were first published in
the Kennel report (NAS, 1980). Although sig-
nificant progress has been attained in some
areas [ionosphere-magnetosphere coupling
following the launch of the Dynamics Ex-
plorer (DE) satellites in 1981; active experi-
ments in the solar wind with the recent
launch of the Active Magnetospheric Parti-
cle Tracer Explorer (AMPTE)], most of these
objectives have remained unfulfilled.

As is evident from the preceding chapter,
the scientific content of solar and space
physics is broad, involving several impor-
tant regions within the solar system — the
Sun, heliosphere, and the terrestrial magne-
tosphere, ionosphere, and upper atmos-
phere and the complex interactions among
them, solar-terrestrial relations. To advance
our understanding in each of these subjects
and the chain of interactions among them, a
broad scientific attack is necessary, which
translates into a major thrust in each of the
central disciplines (i.e. solar/space, plasma,
and atmospheric physics). In the near term
these thrusts are embodied in major space
missions — the Solar Optical Telescope (SOT)
and the Upper Atmosphere Research Satel-
lite (UARS), already approved, and the Inter-
national Solar Terrestrial Physics Program
(ISTP), currently a new start candidate.
These programs together with the base pro-
gram (research and analysis, mission opera-
tions and data analysis, shuttle science,
theory, etc.) result in a level of funding of
about $400M/yr.*

The important scientific measurement ob-
jectives that have been outlined in the pre-
vious chapter could add up to a level sub-
stantially higher than $400M/yr in the long

The funding for solar and space physics in 1964 was
$527M/yr (in FY 85 dollars); funding for the decade 1964-
1974 averaged $377M/yr (in FY 85 dollars).

term. Thus, it was the task of the Committee
to establish priorities and to select among
the many exciting scientific programs that
have been identified, by ordering the se-
quence of mission implementation within an
envelope of about $400M/yr (in FY 85 dol-
lars). The proposed implementation plan
contains only those scientific programs that
address the highest priority objectives. They
are arranged in such a sequence that most
would be accomplished before the year
2000. In the process, several programs con-
sidered of lesser importance have been de-
ferred (e.g.. Heliosphere Boundary Probe),
while even those of high scientific priority
have had to be scheduled for implementa-
tion at a time later than that dictated by
either the maturity of the subject or the tech-
nological readiness of the proposed meas-
urements [e.g., Solar Terrestrial Observa-
tory (STO)]. In all but two of the programs
[the Solar Probe and Solar Polar Orbiter
(SPO)] the technology for implementation is
already at hand. Thus, the budget ceiling
was the determining factor throughout the
strategy.

Program Mix in Solar and Space
Physics

The diversity of environments represented
within the discipline of solar and space
physics demands a broad mix of programs
to implement the stated science objectives.
There is a need for major missions for de-
tailed studies on a global scale, as well as
for exploration of previously unexamined re
gions (e.g., the environment near the Sun);
for moderate missions (Explorer-class) to at-
tack specific, detailed problems; for quick
response techniques such as balloons, rock-
ets (Spartans), and experiments of opportu-
nity best accommodated on the Shuttle; and
for facility-class instruments that are devel-
oped for Shuttle use but that will evolve
towards space platforms that can best be
accommodated as part of the Space Station
concept.

FUNDS REQUIRED FOR SOLAR AND SPACE PHYSICS

FIGURE 4

Resource Requirements for The MO&DA budget pays for the opera-

Recommended Programs tion of missions after launch [currently Inter-

planetary Monitoring Platform (IMP)-8; Inter-
The science priorities outlined in the pre- national Sun-Earth Explorer (ISEE) 1, 2, and

vious chapter and the rationale in program- 3; Solar Maximum Mission (SMM); Solar Me-

matic considerations given above have re- sosphere Explorer (SME); DE; and AMPTE],

suited in an implementation plan with including science team support and data

resource requirements over the next 15 analysis while the data are proprietary to

years as shown in Figure 4. The total is the the selected teams (roughly, one year after

sum of three separate budgetary require- acquisition). The budget for development of

ments: resources for research and analysis flight projects supports approved projects

(R&A), for mission operations and data anal- through launch and currently includes Inter-

ysis (MO&DA), and for development of flight national Solar Polar Mission (ISPM), Corn-

projects. The R&A budget supports a spec- bined Release and Radiation Effects Satel-

trum of activity including balloons and rock- Iite (CRRES), Tethered Satellite System
ets, laboratory experiments, analysis and (TSS), UARS and SOT, and Shuttle instru-

interpretation of data from prior spacecraft mentation under various programs,

missions, and the Solar-Terrestrial Theory In the budget projections presented in Fig-

Program (STTP). The R&A budget addition- ure 4 the Committee has sought to achieve

ally includes the resources to plan future a responsible and attainable funding plan

missions through the pre-project definition that can be implemented within the funding

stage and to undertake early development ceiling outlined previously. This program

of instrumentation for such missions. envisions the launch of the recommended

12

missions before the end of this century. The
level of funding for specific programs is pri-
marily based on NASA projections for each
of the programs, where such exist, and on
informal consultation between the Commit-
tee and officials at NASA centers (princi-
pally Goddard Space Flight Center, Mar-
shall Space Flight Center, and Jet
Propulsion Laboratory) for those programs
where such funding levels have not as yet
been formalized.

The funding timeline incorporates those
programs already approved in FY 85, antici-
pates implementation of Phase 1 of the ISTP
program in FY 86, and foresees utilizing Ex-
plorer program funding for solar and space
physics following the completion of the cur-
rent set of payloads by FY 88. The incorpo-
ration of the Explorer program into the fund-
ing timeline is in accordance with the
recent SSB report. A Strategy for the Ex-
plorer Program for Solar and Space Physics
(NAP, 1984).

In the area of Space Shuttle instrumenta-
tion, the currently approved program [Space-
lab (SL) 1 and 2, Space Plasma Lab (SPL),
Earth Observation Missions (EOM), and Sun-
lab] stays at a constant funding level
launched by the year 2000.

In the area of Space Shuttle instrumenta-
tion, the currently approved program (Spa-
celab (SL) 1 and 2, Space Plasma Lab (SPL),
Earth Observation Missions (EOM), and Sun-
lab) stays at a constant funding level
through the early 1990s. In the late 1980s,
facility-class instruments will be developed,
which have been studied previously as part
of the Solar Terrestrial Observatory (STO)
and the Advanced Solar Observatory (ASO).
The instruments will eventually be assem-
bled onto science platforms, which are in-
tended to become part of the Space Station

in the mid-1990s. The budget timeline also
specifically includes MO&DA funds for the
Space Station activity, in recognition of the
high cost likely to be involved in operating
such facilities.

The solar and space physics programs in
Figure 4 are currently managed by several
divisions within NASA, including Astrophys-
ics, Earth Science and Applications, Shuttle
Payload Engineering, and Solar System Ex-
ploration. The Committee has specifically
excluded from these budget projections the
significant funds that need to be allocated
for experiment payloads on planetary
spacecraft that are recommended for studies
of the magnetospheres and upper atmos-
pheres of the planets. These funds have tra-
ditionally been included as part of the over-
all budget of the specific planetary
missions. The budget also does not include
specific funds to accommodate possible
flights of opportunity that are not currently
identified, such as programs of other federal
agencies (DOD, NOAA, etc.) or programs
arising from international initiatives. A re-
cent example of such a worthwhile opportu-
nity was U.S. instrumentation on the Giotto
spacecraft that was accommodated by the
overall flexibility of the OSSA budget.

The Committee feels that the program en-
visioned in this report is scientifically chal-
lenging, technologically achievable, and re-
flects the maturity of a field that was the
space research program when the nation in-
itially ventured into space. The implementa-
tion plan outlined in Figure 4, by attempting
to achieve a constant yearly funding level
and distributing the new starts over a num-
ber of years, makes it possible for NASA to
strive once again for leadership in solar and
space physics research.

5 SUMMARY OF RECOMMENDED PROGRAMS

Introduction

In this Chapter we briefly summarize the
scientific objectives that were discussed in
detail in Chapter 3. These objectives are to
be achieved through a sequence of research
programs in solar and space physics. We
also summarize the descriptions of these
programs that are discussed in more detail
in Chapters 7, 8, and 9. The primary meas-
urement objectives to be addressed between
now and 2000 include the following:

Solar Heliosphere Physics

• High-resolution observations are needed
to advance understanding of active regions
and the small-scale velocity and magnetic
fields important to chromospheric and co-
ronal energy balance, as well as solar
flares. These require space-borne instru-
ments that achieve 0.1 arcsec resolution in
the spectral range from the infrared to H
Lyman alpha and less than 0.5 arcsec reso-
lution from the extreme ultraviolet to hard X
rays.

• Remote sensing and in situ measure-
ments are needed to provide qualitatively
new information critical to understanding
coronal plasma processes and solar-wind
generation. These require optical instru-
ments that can make spectroscopic meas-
urements out to 5 or more solar radii and a
solar flyby or probe that penetrates as close
to the sun as possible (4 solar radii seems
technically feasible). In addition, measure-
ments of the heliosphere at high helio-
graphic latitudes are required.

• Space observations lasting a significant
portion of the next solar cycle are needed to
infer solar interior dynamics from large-
scale motions and oscillations at the Sun's
surface; to study transient events; to study
(through observations, theory, and model-
ing) such fundamental problems as mag-
netic reconnection, particle acceleration,
and magnetohydrodynamic (MHD) turbu-
lence; to observe the large-scale magnetic
and plasma structures instrumental in cou-

pling energy to the solar wind; and to moni-
tor solar luminosity. (It may ultimately be-
come necessary in the decades following
the 1980s to monitor the effects of solar vari-
ability on luminosity over several solar
cycles.)

Terrestrial Magnetospheric Physics

To advance quantitative understanding of
the time-dependent exchange of energy and
plasma between the solar wind and magne-
tosphere requires measurements of physical
processes in at least six regions simultane-
ously: (1) deep in the Earth's magnetic tail,
(2) in the solar wind upstream of Earth, (3)
near the mid-magnetosphere equatorial
plane, (4) at high altitudes above one polar
cap, (5) from the ground, and (6) at low alti-
tude in polar orbit. (Measurement of this
last area is needed to indicate the dynami-
cal and chemical response of the atmos-
phere to magnetospheric variability.)

This global research program should be
supplemented with an increased level of
support of theory and computer modeling
efforts directed toward understanding mag-
netic reconnection, boundary layer phenom-
ena, and other related problems in magne-
tospheric physics. In addition, active
experiments should be flown that can in-
crease our knowledge of magnetospheric
and plasma processes.

Terrestrial Upper-Atmospheric Physics

A series of space observations is needed to
advance understanding of the interacting
dynamical, chemical, and radiative proc-
esses in the stratosphere, mesosphere, and
thermosphere. The first in this series is the
UARS spacecraft which will provide an al-
most global data set on the chemistry, dy-
namics, and energy input of the middle at-
mosphere to understand basic atmospheric
properties and processes. Thereafter solar-
terrestrial processes should be addressed by
remote sensing of the chemical, dynamical.

14

and thermal response of the mesosphere
and lower thermosphere to solar and mag-
netospheric perturbations. Continuing up-
per-atmospheric observations throughout
the 1990s are needed to provide good solar-
cycle coverage. Complementary high-resolu-
tion studies should be made using Shuttle
facilities.

Evolution of Shuttle Science

It is essential to maintain a strong program
for the development and flight of Shuttle-
class instruments in solar, atmospheric, and
magnetospheric physics. Continued prog-
ress in solar-terrestrial physics requires in-
novative new measurements. The Shuttle
provides cm excellent platform for the flight
of many types of solar-terrestrial instru-
ments and acquisition of short duration (up
to a week or more) measurements of specific
phenomena. Shuttle experiments can in-
clude both in situ and remote observations
of natural phenomena and diagnostics of
active perturbations of the plasma medium
with chemicals, waves and electron or ener-
getic plasma beams.

Ultimately Shuttle instruments can be
used on the Space Station, which combines
the greatest advantages of the Shuttle and
smaller spacecraft, namely high resolution
and long duration.

Theory, Computer Modeling, and
Information Handling

The ultimate goals of the solar and space
physics scientific missions are the resolu-
tion of outstanding scientific questions and
the creation of reliable predictive models of
the solar-terrestrial environment. Critical to
achieving these goals is conversion of the
observations into scientific understanding
through a strong theoretical and computer
modeling program. This process leads to the
resolution of outstanding questions and the
formulation of new ones, which in their turn
lead to the formulation of new missions; it
also leads to the gradual building of relia-
ble, predictive, cause and effect models of
the solar-terrestrial environment. A strong
theoretical and computer modeling program
is a cornerstone for successful solar and

space physics research. Moreover, theory
and quantitative modeling can guide the
entire information chain (data acquisition,
reduction, dissemination, correlation, stor-
age, and retrieval) to a higher level of so-
phistication, so that data can be made
available in a form compatible with the
needs of scientific interpretation.

Coordinated Research

Coordinated research is an essential feature
of solar and space physics, which is con-
cerned with time-variable phenomena span-
ning several regions of space and relying
on several scientific disciplines for interpre-
tation.

The research programs proposed above
are justifiable on their individual merits.
Coordinating them through the ISTP can
greatly increase our understanding of the
solar-terrestrial interaction. Examples of
such coordinated research include the fol-
lowing.

(a) Detailed examination of the three-di-
mensional structure of the Sun's large-scale
magnetic field is made possible by in-eclip-
tic coronal observations that are simultane-
ous with those from the International Solar
Polar Mission (ISPM) spacecraft.

(b) Simultaneous in-ecliptic and ISPM
measurements of the solar wind and cosmic
rays can provide important information
about the large-scale structure of solar-wind
disturbances. These in-ecliptic measure-
ments can be provided by the interplanetary
element (WIND spacecraft) of the global
magnetospheric study proposed above.

(c) As we noted earlier, simultaneous
measurements in the polar upper atmos-
phere and the magnetosphere can provide
new quantitative insight into how solar-
wind perturbations couple to upper-atmos-
pheric winds and chemistry.

The NASA research proposed here pro-
vides a foundation for coordination of re-
search sponsored by other agencies of the
United States government and possibly for-
eign nations. For example, coordination
with other agencies is critical to provide the
ground-based observations recommended
above. We urge that NASA play a prominent
role in developing and coordinating a joint
program as rapidly as possible.

Planetary Research

Since we do not understand other planets as
well as Earth, studies of each individual
planet must continue to be important for the
foreseeable future. Nonetheless, to increase
the impact on space physics we should seek
comparative understanding of the interac-
tion of the Sun and solar wind with planets
and comets. Comparative studies highlight
the physics pertinent to each planet and put
that of Earth in a broad scientific context.
Since many members of the space physics
community also work actively in planetary
research, advances in one area are rapidly
communicated and applied to the other, so
that comparative studies will naturally
emerge provided that planning and data
analysis in each are coordinated. Therefore,
measurements of plasmas, fields, and ener-
getic particles must remain integral parts of
each planetary mission.

Major Missions

Solar and Heliosphere Physics

The Solar Optical Telescope

The first approved facility-class instrument
under development in the Spacelab program
is the Solar Optical Telescope (SOT). SOT
consists of a 1.25-m aperture telescope with
0.1-arcsec resolution, which will provide
sufficient resolution to observe levels in the
solar atmosphere ranging from the photos-
phere through the transition region. The
critical problems to be studied include
plasma-magnetic field interactions related
to the solar dynamo and studies of energy
transport in the solar atmosphere.

SOT will be flown as an attached Shuttle
payload at intervals of 1 to 2 years starting
in 1990, The program is expected to evolve
with the addition of increasingly versatile
focal-plane instrumentation and other com-
plementary experiments. Eventually, SOT
would form the basis for an advanced solar
observatory on a space station platform.

Solar Probe

The Solar Probe is a mission to study the
unexplored region between about 4 and 60
solar radii from the Sun. The basic scientific

goal is to explore the solar atmosphere
where the solar wind becomes supersonic.
The mission should carry a complement of
particle and field instruments to measure
density, velocity, and composition of the
thermal solar wind plasma, as well as the
magnetic fields, plasma waves, and ener-
getic particles present in this unexplored re-
gion of the heliosphere.

Solar Polar Orbiter

The study of the three-dimensional proper-
ties of the heliosphere will require observa-
tions more detailed than those that will be
obtained by the ISPM, the first exploratory
mission to high solar latitudes. A Solar Po-
lar Orbiter (SPO) in near circular orbit about
the solar poles, at heliocentric distance less
than or equal to 1 AU, will be able to distin-
guish latitude from radial variations and,
since it will make several polar passes, to
distinguish spatial from temporal effects.
SPO should cany a full complement of
plasma, energetic particle, magnetic field,
and radio wave instruments, similar to
those flown on ISPM, and should have
pointing capability for detailed solar and
coronal observations. The mission will re-
quire the development of low-thrust, contin-
uous acceleration propulsion. Mission de-
sign for SPO should be undertaken in the
mid-1990s, following a thorough analysis of
the results of ISPM; launch should occur by
the year 2000.

Plasma Physics

International Solar-Terrestrial Physics
Program

The International Solar-Terrestrial Physics
Program (ISTP) is being planned together by
the U.S. NASA, the Japanese Institute of
Space and Astronautical Science (ISAS), and
the European Space Agency (ESA) as a co-
operative effort with launches beginning in
1989 and with operations continuing into the
mid-1990s. The overall scientific objectives
of ISTP are to develop a comprehensive,
global understanding of the generation and
flow of energy from the Sun, through the
interplanetary medium and into the Earth's
space environment (geospace), and to define
the cause-and-effect relationships between
the physical processes that link different re-
gions of this dynamic environment.

ISTP will provide complementary meas-
urements for several other spacecraft, Shut-
tle/Spacelab missions, sub-orbital and
ground-based investigations that are being
conducted in the same time interval. Plans
include coordinated operations and data in-
terpretation with at least the ISPM, the Jap-
anese Exospheric Satellite-D (EXOS-D), the
Upper Atmosphere Research Satellite
(UARS), Shuttle/Space Plasma Lab, and
Shuttle/Sunlab.

Six spacecraft missions are being planned
for ISTP; spacecraft characteristics are de-
scribed as follows:

WIND, provided by NASA, will have seven in-
struments to measure the solar wind magnetic
field, plasma, plasma wave, and energetic parti-
cle characteristics; the orbit is a double lunar
swingby with excursions of 250 R E into the up-
stream solar wind.

GEOTAIL, provided by ISAS, will have seven in-
struments to measure the magnetic and electric
fields, the plasma energy and composition, and
the plasma waves in various regions of the geo-
tail; the orbit initially is to be a double lunar
swingby out to 250 R E in the geotail, to decrease
to 8 R e x 20 R e in the equatorial plane.

POLAR, provided by NASA, will have eleven in-
struments to make comprehensive in situ meas-
urements of the plasma, fields, energy, composi-
tion, and waves with the added capability to
image the Earth at x-ray, ultraviolet and visible
wavelengths from a polar orbit of 1.5 R E x 8.5 R E .
EQUATOR, provided by NASA, will carry nine
instruments to fully characterize the plasma,
fields, energy, composition, and waves in the
equatorial region at an orbit of 2 R E x 12 R E .
SOHO, provided by ESA with nine telescopic in-
struments to measure the solar surface and solar
corona over a wide range of wavelengths and
five solar wind instruments to measure fields,
plasma characteristics, and plasma wave emis-
sions, will be stationed at the L, Lagrangian
point and will be three-axis stabilized.

CLUSTER, provided by ESA, will include four Ex-
plorer-class spacecraft, each with about six in-
struments to carry out spatially separated (100
km - 20,000 km) measurements of magnetic
fields, plasma waves, energetic and thermal par-
ticle distributions, and plasma composition in an
effort to explore turbulent boundary-layer phe-
nomena in the magnetosphere and magnetohy-
drodynamic turbulence in the solar wind. The
orbit is polar, 3 R E x 20 R E .

The first four spacecraft make up the ele-
ments of the first ISTP phase with launches
planned for 1989-1991 called the Global
Geospace Study (GGS). GGS will focus on

the global flow of energy from the solar
wind through the magnetosphere to the ion-
osphere and into the atmosphere. The proc-
esses by which different parts of the geos-
pace environment interact are highly
variable with time, often changing in re-
sponse to fluctuations in the characteristics
of the solar wind on the time scale of tens of
minutes. Thus, the key to success for GGS
is in making simultaneous measurements in
the four regions in which these four space-
craft orbit.

The two ESA spacecraft systems (CLUS-
TER and SOHO) are planned for launch in
1992-1993. Each system makes a unique con-
tribution to the overall science program.
CLUSTER consists of four spacecraft with
adjustable separations designed to make
cross-correlative measurements of plasma
characteristics and processes within the vol-
ume defined by the four spacecraft set.
These measurements provide information on
the nature of the microscopic plasma proc-
esses that occur near boundary layers in the
magnetosphere. The use of 4 spacecraft will
enable the separation of spatial and tem-
poral effects. When in the solar wind, the
spatial resolution made possible by the four
spacecraft will significantly enhance stud-
ies of MHD turbulence.

SOHO performs three types of measure-
ments: observations of global oscillations to
deduce information about the solar interior,
the solar corona including both long-term
variations and transient features of the so-
lar corona through both imagery and spec-
troscopy, and in situ solar wind characteris-
tics. SOHO provides the relation between
solar variations and resulting phenomena in
the solar wind and observed in the magne-
tosphere with the GGS spacecraft.

An essential element of the ISTP program
is a coordinated data analysis and archival
system that will facilitate effective interac-
tion by the participating community of in-
vestigators who will interpret the ISTP and
associated data bases.

The collaborative ISTP Program will bring
a broad international science community to-
gether with enhanced opportunities for sci-
entific accomplishments through an inte-
grated attack on the problems of solar-
terrestrial relations, magnetospheric phys-
ics, space plasma physics, and solar phys-
ics.

Upper-Atmosphere Physics

The highest priority in observatory-class
missions for the 1980's has been UARS, now
a new start in FY 85. UARS is the spacecraft
recommended in the Kennel report and will
provide for the first time an almost global
data set on the chemistry, dynamics, and
energy inputs of the 10-70 km region of the
atmosphere, i.e., the stratosphere and lower
mesosphere. The goals of the UARS pro-
gram are to understand the mechanisms
controlling middle atmospheric structure
and processes and to understand the re-
sponse of the upper atmosphere to natural
and human perturbations. The UARS data
will be critical elements in evaluating the
extent of ozone depletion caused by human
activities and the role of upper atmosphere
processes in climate change. The instru-
ment payload has been carefully selected to
meet the goal of coordinated and comple-
mentary global measurements of ozone,
temperature, pressure, energy input, winds,
and chemical trace species by remote sens-
ing. The UARS program includes theoretical
studies and model analysis as an integral
part of the program to complement the
measurements and data analysis.

