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

Bastin, Gary L.

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https://ntrs.nasa.gov/search.jsp?R=20130010526 2019-08-31T00:14:06+00:00Z
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.' 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 Ihru 
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: 
4	 1/2 
(L1	 5.6• 10 e	 rad/sec 
where 17e is the number of electrons per cubic 
centimeter. 
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/from 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 108 _ 1013 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 _ 1013 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. Gary L. Bastin, ASRC Aerospace, 
Mailstop: 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. 
Wulf B. Kunkel, Plasma Physics in Theory and Application. New York: McGraw-Hill, 1966, p. 7. 
Wulf B. Kunkel, Plasma Physics in Theory and Application. New York: McGraw-Hill, 1966, p. 7. 
Ping Zhang and Wanjun Bi, "Investigation on Microwave Signal Attenuation by Solid Propellant Flames and Plumes." 
AIM PAPER 93-2456, AIAA, SAE, ASME, and ASEE, Joint Propulsion Conference and Exhibit, 29th, Monterey, CA, 
June 28-30, 1993. 
David A. Cooper and Robert A. Frederick, "The Measurement of Electron Density in a Rocket Motor Plume." AIM 
PAPER 93-2453, AIAA, SAE, ASME, and ASEE, Joint Propulsion Conference and Exhibit, 29th, Monterey, CA, June 28-
30, 1993. 
David A. Cooper and Robert A. Frederick, "The Measurement of Electron Density in a Rocket Motor Plume." AIM 
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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presentation August 11-14, 2008 
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER 
Millimeter Wave Communication Through Plazma NAS 10-03006 
5b. GRANT NUMBER 
5c. PROGRAM ELEMENT NUMBER 
6. AUTHOR(S) 5d. PROJECT NUMBER 
Gary Bastin, ASRC Aerospace  
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ASRC Aerospace REPORT NUMBER 
ASRC-48 
Kennedy Space Center, FL 32899 
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12. DISTRIBUTION/AVAILABILITY STATEMENT 
13. SUPPLEMENTARY NOTES 
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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Dr. Gary Bastin a. REPORT b. ABSTRACT c. THIS PAGE
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1 (321) 867-9275
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Millimeter Wave Communication through Plasma

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