Electrostatic modulator for communicating through plasma sheath formed around spacecraft during reentr

Seaton, S. L.

English

NASA Technical Reports Server

. L. SEATON 96,53 
ELECTROSTATIC PLASMA MODULATOR FOR SPACE VEHICLE RE-ENTRY 
COMMUNICATION 
Filed April 29, 1964 
INVENTOR 
STUART L. SEATON 
BY 
https://ntrs.nasa.gov/search.jsp?R=19700032015 2020-03-17T02:11:03+00:00Z
3 ~ 2 9 ~ , ~ 3  1 nite Patented Yam. 3, 1967 
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3,296,531 
ELECTROSTATIC PLASMA M ~ ~ U L A ~ O ~  FQ 
Stuart L. Seaton, Hampton, Va., assignor to the United 
States of America as represented by the A d m ~ ~ ~ o r  
of the National Aeronautics and Space Administration 
Filed Apr. 29,1964, Ser. No. 363,653 
3 Claims. (GI. 325-65) 
SPACE VEHICLE RE-ENTRY G O M M ~ ~ C A ~ O N  
The invention described herein may be manufactured 
and used by or for the Government of the United States 
of America for governmental purposes without the pay- 
ment of any royalties thereon or therefor. 
This invention relates generally to communicating 
through a layer of ionized gases and more particularly 
concerns communicating through the layer of ionized 
gases formed around a space vehicle as it enters or leaves 
a planetary atmosphere. 
Whenever a space vehicle traveling at a hypersonic 
speed enters or leaves a planetary atmosphere, it is sur- 
rounded by a shock-induced layer of ionized gases or 
plasma. If electromagnetic waves of radio frequency are 
directed into this layer of plasma, the free electrons in 
the plasma respond easily to the electromagnetic waves 
and in so doing collide with other gas particles. This 
results in dissipation of the systematic electromagnetic 
wave energy and loss of any information being carried 
by the electromagnetic waves. Consequently, radio fre- 
quency communication ordinarily cannot be maintained 
through the layer of plasma. 
In the past there have been several schemes suggested 
for accomplishing radio wave communication through the 
layer of plasma surrounding a space vehicle while it is 
reentering the earth's atmosphere. Among these schemes 
is the scheme of selecting for use a signal frequency that 
will penetrate or pass through the hypersonically gen- 
erated plasma. Extremely high radio wave frequencies 
will pass through the plasma unaltered. Hotever, since 
most communicating equipment presently in use is de- 
signed for the VHF-UHF bands (30 mc. to 300 mc. and 
300 mc. to 3,000 mc.), there is an equipment acquisition 
problem if the extremely high frequencies are used. Also, 
at the high frequencies there is an atmospheric absorption 
problem. 
Other schemes suggested for accomplishing radio wave 
communication through the layer of plasma includes aer- 
odynamic shaping, material injection and use of the layer 
of plasma as an electromagnetic radiator. However, none 
of these schemes satisfies all foreseeable requirements. 
Plasma is composed of free electrons, positive ions, and 
other constituents. Since it is the free electrons in the 
plasma that are most responsive to electromagnetic wave 
energy, if the free electrons were operated upon in such 
a way as to divert them from a region, then information- 
carrying electromagnetic waves could pass through this 
region substantially undisturbed. It is the primary pur- 
pose of the present invention to use electrostatic means 
to create such a region. This is accomplished by placing 
charged electrostatic plates in the plasma. The negative- 
ly charged plates will repel the free electrons thereby di- 
verting them from a certain region. An antenna is placed 
such that it can emit electromagnetic waves through this 
region; consequently, electromagnetic wave communica- 
tion can be maintained through the plasma. 
It is therefore an object of this invention to provide 
means for maintaining electromagnetic wave communica- 
tion through a layer of ionized gases. 
Another object of this invention is to provide means 
for maintaining electromagnetic wave communication 
through the layer of plasma formed around a space ve- 
hicle as it either enters or leaves a planetary atmosphere. 
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70 
2 
A further object of this invention is to use electro- 
static means to create a region in a layer of ionized gases 
that is substantially devoid of free electrons whereby 
electromagnetic wave communciation can be maintained 
through the layer of ionized gases. 
Other objects and advantages of this invention will 
further become apparent hereinafter and in the drawings 
in which: 
FIG. 1 shows a side view of the outline of a space ve- 