Explorers

Explorers have played a crucial role in the
development of solar and space physics re-
search, and we see their role continuing in
the future. The primary role of Explorer mis-
sions is to attack well-defined scientific
problems of high current interest in a timely
fashion. Explorers may also be used produc-
tively in conjunction with the global pro-
grams required by solar and space physics
research, as identified in "Major Missions"
above.

The basic strategy for use of the Explorer
program in solar and space physics is con-
tained in a recent NAS report (A Strategy for
the Explorer Program for Solar and Space
Physics, NAS, 1984). The recommendations
of that report are as follows:

1. The size, complexity, and management
of future Explorer missions should return to
the originally perceived philosophy of the
Explorer program (i.e., relatively small, sim-
ple satellites) and should be designed to

address focused problems in a timely man-
ner.

2. Scientific opportunities for solar and
space physics research merit an average of
approximately one Explorer satellite oppor-
tunity a year in the future. If an average of
one launch per year is not feasible with
current funding, the Explorer budget should
be augmented.

3. An Announcement of Opportunity (AO)
mechanism and selection process should be
used to identify approximately twice the
number of solar and space physics Explor-
ers that can be expected to be flown in the
time interval between AOs. Further, the se-
lection process should be conducted in two
stages in order to reduce the amount of time
and effort expended by the science commu-
nity. The first stage would be a selection for
definition studies, the second stage a selec-
tion for development.

These recommendations have been incor-
porated in the funding timeline shown in
Figure 4, with a flight frequency of about
one launch per year, to be shared as appro-
priate by solar/heliospheric, magnetos-
pheric, and upper atmosphere missions.

Spacelab/Space Station Payload
Evolution

Initial utilization of the Space Shuttle in
1982-1985 for solar and space plasma phys-
ics investigations is through the OSS-1, Spa-
celab-1, and Spacelab-2 missions. Missions
to follow in the 1986-1990 interval include
Sunlab, Space Plasma Lab, Tether, and
SOT. Instruments and investigation tech-
niques developed for these Shuttle missions
form the basis for two solar and space phys-
ics facilities on the Space Station — the Ad-
vanced Solar Observatory (ASO) and the So-
lar-Terrestrial Observatory (STO).

The early Shuttle/Spacelab missions will
carry solar instruments to measure the total
solar irradiance variation on short and long
time scales and instruments to measure the
emission spectra, the magnetic field config-
uration, and the spatial patterns of solar
active regions. These and additional instru-
ments are to be re-flown in a series of Sun-
lab missions. Derivatives of these instru-
ments will be developed to become part of
the ASO.

The early Shuttle/Spacelab space plasma
missions have emphasized active space
plasma experiments utilizing electron beam
and energetic plasma sources. These
sources perturb the plasma in the immedi-
ate vicinity of the orbiter as well as along
magnetic field lines leading to optical emis-
sions, energetic particles, and electrostatic
waves. The perturbations are observed re-
motely with optical telescopes, spectrome-
ters, and wave receivers as well as in situ
through plasma diagnostics packages.

These plasma perturbation and diagnostics
instruments will become part of the Space
Plasma Lab instrumentation which will
have, in addition, a VLF and HF wave gen-
eration system. In the Space Station time
frame, the Space Plasma Lab instruments
should become part of the STO for the con-
duct of active experiments and for monitor-
ing the Space Station plasma environment.
The STO is also to include instruments for
viewing the Sun and the Earth's atmosphere
to provide cause-and-effect measurements
of the Sun-Earth interactions as well as
measurements of the chemistry, dynamics,
and energies of the middle and upper at-
mosphere.

In 1987 the Tether Satellite System (TSS)
will be initiated to tether a diagnostic satel-
lite 20 km above the Shuttle. With a con-
ducting tether, the system can be utilized to
excite long- wavelength, low-frequency
waves, create controlled plasma wakes and
alter the electrodynamics of the ionospheric
medium. With a non-conducting downward
tether, it becomes possible to drag an at-
mospheric satellite at 130 km altitude — a re-
gion previously inaccessible on a global
scale. The TSS will be implemented on the
Space Station to extend the investigation
periods.

SOT is designed to measure 0. 1-arcsec
scale features of the solar surface in the
visible light range to investigate small
scale convective patterns. After the maiden
flight in about 1990, the SOT will be outfit-
ted with co-observing instruments in the x-
ray and extreme ultraviolet wavelength
ranges to examine the range of processes
on the 0. 1-arcsec spatial scale. The SOT and
its co-observing instruments will become
the core of the ASO on the Space Station.
Also, a Pinhole Occulter Facility (POF) will
be added so that hard x rays produced by

energetic electrons accelerated in solar
flares and other transient phenomena can
be imaged on the sub-arcsec scale and so
that the solar corona can be imaged and
analyzed over a wide wavelength range.
Eventually, instruments can be added to the
ASO to measure the variability in solar irra-
diance, solar energetic particles, and
gamma ray emissions.

Suborbital Program

Suborbital programs employing balloons,
rockets, and aircraft provide an important
and, in some cases, unique platform for cer-
tain scientific investigations. For example,
the effects of solar cosmic rays on atmos-
pheric composition represent a form of so-
lar-terrestrial coupling that can be most di-
rectly observed in situ using rockets and
balloons. Such observations would include
simultaneous in situ measurements of the
high energy particle and bremsstrahlung
spectra of NO x , 0 3 , and other related minor
constituents. Similarly, determination of the
ion composition of the ionosphere below
about 120 km can probably be most effec-
tively performed with in situ instruments.

Suborbital platforms are also valuable in
the development and testing of future
spacecraft instrumentation in a relatively
inexpensive and timely fashion, can serve
to provide "ground truth" for atmospheric re-
mote sensing measurements, and often can
provide data on much finer spatial and tem-
poral scales than those presently achieva-
ble by remote sensors.

Rocketborne payloads also offer frequent
and flexible flight opportunities for the in-
creased quantities of "active experiments"
in atmospheric science. Experiments that re-
quire waiting for appropriate geophysical
conditions cannot be easily accommodated
using Spartan- or Shuttle-type orbiting pay-
loads. An additional aspect of the suborbi-
tal program is the important opportunities it
offers to graduate training by providing
complete formulation to data analysis expe-
rience in space science programs.

Theory and Computer Modeling

The disciplines in solar and space physics
are seeking quantitative understanding of

the relevant physical processes. The inter-
play between theory and experiment, cou-
pled with the tool of computer simulations,
is proving invaluable in advancing this un-
derstanding. Theory provides the mecha-
nisms for unifying laboratory, space, and
astrophysical plasma physics.

The Colgate report ( Space Plasma Physics:
The Study of Solar System Plasmas, NAS,
1978) identified the need for adequate theo-
retical studies in solar and space plasma
physics. In response, NASA established in
1980 the Solar Terrestrial Theory Program
(STTP) to fund " 'critical mass” theoretical
groups in the major discipline areas and to
provide stable career opportunities to
younger theoreticians. The STTP has been
highly successful; groups have been estab-
lished that are providing major new insights
into critical problems such as reconnection,
collisionless shock structure, particle accel-
eration, and radio emission processes. The
STTP is now contributing to basic laboratory
plasma physics and to a better understand-
ing and interpretation of numerous space
data sets. A summary of much of this re-
search is described in Solar-Terrestrial Phys-
ics — Present and Future, ed. D. Butler and
K. Papadopoulos, 1984, which also includes
descriptions of theoretical research spon-
sored by NSF and NASA under other pro-
grams.

Funding for STTP is currently at $3.3 mil-
lion in FY 85. Substantial increases in this
program would provide growth opportuni-
ties for established groups and allow for
new entries. A level of about $6 million (in
FY 85 dollars) to be achieved by FY 90 will
provide the appropriate balance between
theory and the experimental program.

NASA has also recognized the need for
theoretical groups to participate in a princi-
pal investigator (PI) role in NASA missions.
This offers the possibility of establishing
closer quantitative links between mission
planning, data analysis, and theoretical
and computational modeling than has here-
tofore been possible. DE, UARS, ISTP, and
Combined Release and Radiation Effects
Satellite (CRRES) are examples with theoret-
ical PI participation. We recommend that
the policy of theoretical PI team participa-
tion be continued in solar and space phys-
ics and in planetary investigations.

Although many theoretical problems in

solar and space physics can be addressed
with currently available computers, many
problems (especially related to solar dynam-
ics, MHD turbulence, and ISTP related is-
sues) will require availability of supercom-
puters, supported by high data rate
telephone or microwave links to research-
ers, as well as enhancements of local com-
puter processing facilities. A firm NASA
commitment to advanced computer facilities
dedicated to atmospheric and plasma phys-
ics modeling is of critical importance. We
concur with the recommendation in the
Physics Survey Report for a National Com-
putational Program that proposes a large-
scale theoretical modeling and simulation
effort for basic plasma physics, space phys-
ics, and astrophysics.

Mission Operations and Data
Analysis

The MO&DA program is vitally important to
NASA's space research mission. It is
through this program that the scientific re-
turn from space experiments is finally real-
ized; MO&DA funding supports the experi-
ment operations, provides (sometimes) for
extended missions, and is responsible for
the processing and analysis of the data.

Currently operating spacecraft are a na-
tional resource and frequently provide
unique opportunities for gathering scientific
information. For example, Interplanetary
Monitoring Platform-8 (IMP-8) is the only
spacecraft that can provide information on
solar wind parameters at the present time.
The Pioneer Venus Orbiter has been provid-
ing unique and invaluable information on
the solar wind-ionosphere-atmosphere inter-
action processes; its continuously rising per-
iapsis is allowing measurements to be
made in new and unexplored regions of the
Venus plasma environment. The Interna-
tional Comet Explorer (ICE) mission will ex-
plore a comet tail for the first time in Sep-
tember, 1985, and provide essential
measurements of solar wind parameters up-
stream from Halley during its perihelion
passage in 1986. Furthermore, the deep
space missions of Pioneers 10 and 11 and
Voyagers 1 and 2 provide the only means of
studying the global properties of the helios-
phere at large distances from the Sun. Thus,

it is important for NASA to continue MO&DA
funding for existing spacecraft and for
"cruise mode" measurements by planetary
spacecraft.

Historically, NASA has not adequately
funded its MO&DA needs. Since MO&DA is
a critical element of all NASA's science pro-
grams, care must be taken to ensure that it
not be neglected as large programs occupy
increasing attention and funding commit-
ments.

In Chapters 7, 8, and 9 of this report, ex-
amples of MO&DA needs are specified and
recommendations for increased funding are
made.

Research and Analysis

A strong research and analysis program is
the essential foundation for the entire sci-
ence program. Its vital elements include the
following:

1. the theory and analysis essential for
assessing the state of the field, for combin-
ing and interpreting the results of the var-
ious flight projects into a self-consistent
body of physical knowledge, for transfer of
new results to and from the fields of labora-
tory plasmas and astrophysics, and for
planning future research;

2. development of instruments for future
flight projects;

3. correlative observations that enhance
the scientific return from the space flight
projects; and

4. supporting or complementary research
performed in laboratories or with suborbital
flight programs.

Another important function of the R&A
program is to provide the long-term stability
required to maintain the scientific capabil-
ity of research groups through the lean
years between major flight projects.

In Chapters 7, 8, and 9 of this report, we
review the R&A programs in each of the
main disciplines of solar and space physics,

and we recommend areas within the R&A
program where increased funding is re-
quired.

Technology Requirements and
Instrument Development

All of the missions recommended for the
1980s and most of the missions recom-
mended for the 1990s can be implemented
with existing spacecraft technology. The ex-
ceptions are the requirement for a low-abla-
tion heat shield for the Solar Probe and ad-
vanced propulsion (probably solar-electric
powered ion thrusters) for the SPO. If it
were available in time, advanced propul-
sion could also be used to enhance the So-
lar Probe mission by achieving a shorter
period solar orbit. We recommend that
NASA proceed with these developments to
meet the planned new start dates of 1991
and 1997 for the Solar Probe and the SPO,
respectively.

The development of scientific instruments
is now and should continue to be a high-
priority effort. Major emphasis should be
placed on the development of (1) Pi-class
and facility instruments for solar observa-
tions, leading ultimately to the ASO; (2) im-
aging instruments to remotely sense the hot
plasma processes in the magnetosphere;
and (3) post-UARS instruments for detection
of a greater number of chemical species in
the upper atmosphere, particularly impor-
tant free radicals such as OH and H0 2
along with ozone, solar irradiance, and tem-
perature. For all the missions later in our
implementation plan, many instruments
should be enhanced by taking advantage of
new technologies such as better detector ar-
rays, cryogenic systems for sensor cooling,
microprocessors, data storage devices, and
software to process and compress data on
board the spacecraft. Chapters 7, 8, and 9
specify the technology requirements for
each of our main disciplines.

6 SCIENCE HIGHLIGHTS AND ACCOMPLISHMENTS

This Chapter is a brief review of some of
the most significant scientific accomplish-
ments of several past research programs.

We include it in this report to demonstrate
the important contributions to our under-
standing of the Earth's environment and the
basic physical processes of the universe
that have resulted from research activity in
this area.

Skylab

Skylab, with its battery of solar telescopes
in the Apollo Telescope Mount, was
launched in May 1973 and was operated by
three crews until February 1974. Eight in-
struments, including two x-ray telescopes,
an EUV spectroheliograph, a uv spectrohe-
liometer, a uv spectrograph, a visible-light
coronagraph, and H-alpha telescopes, stud-
ied the Sun over the wavelength range 2-
7000 A. Principal scientific results included
the following:

• recognition of the highly inhomogenous
structure of the corona and the close corre-
lation between coronal radiation and mag-
netic field structure, finding that over most
of the surface the elemental structures are
magnetic arches or loops connecting regions
of opposite magnetic polarity (This along
with the Skylab observations of coronal
holes revolutionized our concepts about the
structure of stellar coronae.);

• confirmation that coronal holes are
sources of recurrent high-speed solar wind
streams, resolving a long-standing problem
on the solar origin of these streams and
leading to major revisions in models of the
solar wind at its coronal source;

• discovery of transient mass ejections
from the corona at an unexpected high rate
and an unexpected large scale, significantly
revising concepts about the role of transient
phenomena in the energetics and evolution
of the corona;

• discovery of hot, x-ray emitting mag-
netic loops associated with flares and the
discovery that a substantial fraction (often
greater than 50 percent) of the energy asso-

ciated with large flares is carried away
from the Sun by coronal mass ejections —
observations that led to improved knowl-
edge of the energetics of flares and the rela-
tionships between the diverse phenomena
observed during flares;

• discovery of nearly random spatial dis-
tribution of coronal x-ray bright points iden-
tified with small magnetic bipoles and the
discovery of rapid temporal variations in the
emission from these features, providing in-
sights concerning the emergence of mag-
netic flux from below the surface and the
role of magnetic field dissipation in heating
the coronal plasma; and

• discovery of rapid, large amplitude fluc-
tuations in solar extreme ultraviolet (EUV)
flux, but without evidence for an expected
periodic component, providing evidence that
the corona is not heated by periodic waves
as predicted in some theoretical models.

P78-1

The P78-1 spacecraft is part of the DOD
Space Test Program and was launched by
the Air Force on 24 February 1979. The satel-
lite was built with assistance from NASA,
which provided the stabilization and solar
pointing control systems and other flight
space components from NASA's seventh Or-
biting Solar Observatory (OSO). Solar in-
strumentation includes a white-light corona-
graph, soft x-ray Bragg crystal
spectrometers, and hard x-ray proportional
counters. Some scientific results are as fol-
lows:

• first observation of earth-directed co-
ronal transients, i.e. f "halo” transients,
demonstrating that at least some transients
are bubble, rather loop-like, in shape;

• the accumulation of a data base for
outer coronal activity that extends from 1979
until September 1985, producing many sta-
tistical results, e.g., on average two coronal
mass ejections occurred per day during the
years 1979-1981 near sunspot maximum;

• the discovery that greater than 75 per-
cent of the interplanetary shocks observed

22

by the Helios spacecraft originated with co-
ronal mass ejections;

• the discovery of four sungrazing comets,
none of which were seen after perhelion,
implying either destruction by the solar at-
mosphere, or actual impact into the photos-
phere;

• the first accurate determination of the
temperature of the bulk of the soft x-ray
emitting thermal flare plasma;

• the discovery that 300-500 km s 1 upflows
at temperatures of about 15 x 10 6 K are a
common occurrence during the rise phase of
large solar flares;

• the first systematic study of the time be-
havior of random mass motions in soft x-ray
flare plasmas; and

• the discovery of high density (— 10 12 cm 3 )
coronal plasma (- 2 x 10 6 K) of very small
volume (~ 10 9 km 3 ), produced coincident
with the hard x-ray flare impulsive compo-
nent.

Solar Maximum Mission

The Solar Maximum Mission (SMM) was
launched in February 1980 and repaired on-
orbit in 1984. It is dedicated to coordinated
observations of specific solar activity and
solar flare problems. The payload contains
seven instruments, including an Active Cav-
ity Irradiance Monitor, a coronagiaph, and
several imagers and/or spectrometers cover-
ing the spectrum from uv to gamma rays.
Some of the most significant results include
the following:

• accurately measured changes in solar ir-
radiance associated with solar activity, sug-
gesting the probability of transient energy
storage inside the Sun;

• discovery of near temporal coincidence
of gamma rays produced by energetic ions
and of hard x rays produced by energetic
electrons at times of solar flares, providing
constraints on the energy release mecha-
nisms in flares;

• discovery of frequent occurrence of
small flares producing hard x-ray and EUV
radiation, indicating powerful energy re-
leases on scales smaller than previously
known;

• discovery of hard x-ray and EUV sources
at the foot points of coronal loops, providing
strong evidence for the thick-target model of
x-ray production; and

• discovery of large-scale circulation pat-
terns in the chromosphere and low corona
in active regions, suggesting a solution of
mass conservation dilemmas indicated by
earlier observations.

Orbiting Solar Observatory-8

The Orbiting Solar Observatory-8 (OSO-8)
was launched in June 1975, as the last of a
series of satellites intended to study the Sun
through a solar cycle and to map the entire
sky in ultra violet, x-ray, and gamma-ray
radiation. Some important results include
the following:

• demonstration that the energy flux in
sound waves at the top of the chromosphere
is too low to explain coronal heating and

• verification of widespread down-flow in
the chromosphere-corona transition region.

Heliosphere Missions

Several missions have been valuable in ex-
ploring the heliosphere,

• Pioneer 10 and 11, the first experiments
to the outer solar system (launched in March
1972 and April 1973, respectively), performed
flybys of Jupiter and Saturn and conducted
studies of planetary and interplanetary
magnetic fields, solar wind parameters,
cosmic rays, transition region of the helios-
phere, neutral hydrogen abundance, and
properties of dust particles.

• Voyager 1 and 2, launched in September
1977 and August 1977, respectively, studied
Jupiter and Saturn as well as the interplane-
tary medium.

• The Interplanetary Monitoring Platforms
(IMP) series of missions carried out studies
of interplanetary space and the Earth's mag-
netosphere. The last of the series, IMP-8,
was launched in September 1972.

• Helios, developed by the FRG in cooper-
ation with NASA, was a two-spacecraft mis-
sion, launched in December 1974 and Janu-
ary 1976. The purpose of the mission was to
study the interplanetary medium between
0.3 and 1 AU.

Some scientific results include the follow-
ing:

• discovery that the interplanetary sector
structure is the ecliptic plane projection of a
three-dimensional heliospheric current sheet
(Pioneer 11);

• tracking of type III solar radio bursts to
Earth orbit [Simultaneous measurements of
plasma waves, radio waves, and energetic
electrons (IMP B) provided a global view of
the three-dimensional structure of the inter-
planetary magnetic field.];

• studies of three-dimensional MHD turbu-
lence in the solar wind beyond 1 AU using
magnetic field and three-dimensional
plasma data (Voyagers 1 and 2) — first deter-
mination of the three global invariants of
incompressible, three-dimensional MHD tur-
bulence; and

• discovery that coronal holes are the
source of high-speed solar wind streams
(Helios, Skylab).

International Sun-Earth Explorer

The International Sun-Earth Explorer (ISEE)
was a three-spacecraft mission, with
launches in October 1977 (ISEE-1 and -2) and
August 1978 (ISEE-3), to investigate solar-ter-
restrial relationships near the boundaries of
the Earth's magnetosphere, the solar wind
near the Earth's bow shock, cosmic rays,
and solar flares in the interplanetary region
near 1 AU. ISEE-3 was moved, in June 1982,
from its halo orbit in the solar wind to make
several excursions into the far magnetotail
(1983) and was then directed into a trajec-
tory that will intercept the tail of comet Gia-
cobini-Zinner in September 1985. The signifi-
cant results to date include the following:

• mapping the structure and fundamental
physics of the Earth's bow shock and up-
stream region (ISEE- 1,2);

• demonstration of steady-state reconnec-
tion at dayside magnetopause, thus show-
ing the operation of a physical process that
had long been predicted theoretically and
inferred from global magnetospheric obser-
vations (ISEE- 1,2);

• discovery and characterization of tran-
sient reconnection (flux transfer events) at
dayside magnetopause (ISEE- 1,2), showing
the dynamical importance of a more
"patchy" kind of energy transfer between
the solar wind and magnetosphere;

• measurement of magnetopause wave
structure and motions (ISEE-1, 2), showing
that the magnetopause is a highly complex
and dynamic region as opposed to the sim-
ple laminar region often pictured in models;

• extension of ion composition measure-
ments to high altitudes, demonstrating both
ionospheric and solar wind plasma sources
(ISEE- 1,2);

• electric field measurements throughout
terrestrial magnetosphere and environs
(ISEE- 1,2) (Since electric fields are the
causal agents of particle acceleration and
they effect plasma transfer, the successful
measurement of electric fields represents an
important advance in observational tech-
niques.);

• improved observations of reconnection
in magnetotail, including detailed structure
of plasma sheet (ISEE- 1,2, 3) (Reconnection
processes appear to be very important both
for the quiet time structure of the plasma
sheet and for the temporal evolution of the
magnetotail structure during substorms.);

• demonstration of the importance of sin-
gle particle motion within boundary regions
of the plasma sheet (ISEE- 1,2);

• continuous monitoring of solar wind in-
put functions from upstream libration point
providing critical information about the so-
lar wind electromagnetic fields that "drive"
geomagnetic activity (ISEE-3);

• first detailed survey of distant tail show-
ing the structure, evolution, and dynamics
of the region beyond the lunar orbit (ISEE-3);

• confirmation of plasmoid formation and
escape from magnetotail during substorms
(ISEE-3) (Such plasmoids carry away very
large amounts of mass and energy from the
near-Earth tail and represent a major form
of dissipation as the magnetosphere returns
toward a "ground-state" after substorms.);
and

• first high-resolution measurements of
the isotopic composition of solar flare and
galactic cosmic ray nuclei, thus advancing
our understanding of cosmic-ray accelera-
tion and propagation processes (ISEE-3).

