NASA Technical Reports Server (NTRS) 20130010526: Millimeter Wave Communication through Plasma

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Produced by the NASA Center for Aerospace Information (CASI)

2008 SMD Conference Technology Trek

Millimeter Wave Communication through Plasma

Since the dawn of the space age, astronauts returning
from orbit have encountered communications
blackouts due to plasma encapsulation of the returning
spacecraft. Similarly, communication links during
ascent have relied on the use of expensive-to-maintain
missile communication and tracking annex stations
located far from launch facilities to provide the
necessary look angles to avoid signal attenuation from
rocket motor plasma contrails. In both cases, the issue
is one of attenuation of communication signals due to
plasma. Millimeter Wave Communication through
Plasma is a new approach to designing
communication systems to extend communications
connectivity during launch, and possibly even during
re-entry, despite such plasma attenuation.

Irving Langmuir of the General Electric Research
Laboratory first observed in 1925 that an electron
beam in a discharge tube was being scattered more
rapidly than could be accounted for by the simple
assumption of collisions between electrons. In 1926,
F.M. Penning of the Phillips Research Laboratory in
the Netherlands hypothesized the existence of, and
confirmed the presence of, high-frequency oscillations
in a gas discharge to explain the scattering first
observed by Langmuir. 1 In 1928, Langmuir & Tonks
(also of the GE Research Laboratory) defined plasma
as an ionized gas. In 1929, Langmuir & Tonks
confirmed the presence of the high-frequency
electrostatic oscillations discovered by Penning, and
further derived an equation for the oscillation
frequency that is today commonly called either the
Langmuir-Tonks frequency, or, more commonly, just
the plasma frequency. 2 Plasma frequency is simply
“the characteristic oscillation rate for electrostatic

disturbances in ... plasma.” 3 It is the natural
collective oscillation frequency of a charge species
(electrons, ions, etc.) in plasma.

Figure 1 Studying millimeter wavelength signal attenuation thru
plasma at Kennedy Space Center inside a plasma chamber

Since dynamics are usually of primary importance in
studying plasmas (i.e., ionized gases), research focus
is usually placed on just the plasma electrons, rather
than on any more massive constituent parts of the
plasma. With this assumption, the electron density
essentially solely determines the plasma frequency,
and plasma frequency is estimated by:

co

p

5.6 • 10 4 /i e

1/2

rad/sec

where n e is the number of electrons per cubic
centimeter. 4

During launch, if the plasma frequency of rocket
exhaust is significantly below the operating frequency
of the communication link, there is no significant
attenuation due to either reflection or pass-through
loss from the exhaust cloud to a millimeter wavelength

2008 Space and Missile Defense Conference , Huntsville , AL. 11-14 August 2008

2008 SMD Conference Technology Trek

communication link to/ffom the launch vehicle. The
fundamental issue is therefore the electron density of
the rocket motor plasma exhaust.

Electron density in rocket plumes has been
investigated and has been well documented for
plasmas extending beneath rocket engines. 5 6

Representative electron densities in rocket exhaust
plasma fall between 10 8 - 10 13 electrons cm 3 , where
the lower limits exist at equilibrium exit conditions,
such as in the plume; and the highest densities exist at
locked conditions found in rocket throats. 7 Hence, for
electron densities falling between 10 8 - 10 13 electrons
cm' 3 , plasma frequencies fall between 0.56 Grad/sec to
177 Grad/sec (89.1 MHz to 28.2 GHz). Of course,
during the Apollo Program, operating frequencies at
millimeter wavelengths were not feasible. Hence, the
need for the missile communication and tracking
annex stations that currently exist arose. However,
for millimeter wave communication systems operating
at 35 GHz or higher, operating frequencies are
sufficiently above the worst case plasma frequencies
such that exhaust plasma reflection and pass-through
attenuation effects that could attenuate the
communication link are negligible. Operation at such
frequencies is now possible, unlike during Apollo.

Similarly, for re-entry, plasmas have additionally been
studied and are also understood. However, these
plasmas are more intense than the plasmas extending
beneath departing launch vehicles. Further research
into using millimeter wavelength signals to overcome
re-entry plasmas is needed, prior to being able to
overcome re-entry communication blackouts entirely.

A future vision of a more cost effective launch
capability, involving the use of millimeter wavelength
communications through plasma, is emerging in
NASA’s laboratories. Such communications
technology can reduce annual operating costs that
have historically been associated with maintaining
missile communication and tracking annex stations.
The ultimate goal, of reducing the cost associated with
access to space, while also improving safety for
astronauts through improving communications links,
appears feasible.

Contact : Dr. GaryL. B as tin, ASRC Aerospace,

Mails top: ASRC- 10, Kennedy Space Center, FL
32899 (Gary.L.Bastin@nasa.gov, (321) 867-9275)
http://www. ustdc. com

This ongoing research is sponsored by NASA ’s
Kennedy Space Center under the Emerging
Communications Technologies project.

GB082008

1 E.H. Holt and R.E. Haskell, Foundations of Plasma Dynamics. New York: The Macmillan Company, 1965, pp. 8-9.

2 Holt and Haskell, p. 9.

3 Wulf B. Kunkel, Plasma Physics in Theory and Application. New York: McGraw-Hill, 1966, p. 1.

4 Wulf B. Kunkel, Plasma Physics in Theory and Application. New York: McGraw-Hill, 1966, p. 7.

5 Ping Zhang and Wanjun Bi, “Investigation on Microwave Signal Attenuation by Solid Propellant Flames and Plumes.”
AIAA PAPER 93-2456, AIAA, SAE, ASME, and ASEE, Joint Propulsion Conference and Exhibit, 29th, Monterey, CA,
June 28-30, 1993.

6 David A. Cooper and Robert A. Frederick, “The Measurement of Electron Density in a Rocket Motor Plume.” AIAA
PAPER 93-2453, AIAA, SAE, ASME, and ASEE, Joint Propulsion Conference and Exhibit, 29th, Monterey, CA, June 28-
30, 1993.

7 David A. Cooper and Robert A. Frederick, “The Measurement of Electron Density in a Rocket Motor Plume.” AIAA
PAPER 93-2453, p. 6, June 1, 1993, AIAA, SAE, ASME, and ASEE, Joint Propulsion Conference and Exhibit, 29th,
Monterey, CA, June 28-30, 1993.

2008 Space and Missile Defense Conference, Huntsville, AL. 11-14 August 2008

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Millimeter Wave Communication Through Plazma

August 1 1-14, 2008

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NAS 10-03006

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6. AUTHOR(S)

Gary Bastin, ASRC Aerospace

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ASRC Aerospace
ASRC-48

Kennedy Space Center, FL 32899

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National Aeronautics and Space Administration
Engineering Directorate (KT)

Kennedy Space Center, FL 32899

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NASA/KSC

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14. ABSTRACT

Millimeter wave communication through plasma at frequencies of 35 GHz or higher shows promise in maintaining communications
connectivity during rocket launch and re-entry, critical events which are typically plagued with communication dropouts. Extensive
prior research into plasmas has characterized the plasma frequency at these events, and research at the Kennedy Space Center is
investigating the feasibility of millimeter communication through these plasma frequencies.

15. SUBJECT TERMS

plasma, millimeter, communication

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PAGES Dr Gar Y Bastin

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1 (321) 867-9275

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