hicle for the purpose of describing the theory of this 
invention; 
FIG. 2 shows a top view of the space vehicle shown in 
FIG. 1; 
FIG. 3 shows a side view of the outline of a space ve- 
hicle utilizing the preferred embodiment of this inven- 
tion; and 
FIG. 4 shows a top view of the space vehicle shown in 
FIG. 3. 
In describing the invention illustrated in the drawings, 
specific terminology will be resorted to for the sake of 
clarity. However, it is not intended to be limited to the 
specific terms so selected, and it is to be understood that 
each specific term includes all technical equivalents which 
operate in a similar manner to accomplish a similar pur- 
pose. 
Turning now to FIG. 1 there is shown a side view of 
the outline of a space vehicle 11. When space vehicle 
11 is traveling in a direction indicated by arrow 12 and is 
either entering or leaving a planetary atmosphere, a layer 
of ionized gases or plasma is formed around the space 
vehicle. This layer of plasma is composed of free elec- 
trons and other constituents. These free electrons, rela- 
tive to space vehicle 11, travel in directions indicated by 
arrows 13. Ordinarily, the direction of flow of these free 
electrons is affected only by the space vehicle. Conse- 
quently, there is a layer of these free electrons formed 
around substantially the whole surface of space vehicle 
11. Due to this layer of free electrons, electromagnetic 
wave communication to and from space vehicle 11 be- 
comes practically impossible by conventional means. 
This invention consists of attaching an electrode 14 
and an electrode 15 to the outer skin of space vehicle 11. 
Electrodes 14 and 15 are insulated from the outer skin 
of space vehicle 11 and are connected to a voltage source 
16 shown in FIG. 2. For purposes of explanation, elec- 
trode 14 is shown charged negatively and electrode 15 is 
shown charged positively. Due to the negative charge 
on electrode 14 the paths, indicated by arrows 13, of the 
free electrons are deflected thereby creating a region 17 
that is substantially devoid of any free electrons. An 
antenna 18 is attached to space vehicle 11 within the re- 
gion 17 and a conventional transmitter 19 is connected 
to antenna 18. The electromagnetic waves emitted by 
antenna 18 will pass through the layer of plasma formed 
around space vehicle 11 in the region 17 thereby en- 
countering relatively few free electrons. Therefore, any 
information carried by the electromagnetic waves emitted 
by antenna 18 will pass through the layer of plasma sub- 
stantially unaltered. 
The embodiment of the invention shown in FIGS. 1 
and 2 is not practical since in a short time charge ac- 
cumulation on electrodes 14 and 15 make them ineffec- 
tive for deflection purposes. The preferred embodiment 
shown in FIGS. 3 and 4 overcomes this difficulty. FIG. 
3 shows a side view of the outline of a space vehicle 21. 
Space vehicle 2% travels in a direction indicated by ar- 
row 22. The directions of travel of the free electrons, in 
the layer of plasma formed around space vehicle 21, 
An electrode 24 and an electrode 25 are attached 
to the outer skin of space vehicle 21. Electrodes 24 and 
, relative to space vehicle 21 are shown by arrows 23. 
25 are insulated from the outer skin of space vehicle 21 
and are connected to a voltage source 26. Connected 
between voltage source 26 and electrodes 24 and 25 is 
a switching device 27. The function of switching device 
27 is to intermittently reverse the polarities of the voltages 
applied to electrodes 24 and 25. Under these conditions, 
two regions, 29 and 30, alternately devoid of electrons 
will be developed successively. That is region, 29 will 
be devoid of electrons while electrode 24 is charged nega- 
tively and electrode 25 is charged positively and region 30 
will be devoid of electrons while electrode 24 is charged 
positively and electrode 25 is charged negatively. An an- 
tenna 31 is attached to the outer skin of space vehicle 
21 in the region 29 and an antenna 32 is attached to the 
outer skin of space vehicle 21 in the region 30. A con- 
ventional transmitter 33 is connected to both antenna 31 
and antenna 32. The electromagnetic waves emitted by 
antennas 31 and 32 will pass through the layer of plasma 
formed around space vehicle 21 in the regions 29 and 
30, respectively. 
If a sufficient time elapses between the time that the 
polarities of electrodes 24 and 25 are reversed and the 
time that the charge accumulation on the electrodes makes 
them ineffective for deflection purposes, then continuous 
communication can be maintained through the plasma. 