Dynamics Explorer

Dynamics Explorer (DE), launched in August
1981, was a two-spacecraft mission de-
signed to study the strong interactive proc-
esses coupling the Earth's magnetosphere
and ionosphere. The spacecraft were placed
in polar orbits to permit simultaneous meas-
urements at high and low altitudes on the
same field lines. Significant results to date
include the following:

• first global images of auroral oval and
polar cap showing substorm evolution;

• strong coupling between convectively
driven ions and the neutral atmosphere, im-
plying an important form of energy and mo-
mentum coupling at ionospheric altitudes;

• a new relationship between the convec-
tion electric field and field-aligned currents
and interpretation of this in terms of the
mechanism for driving the magnetospheric-
ionospheric coupling currents;

• first observation of postulated non-ther-
mal line profiles of oxygen in the nighttime
thermosphere;

• neutral winds of very high speed (ap-
proximately 1500 km/hr) — over twice maxi
mum speed observed during the Atmos-
pheric Explorer (AE) mission — implying
great variability of the upper atmospheric
wind system;

• polar wind at high latitudes, which, pre-
dicted theoretically, demonstrates that the
polar ionosphere is an extensive source of
magnetospheric plasma during magnetic
storms;

• nitrogen ions in the magnetospheric
plasma, clearly of low ionospheric origin
and previously unobserved;

• correlated magnetic and electric field
variations that provide remote sensing of
ionospheric current and conductivity, which
determine, in significant measure, the lev-
els of energy dissipation in the ionosphere;

• first global scale mapping of thermos-
pheric winds and temperatures that showed
neutral atmospheric circulation patterns (In
particular, the mission confirmed that ion
drag is a dominant force on high latitude
neutral atmosphere in polar regions.);

■ first measurement of height of auroral
hiss emission region; and

• frequent occurrence of extremely high
densities of field-aligned currents, suggest-
ing a "clumping" and localization of current
patterns rather than broad, uniform distribu-
tion over large polar regions.

Shuttle/Spacelab — Space Plasma
Physics

• Electron beam and plasma emitters suc-
cessfully operated on the Shuttle without
any significant charging. There is evidence
for strong beam-plasma interactions with

particle energization and generation of in-
tense electrostatic waves.

• In most cases, the onset of plasma ener-
gization and anomalous ionization limited
charging to below 100V. In one case, kV
charging was detected. The preliminary ex-
planation for this is inaccessibility of the
conducting areas to the plasma energized
by the beam injection.

• Discovery of the "Shuttle Glow" and its
correlation with electrostatic wave and par-
ticle energization phenomena caused by col-
lective plasma interactions may support a
plasma hypothesis for this phenomena.

• Major enhancement in ionization when
N 2 was released in the "ram" direction from
the Shuttle, may be similar to "Critical Ioni-
zation" although the speed of the release
was subcritical.

Planetary Magnetosphere/
Atmosphere Missions

The Pioneer and Voyager missions were de-
scribed in the section on Heliosphere Mis-
sions. The significant results of their inves-
tigations of the magnetospheres and
atmospheres of Jupiter and Saturn include
the following.

• Jupiter is the dominant source of 1-40
MeV cosmic-ray electrons in the helios-
phere.

• Jupiter's magnetosphere is the largest
object in the solar system, 10 solar diame-
ters in width, with an identifiable tail that
extends at least beyond the orbit of Saturn
(Pioneer 10 and 11 and Voyager 1 and 2).

• Jupiter's moon, Io, serves as a source of
heavy ions that form a torus surrounding
Io's orbit in the inner magnetosphere. Ions
from the torus are accelerated to relatively
high energies (tens of keV) and are found
throughout the magnetosphere (Voyager 1
and 2) at extremely high temperatures
(about 3 x 10 8 K). Because of Io's plasma to-
rus, radio emissions from Jupiter's iono-
sphere and magnetosphere reveal a com-
plex pattern in frequency and space
unanticipated from ground-based observa-
tions (Voyager 1 and 2).

• Saturn's magnetosphere is intermediate
in structure between Earth's and Jupiter's,
both in scale and in importance of centrifu-
gal distortion. Internal plasma sources in-

elude the atmosphere, moons, and rings,
which serve as sources of both protons and
heavy ions (Pioneer 11, Voyager 1 and 2).

• Radio emissions from Saturn define a
stable rotational period, but the intrinsic
magnetic field is symmetric about the rota-
tion axis, so the cause of the modulated
emissions is not established (Voyager 1 and
2 ).

• Elongated radial features ("spokes") are
found in the B-ring near the orbit synchro-
nous with planetary rotation, and are best
understood by invoking charged dust grains
electrostatically coupled to local plasmas
(Voyager 1 and 2).

• Saturn's atmospheric structure is similar
to Jupiter's, but equatorial wind speeds up
to 1500 km/hr are four to five times faster
than those on Jupiter (Voyager 1 and 2).

• Titan's exosphere generates strong EUV
emission by magnetospheric interactions
(Voyager 1 and 2). This interaction is impor-
tant in the evolution of Titan's atmosphere.

Atmosphere Explorers

The Atmosphere Explorer (AE) series of
spacecraft were designed to study the
Earth's upper atmosphere. The last of the
series was launched in November 1975. The
principal results include the following:

• comprehensive measurements and un-
derstanding of the ion and neutral photo-
chemistry of the thermosphere and inference
of various reaction rate coefficients, which
led to the solution of outstanding photo-
chemical problems of the thermosphere;

• detailed measurements of the diurnal,
latitudinal, longitudinal, and seasonal vari-
ation of the neutral constituent concentra-
tions in the thermosphere, which indicate
the importance of solar and geomagnetic
activity on the thermosphere;

• in-situ measurements of vertical veloci-
ties, kinetic temperature, and interhemis-
phere transport induced by neutral meri-
dional winds that provided a firm basis for
understanding compositional changes in the
thermosphere;

• direct measurements of the winter he-
lium and hydrogen bulges, demonstrating
the importance of transport by interhemis-
pheric wind systems;

• high resolution, low energy particle

measurements of the daytime photoelectron
spectra, electron spectra in the high latitude
ionosphere and quiet dayside cusp that pro-
vided accurate electron impact emission
rates of auroral and airglow features that
are diagnostic of energy input to the ther-
mosphere;

• measurements of solar wind plasma in-
jection in the dayside cusp, of convection in
dayside auroral arcs, of polar cap electron
acceleration regions and substorm effects
on the auroral plasma that provided impor-
tant data to understand magnetosphere-ion-
osphere coupling; and

• detailed in-situ measurements of plasma
bubbles and irregularities in the equatorial
ionosphere, which are important signatures
of plasma instabilities in the F region,

Nimbus-7

The Nimbus-7 Satellite, which is the last in
the Nimbus series, was launched October
24, 1978, for the purpose of sounding the
oceans, Earth radiation budget, and the
middle atmosphere. Four experiments were
dedicated to study of the middle atmos-
phere, three of which were limb sounders
(LIMS, SAMS, and SAM II) and the fourth,
the SBUV experiment, used nadir backscat-
tered ultraviolet radiation. A collective sum-
mary of middle atmosphere scientific results
is as follows:

• Provided first global distributions of
H 2 0, N0 2 , HN0 3 , N 2 0, and CH 4 showing lati-
tudinal gradients, significant variability,
seasonal changes, and important new chal-
lenges to theory. Concurrent observations of
CH 4 and H z O provide a unique opportunity
to study the production of H z O through the
tropical tropopause.

• Produced first experimental evidence of
downward transport of NO x from high alti-
tudes to the mesosphere and upper strato-
sphere in high latitude winter providing de-
tailed observations for comparison with
theoretical results, for study of impact on
the NO x budget in the stratosphere, and for
analysis of photochemical time constants,
vertical velocity, and lower mesosphere
wave activity.

• Provided detailed observations of rapid
N0 2 decreases with latitude at high winter
latitudes in the stratosphere (the N0 2 "cliff")

and showed importance of including inter-
action between dynamics and chemistry to
explain the phenomenon.

• Demonstrated strong correlations be-
tween potential vorticity and temperature,
0 3 , HN0 3 , and H 2 0 fields, illustrating the
utility of potential vorticity for tracer stud-
ies. Observations give evidence of species
transport associated with breaking plane-
tary waves.

■ Confirmed N0 2 diurnal change theory
and provided latitude cross sections of the
day/night ratio (Observations provided of
diurnal change in lower mesospheric
ozone). These results provide important data
for in situ tests of photochemical theory.

• Provided detailed observations of con-
stituents and temperature distributions dur-
ing the major stratospheric warming event
of the winter of 1979. This provides data for
analyses of the warming period through cal-
culation of derived dynamical quantities
(e.g., winds, heat, momentum, and Elias-
sen-Palm fluxes) and by study of the global
morphology and variability of constituent
and temperature patterns.

• Discovered the presence and measured
the variability of polar stratospheric clouds
in both the northern and southern winter
polar regions. These clouds, observed glob-
ally for the first time, have important impli-
cations for the water budget and heteroge-
neous chemistry.

• Measured optical depths of aerosols in
polar regions that had been transported
from much lower latitudes after an eruption
of the El Chichon volcano on the Yucatan
peninsula, providing information on hori-
zontal transport times for use in model stud-
ies.

• Developed six-year climatology of polar
stratospheric aerosols for use in climate im-
pact studies. This is significant because of
the suggestion that polar aerosols may have
an important effect on climate.

• Detected S0 2 in the stratosphere directly
(from the El Chichon eruption) for the first
time. This gas is a precursor to sulfuric acid
formation which is the main component of
the stratospheric sulfate layer.

• Confirmed the effect of solar particles on
stratospheric ozone during a solar proton
event and found strong correlations of ozone
variations at the 3 mb level with 27-day
solar flux changes.

Solar Mesosphere Explorer

The Solar Mesosphere Explorer (SME) satel-
lite was launched in October 1981. Its pur-
pose was to investigate some of the factors
influencing the ozone balance of the mesos-
phere and upper stratosphere, thus adding
to our knowledge of the behavior of this
very important atmospheric constituent.
Some of the most significant discoveries
noted to date include the following.

• Systematic observation revealed the
ozone distribution at about 50-70 km by two
techniques and 50-95 km by one technique.

• Observations of water vapor in the up-
per stratosphere are now also being ob-
tained and their relationship to ozone is un-
der study.

• It was discovered that day-to-day ozone
variations at mesospheric heights are prin-
cipally driven by temperature variations.

• It is indicated that solar flux variability
significantly influences ozone distributions
near the stratopause over the time scale of
a solar rotation.

• Observation was made of the distribu-
tion and variability of stratospheric N0 2 , a
species which catalytically destroys ozone
in the stratosphere. The sharp decreases in
wintertime N0 2 at high latitudes (the "N0 2
cliff") were confirmed.

• Detailed observations of the response of
mesospheric ozone to solar proton events
showed very good agreement with photo-
chemical theory, confirming that the cata-
lytic destruction of ozone by hydrogen radi-
cals (OH, H0 2 ) proceeds as expected.

• Large seasonal variations have been de-
tected in ozone near the 80 km level. Present
study suggests that these changes are due
to the influence of breaking small-scale
gravity waves.

Pioneer Venus

Pioneer Venus (launched in May 1978) was a
two-spacecraft mission, with 4 entry probes,
designed to conduct a comprehensive study
of Venus' atmosphere. The most significant
results include the following.

• Lack of an intrinsic planetary magnetic
field was established.

• Shape of the bow shock and the volume
of the solar wind interaction with the planet
were clarified.

• Intense magnetic flux ropes were ob-
served deep in the ionosphere.

• Ionospheric composition and tempera-
tures were established.

• Nighttime auroral precipitation and
emissions were observed.

• The extent of the nighttime ionosphere
was established showing that it is main-
tained by a combination of transport from
the day side and electron precipitation.

• An extended gas envelope, consisting of
hot oxygen and hydrogen atoms, was ob-
served, confirming the loss of hydrogen and
oxygen from Venus by solar wind scaveng-
ing.

• Extremely low (about 100 K) nighttime
thermospheric temperatures were observed.

• Lightning was detected by wave obser-
vations.

• At least four distinct cloud layers were
found.

• Haze layers contain small aerosol parti-
cles, possibly droplets of sulfuric acid.

• Atmosphere circulation is dominated by
large planetary-scale systems.

• A collar of polar clouds discovered,
which may be part of a large atmospheric
polar vortex.

Theory Program

The following are representative of a host of
recent achievements in the areas of theory
and computer simulations.

• Quasi-perpendicular bow shocks have
been simulated at a new level of sophistica-
tion and have produced results in remarka-
ble agreement with high resolution ISEE ob-
servations.

• Acceleration by self -generated, convect-
ing, hydromagnetic waves has explained
many properties of energetic diffuse ion
populations observed upstream of both
Earth's bow shock and traveling interplane-
tary shocks.

• First generation, two- and three-dimen-
sional, global MHD models of Earth's mag-

netosphere have been obtained computa-
tionally; features such as the bow shock,
magnetopause, cusp, tail lobes, and neutral
points are all evident.

• Two- and three-dimensional simulations
of magnetotail reconnection have shown
many of the features predicted by fluid dy-
namics and seen in magnetospheric plasma
observations.

• Analysis and simulations illustrated
many important processes operating in the
auroral zones and responsible for key obser-
vational features. Lower hybrid and ion cy-
clotron waves effectively heat and acceler-
ate heavy ions; double layers and resistivity
caused by spiky turbulence drive the elec-
tric fields necessary to produce auroral
beams; and the electron cyclotron maser in-
stability causes the terrestrial kilometric ra-
diation.

• Major advances in our understanding of
both fluid and MHD turbulence have been
achieved. In the ionosphere, key features of
the natural and artificial spread F have
been reproduced in simulations. In the solar
wind, magnetic data have been used to con-
struct the three rugged MHD invariants and
led to the suggestion that the solar wind is
a strongly turbulent medium.

• Major progress in the theoretical under-
standing of beam plasma interactions re-
sulted in the resolution of several outstand-
ing issues. In the interplanetary medium it
led to the most sophisticated modeling of
type III bursts; in the ionosphere to the un-
derstanding of the extremely short energy
deposition lengths associated with artificial
beam injection.

• Compressible convection studies of the
solar convection zone have shown that en-
ergy transport occurs on the space scale of
giant cells and have demonstrated the exist-
ence of convective overshoot.

• Global thermospheric and ionospheric
models have been developed and show that
magnetospheric influences have an unex-
pectedly great importance, e.g., by inducing
convection.

7 DETAILED MISSION PLANS — SOLAR AND HELIOSPHERIC PHYSICS

Introduction

The strategy for advancing solar and helios-
pheric physics combines in-situ measure-
ments of the heliosphere with remote obser-
vations of the Sun from low-Earth orbit
(LEO). Below we first describe the several
pieces of the program and then, in Section
C, discuss their relative priorities.

Program Descriptions

Free-Flyers for Solar and Heliospheric
Physics

WIND

The WIND spacecraft is one of a network of
spacecraft proposed as part of the Interna-
tional Solar Terrestrial Physics Program
(ISTP). The overall goal of the ISTP is to
develop a comprehensive and global under-
standing of the physical mechanisms by
which energy generated at the Sun flows
through the interplanetary medium and fi-
nally enters the Earth's magnetosphere and
upper atmosphere. Understanding the cou-
pling between solar and interplanetary
processes and the Earth's magnetosphere,
ionosphere, and atmosphere requires de-
tailed knowledge of the source function.

This can be obtained only through in situ
measurements in the solar wind.

The WIND spacecraft has a central role in
ISTP, for without detailed knowledge of the
behavior of the solar wind upstream of its
interaction with the Earth's magnetosphere,
no comprehensive understanding of the ef-
fects of this interaction is possible. WIND
will measure the properties of the helios-
phere at 1 astronomical unit (AU) in the
ecliptic plane while the International Solar
Polar Mission (ISPM) acquires similar data
far from the ecliptic. Study of magnetohy-
drodynamic turbulence, important for under-
standing both the formation and evolution
of the solar wind and the behavior of labo-
ratory plasma devices, requires the nearly
continuous data coverage and the extensive

data bases to be provided by the WIND in-
struments.

Further discussion of WIND will be found
in the section on ISTP in Chapter 8.

SOHO

SOHO is a mission aimed at three distinct,
yet interrelated plasma regimes, the solar
interior, the corona, and the solar wind. Ex-
periments on SOHO will use the methods of
solar seismology, spectroscopic plasma di-
agnostics, and in-situ measurements to de-
rive the physical state, chemical composi-
tion, and the internal and bulk motions of
the plasma structures that make up the Sun
and heliosphere. The objects of the study
will range from the dense matter hidden in-
side the Sun, in the thermonuclear furnace
and in the radiation and convection zones;
through the tenuous corona, where matter is
held together and possibly heated and ac-
celerated by magnetic fields; far out into the
interplanetary medium, where the solar
mass loss manifests itself as the solar wind.
The detailed data acquired by SOHO, com-
bined with sophisticated, well-developed
methods of interpretation, will allow tests of
the numerous models of plasma structures.
Examples of such structures are the solar
convection zone, coronal magnetic loops,
and the sharp boundary layers between low
and high speed solar wind streams.

The primary objectives of SOHO are as
follows.

• Use solar oscillations to probe the solar
interior structure from the core to the solar
"surface", or photosphere.

• Determine the angular rotation profile of
the solar interior and measure the solar
gravitational quadrupole moment.

• Measure variations in solar irradiance
from minutes and days to weeks and years
to ascertain effects of solar activity on solar
luminosity.

• Study the generation of the solar wind
through measurements of plasma velocities,
temperatures and densities out to 5 solar
radii.

• Locate sources of low speed solar wind.

29

• Determine how coronal transients propa-
gate through the corona and how and where
they are accelerated.

• Obtain high resolution temperature,
density, velocity, and magnetic measure-
ments in an effort to determine the origin of
coronal heating.

SOHO is a three-axis stabilized spacecraft
that is to be placed in a halo orbit around
the Li Lagrangicm point at 1.5 x 10 6 km from
Earth. The spacecraft is to be built by the
ESA with experiments provided by both Eu-
ropean and U.S, scientists.

Solar Probe

The general problem of the origin of the
solar wind has been a focus of observa-
tional and theoretical activity since the orig-
inal theoretical work of E.N. Parker. Direct
measurements of the solar wind plasma, the
interplanetary magnetic field, the energetic
particle population, and associated wave-
particle interactions are available, but only
at distances greater than the 0.3 AU perihe-
lion distances of Helios 1 and 2. From the
solar surface out to a distance of about 60
solar radii, we must rely on indirect obser-
vations and theoretical extrapolations. We
recommend a Solar Probe mission whose
primary objective is to carry out the first in
situ observations of the solar wind plasma
and fields (electric and magnetic) near the
source of the wind in the solar atmosphere.
Included will be a detailed study of ener-
getic particles which will yield important
diagnostic data on particle acceleration
processes and coronal structure.

The spacecraft must be placed in an orbit
that will bring it as close to the Sun as
possible and still survive to provide useful
data near closest approach. We anticipate a
perihelion distance of 4 solar radii, where
we expect the local wind speed to be about
50 km/s, the electron and ion plasma tem-
peratures to be about 10 6 K, and the plasma
density and magnetic field strength to be
less than 10 6 electrons/cm 3 and 10 5 gamma,
respectively.

Theories of solar wind origin place the
transition region from subsonic plasma flow
to supersonic flow somewhere between 1
and 10 solar radii. Radio scattering experi-
ments on Viking during superior conjunction
suggest a critical point closer to 10 solar

radii. In situ measurements should clarify
this issue.

The location of the critical point and the
plasma properties (speed and temperature)
of the supersonic wind will depend greatly
on the physical processes that heat the cor-
ona. Theoretical studies suggest that the
proton temperature profile is very sensitive
to these heating processes. It is not clear
whether the corona contains an extended
region of heating (out to as far as 20 solar
radii) or undergoes adiabatic expansion be-
yond the solar surface. Plasma temperature
data and observations of the wave types
and amplitudes should lead to the identifi-
cation of the important heating and acceler-
ation mechanisms.

Many other important problems can be
studied with Solar Probe, including a de-
tailed characterization of coronal streamers,
the place of origin and the boundaries of
high speed and low speed flows close to the
Sun, the extent of heavy element fractiona-
tion and elemental abundance variations,
and the scale sizes of inhomogeneities and
the development of the magnetohydrodyn-
amic turbulence that characterizes the solar
wind near 1 AU and beyond. The Solar
Probe mission can also study the solar spin
down rate through measurements of solar
wind angular momentum flux.

Further study needs to be carried out to
determine the best method of designing de-
tectors that are required to look in the direc-
tion of the Sun.

In previous studies on the concept of a
solar probe {Starprobe: Scientific Rationale ,
J.W. Underwood and J.E. Randolph, JPL
Publ. 82-49, 1982), several other investiga-
tions were also included in the potential
payload, e.g., imaging, a drag-free experi-
ment for studying relativistic effects, and
measurement of the solar gravitational
quadrupole moment*. While these investiga-
tions undoubtedly have important scientific
objectives, the primary objective of the mis-
sion is the study of the solar wind accelera-
tion region. In order to fit this mission into
our implementation plan (Figure 4), cost
considerations have forced us to define the
mission to address the prime objective only .

* Much progress can be made in measuring the solar
gravitational quadrupole moment from solar oscillation
studies.

With additional funds, these other worth-
while objectives could also be addressed.

