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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. 


Committee on Solar and Space Physics 
Space Science Board 

Commission on Physical Sciences, Mathematics, 
and Resources 

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 

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. 







Solar Physics . 5 

Physics of the Heliosphere 5 

Magnetospheric Physics 7 

Upper-Atmospheric Physics 7 

Solar-Terrestrial Coupling 10 

Comparative Planetary Studies 10 


Rationale 11 

Program Mix in Solar and Space Physics 11 

Resource Requirements for Recommended Programs 12 


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 


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 


Introduction 29 

Program Descriptions 29 

Priorities 37 



Introduction 39 

Program Descriptions 39 

Priorities 49 


Introduction , 51 

Program Descriptions 51 

Priorities 58 


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 





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 


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


Thomas M. Donahue, University of Michigan 

Devrie S. Intriligator, Carmel Research Center 

Robert M. MacQueen, National Center for Atmospheric Research 


Richard C. Hart 


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 


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 

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 


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 

Thomas M. Donahue 
Chairman, Space Science Board 


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 



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 

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 

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- 


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- 

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- 

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. 


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- 

• 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 . . . 



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- 










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

What Are th 
Corona's En 

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

How Is Solar 
Wind Generated? 

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






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. 


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

• 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- 





Moon ^ ' 


3-0 shocked solar wind 





What is Origin and Fate of ^ - 

Magnetospheric Plasmas? 

How Does Solar 
Wind Couple to 



How is Energy Stored 
and Released in 
Magnetic Tail? 

j \ shocked solar wind 

How Does Magnetosphere co7/>> 

Couple with Atmosphere '° n/ es^-^. 

and Ionosphere? 









>t> shocked solar wind 




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. 






Sola* uK*av<o*ef 

pooions Magnetosphere pa*lu . IPs 

1 30 km 

f *S. 


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 

Sola* jl'avtota* 

Magnetosphere parities 

What Are the World-Wide 
Effects of the 

Magnetosphere's Interaction 
with the Upper Atmosphere? 

electric winds 


mesosphere and stratosphere 


Solar utravioM 

photons Magnetosphere policies 



/ *$, % 

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- 

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 



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 

Program Mix in Solar and Space 

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 



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 


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. 



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 

• 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 

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. 


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 

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- 

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- 

(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 

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 

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- 

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 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" 

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- 

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 

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- 

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 

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- 

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 

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 

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- 

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

Research and Analysis 

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

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- 

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, 

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. 


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, 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. 


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- 

• 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 


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- 

• 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- 

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 

• 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- 

• 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- 

• 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.); 

• 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 

• 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 

• 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 

• 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- 

• 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 

• 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- 

• 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, 


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- 

• 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- 

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

• Lightning was detected by wave obser- 

• At least four distinct cloud layers were 

• 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- 

• 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 

• 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- 

• 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 



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 


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- 

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


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 

• 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 

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

• Locate sources of low speed solar wind. 


• 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, 

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 

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- 

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- 

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 

• 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- 

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 

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 

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- 

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- 

Explorers for Solar and Heliospheric Physics 

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 

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 

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- 

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 

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- 


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- 

• 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 

• Shuttle Missions 

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

— 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. 




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- 

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 

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 

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, 

• 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 

• 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 


• 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 
POLAR will have the following magnetos- 
pheric and ionospheric plasma physics ob- 

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

• 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 

• 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- 

• 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 

• 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 

• 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 

• 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- 

• 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 

Explorers for Magnetospheric Plasma 

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- 

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 

• 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- 

Combined Release and Radiation Effects 

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 

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- 

• 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 

• 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- 

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- 

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 

• 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 

• 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- 


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 

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 

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

• 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- 

• 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 

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- 

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 

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 

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 


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 

• 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 

• 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?); 

• the interaction between plasma and 

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 

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 

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- 

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 

Technology Requirements/Instrument 

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 

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. 


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 

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. 



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. 



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- 

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 

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- 


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. 


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 

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- 

• the global electric circuit, 

• upper atmospheric dynamics, 

• upper atmospheric chemistry and ener- 

• 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 

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 

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- 

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- 

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 

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. 


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. 




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 

Several of these issues, discussed in turn 
below, are 

• assessing program costs for planning 

• controlling mission costs, and 

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


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- 

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

• 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- 

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- 

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. 


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 

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 

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 


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. 





FIGURE A-1 (continued) 






























m m 



fc*a Kii 





t-y.-i FSffi 

' ' m m 


















































M fit I:!: 







LVl l.’ZL It- 

t- l L'il L7 





a i t i 

ttm m m m ET 




1 E:4 k ; :l 

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FIGURE A-4 (continued) 

FIGURE A-4 (continued) 




Atmosphere Explorer 


Active Magnetosphere Particle Tracer Explorer(s) 


Announcement of Opportunity 


Advanced Solar Observatory 


astronomical unit 


Committee on Planetary and Lunar Exploration 


Combined Release and Radiation Effects Satellite 


Committee on Solar and Space Physics 


Dynamics Explorer 


Deep Space Network 


Environmental Observation Mission 


European Space Agency 


extreme ultraviolet 


EUV telescope 


Global Geospace Study 


High Energy Astronomical Observatory 


International Comet Explorer 


Interplanetary Monitoring Platform 


Institute of Space and Astronautical Science, lapanese 


International Sun-Earth Explorer 


International Solar Polar Mission 


International Solar-Terrestrial Physics (program) 




Mesosphere-Lower Thermosphere Explorer 




mission operations and data analysis 


Orbital Maneuvering Subsystem 


Orbiting Solar Observatory 


Office of Space Science and Applications 


principal investigator 


Payload Operations Control Center 


Pinhole Occulter Facility 


research and analysis 


Recoverable Plasma Diagnostics Package 




Solar Mesosphere Explorer 


Solar Maximum Mission 


Solar Optical Telescope 


Space Physics Analysis Network 


Space Plasma Lab 


Solar Polar Orbiter 


Solar-Terrestrial Observatory 


Solar-Terrestrial Theory Program 


soft x-ray telescope 


Tracking and Data Relay Satellite System 


Tethered Satellite System 


Upper Atmospheric Research Satellite 


X-ray/Ultraviolet Telescope