However, since this time laspe is so short as to require 
an impracticably high switching frequency, a different 
approach is taken by this invention. Information is 
transmitted from space vehicle 21 by supplying antennas 
31 and 32 with a continuous wave energy and encoding 
the reversal of the electrostatic field created by electrodes 
24 and 25 in the nature of a pulse code modulation. 
Transmitter 33 supplies antennas 31 and 32 with a con- 
tinuous wave energy of a suitable frequency, e.g., 5 
kmc/sec. Switching device 27 can then be used to re- 
verse the polarity of voltage source 26 applied to elec- 
trodes 24 and 25 in accordance with a pulse modulation 
code. Accordingly, switching device 27 is actuated by a 
pulse code modulator 28. Thus, the continuous wave 
emission from space vehicle 21 is alternately permitted 
to exit, and be blocked off from the exit in response to the 
application and reversal of the electrostatic field applied 
to electrodes 24 and 25 by switching device 27 in con- 
sonance with a predetermined encoding system having a 
one-to-one corrsepondence with a useful symbolism. 
The operation of the preferred embodiment of the 
invention disclosed in FIGS. 3 and 4 will now be de- 
scribed. Transmitter 33 is continuously supplying wave 
energy at a suitable frequency to antennas 31 and 32. 
Switching device 27 reverses the polarity of the voltage 
source 26 applied to electrodes 24 and 25 in accordance 
with information to be transmitted. Each time the po- 
larity is reversed either region 29 or region 30 becomes 
deviod of electrons for a short period of time. During 
these short periods of time, the electromagnetic waves 
emitted by antennas 31 and 32 pass through the layer 
of plasma formed around space vehicle 21 unattenuated. 
4 
These waves can be picked up by a remote receiver and 
then decoded to obtain the information supplied to switch- 
ing device 27. 
Pluse code modulator 28 can be any well known pulse 
6 code modulator. For example, the ones supplied by 
ITT Laboratories. The details of switching device 27 
have not been dis;losed since it is obviously within the 
skill of one having ordinary skill in the electrical arts to 
decign such a switch. The function of switching device 
10 27 is to reverse the connections of voltage source 26 to 
electrodes 24 and 25 each time a pulse is received from 
pulse code modulator 28. It is also possible for switch- 
ing device 27 to be a hand-operated switch. Then there 
would be no need for pulse code modulator 28. 
It is to be understood that the form of the invention 
herewith shown and described is to be taken as a preferred 
embodiment. Various changes may be made in the shape, 
size, and arangement of parts. For example, equivalent 
elements may be substituted for those illustrated and 
20 described herein, parts may be reversed, and certain fea- 
tures of the invention may be utilized independently of 
the use of other features, all without departing from the 
spirit or scope of the invention as defined in the following 
claims. 
15 
25 What is claimed is: 
1. Means for communicating through the layer of 
ionized gases formed around a space vehicle as it enters 
or  leaves a planetary atmosphere comprising: electro- 
static means mounted on said space vehicle for alternately 
30 producing two regions in said layer that are devoid of 
free electrons; antenna means attached to said space 
vehicle in said regions; and a radio transmitter means 
connected to said antenna means for transmitting electro- 
magnetic waves through said regions. 
2. Means in accordance with claim 1 wherein said 
electrostatic means comprises: two electrodes attached 
to  the outer surface of said space vehicle; a voltage source 
connected across said two electrodes; and switching means 
for reversing the connections of said voltage source across 
3. Means in accordance with the claim 2 wherein said 
switching means reverses the connections of said voltage 
source across said two electrodes in accordance with a 
predetermined encoding sjstem whereby useful informa- 
References Cited by the Examiner 
UNITED STATES PATENTS 
3,176,227 311965 Bender _ _ _ _ _ _ _ _ _ _ _  325-65 
3,176,228 31196.5 Phillips et al. _ _ _ _ _ _ _ _ _ _  3 2 5 - 6 5  
FOREIGN PATENTS 
35 
40 said two electrodes. 
45 tion can be transmitted. 
50 3,128,965 411964 Ziemer. 
55 635,784 4/1950 Great Britain. 
DAVID G. REDINBAUGH, Primary Examiner. 
JOHN W. CALDWELL, Examiner. 


Electrostatic plasma modulator for space vehicle re-entry communication Patent

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