Solar Polar Orbiter

The heliosphere is known to have a compli-
cated three-dimensional structure. The mag-
netic field is a tight spiral near the solar
equatorial plane, but is expected to be es-
sentially radial over the solar poles. Co-
ronal holes, one of the sources of high
speed solar wind, are expected to produce
quasi-steady high speed flows over the so-
lar poles during much of the solar cycle,
whereas at low latitudes interacting high
and low speed flows predominate.

To understand heliospheric conditions at
low solar latitudes has required numerous
missions, e.g., Explorers, Pioneers, Mari-
ners, and Voyagers. To understand helios-
pheric conditions at high latitudes will simi-
larly require repeated missions. In 1986,
NASA and ESA will fly the first exploratory
mission over the solar poles, the ISPM.
However, as with most exploratory mis-
sions, ISPM will probably uncover more
questions than it will answer, and follow-on
missions will be required.

The objective of the Solar Polar Orbiter
(SPO) would be to provide a detailed, re-
peated study of conditions at all helio-
graphic latitudes. In circular orbit, SPO will
observe the heliosphere at constant radius
and thus will distinguish latitude from ra-
dial effects. With a circular orbit at less
than or equal to 1 AU, and thus an orbital
period less than or equal to 1 year, SPO
should be able to make several passes over
the solar poles in a nominal mission life-
time, and thus distinguish spatial from tem-
poral effects.

No detailed study of an SPO mission has
been done in recent years. However, the re-
quired orbit should be achievable through
the use of a low-thrust, continuous accelera-
tion propulsion system such as solar-electric
propulsion. For example, it may be possible
to launch SPO in the direction of the Earth's
orbit, and use solar electric propulsion to
tilt the orbital plane in heliographic lati-
tude.

The SPO spacecraft should carry a full
complement of plasma, energetic particle,
magnetic field, and radio wave instruments,
similar to what is to be flown on ISPM. In

addition, SPO should have pointing capabil-
ity, through the use of a despun platform on
a spinning spacecraft, or as a three-axis
stabilized spacecraft, for detailed solar ob-
servations using a coronagraph, x-ray tele-
scope, and similar photon observing instru-
ments.

Mission design for SPO should be under-
taken in the mid-1990s, following a thorough
analysis of the results from ISPM. Launch
should occur in the late 1990s.

The principal technical development re-
quired for SPO is solar-electric propulsion
system, or its equivalent, for low-thrust,
continuous acceleration. In the cost projec-
tions for SPO it is assumed that such devel-
opment will not be charged against the mis-
sion costs, because the need is common to
several proposed programs. Also, studies
need to be conducted on the impact of a
continuous propulsion system on particle,
field, and photon instrumentation, and on
the measurements these instruments make.

Solar-Heliospheric Research with the Shuttle

Remote observations of the sun and corona
will be made with Shuttle-borne instruments
ranging in size from small Spartan experi-
ments to moderate Spacelab/Sunlab instru-
ments to large facility-class instruments. Af-
ter Shuttle experience is obtained, we
envision that appropriate facilities and
moderate instruments will evolve into a
Space Station-based Advanced Solar Ob-
servatory (ASO) as the primary means for
remote sensing in the next decade. Develop-
ment of new instrumental techniques and
exploration of some solar phenomena do not
require large facilities. These problems can
be addressed using smaller experiments of
the PI class, suitable for Shuttle, free-flyers,
sounding rockets, and balloons. Shuttle-
based observations include measurements
of

• energy and mass flux from the photos-
phere through the corona;

• magnetic and velocity fields and their
evolution and interactions;

• temperature and density structure of the
solar atmosphere;

• changes in solar radiative flux; and

• some coronal processes that may govern

the generation, structure and variability of
the solar wind.

We have identified three Shuttle programs
that are critical for solar-heliospheric phys-
ics.

1. Spartan. The Spartan program, which
is a successor to the sounding rocket pro-
gram, can fly innovative, relatively small
and inexpensive instruments prepared on a
rapid time scale. The Spartan carrier will
contain a pointing system, power supply,
and tape recorder. When placed into orbit
by the Shuttle, the Spartan will be a free-
flyer for one to two days before being
recovered by the Shuttle. To continue ade-
quately research currently done with sound-
ing rockets, Spartan flights with solar-he-
liospheric experiments should be flown at
least three times per year.

2. Spacelab/Sunlab. This program pro-
vides opportunities to fly moderate sized in-
struments in complementary groups
mounted on the Instrument Pointing System
(developed by the ESA). The experiments
will be attached to a pallet fixed in the
Shuttle bay. Interactive control of the exper-
iments by payload specialists is an impor-
tant part of this program. Flight opportuni-
ties should be roughly every two years to
provide for orderly instrumental evolution
from Spartan to more advanced programs.

3. Facility Class Instruments. To attain
the highest spatial, spectral, or temporal
resolution requires experiments that take
full advantage of the Shuttle's electrical
power, large payload capacity, and data
handling capabilities. Instruments in the
Facility Class include telescopes, spectrom-
eters, filters, photometers, polarimeters, and
imaging detectors covering most of the elec-
tromagnetic spectrum. Facility development
begins with the Solar Optical Telescope
(SOT), designed to measure physical phe-
nomena from the photosphere through the
transition region, followed by the Pinhole
Occulter Facility (POF), designed to image
high energy events in the corona and to
measure dynamical phenomena of the cor-
ona. Three additional facilities have been
identified: a soft x-ray facility, a high en-
ergy facility, and an extreme ultraviolet tel-
escope (EUVT). These facilities should be
developed as soon as possible to comple-
ment SOT and POF.

The Solar Optical Telescope

The purpose of SOT is to study physical
processes on the Sun with an instrumental
angular resolution of 0. 1 arcsec. This corre-
sponds to 70 km and is about half an atmos-
pheric density scale height. We know that
much of the fine structure and energy trans-
port in the solar atmosphere are closely as-
sociated with the strong magnetic field con-
centrations associated with sunspots and
smaller flux tubes in the chromosphere and
corona.

SOT will study (by remote sensing) the
solar atmosphere from the photosphere,
where the gas pressure plays a major role
in containing the magnetic fields, to the up-
per chromosphere and lower transition re-
gion, where magnetic forces are dominant.
This requires spectral coverage extending
from the near infrared to the far ultraviolet.

Two specific scientific problems can be
described that illustrate some of the capa-
bilities of this facility.

1. In the solar atmosphere, the magnetic
fields and fluid motions interact in such a
way that at the solar surface the fields are
highly inhomogeneous. A large fraction of
the magnetic flux is clumped into very in-
tense flux tubes. Field strengths of 1500
gauss contained within flux tubes of a few
hundred kilometers in diameter are common
even outside of sunspots. SOT will help an-
swer questions of how this clumping arises
and how the magnetic flux ultimately disap-
pears after reaching the surface. Both proc-
esses may be an essential part of the dy-
namo mechanism of solar magnetic field
generation that is believed to be responsi-
ble for the solar magnetic field and cycle,

2. It has become increasingly clear that
the solar magnetic fields play a key role in
the heating of both the chromosphere and
the corona. Skylab data showed that co-
ronal forms are tied to magnetic field geom-
etry while OSO-8 data showed that acoustic
shock waves are not sufficiently strong to
carry the necessary energy into the corona,
SOT is expected to provide quantitative
measures of the coupling between photos-
pheric magnetic field stresses and chromos-
pheric and coronal heating.

The Pinhole Occulter Facility

The Pinhole Occulter Facility (POF) is de-
signed to image hard x-ray sources with un-
precedented angular resolution. The goal is
to study the production of solar energetic
electrons, which constitute the bulk of the
initial energy release in solar flares. Stud-
ies by POF of the sites and phase relation-
ships of particle acceleration relative to the
magnetic field and fluid dynamics will pro-
vide insight into the physical mechanisms
operating. POF will provide more than an
order of magnitude improvement in spatial
resolution.

A second major area of study is the mas-
sive acceleration of large volumes of co-
ronal plasma in the form of coronal tran-
sients. These mass ejections have been
studied in the outer corona at low resolution
by Skylab, SMM, and the P-78 satellites. Be-
cause of its 50-m length and larger tele-
scopes, POF will be able to improve signifi-
cantly the angular resolution of previous
studies, to obtain clean observations of both
the middle and outer corona and to perform
detailed spectroscopy of the coronal
plasma. Two specific objectives of POF us-
ing these instruments are described below
in more detail.

1. Coronagraphs. These instruments will
provide new data on some of the processes
by which energy and momentum are depos-
ited in both the expanding open field re-
gions and in the more slowly evolving
closed magnetic field regions of the corona.
It is not currently known whether the heat
input to the corona is evenly distributed or
localized; nor is it known whether the heat-
ing occurs continuously or sporadically. The
spectral diagnostics of the coronal plasma
together with observations of its dynamical
properties at high spatial resolution are ex-
pected to provide answers to these ques-
tions.

2. Solar X Rays, Imaging hard solar x
rays will aid in understanding the mecha-
nisms by which electrons are accelerated to
high energies during the impulsive phases
of solar flares. It is currently thought that
hard x rays are produced by the impact of
these electrons on the denser regions of the
lower atmosphere. Observations using POF,

coupled with the high resolution studies us-
ing SOT, will provide essential knowledge
of the spatial and temporal relationships
between the energy releases in electromag-
netic radiation over the range of a few eV to
over 100 keV.

The Soft X-Ray Telescope

The primary purpose of the Soft X-Ray Tele-
scope (SXRT) is to study the thermodynamic
and hydrodynamic structure of the corona in
relation to its magnetic field patterns. High
to moderate resolution spectrographs pro-
vide plasma diagnostics in the temperature
range from approximately 10 6 K to 10 8 K. This
soft x-ray spectral data, arising mainly from
the thermal plasma, is complementary to
the hard x-ray data from the POF, arising
mainly from non-thermal electron streams.

Past experience has shown that the soft x-
ray region from approxmately 300 A to 1,75
A (40 eV to 7. 1 keV) is the richest spectral
region for studies of the corona. The ab-
sence of strong background radiation from
the photosphere and chromosphere in this
spectral region allows the corona to be ob-
served against the disk of the Sun. This has
the triple advantage over limb observations
of greatly simplifying the effects of line-of-
sight integration, of showing the lateral
structure of the corona in two dimensions,
and of showing the locations of coronal
structures relative to magnetic field patterns
in the photosphere.

Soft x-ray data obtained with Skylab and
other space experiments have radically al-
tered our concepts of the corona, particu-
larly with respect to the importance of mag-
netic fields in both heating and shaping the
coronal structure. However, it is clear from
these same observations that the true co-
ronal structure is unresolved at 2 arcsec,
which is the best resolution yet attained for
a sustained period of time.

The SXRT has a design goal of 0.5-arcsec
spatial resolution. The collecting area of
1140 cm 2 is approximately twice the collect-
ing area of the High Energy Astronomical
Observatory(HEAO)-2 telescope and 27 times
that of the experiment on Skylab. As such it
will offer major advances in both spatial
resolution and sensitivity.

Two examples selected to illustrate the

objectives of the SXRT are (1) study of the
heating of coronal plasma and (2) investiga-
tion of the thermal properties of flares and
the conversion of stored magnetic energy
into thermal energy during the flare main
phase. Coronal heating is known to fluc-
tuate spatially on scales down to 1 arcsec or
less and temporally on scales of minutes.
The spatial resolution of 0.5 arcsec provided
by the SXRT should be sufficient to isolate
regions in which the heating fluctuations
and fluid motions are relatively coherent. By
combining the SXRT with the SOT, the fluc-
tuations in coronal heating and fluid motion
can be correlated with related fluctuations
in the chromosphere and with photospheric
magnetic field fluctuations.

Major flares typically heat the thermal
plasma in the corona to temperatures in ex-
cess of 10 7 K over volumes that are large
compared to those in which the non-thermal
electrons are concentrated. Just how the
thermal flare plasma relates to the preced-
ing impulsive non-thermal flare events is
unclear. The SXRT, in combination with the
POF and the SOT, will provide the type of
data needed to answer such questions.

The EUV Telescope

The primary purpose of the EUV Telescope
(EUVT) is to study the upper chromosphere
and the chromosphere-corona transition re-
gion with high spatial resolution 0.5 arc-
sec). Within these regions the temperature
rises from below 10 4 K to over 10 6 K in a
short distance. The principal radiation from
these reaions lies in the EUV and XUV at
wavelengths below 1600 A. The exceedingly
high temperature gradients lead to a major
flow of energy from the corona back down to
the chromosphere by thermal conduction.
Additionally, there are strong vertical fluid
currents with average mass fluxes exceed-
ing those in the solar wind by about two
orders of magnitude. The upper chromos-
phere and transition region are the least
understood regions of the solar atmosphere.
The temperature gradients are so steep that
electrons in the high energy tail of the ther-
mal velocity distribution penetrate into re-
gions of much different temperature giving
rise to non-Maxwellian distributions and a
breakdown of classical thermal conduction.
Moreover, the vertical fluid currents are im-

portant components of the energy transport.

Two objectives for the EUVT are (1) to un-
derstand the mechanisms giving rise to the
fluid motions in the transition region and
upper chromosphere and (2) to understand
the multifaceted energy transport within
and through these layers. How are the up-
flows and downflows related? Are the driv-
ing forces hydrodynamic or are magnetic
forces essential? How does the solar wind
emerge from these more massive flows?
These questions are typical of those that
can be addressed by the EUVT, particularly
when used in concert with the SOT, the
XUVT, and the SXRT.

High Energy Facility

The primary purpose of the High Energy Fa-
cility is to study acceleration of ions. Obser-
vations acquired during the last solar maxi-
mum demonstrated that gamma-ray
measurements open up a new window for
studying particle acceleration on the Sun,
the most powerful natural particle accelera-
tor in the solar system. Gamma-ray lines
from many different elements (C, H, O, Fe,
Mg, Sc, N and Ne) have been detected in
solar plasmas. SMM observations indicate
that ion acceleration to about 10 MeV is a
common phenomena in solar flares. In addi-
tion, energetic neutrons (50-500 MeV) have
been detected. Because of these results,
there is strong interest in new observations
with instrumentation of high sensitivity, as
could be provided by a high energy facility.
The High Energy Facility, together with
other solar facilities such as POF and SOT,
provides a powerful tool for addressing the
fundamental processes of particle accelera-
tion.

Explorers for Solar and Heliospheric Physics
Studies

The active utilization of the Explorer Pro-
gram would be a great benefit to solar and
heliospheric physics. Rather than endorse
any particular mission, however, we recom-
mend that the selection be the result of a
competitive process that encourages innova-
tion, in accord with the recent recommenda-
tion of this committee contained in A Strat-

egy for the Explorer Program for Solar and
Space Physics , NAP 1984. We briefly present
two examples of such missions that are dis-
cussed in greater detail in that report.

Advanced Solar-Wind Composition
Explorers

A complete chemical and isotopic analysis
of the solar wind would provide information
on some, and probably all of the following
topics: improved knowledge of solar-wind
mass/charge fractionations which, in turn,
would shed light on the solar-wind acceler-
ation process and refined solar system
abundances; tests of the fundamental as-
sumption that the Sun and planets formed
from a common reservoir; limits on inte-
grated solar surface nuclear processes; and
constraints on solar structure and evolution.
Instrumentation to be flown on ISPM and
WIND will allow determination of the ele-
mental and ionic-charge compositions of all
major solar-wind ions from H through Fe.
Advanced instrumentation is required for
studies of the rarer elements and isotopic
abundances. Two different, complementary
approaches appear to be possible within the
budgetary constraints of the Explorer pro-
gram. In one approach an advanced ener-
getic ion mass spectrometer would be
placed on a spacecraft that spends a signifi-
cant amount of time beyond the Earth's bow
shock. Direct samples of coronal material
can also be provided by energetic solar par-
ticle measurements spanning the energy
range from about 10 keV/nucleon to 100
MeV/nucleon which would significantly en-
hance the interpretation of the solar wind
measurements by providing data for many
additional elemental and isotopic species.
Because this set of instrumentation would
probably be quite massive, there might be
few, if any, other instruments on board. Al-
ternatively, it is possible to perform a solar-
wind sample return mission in which high-
purity collector material is exposed to the
solar wind for about 2 years, and is then
retrieved for performance of chemical and
isotopic analyses in terrestrial laboratories.

Coronal Radio Probe Explorer

The objectives of this mission would be to
obtain new data on the coronal plasma be-

low the solar altitude accessible to the Solar
Probe. This lower region of acceleration of
the solar wind can be probed with radio
techniques (time delay, spectral line broad-
ening, scintillation, and Faraday rotation)
by placing a spacecraft carrying a radio
beacon (at several frequencies) on the far
side of the Sun from the Earth. Orbits could
be picked so the ray path would either
slowly circle around the solar disk or move
along a solar radius vector.

Long-Term Solar and Heliospheric
Measurements

Solar and heliospheric phenomena vary
over a great range of time scales. Well-es-
tablished, cyclic phenomena occur at the 11-
year and 22-year sunspot and magnetic
cycle periods. Careful study of the long-term
time dependences of selected solar and he-
liospheric parameters will provide valuable
insight into fundamental solar and helios-
pheric processes that is not available in any
other way.

Solar Constant

Variations in the solar radiative output not
only have impact on the Earth's ionosphere
and atmosphere, but also provide funda-
mental knowledge about the Sun and its
internal structure and dynamics. For our un-
derstanding of deviations of the Sun from its
equilibrium steady state to progress, long-
term satellite monitoring of the total solar
energy output and its distribution over
wavelength should take place. Unfortu-
nately, there is no one agency dedicated to
the support of long-term monitoring of this
type, and no one agency has devoted suffi-
cient resources or interest in this area to do
it properly. Long-term, synoptic observa-
tions are often the only means of discover-
ing linkages in the behavior of elements of
the system, despite the absence of clear
cause-and-effect relationships.

Long-Term Monitoring of Interplanetary
Particles and Fields

The study and elucidation of solar and ter-
restrial interactions that are mediated by
the solar wind or by solar energetic parti-
cles requires a commitment to long-term

and continuous monitoring of the interpla-
netary plasma, magnetic field, and cosmic
rays. For example, further study of sus-
pected 22-year effects in the intensity of
cosmic rays may lead to better understand-
ing of the solar magnetic cycle and the tur-
bulent dynamo that is the source of the so-
lar magnetic field. Studies of
magnetohydrodynamic turbulence are seri-
ously hampered by discontinuous data rec-
ords caused by incomplete satellite track-
ing.

Theory and Modeling

Magnetic field reconnection should form one
important aspect of theoretical studies sup-
ported by ISTP, as should the study of large-
scale plasma flows within the magnetos-
phere and ionosphere. In the Plasma Turbu-
lence Explorer Study report, the need for a
multi-spacecraft analysis of interplanetary
fields and fluid velocity data coupled with
theoretical studies was proposed as one
means of progressing in understanding of
magnetohydrodynamic turbulence. Such a
study, which might include three-dimen-
sional modeling of MHD turbulence using
Cray-class computers, might lend itself to a
"non-hardware" mission because the man-
power and computer resources required ex-
ceed the nominal magnitude of awards un-
der the STTP. Preliminary work in this area
has been supported by R&A funding, guest
investigator grants under the ISEE program,
and other institutional support provided by
NASA.

Mission Operations and Data Analysis

An example of an extended mission requir-
ing MO&DA support may be provided by
ISPM. The prime mission phase allows for a
pole-to-pole passage during solar maximum
conditions. If as expected, ISPM survives
beyond the second polar pass, an extended
mission could provide invaluable data on
solar and heliospheric conditions at high so-
lar latitudes during other portions of the so-
lar cycle.

A second example is the complement of
deep-space planetary missions, Pioneer 10
and 11 and Voyager 1 and 2. These contrib-
ute unique information about the helios-

phere and, at present, provide the only pos-
sible means of detecting the boundary
between the solar system and the interstel-
lar medium.

Finally, IMP-8 is, at present, the only
means of studying the solar wind and its
effects on the terrestrial environment.

Research and Analysis

The early stages of instrument development
(preflight through testing with sounding
rockets) are supported by the R&A program.
Several such developments are crucial to
the success of the flight programs described
in the paragraphs above. Examples are a
multilayer mirror for imaging solar x rays, a
space qualified instrument for mapping so-
lar oscillations with the SOHO spacecraft,
and advanced solar-wind and energetic-par-
ticle composition analyzers.

Another component of the solar and he-
liospheric R&A program is obtaining and
analyzing correlative data from many types
of ground-based observatories. The value of
solar observations from SMM, the SOHO
spacecraft of ISTP, the Shuttle, and the
space station/platform can be greatly en-
hanced by simultaneous observations of ad-
ditional facets of the phenomena under
study. Examples include coronagraphic and
magnetographic observations from ground-
based solar observatories, maps of solar ra-
dio emission obtained with the Very Large
Array and other facilities, and the observa-
tion of scintillation of radio sources caused
by coronal and interplanetary disturbances.

Finally, there are several types of labora-
tory and suborbital research that comple-
ment and enhance the rest of NASA's solar
and heliospheric physics program and
should therefore be supported by NASA as
well as by other agencies (e.g., NSF, DOD).
This research includes laboratory simula-
tions of solar plasma processes, such as
magnetic reconnection in solar flares, and
the measurement of cross sections required
to interpret solar data. Long duration bal-
loon flights may prove to be a very cost
effective and valuable technique for obtain-
ing data on hard x rays and gamma rays
emitted during solar flares.

The four principal components of the R&A
program — theory and analysis, instrument

development, correlative observations, and
complementary research — are listed here in
approximate priority order. The scientific re-
turn from the R&A program is high, and we
recommend an increase in its level of fund-
ing starting in 1990, after the peak spending
years for UARS and ISTP.

Technology Development

The new technology requirements of the so-
lar and heliospheric physics program can
be conveniently divided into components,
instruments, and spacecraft capabilities.

Many different instrument and facility de-
velopment requirements have been dis-
cussed in the paragraphs above. Except for
the components listed immediately above,
development of these instruments/facilities
requires the normal sequence of detailed
design and hardware development, but lit-
tle or no new technology. Thus, although
the developments require significant fund-
ing for the design and test of space-quali-
fied hardware, the risks of significant
schedule slips or cost growth are not high.

All the approved solar and heliospheric
physics missions, ISTP, and the solar instru-
ments/facilities planned for the Shuttle or
space station/platform can be implemented
with existing spacecraft technology; i.e., no
enabling technology development is re-
quired for those missions. New technology
is needed for the Solar Probe and SPO, how-
ever. The concept of obtaining data with a
spacecraft located 3 solar radii from the so-
lar surface is predicated on the develop-
ment of a heat shield that keeps the instru-
ments and spacecraft within operating
temperature range, without ablation of
enough material to prevent the observation
of the ambient coronal plasma. NASA has
already started the development of such a
heat shield and we recommend that this de-
velopment be continued at a pace consistent
with a new start for the Solar Probe in 1991.

Advanced propulsion is required for the
SPO. Our proposed time line of mission se-
quences is based on the assumption that
such a capability, probably based on solar
powered ion thrusters, will be available by
1997. If it were available, a low-thrust pro-
pulsion system could also be used to en-
hance the scientific return of the Solar Probe

Mission by decreasing the period of the ec-
centric solar orbit to allow more than one
close solar passage within the useful life-
time of the spacecraft. Advanced propulsion
is also under consideration by the planetary
community for a multiple asteroid rendez-
vous mission. Thus, we recommend that
NASA either accelerate its development of
this technology or join forces with some
other agency working on advanced propul-
sion.

Priorities

We assume that the following missions are
approved and will be flown: International
Solar Polar Mission, solar instruments on
Spacelab 2 and Spartan 2, and the Solar
Optical Telescope Facility. For new mis-
sions for solar-heliospheric physics, we
have identified the first and second priori-
ties.

• WIND and SOHO components of ISTP

• Pinhole Occulter Facility

In addition, we have prioritized other pro-
grams in the following categories:

• Major Free-Flying Missions

— Solar Probe

— Solar Polar Orbiter

• Explorer Missions

— Solar-heliospheric Explorer missions
at the rate of one per two or three
years

• Shuttle Missions

— Additional moderate-sized solar in-
struments beyond the Spacelab-2 ex-
periments

— Spartan missions to succeed the
sounding rocket program

— Additional flights of the SOT with co-
observing instruments and enhanced
focal plane instruments

— Additional solar facilities: Soft X-ray
Telescope, High Energy Facility, and
EUV Telescope Facility

• Space Station Missions

— Deployment of Solar Optical Tele-
scope and other facility class and ap-
propriate instruments as the start of
the Advanced Solar Observatory

There are several important activities that
are not specifically mission related. These
include the Theory and Modeling Program
and Research and Analysis. Both of these

activities are prerequisites for a healthy
program in solar-heliospheric physics.
Within the Research and Analysis program
we assign priorities in the following order:

(1) theory and analysis , (2) instrument devel-
opment , (3) correlative observations f and (4)
complementary research.

The time line shown in Figure 5 for the
solar and heliospheric physics program re-
sulted from considerations of scientific
priorities, funding constraints, technological
readiness, and the phase of the solar activ-
ity cycle.

The program of solar-heliospheric physics
discussed here is constrained by funding.

As a result we excluded a number of excit-
ing missions that might be reconsidered in
the twenty-first century. For example, a he-
liostationary orbiter, whose period equals
the rotation period of the Sun, would permit
continuous observations of the evolution
and decay of solar activity and unique in

situ measurements of the evolution of the
heliosphere at one solar longitude. Another
example is a Heliosphere Boundary Probe
intended to locate and explore the helio-
pause and to explore the particle, field, and
plasma environment of interstellar space.

Funding constraints also caused us to re-
duce the capabilities of several proposed
missions. For example, an early study of the
Solar Probe ( Starprobe : Scientific Rationale,
J.H. Underwood and J.E. Randolph, JPL Publ.
82-49, 1982) with an experiment payload that
included imaging, drag-free experiments,
and a maser clock was estimated to cost
approximately $1 billion. The mission rec-
ommended here, however, addresses only
our highest priority objective, i.e., the inves-
tigation of the sources of the solar wind.
More comprehensive missions should be
considered for implementation early in the
twenty-first century.

38

8 DETAILED MISSION PLAN S — PLASMA PHYSICS

Introduction

The critical scientific objectives of space
plasma physics are to

* trace the transport of energy, momen-
tum, and matter from the Sun, through the
interplanetary medium, across the magne-
tospheric boundaries, through the magne-
tospheres and ionospheres into and out of
the upper atmospheres;

• understand the physical processes that
control the entry, transport, storage and re-
lease of plasma and of energy and momen-
tum in magnetospheric systems, with spe-
cial emphasis on understanding basic
physical processes not readily accessible to
laboratory investigation;

* investigate the processes that couple
distinct parts of the system including the
solar wind, magnetospheres, ionospheres,
and upper atmospheres; and

• describe and understand fully the
sources and sinks of magnetospheric plas-
mas.

These objectives are implicitly included in
the report, Solar-System Space Physics in
the 1980's: A Research Strategy prepared by
the Committee on Solar and Space Physics
in 1980. Mission planning must recognize
the requirement to perform measurements
directed toward these objectives. Integration
of theoretical activities in support of mission
design and development and in analysis of
measurements will accelerate progress in
understanding the complex magnetospheric
system.

Program Descriptions

In this section a mix of major, moderate,
and small programs with associated
MO&DA and R&A resource requirements is
discussed. The near-term program through
the early 1990s and a longer-term program
that utilizes the Shuttle/Space Station/Plat-
form systems beyond 1992 are described.

Major Programs

International Solar-Terrestrial Physics
Program

The International Solar-Terrestrial Physics
Program (ISTP) is being planned by NASA,
ISAS, and ESA in order to develop a com-
prehensive global understanding of the pro-
duction and flow of energy within the Sun,
the heliosphere, and Earth's magnetosphere
and ionosphere. As of the summer of 1984,
the ISTP program is planned to begin devel-
opment in 1986 and will continue operations
through the 1990s. The program will define
the complex relationships that exist within
the solar-terrestrial system. Here we de-
scribe each of the six spacecraft compo-
nents of ISTP.

WIND . WIND is proposed to be built and
launched by NASA (1989) as the first of this
series. It will utilize lunar swing-bys to
maintain its apogee on the day side of Earth
and thus to survey the upstream region out
to distances of 250 R E during perhaps the
first two years after launch. After that time,
plans include the possibility of placing
WIND into a halo orbit about the libration
point. WIND will make correlative measure-
ments with the rest of the network of space-
craft in the ISTP program (SOHO, POLAR,
EQUATOR, GEOTAIL, and CLUSTER). WIND
will

• investigate sources, acceleration mecha-
nisms, and propagation processes of ener-
getic and solar wind particles in correlation
with SOHO;

• provide the complete solar wind plasma,
energetic particle and magnetic field inputs
for magnetospheric and ionospheric studies
to support POLAR, EQUATOR, GEOTAIL,
and CLUSTER;

• determine the magnetospheric output
(particles, beams, and waves reflected from
the bowshock and the magnetopause) in the
upstream region;

• investigate basic plasma processes oc-
curring in the solar wind near Earth; and

39

• provide baseline observations in the
ecliptic plane to be used in correlation with
observations made at high heliospheric lati-
tudes by the ISPM spacecraft.

POLAR. POLAR is one of the three magne-
tospheric components of ISTP. It would be
built and launched by NASA (1991) into an
eccentric polar orbit having perigee at ap-
proximately 2 R e and apogee at about 8.5
R e . It will make correlative measurements of
plasma, energetic particles, and electric
and magnetic fields in conjunction with
WIND, EQUATOR, GEOTAIL, and CLUSTER.
POLAR will have the following magnetos-
pheric and ionospheric plasma physics ob-
jectives:

• determine the role of the ionosphere in
substorm development and in the overall
magnetospheric energy balance, correlating
data with those from EQUATOR and GEO-
TAIL;

• measure plasma energy input through
the dayside cusp region, correlating data
with those from WIND and SOHO;

• determine characteristics of ionospheric
plasma outflow and energized plasma in-
flow to the atmosphere, in support of the
UARS mission;

• study the characteristics of the regions
wherein auroral plasma is accelerated, cor-
relating data with those from CLUSTER;

• provide global, multispectral auroral im-
ages of the footprint of magnetospheric en-
ergy deposition into the ionosphere and up-
per atmosphere at high latitudes; and

• measure magnetic field signatures of
field-aligned currents.

EQUATOR. EQUATOR is another of the
three magnetospheric components of the
ISTP Program. It would also be built and
launched by NASA (1991) into an equatorial
orbit with perigee at about 2 R E and apogee
near 12.4 R E . It will make correlative meas-
urements of plasmas, energetic particle
populations, and of electric and magnetic
fields in conjunction with POLAR, GEOTAIL,
and CLUSTER. EQUATOR will have the fol-
lowing magnetospheric objectives:

• determine overall magnetospheric en-
ergy balance and the effects of substorms in
populating the ring current and inner mag-
netosphere, correlating data with those from
POLAR and GEOTAIL;

• help determine the role of internal mag-
netospheric substorm trigger mechanisms
and separation of such effects from external
trigger mechanisms through correlations
with SOHO and WIND;

• provide direct observations of the inter-
actions between geomagnetic tail and iono-
spheric plasmas in the equatorial magne-
tosphere;

• measure the transport, energization, and
storage of ionospheric and tail plasmas in
the near-Earth plasma sheet and ring cur-
rent, correlating data with those from GEO-
TAIL and POLAR; and

• measure the coupling between the solar
wind and the magnetosphere at the sub-
solar magnetopause, correlating data with
those from WIND and SOHO.

GEOTAIL . GEOTAIL is the third magnetos-
pheric component of ISTP. It would be built
by Japan and launched by NASA (1991) into
a lunar swing-by orbit in order to maintain
an apogee in the distant (80-250 R E ) magne-
totail for a period of about 1 year. After this
time, a propulsion system will place GEO-
TAIL into an equatorial orbit of 8 R E by 20 R E
for making detailed measurements of sub-
storm processes in that region. GEOTAIL
will have the following important magnetos-
pheric objectives:

• determine the overall plasma and field
properties in the distant geomagnetic tail
region;

• determine the relative roles of the dis-
tant and near geomagnetic tail in substorm
processes, and in the overall magnetos-
pheric energy balance correlating data with
those from EQUATOR, POLAR, and WIND;

• study the initiation of reconnection proc-
esses in the geomagnetic tail and observe
the microscopic properties of the energy
conversion mechanisms in this reconnection
region, correlating data with those from
EQUATOR, CLUSTER, and POLAR;

• separate the relative contributions of the
ionosphere and solar wind to the geomag-
netic tail plasma; and

• study the entry, energization and trans-
port of plasma in interaction regions such
as the inner edge of the plasma sheet, mag-
netopause and bow shock.

CLUSTER. CLUSTER consists of one main
and three companion spacecraft, each hav-

ing on-orbit propulsion capability to adjust
inter-satellite separations from 100 km to up
to several Earth radii. The CLUSTER would
be an ESA program designed for launch
either by an Ariane IV booster or by a Space
Shuttle flight. Data from CLUSTER will be
correlated with those from other ISTP space-
craft as part of the overall international pro-
gram. The proposed mission plan is to place
the CLUSTER spacecraft into a polar orbit 20
R E x 3 R e . CLUSTER will perform correlative
multipoint measurements at known separa-
tions of its four individual spacecraft, and
will

• explore the boundary regions of the
magnetosphere as a readily accessible ex-
ample of the sharp interface between two
cosmical plasmas and thereby to investi-
gate the detailed processes by which mass,
momentum, and energy are transported
across boundaries such as the magneto-
pause;

• study the magnetic reconnection proc-
esses and the small scale MHD structure
and plasma acceleration associated with re-
connection regions;

• study MHD turbulence, vortex formation,
and eddy diffusion, especially in the polar
cusp and boundary regions;

• investigate the structure and properties
of collisionless shocks, including the bow
shock, and the associated wave generation
and particle acceleration;

• determine the small scale properties of
the solar wind flow around the Earth; and

• utilize the four-spacecraft configuration
to determine unambigously the three-dimen-
sional shape and dynamics of magnetic
structure with scale sizes from 0.1 R E to 10
R E (four-point measurements can determine
the curl of a vector field, i.e., the spatial
current density).

SOHO. The SOHO spacecraft is proposed to
be three-axis stabilized to allow a variety of
optical instruments to view the solar surface
and corona from an Lj libration point orbit.
SOHO is proposed to be an ESA program,
and will be designed to be launched by
either an Ariane IV booster or from the
Space Shuttle (1993). Although its primary
objectives are to observe solar phenomena
(see Chapter 7), it is planned to carry
plasma instrumentation for in-situ measure-
ments of the solar wind. SOHO will have

the following objectives that are important
to the magnetospheric plasma physics in-
volved in the overall ISTP program:

• study the solar wind plasma, collision-
less shocks in the solar wind and other ir-
regularity structures, correlating data with
those from WIND; and

• provide information on solar wind input
functions for use in interpreting data from
WIND, POLAR, EQUATOR, GEOTAIL, and
CLUSTER.

Explorers for Magnetospheric Plasma
Physics

While many of the important global aspects
of magnetospheric plasma physics will be
addressed by the comprehensive ISTP mis-
sions involving WIND, EQUATOR, POLAR,
GEOTAIL, and CLUSTER, there are specific
scientific objectives and measurements that
are more limited and can only be addressed
by Explorer-class missions of low-to-moder-
ate cost. Recent examples include the Dy-
namics Explorers (DE) spacecraft, measure-
ments from which have significantly
advanced our understanding of magnetos-
phere-ionosphere coupling processes; and
the Active Magnetosphere Particle Tracer
Explorers (AMPTE), which investigated
plasma entry into the magnetosphere via
tracer ion releases in the solar wind. These
and previous Explorer missions have been
the mainstay of research in space plasma
physics and their availability in the future
is crucial to the development of this disci-
pline.

Explorer missions in space plasma phys-
ics generally require orbits that are high
(greater than 1 R E ) altitude and are intended
to provide measurements over extended pe-
riods of time (greater than 1 year), i.e., not
compatible with Shuttle or Space Station or-
bits. Potential missions have been studied
by NASA in the past (e.g., Plasma Turbu-
lence Explorer) but have not been carried
out because of budget limitations. Other il-
lustrative mission concepts are given in the
report A Strategy for the Explorer Program
for Solar and Space Physics, NAP, 1984.
Among these missions are spacecraft to
study

• acceleration at heliospheric shocks,

• magnetopause structure and dynamics,

• active plasma injection (seeding) experi-
ments, and

• ionospheric instabilities and turbulence.

These mission concepts represent only a

few examples, and a solicitation of the sci-
entific community through the AO process
will undoubtedly produce a variety of mis-
sion ideas addressing first-class scientific
problems. It should be noted that the instru-
mentation and spacecraft technology for the
few illustrative missions given above is all
within current state-of-the-art, and no new
developments are necessary.

Active Experiments

Active experiments, where the environment
can be perturbed with injections of parti-
cles, beams, or waves and then studied to
determine its responses, are a unique op-
portunity to perform laboratory-style experi-
ments in space. Such experiments are ex-
tremely valuable in aiding our
understanding of basic plasma processes
because the experimenter has a great deal
of control of the experiment and can there-
fore address sharply focused questions. Ex-
periments in this category include the fol-
lowing:

Combined Release and Radiation Effects
Satellite

Combined Release and Radiation Effects
Satellite (CRRES) is a free-flying spacecraft
mission undertaken jointly by DOD and
NASA. The NASA portion of the mission in-
volves chemical release experiments solic-
ited by an AO, evaluated by a peer review
committee, and selected by NASA/OSSA.
This chemical release program is designed
to replace partially the cancelled Chemical
Release Module program, and has research
goals consistent with those in the Kennel
report.

CRRES is a two-part mission. The space-
craft will be launched initially into a low-
Earth-orbit (LEO) where it will remain for a
period of 45 to 90 days. During LEO, se-
lected chemical releases will be carried out
at specific locations designed to be observa-
ble from suitable ground-based diagnostics
facilities such as the Arecibo and Jicamarca
Observatories or high-altitude ground sites

in the southwestern United States, as well
as by aircraft-borne instrumentation.

The CRRES payload will include the fol-
lowing:

• tracer experiments in which releases of
foreign elements can be used to trace geo-
magnetic field lines, assess natural electric
fields and potential structures, and measure
winds;

• modification experiments involving mas-
sive releases that can significantly perturb
the ambient ionosphere; and

• simulation experiments in which re-
leases are used to simulate plasma physical
phenomena not amenable to laboratory ex-
perimentation.

Once the CRRES is transferred to a geos-
tationary transfer orbit, several high alti-
tude releases will occur. These releases are
primarily for tracing magnetic field lines
and for modifying the immediate region at
low latitudes just at the plasmapause.

Tethered Satellite System

The Tethered Satellite System (TSS) is a
joint project for NASA and Italy's National
Research Council. NASA is responsible for
producing the Shuttle-borne deployment
mechanism and tether, while the Italian Na-
tional Research Council is to furnish a sat-
ellite system to carry scientific experiments
attached to the tether. The tether may be
either a conductor or insulator, depending
on the type of scientific mission. It can be
utilized to study electrodynamic processes
in the ionosphere or atmospheric phenom-
ena in regions down to 130 km where few
measurements have been made and are dif-
ficult to achieve by other means (rockets or
satellites). Here we discuss only the con-
ducting tether missions and refer to Chapter
9 for discussion of atmospheric tether mis-
sions.

Two electrodynamic tether missions are
planned, TSS-1 and TSS-3. TSS-2 is to be an
atmospheric mission (see Chapter 9). TSS-1
is planned for a mid- 1987 Shuttle launch,
TSS-3 to fly about mid 1990. These missions
will be in a nominal 28° inclination orbit at
300-400 km altitude. On TSS-1, the conduct-
ing tether and its attached satellite will be
deployed upward to a distance 20 km above
the Shuttle. The tether will be attached to

the conducting surface of the satellite, and
through an electron gun to the orbiter's
ground plane, to return electron current to
the ionospheric plasma. The entire duration
of the TSS-1 test will be 36 hours. Scientific
experiments will be limited on TSS-1, which
is an engineering test of the TSS, while
TSS-3 is planned to carry a more sophisti-
cated scientific payload.

The objectives of TSS-1 and TSS-3 are the
following:

• determine the current/voltage character-
istics of the system at high voltages;

• study management of electrical charge
on the orbiter;

• produce Alfven waves in the ionosphere
using the tether current source;

• produce LF (< 1 kHz) waves by modula-
tions of the tether current and study their
propagation;

• study nonlinear plasma physical proc-
esses in the dynamic sheath around the sat-
ellite; and

• utilize the conducting tether as an effi-
cient antenna for transmitting diagnostic
VLF waves to distant receivers.

Shuttle/Spacelab Programs

The Shuttle/Spacelab capabilities are espe-
cially suited to accommodate active experi-
ments, since they are massive and have en-
ergy, power, and heat rejection
requirements that exceed the usual capabil-
ities of unmanned free-flyers. Of particular
interest is the use of this carrier to perform
active experiments in which electromag-
netic wave energy, energetic charged parti-
cle beams, plasmas, and neutral gases, and
controlled releases of various chemical spe-
cies are effected during 7- to 9-day mis-
sions. In addition, these instruments can be
reflown on subsequent Shuttle missions in
either their original form, or refurbished or
upgraded as results from previous flights
may dictate.

An attractive use of such Shuttle/Spacelab
missions is also apparent: active experi-
ment instrumentation can be developed in
an evolutionary fashion, using the Shuttle/
Spacelab flights as test beds for develop-
ment of instruments in a form for later use
in the Space Station and/or associated plat-

forms similar to the STO. Such equipment
as that used to inject large amounts of elec-
tromagnetic wave energy into the iono-
sphere and magnetosphere, or inject power-
ful electron or ion beams into those regions,
can benefit greatly from on-orbit residence
times much greater than the 7 to 9 days
available on Shuttle missions, but an or-
derly program of preliminary developmental
flights on the Shuttle would allow final de-
velopment of a flight-qualified inventory of
such equipment for use in plasma physical,
magnetospheric, and ionospheric research
on a station or platform of several months to
a year mission duration. The effects of these
active experiments can be diagnosed with
near-by probes and through the constella-
tion of magnetospheric free-flying satellites
from programs such as ISTP and the Explor-
ers.

Spacelab-2

Spacelab-2 (SL-2) is a multidisciplinary mis-
sion carrying 12 Pi-class experiments on a
nominal 7-day mission planned for launch
in April 1985 into a 50° inclined orbit. Three
SL-2 experiments are plasma physical or
ionospheric in nature. The VCAP experiment
involves an electron gun capable of pulsed
operation up to 500 kHz at peak currents of
0. 1 A at 1 kV. It also has diagnostics, in-
cluding a capacitive probe to measure orbi-
ter charge states, and can carry out orbiter
charge management experiments. A free-
flying Recoverable Plasma Diagnostics
Package (RPDP) will measure electromag-
netic interference levels in and around the
orbiter cargo bay, diagnose effects of the
VCAP electron beam (waves and particles),
and perform wake and sheath measure-
ments near the orbiter (up to 1 km separa-
tion). A third experiment uses dedicated en-
gine bums of the Shuttle's Orbital
Maneuvering Subsystem (OMS) in a series
of active experiments for plasma depletion
studies in ionospheric and radioastronomi-
cal areas. The primary diagnostics employ
ground-based radars and optical imaging
systems.

Spacelab Reflight Missions

A series of reflight opportunities utilizing
existing Spacelab instruments can be ex-

ploited. An example is the EOM-1 mission,
on which it is planned to carry the Japanese
SEPAC instrument and the diagnostic AEPI
instrument to support it, both flown on SL-1,
These instruments will carry out electron
beam injections and observations associ-
ated with geomagnetic field line tracing,
electrical potential structures, beam-plasma
discharge phenomena, artificial auroral dis-
plays and neutral or plasma gas injections.
Other reflights-of-opportunity should be
planned or identified.

Space Plasma Lab Program

Space Plasma Lab-1 (SPL-1) is planned for a
launch on a near-polar (77°) orbit at about
350-500 km in December of either 1988 or
1989, depending upon budget constraints
and development schedules. It is to carry a
wave injection instrument with capability to
radiate VLF from 1 to 30 kHz with up to 1 kW
power input to a dipole antenna of length
between 100 and 300 m. A Canadian-fur-
nished HF transmitter and receiver will
transmit and receive sounding signals be-
tween 100 kHz and 30 MHz. The SEPAC in-
strument from SL-1 will perform electron
beam injections, with the AEPI instrument to
support it with optical observations and a
set of newly developed plasma diagnostics
(TEBPP). To support the active experiments
by making in situ measurements at prede-
termined distances along magnetic field
lines connecting to the orbiter, a RPDP will
be flown.

The scientific objectives of SPL are to

• test the ability of a dipole antenna in
the ionospheric plasma to radiate VLF wave
energy;

• study the nonlinear plasma physical
phenomena around the high-voltage dipole
antenna;

• study wave-particle interactions in the
trapped electron population produced by
VLF signals from an antenna above the F-
layer maximum;

• perform VLF propagation studies for all
paths possible out to 100 km from the orbiter
and including radiation to ground stations;

• perform bistatic HF sounding measure-
ments with orbiter and RPDP receivers to
study ionospheric irregularities, travelling
ionospheric disturbances, and coupling to
gravity waves;

• perform high-current, high-voltage elec-
tron beam experiments and study the beam-
plasma discharge and artificial auroral dis-
plays;

• perform field-line tracing and electrical
potential structures diagnostics using the
electron beam from SEPAC; and

• perform Shuttle wake and sheath meas-
urements, antenna radiation efficiency esti-
mates, electron beam evolution, and OMS
thrusher firings diagnostics using the RPDP,
AEPI, and ground-based instrumentation.

Space Station/Platform Programs

The Space Station/Platform capability pro-
vides an ideal vehicle for missions involv-
ing the active experiments using energetic
particle beams, wave energy injections, and
chemical releases. The capability to re-
cover, service, and change out scientific ex-
periments on-orbit opens new possibilities
for experimentation using these heavy,
power consuming experiments that can ben-
efit from extended mission durations in low-
Earth orbits.

It is desirable that such active instrumen-
tation be developed in an evolutionary man-
ner using earlier Shuttle/Spacelab flight op-
portunities for test-bedding and check-out.

Since the Space Station architecture (in-
cluding the question of inclusion of one or
more science platforms) remains to be deter-
mined, only general statements can be
made. One can suggest missions up to 6-
months duration on platforms that provide
up to perhaps 25 kW of power, with energy
storage units capable of furnishing high-
peak-powers for pulsed operation of active
experiments. Platforms in near-polar orbit
would be ideal for wave and beam injec-
tion, while lower inclinations may be useful
for missions involving the TSS. A compre-
hensive study of possible missions and pay-
loads can be found in the final report of the
science study group: Solar-Terrestrial Ob-
servatory, October 1981, and in Solar-Terres-
trial Observatory: Conceptual Design and
Analysis Study, April 1982, both NASA Mar-
shall Space Flight Center documents.

The objectives of an STO-like Space Sta-
tion Platform are to increase the under-
standing of wave-particle processes; magne-
tospheric-ionospheric mass transport; the

global electric circuit; ionosphere irregular-
ity structure, travelling ionospheric disturb-
ances, and their coupling to atmospheric
gravity waves; electrodynamic tether inter-
actions including Alfven, magnetosonic,
and plasma wave production; non-linear
plasma physics; beam-plasma interactions;
and plasma physics experiments in micro-
gravity and without walls.

The latter area is of special interest, and
should be examined carefully. There are
laboratory plasma experiments that can be
defined ideally but not carried out on Earth
because of the presence of chamber walls.
Some of these are related to the fusion en-
ergy program. For example, storage rings
could be formed taking advantage of zero-
gravity to eliminate support structures that
represent plasma sinks or contribute un-
wanted impurities into the experimental
plasma. A set of plasma physics experi-
ments should be identified and examined
for possible performance in a Space Station
facility.

Suborbital Programs

The suborbital programs have traditionally
included balloon, rocket, and aircraft sys-
tems. For some types of measurements
these programs are appropriately being
supplanted by Shuttle and Space Station
programs. However, there are measure-
ments of the stratosphere, middle atmos-
phere, and ionosphere for which the mainte-
nance of vigorous suborbital capabilities is
desirable and, indeed, imperative for the
unique capabilities not achievable with
Shuttle or satellites.

Balloon payloads can measure atmos-
pheric electric fields and atmospheric poten-
tials. Payloads for magnetosphere studies
can include bremsstrahlung X-ray sensors,
photometers, and even neutron (or other)
sensor systems. Balloons also provide an in-
expensive way to test new instrument con-
cepts. Furthermore, a relatively long dura-
tion set of measurements can be made in a
nearly constant location in latitude, longi-
tude, and altitude. Correlations with ground
radar and with spacecraft measurements in
this way have proven very efficacious.

Similarly, rockets provide unique advan-
tages in terms of specific local measure-

ments at relatively low cost and low risk.
Developmental testing of spaceflight hard-
ware can be accomplished readily on rocket
flights. Furthermore, many auroral studies
and active experiments (e.g., beam experi-
ments, chemical releases) can be accom-
plished most cheaply and most readily
through rocket campaigns.

Finally, aircraft facilities can also be a
valuable asset. Aircraft are utilized to meas-
ure electric fields associated with weather
systems, for example. Also, testing of opti-
cal systems in safe and inexpensive ways is
possible. Such testing can be most helpful
in preparation for full spaceflight develop-
ment work. Rapid deployment capability is
also an attractive feature of aircraft facili-
ties.

In summary, we recommend the mainte-
nance of a strong suborbital program where
it makes scientific, technical, and financial
sense. Those programs that can use Shuttle
capabilities effectively should be encour-
aged to use the Spartan and Hitchhiker sys-
tems, for example, but where scientific ob-
jectives can be achieved effectively,
expeditiously, and at lower cost by use of
balloons, rockets, or aircraft, these alterna-
tives should be provided.

At present there is a funding level of ap-
proximately $3M for rocket and balloon pay-
load in the space plasma physics budget.

As illustrated in our budget timeline, we
recommend that this level be increased
modestly (to about $4M) through FY 88 and
then be decreased. We recommend that the
Spartan program be funded at the $2M level
in FY 85 (in part with funds otherwise allo-
cated to the rocket program). We then sug-
gest that by FY 87 there be a constant level
of funding, at about $4M/yr, through the mid
1990s in the Spartan program and an equiv-
alent amount for the Hitchhiker program.

Planetary Magnetospheres

Studies of the plasma environments of other
planets can yield data relevant not only to
planetary science but also to understanding
Earth's environment in broad scientific
terms.

Magnetospheric structure and dynamics
depend upon many aspects of the interac-
tion between an object and its environment.

The planet or other central body (we include
moons embedded in corotating planetary
plasmas) may be unmagnetized (Venus, pos-
sibly Mars, major moons) or magnetized
(Mercury, Jupiter, Saturn, possibly Mars
and/or Io); may lack an atmosphere (Mer-
cury, Ganymede, Europa, Callisto) or have
an atmosphere (Venus, Mars, Jupiter, Sat-
urn, Io, Titan); may be embedded in sub-
Alfvenic flows (Io), near-Alfvenic flows (Ti-
tan), or super-Alfvenic flows (all others).
There may or may not be secondary plasma
sources such as Io's volcanoes or Saturn's
rings within the magnetosphere. Rotation
may be slow enough to be ignorable (e.g..
Mercury) or may dominate dynamical be-
havior (e.g., Jupiter). For each combination
of parameters, the relative importance of
different physical processes changes, and
spacecraft measurements can provide
unique insights.

Mercury's magnetosphere is small, even
on the scale of the planetary radius, be-
cause its magnetic field can barely stand off
the solar wind. Yet there is evidence that
substorms and particle acceleration occur at
Mercury much as at Earth. Data from two
flybys raise questions (e.g., what is the na-
ture of hydromagnetic flow in a magnetos-
phere so small that an ion Larmor radius is
not negligible?) but do not give answers.

Venus missions have illuminated the way
in which solar wind plasmas interact with
dense ionospheres. The solar wind mag-
netic field drapes around the ionosphere,
and some magnetized plasma convects into
the ionosphere, producing spatially con-
fined regions of large, twisted magnetic
fields (flux ropes) deep inside the iono-
sphere. Magnetic flux tubes couple iono-
spheric plasma to the solar wind and pro-
vide direct paths for particle losses from the
ionosphere.

Past missions to Mars have not yet com-
bined appropriate fields and particle instru-
mentation and spacecraft trajectories for
studies of the magnetosphere. Thus, it re-
mains uncertain whether Mars has an in-
trinsic magnetic field or not. Some think
that Mars represents an important "interme-
diate" case, standing off the solar wind
partly with a magnetic field (like Mercury)
and partly with an ionosphere (like Venus).

Jupiter's large magnetic field, rapid rota-

tion rate, and internal plasma source, Io, is
radially distorted into a disc-like configura-
tion modulated at the 10-hour rotation pe-
riod. Indeed, the 10-hour modulation and
control by Io of radio frequency emission
probability were first noted by Earth-based
observers. Those observations were con-
firmed in situ and features of the Jovian
environment (magnetic field magnitude and
direction, existence of field-aligned cur-
rents) inferred from remote observations
proved remarkably accurate. The Galileo
mission, to reach Jupiter in 1988, will permit
an orbiting spacecraft to monitor the tem-
poral variability of Jupiter's giant magnetos-
phere. In addition, Galileo will traverse the
regions in which the Galilean moons form
secondary magnetospheres within the rotat-
ing Jovian plasma, thus extending studies
of comparative magnetospheres.

Saturn has a magnetosphere much like
that of Earth, but modified by embedded
moons and rings. Radio frequency emis-
sions from Saturn are modulated at the pla-
netary rotation period, but there is no evi-
dence for asymmetries needed to explain
the modulation.

Insights gained from studies of magnetos-
pheres of other planets are of great impor-
tance to our evolving understanding of
space plasmas. The next steps in planetary
exploration should include the following:

• a Mars orbiter instrumented for fields
and particles investigations, with orbits op-
timized for magnetospheric measurements;

• a Saturn orbiter with trajectory selected
to allow high latitude measurements from
which field asymmetries and radio sources
can be investigated;

• a spacecraft placed in orbit about Mer-
cury, the only known magnetized planet
without an atmosphere, to illuminate the
role of atmospheres in substorms and other
magnetospheric processes; and

• exploration and intensive study of the
inner Jovian system — density, composition,
and energy of the magnetospheric particles;
large-scale structure and rotation, time-de-
pendent phenomena and relation to Io,
other satellites, and orbiting gas and
plasma; auroral activity on Jupiter; and
electromagnetic emissions. [This objective,
from the Space Science Board's Committee
on Planetary and Lunar Exploration report.

A Strategy for Exploration of the Outer Solar
System (in preparation), is endorsed by the
CSSPL

Comets

The exploration of comets is a step into a
new regime of space plasma physics in
which a flowing magnetized plasma inter-
acts with a dilute neutral gas in the pres-
ence of a source of ionizing radiation.
Ground-based observations and satellite-
based remote sensing of cometary plasma
still have many unanswered questions
about

• the range of physical mechanisms re-
sponsible for the rapid ionization of the
gases released from the nucleus;

• the mechanism(s) responsible for the
pick up of newly ionized material by the
solar wind (i.e., acceleration and thermali-
zation of the cometary ions and the deceler-
ation and heating of the solar wind);

• the details of the mechanisms responsi-
ble for acceleration of plasma into the ion
tail;

• the magnetohydrodynamic topology of
the interaction region (e.g., Is there a thin or
a thick ionopause? Are there flux ropes? Is
there a shock internal to the ionopause?);
and

• the interaction between plasma and
dust.

A series of cometary exploration missions
have recently been initiated.

• The International Cometary Explorer
will fly through the tail of comet Giacobini-
Zinner in September 1985.

• A series of five spacecraft will pass sun-
ward of the nucleus of comet Halley in
March 1986. One of these spacecraft, ESA's
Giotto, is planned to pass close enough to
the nucleus to penetrate the ionopause (if
such an identifiable structure exists) and
very briefly sample the cometary iono-
spheric plasma.

• A mission to rendezvous with a short-
period comet is currently under study by
NASA's Solar System Exploration Division.

The comet rendezvous mission offers the
possibility of obtaining qualitatively differ-
ent types of measurements than those that
can be obtained with the flyby missions.

• It will be possible to study the evolution
of the comet-solar wind interaction as a
function of the level of cometary activity.

• It will be possible to map the major
close-to-the-nucleus features of the comet-
solar wind interaction in order to under-
stand the major ionospheric processes such
as ionization, acceleration, and heating of
the plasma, which ultimately forms the tail.

• It will be possible to determine the
abundances and velocity distribution func-
tions of the minor as well as the major ion
species in the inner coma where the local
chemical composition is determined by ion-
neutral reactions. Measurement of the elec-
tron temperature is also vital to understand-
ing the inner-coma chemistry.

In view of the important and essential
plasma physics that can be learned on a
comet rendezvous mission, such a mission
should include instruments for the measure-
ment of plasma parameters — at a minimum,
an ion mass-velocity spectrometer, an elec-
tron spectrometer, a magnetometer, and a
plasma wave analyzer.

Theory and Modeling

NASA's Solar-Terrestrial Theory Program
(STTP), initiated in response to the Colgate
Report, has been one reason why solar sys-
tem plasma research has reached a new
level of precision, whereby it is strongly
contributing to both general plasma physics
and to the interpretation of space data.

Although this program has resulted in
substantial progress toward the goal of as-
similating our accumulated knowledge into
comprehensive theories, several important
problem areas remain. The level of support
of particle acceleration as a generic topic
with application to almost every area of
space physics research is incommensurate
with its prominence and the available theo-
retical knowledge and tools. The same is
true for particle confinement and transport.

It is worth noting that while over 50 active
beam injection experiments from rockets
and the Shuttle have been performed, the
theoretical effort to interpret these results
has only just begun. As a result, the subject
of controlled beam experiments is scientifi-
cally behind, despite the enormous progress
in the understanding of natural beam and

radioemission physics. A newly emerging
area that needs attention deals with neutral
gas plasma interactions including the ef-
fects of large structures. Research on these
topics is a must in the era of cometary ex-
ploration and of space station research. A
major increase in funding is immediately
necessary for these high-leveraged scientific
investigations.

Specific theoretical problems may be
identified that are too complex to be ad-
dressed with current funding levels and
whose solution within a specified time pe-
riod is judged important. A concerted theo-
retical attack on such problems should be
approached through the use of an AO or a
"Dear Colleague" letter, by which one or
more groups should be chosen and funded.
Computer time should be made available to
these groups on national computer facili-
ties, and support provided for their addi-
tional manpower needs. The subject of ener-
getic beam injection in space is a potential
example: by collecting the many experimen-
tal results produced over the years and uti-
lizing the computational theoretical tools
available, the scientific return to the tens of
millions of dollars spent on experimental in-
vestigations over the years can be substan-
tially increased at a total cost of less than
$lM/yr.

Mission Operations and Data Analysis

The scientific value of space missions
comes, quite obviously, from the data that
are returned and processed through ground
systems. Hence, a primary consideration of
space programs has to be the proper plan-
ning of data systems from the earliest
stages. Equally important is the recognition
that scientists — the true users of the data —
should be involved in all phases of the
planning and implementation of data sys-
tems.

Many space plasma missions have contin-
ued to operate well beyond the primary mis-
sion phase. Funding in the MO&DA pro-
gram must therefore be provided with the
recognition that the data from the extended
mission period are an extremely important
scientific asset. These data provide the ba-
sis for testing the hypotheses developed
during the primary mission phase.

Because of the wealth of scientific data
provided by space physics missions and be-
cause of the inherent need for correlative
analyses, the space physics community has
been a leader in improved data analysis
techniques. In fact, the Space Physics Anal-
ysis Network (SPAN) system has grown out
of the need in the space plasma community
to merge, correlate, and intercompare very
diverse data sets. SPAN arose from a "grass
roots" effort among space physicists and
now is leading virtually all NASA disci-
plines in scientific data interchange and in
the associated development and implemen-
tation of networking, graphics standardiza-
tion, and data formatting techniques.

Based upon the direct "hands on" experi-
ence provided by the SPAN system, pro-
grams such as ISTP and UARS are develop-
ing data facilities around well-tested
concepts of data handling and data process-
ing. Superior, cost-effective scientific return
will result within these new programs. Ex-
isting and future programs of other types
will benefit from this continuing experience.
We recommend that increased MO&DA
funding be provided to allow data archiving
and cataloging, improved networking, and
enhanced analysis capability in a discipline
with proven experience, capability, and net-
working infrastructure.

Research and Analysis

Funds associated with individual space
missions increase and decrease on rela-
tively short time scales whereas the train-
ing, assembling, and maintenance of scien-
tific teams is, and should be, a much longer
term activity. The expertise and capability
of a scientific staff must be continued and
nurtured in order to allow progress in basic
research. The kind of long-term stability in
funding that leads to real success in the
space sciences comes about from the R&A
funding program.

Analyses have shown an alarming de-
crease in the R&A funding in space plasma
physics. In terms of constant FY 84 dollars,
this decrease has amounted to $4M from
$15M to $11M between FY 78 and FY 84. In
order to restore cm appropriate level of fund-
ing R&A, and in order to establish a more
proper balance of R&A among the space sci-

ences disciplines, we recommend an in-
crease from $11. 5M in FY 85 to $16M in FY
86. From FY 87 forward we strongly recom-
mend a level of about $20M in space plasma
R&A funding.

An area requiring particular attention in
space plasma physics is advanced instru-
ment development. If one relies solely on
funding associated with new missions to
provide instrumental design improvement
(and innovation), then hardware progress
will be unacceptably inadequate. We rec-
ommend that NASA provide a vigorous pro-
gram of R&A support explicitly earmarked
for instrument development including new
detection techniques, improved onboard
processing capabilities, higher spatial and
temporal resolution, and other instrument
improvements.

Technology Requirements/Instrument
Development

It is evident from the description of the rec-
ommended missions that current spacecraft
technology is adequate in all cases to carry
out the program. Recent advances in micro-
processor systems and custom-made VLSI
chips suggest that onboard data processing
techniques may well result in acquisition
and evaluation of much larger volumes of
data than previously thought possible, with-
out a consequent increase in data rates
transmitted to the ground. Incorporation of
reliable data storage devices aboard space-
craft will minimize requirements for continu-
ous tracking coverage by the Deep Space
Network (DSN) [for spacecraft in orbits that
cannot use Tracking and Data Relay Satel-
lite System (TDRSS)], thereby decreasing
costs in manpower and facilities for data
acquisition.

Science instrument development, on the
other hand, is an ongoing process. Funding
for such development is included in the rec-
ommended R&A program, except in those
cases where major, facility-class instru-
ments are required to carry out any of the
missions recommended for space plasma
physics. Nevertheless, science from mis-
sions later in the timeline is likely to be
enhanced by the development of more ad-
vanced instruments and techniques, as they
become available.

Long-Term Studies

Mission objectives are typically restricted to
those attainable within a few years, yet in
studies of solar cycle variations and other
long-term changes of magnetospheric prop-
erties, it is crucial to monitor key regions of
the magnetosphere over long periods of
time. For this purpose, geostationary satel-
lites are particularly well suited; it is essen-
tial that scientific instrumentation be pro-
vided on geostationary satellites or Space
Station Platforms for continued monitoring
of fields, particle fluxes, and plasma com-
position over many solar cycles.

Priorities

The highest priority for magnetospheric
plasma physics is clearly the ISTP program.
The other recommended missions of the
space plasma physics program are a
healthy and diverse mix of free-flyer space-
craft and active experiments. The elements
of the program are dictated by the overall
discipline funding profile and integration
with the phasing of Shuttle, Space Station,
and other capabilities.

The rededication of a vigorous Explorer
program is imperative to perform small-to-
moderate cost, specialized missions in solar
and space physics that complement the ma-
jor magnetospheric plasma physics mis-
sions represented by ISTP spacecraft.

On a comparable level are missions to
carry out the programs that will lead to evo-
lutionary production of active experiments
for use in the Space Station era. These are
the Shuttle/Spacelab and Tethered Satellite
System programs, including SPL, SL ref-
lights such as EOM-1, and the TSS-1 and -3
missions.

Strong MO&DA and R&A programs and
mission-directed theory and modeling ef-
forts must be inseparable components of the
above flight missions. These programs must
be supplemented by stable programs sup-
porting more general R&A and space
plasma physics theory and modeling.

Space Station/Platform missions are long-
term but have a priority set by their time-
line. Development of the active experimen-
tal instrumentation should proceed so that it
can be easily retrofitted to Space Station use.

MAGNETOSPHERIC/PLASMA PHYSICS

FIGURE 6

Suborbital programs have not been priori-
tized here. It is assumed that a steady level
of funding will be provided by which these
small programs-of-opportunity can be sup-
ported as they are identified and defined.
CRRES and SL-2 are not prioritized because
they are approved programs.

New opportunities to provide frequent
flight opportunities at relatively low cost are
developing on the Shuttle through the Spar-
tan and Hitchhiker programs. These pro-
grams should be encouraged and managed
in the same manner as the sub-orbital pro-
gram. New research ideas can be developed

and tested by a larger segment of the com-
munity at rather low cost.

Figure G shows the timeline for the pro-
gram in space plasma physics. There are
several programs that we consider scientifi-
cally important but could not include in our
timeline because of the funding constraints
that we have imposed on this implementa-
tion plan. Most important among these are
missions to study the magnetospheres of
other planets (Mars, Saturn, Mercury), a
comet rendezvous mission, and a helios-
phere boundary probe.

9 DETAILED MISSION PLANS— UPPER ATMOSPHERIC PHYSICS

Introduction

The upper atmosphere is defined here as
the region above the tropopause (about 12
km) and includes the stratosphere, mesos-
phere, thermosphere (and ionosphere), and
exosphere. The program is constructed on
the premise that this entire region should be
investigated as one dynamic, radiating, and
chemically active fluid. Historically, the up-
per atmosphere was investigated by remote
observations of limited regions or layers.

The satellite era led to intensive study of
the Earth's thermosphere by in situ meas-
urements. Complementary observations
were obtained with sounding rockets and
ground-based incoherent backscatter ra-
dars.

In-situ measurements of the stratosphere
have been made by balloon-, rocket-, and
airplane-based instruments whose flight du-
rations are short, and the resulting data are
restricted in geographic coverage as defined
by their trajectories or launch locations.
Rockets, for example, have provided limited
knowledge of vertical structure in composi-
tion and temperature at isolated locations.
Recently, ground-based capability to probe
these regions have been demonstrated by
MST radars and lidar, but again at only a
few locations.

To gain a global perspective of the upper
atmosphere in both horizontal and vertical
coverage and investigate the upper atmos-
phere as one interactive fluid, comprehen-
sive remote sensing measurements from
space platforms are the major directions for
the future. Thus, the upper atmospheric
physics program was designed around the
Upper-Atmosphere Research Satellite
(UARS) spacecraft — one of the principal rec-
ommendations of the Kennel report.

Another area of upper atmospheric study
is solar-terrestrial coupling, which is con-
cerned with the response of the Earth's mag-
netosphere, ionosphere, and atmosphere to
solar inputs and their variability. Studies of
solar-terrestrial phenomena are of consider-
able practical importance and provide an

incentive for coordination of individual pro-
grams in solar physics, magnetospheric/
space plasma physics, and upper atmos-
pheric physics to achieve a better under-
standing of the effects of solar cycle, solar
activity, and solar-wind disturbances upon
the Earth's atmosphere from the thermos-
phere down through the troposphere.

Program Descriptions

Major Missions

The highest priority in observatory-class
missions for the 1980s has been the Upper-
Atmosphere Research Satellite (UARS), now
a new start in FY 85. It will provide, for the
first time, an almost global data set on the
chemistry, dynamics, and radiative inputs
of the 10 to 70-km region of the atmosphere,
i.e., the stratosphere and lower mesosphere,
although some instruments are capable of
useful measurements to an altitude of ap-
proximately 200 km (Figure 7). The goals of
the UARS program are to understand the
mechanisms controlling middle atmospheric
structure and processes, to understand the
response of the upper atmosphere to natural
and human perturbations, and to define the
role of the upper atmosphere in climate and
climate variability. To accomplish these
goals, several areas of scientific study will
be fostered by the mission, including energy
input and loss, global photochemistry, dy-
namics, coupling among processes, and
coupling between the upper and lower at-
mosphere. The UARS data will be critical in
evaluating the extent of ozone depletion
caused by human activities and the impact
of upper atmosphere processes on climate
change.

The instrument payload has been care-
fully selected to meet the goal of coordi-
nated and complementary global measure-
ments of ozone, temperature, pressure,
energy input, winds, and chemical trace
species by remote sensing. A broad comple-
ment of stratospheric constituents will be

measured as part of the UARS payload.
Many of the important free radical species
(CIO, N0 2 ) will be measured simultane-
ously, as well as ozone densities. Further,
most of the long-lived species (e.g., CH 4 ,
N 2 0, CF 2 C1 2 ) that are the source of these
radicals will also be observed.

It is well known that stratospheric ozone
and other stratospheric trace gases are de-
pendent not only on photochemistry, but
also on atmospheric dynamics. Perhaps the
most important aspect of the UARS mission
is that direct measurements of atmospheric
winds will be made simultaneously along
with the photochemical observations, so
that the interactions between photochemis-
try and dynamics can be examined better
than from previous satellite missions where
only temperature was measured.

The UARS program includes theoretical
studies and model analyses with theoretical

principal investigators as an integral part of
the program to complement the measure-
ments and data analyses. Through this co-
ordinated program in measurements, data
and model analyses, and theoretical investi-
gation, it is anticipated that substantial
progress will be made in solving the out-
standing physical and chemical problems
above the tropopause.

UARS will be launched in the fall of 1989
using the Shuttle, which will deliver it di-
rectly to the operational circular orbit at 600
km and inclined 57° to the Equator. At this
altitude and inclination the remote sensors
looking 90° to the spacecraft velocity vector
can see to 80° latitude, providing nearly
global coverage. The inclination of the orbit
plane also produces a precession of the
plane to allow all local solar times to be
sampled in about 33 days, which should
give resolution of diurnal atmospheric ef-

52

fects in a period that is short relative to
seasonal effects.

The UARS spacecraft can be retrieved by
the Shuttle and is designed to be refur-
bished, thus allowing for an extended UARS
mission. For an extended mission, new re-
mote sensing instruments developed under
the instrument development program (dis-
cussed below) to investigate the same and/
or another region of the atmosphere could
replace the existing instruments. Since the
selection of the UARS instruments, technol-
ogy has advanced sufficiently that it is now
possible to remotely sense key radicals
(e.g., HO 2 ) that play a critical role in the
photochemistry of the middle atmosphere.
These measurements should have high
priority on an extended UARS mission.

The UARS objectives include the need for
coverage of seasonal phenomena, probably
requiring at least 3 years of observation.

The planned first mission of 18 months will
not fulfill this requirement, and an extended
mission is therefore highly desirable.

UARS also could be inserted in a high
inclination (polar) orbit for its extended mis-
sion and accomplish the global coverage as
originally proposed for the second space-
craft of the UARS mission. High latitude
phenomena are of particular importance in
improving our understanding of global dy-
namics, chemistry, and particle inputs.

Alternatively, in this time frame (FY 94),
the Space Station and/or STO may prove to
be a better platform for remote sensing in-
struments. Current plans allow for consider-
able flexibility in selecting the best platform
for remote sensing of the atmosphere in the
late 1990s. Based on current projected UARS
mission costs, an extended UARS mission
would cost about $270M in FY 85 dollars,
assuming $80M for new instruments.

Explorers

The Explorer Satellite program has been es-
sential to the development of upper atmos-
pheric physics, as evidenced by the impor-
tant contributions from AE, SME, and DE
(Chapter 6). In the solar-terrestrial context,
perhaps the most important region of the
atmosphere is the mesosphere and lower
thermosphere where electric fields and par-
ticles from the magnetosphere deposit most

of their energy. These energy inputs cause
significant perturbations to the chemistry,
dynamics, and thermal structure of the
lower thermosphere and can also propagate
to the other regions of the atmosphere. For
example, as discussed in the Kennel and
Explorer reports, it is known that nitric ox-
ide (NO) can be produced in the lower ther-
mosphere by aurorae and solar proton
events and subsequently be transported
down into the mesosphere, and possibly
into the stratosphere where it can affect
stratospheric ozone concentrations. Another
result of energy deposition is thermospheric
heating during geomagnetic storms that
drives an upward expansion of the neutral
atmosphere, increasing satellite drag and
causing global ionospheric perturbations
via chemical and dynamical processes that
are still poorly understood.

Because neither UARS nor ISTP missions
will directly address these scientific ques-
tions, we suggest a mesosphere-lower ther-
mosphere explorer (MELTER) to remotely
sense the chemical, dynamical, and thermal
response of the 70- to 150-km region to solar
and magnetospheric perturbations. This re-
gion has been called the "ignorosphere" be-
cause of the great difficulty in measuring its
properties. It is desirable that the MELTER
mission occur simultaneously with the
UARS and ISTP missions to acquire a com-
prehensive solar-terrestrial data base. Sub-
stantial cost savings are possible in this sit-
uation as critical instruments on UARS and
ISTP would not have to be duplicated on
MELTER. Although the complexity of the in-
strument payload will have to be limited,
preliminary studies suggest that such a mis-
sion can be successfully accommodated
within the guidelines for the Explorer Pro-
gram as specified in our earlier report.

To study the dynamics and photochemis-
try of the mesosphere-lower thermosphere,
measurements of the following geophysical
quantities are important: winds, tempera-
tures, concentrations of NO, 0 3 , O, and odd-
hydrogen radicals, electric fields, particle
precipitation, and tracers such as H 2 0 and
CO. Since all of these quantities cannot be
measured by a single Explorer satellite, a
selection of quantities from this list must be
made.

Another Explorer-class spacecraft is the
Combined Release and Radiation Effects

Satellite (CRRES). This NASA/DOD joint ef-
fort will perform experiments in the solar-
terrestrial system by means of active prob-
ing with injections of matter and energy.

The research goals of CRRES are to provide
a better understanding of the solar-terres-
trial environment and also to study physical
processes in the magnetosphere, iono-
sphere, and upper atmosphere. The scien-
tific objectives, programmatic details, and
recommendations regarding this mission
are outlined in Chapter 8.

Additional Explorer missions will be pro-
posed by the upper atmospheric physics
community to investigate important scien-
tific problems. One of the goals of the Ex-
plorer program is a quick-reaction capabil-
ity to respond to mission targets of
opportunity; therefore, we should not now
attempt to predict what will be the most
important scientific opportunities in the mid
to late 1990s.

Space Station/Solar Terrestrial Observatory

Requirements for the Space Station Program
are only now being defined, so it is difficult
to present definitive plans for a scientific
program. Nonetheless, the STO, which was
recommended by the Kennel Report and
studied in some depth by NASA, is compati-
ble with the Space Station Platform from the
perspective of upper atmospheric physics.

The STO is a problem-oriented instrument
payload based on a platform approach, i.e.,
the payload is located on a space platform
and is set in orbit, serviced, and retrieved
by the Space Shuttle. The central scientific
goal of the STO is to understand the physi-
cal processes that couple the major regions
of solar-terrestrial space. This goal encom-
passes the solar atmosphere, the interplane-
tary medium, the Earth's magnetosphere
and ionosphere, and the entire neutral at-
mosphere of the Earth.

The platform approach offers a unique
combination of capabilities, different from
those of both conventional free-flyers and
Shuttle/Spacelab. The characteristics that
are important for the STO are

• large Shuttle-class instrumentation,

• long duration in orbit,

• high power generation,

• regular in-orbit servicing, and

• multidirectional pointing.

The STO Science Study Group discussed
eight representative solar-terrestrial scien-
tific objectives that benefit from the platform
approach and a program of measurements
for each. These objectives are to understand

• solar variability,

• wave-particle processes,

• magnetosphere-ionosphere mass trans-
port,

• the global electric circuit,

• upper atmospheric dynamics,

• upper atmospheric chemistry and ener-
getics,

• lower atmospheric turbidity, and

• planetary atmospheric waves.

A two-stage approach to a multidiscipli-
nary payload is proposed: an initial STO
that uses a single platform in a low-Earth-
orbit and an advanced STO that uses two
platforms in differing orbits. Coordination of
STO with an interplanetary companion,
such as WIND or SOHO, would be highly
desirable. In addition, properly planned and
implemented operations, data handling,
data analysis, and theoretical modeling
must be treated as an inseparable part of
the STO mission. With the characteristics
outlined above, the Solar Terrestrial Ob-
servatory can make a unique and valuable
contribution to NASA's Space Station pro-
gram for solar-terrestrial physics and inte-
grate the subdisciplines of solar and space
physics into a true terrestrial program.

Spacelab/Shuttle Science

Scientific observations from the Shuttle
have just barely begun. More frequent use
of this platform for passive and active ex-
periments is an absolute requirement. In the
time line of Table 7 are indicated the
launches of Spacelab 2 and 3, Space
Plasma Laboratory 1 and 2, along with Shut-
tle reflights as part of the Environmental
Observation Missions (EOM). Important at-
mospheric observations will be made during
these missions even though atmospheric
physics is not the primary driver for SL and
SPL flights. These missions are discussed in
more detail in the magnetospheric/plasma
physics section (Chapter 8).

The payload for the first EOM uses five
proven instruments from Spacelab 1, 2, and
3 missions in a continuing effort to monitor
variations in the total solar irradiance and

the solar spectrum with state-of-the-art pre-
cision and to characterize some of the at-
mospheric responses to changes in the inci-
dent solar energy. A series of flights is
planned so that similar measurements can
be made over a complete 11-year solar
cycle.

The Tethered Satellite System (TSS) will
provide an important new facility for con-
ducting space experiments in regions re-
mote from the Space Shuttle Orbiter. Pay-
loads of 200 to 500 kg can be deployed to
distances of 100 km and held in fixed posi-
tion with respect to the orbiter by means of
a closed-loop control system acting upon a
tether. Data handling and command capa-
bilities will permit active experiment inter-
pretation and control by orbiter and Payload
Operations Control Center (POCC) ground
personnel.

The TSS is expected to open the way to
several entirely new areas of long-term sci-
entific experimentation not heretofore possi-
ble. For upper atmospheric physics these
areas include

• direct observation of magnetospheric-
ionospheric-atmospheric coupling processes
in the 125- to 150-km region of the lower
thermosphere and

• the in situ observation of important at-
mospheric processes occurring within the
lower thermosphere.

We recommend continued development of
the TSS for use on the Space Station/Plat-
form missions. Multiple tethered satellite
deployments would allow simultaneous
measurements of the ionosphere and atmos-
phere at several altitudes and controlled
electrodynamic perturbations of the iono-
sphere.

Achievement of polar orbital capability
and long-duration use of Shuttle instru-
ments are related goals toward which Shut-
tle operations should evolve in the 1980s.
Many important magnetospheric and atmos-
pheric processes can only be studied from
polar orbits; they are necessary to provide
complete geographical coverage of the at-
mosphere and are excellent vantage points
from which to view the Sun. Lack of polar
orbital capability would therefore seriously
weaken the impact of the Shuttle on solar-
terrestrial physics.

We also recommend that the time on orbit
of Shuttle-class instrumentation be ex-

tended. Current Shuttle instrument develop-
ment should be compatible with providing
an eventual continuous presence in space of
Shuttle-class instrumentation for solar-ter-
restrial research. NASA should consider use
of existing low-cost payloads, with prime
candidates being engineering models left
over from SAGE and Nimbus 7 (e.g., SBUV,
SAGE, SAMS, LIMS). These could be flown
on Shuttle missions or, more preferably, on
a longer term platform such as the Euro-
pean Shuttle-launched spacecraft (EURECA).

Theory and Modeling

Theory and computer modeling play a fun-
damental role in upper atmospheric and so-
lar-terrestrial research. They are crucial in
the identification of key observations that
must be made to establish a correct under-
standing of the processes at work. Com-
puter models are useful for simulating large
systems, for testing the importance of com-
peting coupling processes on a global scale,
and for providing a framework within which
large amounts of data may be analyzed.

In upper atmospheric physics, the ulti-
mate objective is a quantitative model that
predicts the upper atmosphere's response to
internal and external perturbations and de-
scribes how changes in it influence the
lower atmosphere and the plasmasphere.
Comprehensive models must take into ac-
count chemistry, energetics, and dynamics,
because they are tightly coupled. In some
areas, such as the non-LTE radiation budget
of the upper mesosphere, current models
are primitive and a substantial effort will be
required. In others, where more complete
understanding of composition, radiation,
and dynamics currently exists, continuing
interaction between model development and
observation is the primary need.

The Solar-Terrestrial Theory Program
(STTP) can contribute towards attaining
these goals but additional effort and funds
will be needed in the future for specifically
upper atmospheric physics to complement
the present modeling emphasis on the mag-
netosphere as well as our recommended ex-
perimental program.

Mission Operations and Data Analysis

As the Friedman-Intrilligator report, Solar-
Terrestrial Research for the 1980's , pointed

out, unprecedented amounts of scientific
data have accumulated from past space
missions. Data handling and management
have become a problem due to a variety of
factors: e.g. f scattered location, incompati-
ble formats, obsolete technology (see Solar-
Terrestrial Data Access Distribution and Ar-
chiving , NAP, 1984). Planning efforts for sev-
eral recent missions (e.g., AE and DE) and
future missions (UARS and ISTP) have given
careful consideration to the difficulties, and
the trend is toward requiring experimenters
to meet specified data-management condi-
tions designed to speed up the data reduc-
tion time, to use common physical units and
data formats, and to render the data base
available to the scientific community rap-
idly and in a "user-friendly" form. Objec-
tives to be met include the provision of im-
mediate and remote access to data by
principal investigators and their teams dur-
ing a mission, similar remote access by the
scientific community at-large as soon as
proprietary requirements have been ful-
filled, and timely and automatic acquisition
of the data by the National Space Science
Data Center in order to satisfy all archiving
requirements and the future needs of the
entire scientific community.

Currently, in years following the end of
Explorer and observatory-class missions,
funding levels have not been adequate to
analyze and interpret much of the acquired
data to its full potential. In order to meet
the above goals and ensure that the princi-
pal investigators and scientific community
at large have adequate resources to analyze
their expensively acquired data, we recom-
mend a significant increase in MO&DA
funds. We do note that NASA has made a
start in this direction with their strato-
spheric data analysis program.

Research and Analysis

The health of upper atmospheric physics de-
pends crucially on long-term support of indi-
vidual scientists, research associates, and
graduate students. The Research and Analy-
sis (R&A) funds provide the foundation of
the creative and innovative research base
and graduate education that has made the
United States preeminent in space science.

It is essential that sufficient funds are avail-
able to maintain strong research groups at

universities, national laboratories, and pri-
vate industry, which provide the scientific
expertise and leadership to carry out the
more ambitious efforts outlined in this re-
port.

Technology Requirements/Instrument
Development Program/Suborbital Programs

The upper atmosphere cannot be studied in
isolation. The source molecules of critical
importance to stratosphere chemistry (N 2 0,
CH 4 ) are produced in the troposphere by
complex biological processes, some of
which are certainly subject to anthropogenic
perturbations (e.g., use of nitrogen fertili-
zers). Thus, effective study of the strato-
sphere must involve analysis of (a) ex-
change processes with the troposphere and
(b) further study of biosphere-ocean-atmos-
phere interactions. To some degree, these
can best be performed in the near term from
aircraft and balloons with the development
of instrumentation to measure gas abun-
dances and fluxes. A global perspective
will, however, require remote sensing from
an appropriate space platform with ad-
vanced instruments.

A high priority should be given to funding
advanced instrumentation development for
upper atmospheric studies because the vi-
tality of the field requires the continuous
development of "state-of-the-art" technology.
Technological advances are anticipated in
detector arrays, electro-optical subsystem
and component technology, onboard infor-
mation processing, and cryogenic cooler de-
velopment using both active and passive
systems. These advances should impact the
next generation science requirements and
instruments for STO, Space Station, and/or
the extended UARS Mission. Development
and testing on sub-orbital platforms must be
an integral part of such instrumentation ad-
vances. Exclusive of Shuttle launch and op-
erations cost, a funding level of about $15M/
yr is estimated as required for development
of the next generation of scientific instru-
ments through the demonstration test
phase.

A strong rocket and balloon program is
needed to measure the ionic content, the
concentrations of a number of minor spe-
cies, the electrical state, and other proper-
ties of the middle atmosphere that cannot

be observed remotely. Further, the unique
ability of rockets and balloons to measure
small-scale spatial and temporal variability
is essential to our understanding of middle-
atmospheric transport processes. Balloons
and rockets also provide in situ corrobora-
tion of remote-sensing spacecraft observa-
tions. In addition, only rockets can make in
situ vertical profile measurements in the 40-
to 120-km altitude region. Active experi-
ments in the thermosphere and lower iono-
sphere are also most effectively conducted
using rockets.

When the low cost, fast- turn-around Geta-
way Specials ("GAS CAN"), ''Hitchhikers",
and Spartan experiments become a reality
on the Shuttle, we recommend a phase out
of all non-in situ rocket experiments. We
recommend the development and perfection
of long-duration (2-4 weeks) balloons to
carry out in situ and long-duration remote
sensing measurements.

Planetary Atmosphere Studies

A thorough understanding of the evolution
and behavior of our own atmosphere re-
quires that it be viewed in the broader con-
text of comparative planetary studies. We
heartily endorse the SSEC recommended
core missions that contain atmospheric ex-
ploration components: Mars Geoscience/Cli-
matology Orbiter, Comet Rendezvous/Aster-
oid Flyby, and Saturn Orbiter/Titan Probe
Missions. We also recommend the prompt
implementation of the Mars Aeronomy Orbi-
ter Mission after the completion of the ini-
tial core program. These intensive studies of
other planetary atmospheres will comple-
ment our recommended program for the
Earth's upper atmosphere. A detailed under-
standing of the photochemistry, dynamics,
and energetics of these planetary atmos-
pheres will provide a proper context to un-
derstand the complex interplay of chemical
and physical processes in our atmosphere
that sustain life.

Long Term Programs

Solar Constant

Radiative-balance climate models indicate
that the Earth's surface temperature is sen-
sitive to changes in the solar radiant energy

flux as small as 0.1 percent. For our under-
standing of the influence of solar variability
on climate to progress beyond speculation,
long-term satellite monitoring of the total
solar radiant energy flux is an absolute ne-
cessity. Monitoring the solar spectral irradi-
ance is highly desirable, because the ultra-
violet part of the spectrum below 1800 A is
known to vary significantly (> 20 percent)
with solar activity.

Long-term observations of solar spectral
irradiance and solar-wind parameters are
prime examples where there has been inad-
equate past commitment of resources and
effort. Spectral irradiance monitoring has
been recognized in the past as essential to
ionospheric/magnetospheric research. How-
ever, these observations have been sup-
ported only in piecemeal fashion by various
government agencies. No one agency is
dedicated to the support of long-term moni-
toring of this type, and no one agency has
devoted sufficient resources or interest in
this area to do it properly. NASA is the suit-
able agency to assume responsibility for
these observations, and it is our recommen-
dation that NASA assign high priority to
suitable instruments on space platforms
over the next 15 years to acquire these ex-
tremely valuable data.

Monitoring of Ozone

Ozone is one of the most important atmos-
pheric species because it is the only constit-
uent capable of effectively absorbing bio-
logically harmful ultraviolet radiation in the
wavelength range from about 2500 to 3000 A.
Since the ozone layer's absorption at these
wavelengths effectively protects life at the
surface, the study of the stability of the
ozone layer is of prime concern.

Our understanding of the ozone layer has
evolved considerably over the last decade.

In particular, refinement of our understand-
ing of stratospheric photochemistry has led
to substantial reductions in the estimated
changes in ozone expected to result from
chlorofluorocarbon releases. Current models
predict maximum local changes near the 40-
km level, with much smaller changes be-
low. The total column changes are likely to
be strongly dependent on dynamical and ra-
diative feedbacks, because much of the to-
tal column resides at low altitudes (i.e., be-
low 20 km) where ozone is controlled by

dynamical processes. Model calculations in-
dicate that the long-term response of strato-
spheric ozone to increasing chlorine abun-
dances may be closely coupled to radiative
feedbacks related to simultaneous increases
in C0 2 , N 2 0, and other species.

Therefore, it is important to monitor ozone
both at the 40-km level where changes are
predicted to be greatest, and at altitudes of
about 10-30 km, where most of the total col-
umn is located. The methods currently
being used for long-term monitoring of these
regions are substantially different. At the
40-km level observations are provided by
ultraviolet sensors onboard satellites, which
offer complete coverage, reasonable altitude
resolution, and good climatology. The low
altitudes (near 10-20 km) are not very acces-
sible to ultraviolet satellite technology and
are best addressed either by infrared remote
sensing or perhaps by a concerted balloon
program using optical in-situ or perhaps
chemiluminescent sampling. An important
problem, however, remains — that of satellite
calibration. Since many of the available sat-
ellite measurements are subject to possible
instrument drift, their accuracy may not be
sufficient to conclusively detect changes of
the magnitudes expected to be found in the
1990s. This highlights the need to develop
accurate in-situ instrumentation for use in
connecting satellite data. It is particularly
important to improve current balloon instru-
mentation so that reliable soundings can be
made at high altitudes.

Thus, a balloon program should represent
an integral part of the future long-term pro-
gram, both because of the dominant role of
the lower stratosphere in the global total
ozone budget, but also because of the need
for calibration of satellite instruments. We
recommend that NASA continue its program
in monitoring ozone and improve calibration
of future satellite data to meet accuracy re-
quirements to detect predicted ozone
changes in the 1990s.

Priorities

In Figure 7 the time line for the upper at-
mospheric physics program is presented.

Priorities considered when constructing this
time line were primarily funding constraints
and already-approved new starts that NASA
is committed to execute to completion. The
FY 85 new start for UARS represents a major
commitment of funds into the early 1990s.

Current NASA planning indicates that the
Space Station will be available for scientific
research in the middle 1990s. It is essential
that appropriate instruments be developed
to fully exploit its capability. An FY 88 start
is thus essential for the instrument develop-
ment program to provide the needed 5 years
for development through flight testing on
the Shuttle. An additional 2 to 3 years is
required to select from the successfully de-
veloped instruments that should be built for
long-duration use on the Space Station. In
the event that the Space Station encounters
difficulties similar to those that plagued the
Shuttle program, we recommend the back-
up option of retrieving and refurbishing the
UARS spacecraft. Scientific progress can
thus be maintained.

The CRRES and Tethered Satellite pay-
loads are approved missions along with SL-
2 and 3, SPL 1 and 2, and EOM 1, 2, and 3
Shuttle flights. Funding constraints limit the
new start of the MEL TER mission in the Ex-
plorer program to FY 88 at the earliest. It
would be highly desirable to launch this
Explorer within 6 months of the UARS
launch to obtain the maximum overlap in
data coverage. For reasons previously
noted, the research and analysis program is
of utmost importance for the continued
health of the field and therefore the mainte-
nance of this budget item at the indicated
levels is of the highest priority.

Although the detailed understanding of
planetary atmospheres complements terres-
trial atmospheric studies, we did not make
specific recommendations in this area nor
include it in our budget time line because of
programmatic reasons. Nevertheless, we
strongly recommend a continued and in-
tense exploration of planetary atmospheres.

58

10 PERSPECTIVES

Introduction

Our intent in this chapter is to highlight
several items that are important to the gen-
eral health and conduct of our discipline.
They are organized into this chapter be-
cause they are applicable to all of the sub-
disciplines (solar, plasma, atmosphere),
they do not necessarily involve specific pro-
grams, and they are not explicity included
in our recommendations. They are nonethe-
less, extremely important to the future of
solar and space physics and need to be con-
sidered in terms of the broad context of NA-
SA's role of conducting science in space.

Data Management

The management of space science data has
not received the attention necessary to most
effectively utilize this national resource. The
problems of past and present data manage-
ment systems and organizations were iden-
tified in CODMAC - Volume 1. The recent
NAS Report, Solar-Terrestrial Data Access,
Distribution, and Archiving (NAS, 1984),
made recommendations for improved data
management for solar and space physics. In
particular, that report identified access to
data as the main problem in the discipline
and developed plans including a Central
Data Catalog and Data Access Network to
alleviate the problem. The report also rec-
ommended a pilot program, to be initiated
by NASA's Information Systems Office, that
would develop the detailed plans necessary
for establishing the catalog and network.
NASA has not yet acted on this recommen-
dation. We believe that this pilot program is
a necessary step for constructing the data
system for the ISTP, the highest priority new
program in solar and space physics, and we
urge NASA to implement the pilot study as
soon as possible.

International Cooperation

At a recent meeting of scientific representa-
tives of the United States and Western Eu-

rope, organized by the U.S. Space Science
Board and the European Science Founda-
tion's Space Science Committee, (An Inter-
national Discussion on Research in Solar
and Space Physics, NAS-ESF, 1984), the con-
ferees recommended that an international
program in solar and space physics be es-
tablished to address the mutual scientific
objectives of this discipline.

This conference was valuable not only in
attempting to structure an integrated pro-
gram of scientific activities directed at spe-
cific goals, but also in enabling the two
communities to discuss, frankly, scientific,
programmatic, and institutional issues.

Such conferences are therefore important as
forums for the exchange of views at the
level of working scientists and should be
expanded in the future to include other com-
munities interested in this area of research,
most notably, Japan.

The ISTP Program as currently planned is
certainly responsive to the recommendation.
We emphasize, however, that the science
objectives are the essential goal to accom-
plish — if, for any reason, the international
agreements for missions to address these
objectives cannot be implemented, the pres-
ent plans will have to be modified so that
the science objectives can be accomplished.

Mission Costs

The issues concerning costs of space sci-
ence programs are particularly difficult for
scientists to address because of their lim-
ited engineering, project management, and
accounting expertise. Nonetheless, such is-
sues are important to scientists because
high program costs or low budgets lead to
situations where access to space becomes
impossible.

Several of these issues, discussed in turn
below, are

• assessing program costs for planning
purposes,

• controlling mission costs, and

• maintaining basic research capability
within a mission-oriented environment.

Planning

In establishing future program priorities
based upon cost and budget projections,
there is some risk that the projections are
not completely accurate. Such is the case
for this report. While we have attempted to
obtain the best possible information on pro-
gram costs, we realize that they are, at
best, only estimates and are likely to
change as project definition proceeds. Thus ,
our approach of establishing temporal prior-
ities is, we believe , still valid because the
mission sequences and program emphasis
are based on relative costs compared to a
reasonable budget allowance .

Controlling Costs

Although the responsibility for controlling
program costs belongs, rightly, to NASA
managers, scientists are concerned about
such matters because space research de-
pends directly on funding allocations. Since
the costs associated with space research are
inherently high, it is important to attempt
experiments and to develop approaches
aimed at reducing costs. Our Committee re-
cently identified a few ideas that we believe
would prove useful in reducing costs of Ex-
plorer missions (A Strategy for the Explorer
Program for Solar and Space Physics , NAS,
1984). These ideas included the following:

• reducing mission complexity by focusing
on specific, sometimes limited, science ob-
jectives;

• providing budgets large enough to keep
development times reasonably short,
thereby avoiding the cumulative effects of
inflation;

• more thoroughly preparing for high-risk
technological development;

• adjusting reliability and quality assur-
ance controls to suit program objectives and
to achieve realistic risk/cost tradeoffs; and

• using more standardized or commer-
cially available hardware.

While these suggestions were made spe-
cifically for NASA's Explorer Program, we
believe that they may well be more gener-
ally applicable. We urge NASA to consider
these approaches and to work to develop
others that will reduce the costs of space
missions and thereby make the whole enter-
prise of space research more effective.

Research Base

Because NASA is a mission-oriented agency
where success is frequently measured in
terms of flight programs, basic research ca-
pability rarely receives high priority atten-
tion. If the funding in this area continues to
erode, as it has in the past few years, the
ability to conduct missions in the future
may be dangerously compromised. It is im-
portant that NASA

• establish adequate funding for R&A,

• protect these funds from development
demands, and

• regularly review the funding, and aug-
ment it if necessary, in order to maintain
the basic research capability.

The recent NASA Space and Earth Science
Advisory Committee report on Research &
Analysis in the Space and Earth Sciences
Quly 1984) addressed the role and health of
a continuing Research and Analysis Pro-
gram in NASA and concluded that inade-
quate funding is the most pressing problem.
We concur.

Facility Management and Operation

In several areas of space science, we can
foresee the need for long-lived, multi-instru-
mented space facilities. It is therefore im-
portant that we now begin to consider how
these facilities will be managed and oper-
ated. Questions such as management ap-
proach (principal investigators, guest ob-
servers, science institutes), on-orbit
maintenance requirements, and frequency
of instrument change-out will require care-
ful study if we wish to make such facilities
available to a large segment of the scien-
tific community and to control costs so as to
ensure that they are affordable.

Computer Facilities and Modeling

Modem research in solar and space physics
involves cm interaction between experiment
and theory that is essential to continued
progress. In addition, the need for employ-
ing a variety of diverse data sets to address
certain problems, the large volume of data
expected from some programs, the special
processing requirements for certain types of

data (e.g., imaging), and the need for large,
multidimensional modeling studies will re-
quire more emphasis on the availability of
large computing facilities and of special-
purpose facilities (i.e., array processors) for
general use by the scientific community.
NASA should take the lead in making such
facilities available not only because the
agency is responsible for generating, ana-
lyzing, and interpreting much of this data,
but also because NASA should be at the
forefront of technological advances in space
physics and should be supporting techno-
logical innovation in the use of large com-
puters.

Space Station

In this report we have described several
areas where Spacelab instruments would
evolve toward use on the Space Station.

Here we describe a possible scenario of how
solar instruments (ASO and STO), for exam-
ple, could do this. At present, it is possible
only to take a preliminary look at the ac-
commodation of science instruments on the
Space Station. This is because we are only
at a requirement-gathering stage of the
Space Station program. There will be a pe-
riod of iterative matching of science require-
ments with engineering design that will
take place over the next 2 years. In this
discussion we will only sketch some of the
requirements and raise some issues that
will need to be dealt with in the Space Sta-
tion accommodations studies.

• Manned Involvement. Scientific involve-
ment will be required in the acquisition of
data and operation of the instruments of
ASO or STO. Examples include control of
pointing of SOT or other telescopes at differ-
ent solar features of interest, and adjust-
ment of the instrument modes to match the
study of the specific solar phenomenon in
progress. Also, the initiation of an active
experiment such as a chemical release or
an electron beam injection and the tracking
of the subsequent cloud or diagnosis of the
plasma instabilities generated would re-
quire continuous scientist interaction. The
scientist involvement in the operation of
ASO could be on-orbit direct, on-orbit re-
mote, from the ground, or a combination of
all of the preceding options.

• Evolutionary Approach . The four main
ASO elements, SOT, POF, SXRT, and EUV
should be ultimately on the same platform.
Each element, however, will be developed
individually, beginning with SOT. Each ele-
ment would be flown initially as a Shuttle
facility and later integrated onto a perma-
nent platform. In our time line (Chapter 7),
we show that when the third element, SXRT,
is completed it can join SOT and POF, and
the instrument collection then becomes
known as ASO.

This evolutionary approach should also
be used for STO. The active experiment ele-
ments of STO should be set up with close
manned involvement in the early experi-
ments. Direct attachment to the manned sta-
tion would permit early studies of the opera-
tion of the equipment, i.e., beam injection
at various current levels and spacecraft
neutralization, wave injection coupling to
the ionospheric plasma, and methods of
tracking chemical releases and dealing with
free-flying multiprobe and recoverable sub-
satellites. Basic plasma studies could be
conducted in the 28° inclination orbit and
the equipment operation techniques con-
firmed. Following this period, the active ex-
periment package should be transferred to
the 90° inclination orbit and operated with
the scientist involved from the manned sta-
tion or on the ground.

• Orbital Mode. ASO and STO will likely
utilize both 90° and 28° platforms — atmos-
pheric experiments on both, solar telescopes
(ASO) on either with a slight preference for
90°, the solar variability portion of STO on
either platform, and the active experiments
on a manned station or a 90° inclination
platform, depending on their state of evolu-
tion.

Planetary Exploration

In light of the evolving plans to implement
the recent SSEC report, our Committee re-
viewed the future role of research in aeron-
omy and plasma physics in NASA's plane-
tary program. Such research is an integral
part of the planetary program and accord-
ingly appropriate resources and portions of
experiment payloads are to be allocated for
such investigations. However, a trend is de-
veloping whereby aeronomy and plasma

physics objectives appear to be relegated to
low priorities in planned missions and little,
if any, spacecraft resources are being allo-
cated for their implementation.

We feel that the manner in which the rec-
ommendations of the SSEC report are being
implemented overlooks the essential contri-
butions made by aeronomy and plasma
physics to our understanding of planetary
environments and planetary evolution. Fur-
ther, investigations of planetary environ-
ments have in the past and will certainly
continue to result in important contributions
to studies of the Earth's environment. Fi-

nally, the astrophysical implications of pla-
netary exploration will rest in an important
way on the study of plasmas.

We recommend that NASA continue its
past policy of planning an appropriate mix
of special purpose missions and/or missions
of more general objectives with sufficient
allocation of resources to permit broad in-
vestigations that include aeronomy and
plasma physics. We also suggest that re-
sources within the planetary R&A budget
continue to be devoted to developing inves-
tigations in aeronomy and plasma physics
for future planetary programs.

11 ORGANIZATIONAL STRUCTURE

A major intellectual thread linking several
recent NAS/NRC advisory committee reports
has been the essential unity of the disci-
plines comprising solar and space physics.
The study, Space Plasma Physics (Colgate
report), requested of the Space Science
Board by NASA, attested to the scientific
importance and intrinsic merit of the disci-
plines of space plasma physics and solar
physics. The study committee, which was
composed primarily of laboratory plasma
physicists and astrophysicists working in
areas outside the disciplines examined, con-
cluded that the research in solar and space
physics is also important because it contrib-
utes to significant developments in other
areas of science. This conclusion was re-
cently reiterated by the Physics Survey
Committee.

Using the Colgate report as a basis, the
SSB Committee on Solar and Space Physics
developed the scientific strategy for future
space research in the field (Kennel report).
This strategy is based on a high degree of
coherence among the disciplines of solar
and space physics. In addition, a Geophys-
ics Research Board study (Friedman-Intrili-
gator report) emphasized the unity of solar-
terrestrial physics and recommended direc-
tions for solar-terrestrial research in the
1980s.

This unity is not realized in NASA's orga-
nizational and management structure at
present. The elements of the on-going solar
and space physics program are managed by
several Office of Space Science and Appli-
cations (OSSA) divisions: The Astrophysics
Division is responsible for the scientific di-
rection of SOT and ISPM, as well as manag-
ing the Explorer, sounding rocket, and bal-
loon programs; the Solar System Exploration
Division is concerned with the atmospheres
and magnetospheres of all solar-system ob-
jects except the Sun and Earth; the Earth
Science and Applications Division manages
space plasma physics and upper atmos-
pheric research, including UARS; the Shuttle
Payload Engineering Division handles Spa-
celab instrumentation.

Coordinated research among the disci-
plines that comprise solar and space phys-
ics is an essential feature of our strategy.
Such coordination will not easily be
achieved with management of the various
pieces split among several organizations,
each with its own set of goals and priori-
ties. The program we have proposed is sub-
stantial in terms of both scientific content
and cost. We believe that NASA should con-
sider whether its present management
structure is appropriate for supporting this
program.

APPENDIX: LEVELS OF INVESTIGATION *

In Report on Space Science 1975 , the Com-
mittee on Planetary and Lunar Exploration
(COMPLEX) identified three stages of space
investigations. Reconnaissance, the first
penetration of a region of space by an in-
strumented spacecraft, has discovery as its
objective. Reconnaissance is followed by ex-
ploration, whose aim is phenomenological
identification of important processes. With
phenomenology clear and physical proc-
esses identified, intensive study begins.
Here, research focuses on quantitative eval-
uation of physical mechanisms and the link-
age of one mechanism to another in compre-
hensive models.

These categorizations apply equally well
to in situ spacecraft investigations in solar
and space physics. Slightly different ones
apply to remote-sensing studies. Detection
and first preliminary surveys are followed
by global surveys with sufficient coverage
and resolution to identify basic physical
mechanisms. These are again followed by
intensive studies, usually requiring high
space and time resolution, whose aim is
quantitative understanding of specific proc-
esses. In addition, most of our major subdis-
ciplines can use or have made use of active
experiments. Because of their diversity it is
difficult to identify all but two extreme lev-

This Appendix is an update of the similar section of
the Kennel report.

els of investigation. The first exploratory
uses of a given technique determine its fea-
sibility and identify research objectives. At
the opposite extreme is its systematic use to
produce basic physical information. In Fig-
ure A. 1 we estimate the status of in situ
spacecraft investigations, in Figures A. 2
and A. 3 of remote sensing investigations
and selected active experiments.

When research approaches its intensive
study phase, one can judge its progress by
the quantitative understanding it has
achieved. One way to do so is to evaluate
comprehensive models that link together
several interacting processes. Here we have
defined four evolutionary phases. The first
is phenomenological identification of perti-
nent physical processes and their interac-
tions. This done, it becomes feasible to con-
struct preliminary quantitative models.
Whether they are correct or not, their exist-
ence signifies that moderate quantitative
understanding has been achieved. They mo-
tivate further observations and theory lead-
ing to accurate quantitative models, suita-
ble for systematic comparison with
experiment. These then evolve into predic-
tive models, at which point the threshold of
practical utility has been reached. Figure
A. 4 contains our perception of the 1984 sta-
tus of models of several problems in solar-
system space physics, selected for their il-
lustrative value.

PRECEDING PAGE BLANK NOT FILMED

65

FIGURE A 1

66

FIGURE A-1 (continued)

67

LEVELS OF REMOTE-SENSING INVESTIGATIONS

DISCIPLINE

SUBJECT AREA

AWAITING

PRELIMINARY

SURVEY

PRELIMINARY

SURVEY

GLOBAL

SURVEY

INTENSIVE

STUDY

PHYSICAL

UNDER

STANDING

SOLAR PHYSICS

CORONAL HOLES, LARGE SCALE
MAGNETIC FIELDS

RADIO BURSTS

GLOBAL OSCILLATION

FLARES

INTERNAL STRUCTURE &
DYNAMICS - SOLAR DYNAMO

SURFACE PLASMA MAGNETIC
FIELD INTERACTIONS

ENERGY STORAGE AND RELEASE
ATMOSPHERIC HEATING

STRUCTURE AND DYNAMICS OF
CORONA AND SOLAR WIND

1

]

I

SOHO

m m

m

SOTfASO

fc*a Kii

SOTfASO

1

SOHO

POFfASO

t-y.-i FSffi

' ' m m

HELIOSPHERE PHYSICS

INTERSTELLAR NEUTRALS

1

TERRESTRIAL,

MAGNETOSPHERE

PHYSICS

GLOBAL AURORAL MORPHOLOGY

REMOTE SENSING OF
MAGNETOSPHERE STRUCTURE

m

X

ISTP

TERRESTRIAL,
ATMOSPHERIC
IONOSPHERIC PHYSICS

MIDDLE ATMOSPHERE
MESOSPHEREilOWER
THERMOSPHERE

UARS

|

EXPLORERS/S

;to

mnm

hi

s

KEY: | | COMPirrEDiAPPROVED E$l Efl RECOMMENDED

FIGURE A 2

FIGURE A 3

69

FIGURE A4

70

STATUS OF PHYSICAL MODELS
(continued)

DISCIPLINE

PROBLEM

RUDIMENTARY

UNDERSTANDING

SOME

PHENOMENOLOGICAL

UNDERSTANDING

FIRST

QUANTITATIVE

MOORS

ACCURATE

QUANTITATIVE

MODELS

PREDICTIVE

MODRS

TERRESTRIAL,

MAGNETOSPHERIC

PHYSICS

(continued]

COUPLING TO IONOSPHERE
AND THERMOSPWRE

TRAPPED RADIATION BELTS

m

M fit I:!:

in

TERRESTRIAL AT
MOSPHERIC PHYSICS

MESOSPHERIC COUPLING AM)
DYNAMOS

GENERATION OF THERMO
SPHERIC WINDS
EFFECTS OF PHOTONS AND
ENERGETIC PARTICLES ON
UPPER ATMOSPHERE
STATIC UPPER ATMOSPHERE
MODELS

GENERAL CIRCULATIONAL
MODELS OF MIDDLE
ATMOSPHERE

|

LVl l.’ZL It-

t- l L'il L7

ETETE

FTTTTiT

SUNCUMATE
WEATHER RELATIONS

ENTIRE AREA

a i t i

ttm m m m ET

PLANETARY
MAGNETOSPHERES,
IONOSPHERES, AND
ATMOSPHERES

MAGNETOSPHERES OF MARS.
URANUS, NEPTUNE, AND
COMETS

MAGNETOSPWRES OF MER
CURY AND SATURN
STATIC MODELS OF
PLANETARY ATMOSPHERES

1 E:4 k ; :l

;a m et h

1

1

KEY: | 1 COMPlETEDlAPPflOVTD g g RECOMMENDED

FIGURE A-4 (continued)

FIGURE A-4 (continued)

72

GLOSSARY

AE

Atmosphere Explorer

AMPTE

Active Magnetosphere Particle Tracer Explorer(s)

AO

Announcement of Opportunity

ASO

Advanced Solar Observatory

AU

astronomical unit

COMPLEX

Committee on Planetary and Lunar Exploration

CRRES

Combined Release and Radiation Effects Satellite

CSSP

Committee on Solar and Space Physics

DE

Dynamics Explorer

DSN

Deep Space Network

EOM

Environmental Observation Mission

ESA

European Space Agency

EUV

extreme ultraviolet

EUVT

EUV telescope

GGS

Global Geospace Study

HEAO

High Energy Astronomical Observatory

ICE

International Comet Explorer

IMP

Interplanetary Monitoring Platform

ISAS

Institute of Space and Astronautical Science, lapanese

ISEE

International Sun-Earth Explorer

ISPM

International Solar Polar Mission

ISTP

International Solar-Terrestrial Physics (program)

LEO

lower-Earth-orbit

MELTER

Mesosphere-Lower Thermosphere Explorer

MHD

magnetohydrodynamic

MO&DA

mission operations and data analysis

OMS

Orbital Maneuvering Subsystem

OSO

Orbiting Solar Observatory

OSSA

Office of Space Science and Applications

PI

principal investigator

POCC

Payload Operations Control Center

POF

Pinhole Occulter Facility

R&A

research and analysis

RPDP

Recoverable Plasma Diagnostics Package

SL

Spacelab

SME

Solar Mesosphere Explorer

SMM

Solar Maximum Mission

SOT

Solar Optical Telescope

SPAN

Space Physics Analysis Network

SPL

Space Plasma Lab

SPO

Solar Polar Orbiter

STO

Solar-Terrestrial Observatory

STTP

Solar-Terrestrial Theory Program

SXRT

soft x-ray telescope

TDRSS

Tracking and Data Relay Satellite System

TSS

Tethered Satellite System

UARS

Upper Atmospheric Research Satellite

XUVT

X-ray/Ultraviolet Telescope

73