U.S. patent number RE28,725 [Application Number 05/060,779] was granted by the patent office on 1976-02-24 for satellite and space communications systems.
This patent grant is currently assigned to Satellite and Space Communications Systems, Inc.. Invention is credited to Paul R. Arendt, Henry P. Hutchinson.
United States Patent |
RE28,725 |
Hutchinson , et al. |
February 24, 1976 |
Satellite and space communications systems
Abstract
1. The method of communicating intelligence by radio waves
between at least two bodies in space in motion with respect to each
other where a first of said bodies includes an antenna having at
least one null orientation with respect to radio waves received
from a predetermined direction, said method comprising the steps
of: (a) transmitting the intelligence simultaneously via at least
two separate radio waves from at least two geographically widely
separated transmitting stations on said second body respectively
and with said stations having sufficient separation that the two
lines of sight from the location of said antenna on said first body
to each of said separated transmitting stations on said second body
form a finite angle therebetween which exceeds the angular cross
section of the antenna null; (b) and responding at said first body
in space only to strongest of the several signals received from
said transmitting stations on said second body; whereby said
antenna on said first body can have at any time a null orientation
with respect to, at most, one of said radio waves and said first
body thereby continually receives said intelligence from said
second body.
Inventors: |
Hutchinson; Henry P.
(Ridgewood, NJ), Arendt; Paul R. (Eatontown, NJ) |
Assignee: |
Satellite and Space Communications
Systems, Inc. (Summit, NJ)
|
Family
ID: |
27363411 |
Appl.
No.: |
05/060,779 |
Filed: |
July 31, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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29111 |
May 13, 1960 |
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Reissue of: |
338179 |
Jan 16, 1964 |
03262116 |
Jul 19, 1966 |
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Current U.S.
Class: |
342/353; 342/354;
342/430; 455/25; 455/75; 342/423; 455/111; 455/12.1 |
Current CPC
Class: |
B64G
1/1007 (20130101); H04B 7/145 (20130101); H04B
7/185 (20130101) |
Current International
Class: |
B64G
1/10 (20060101); B64G 1/00 (20060101); H04B
7/145 (20060101); H04B 7/185 (20060101); H04b
007/20 (); B64g 003/00 () |
Field of
Search: |
;343/1ST,117R,7.4
;325/4,56,58,115,17 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Bailey, "The Loctracs Air Traffic Surveillance Systems,"
Navigation, Vol. 6, No. 8, Winter 1959-1960, pp. 497-506. .
Baker, I.R.E. National Convention Record, Vol. 7, Part 5, pp.
143-151. Convention held Mar. 23-26, 1959. .
Bartow et al., "Design Considerations for Space Communications,"
IRE Transactions on Communications Systems, Vol. CS-7, No. 4, Dec.,
1959, pp. 232-240. .
Haviland, Astronautica Acta, Vol. 4, No. 1, 1958, p. 74 relied on
(complete article pp. 70-89). .
NASA Memo 5-25-59W, Vol. 1, June 1959, 84 pp. 1, 2, 64 and 65.
.
Oltman et al., I.R.E. National Convention Record, Vol. 4, Part 1,
July 1956, pp. 83-86..
|
Primary Examiner: Wilbur; Maynard R.
Assistant Examiner: Berger; Richard E.
Attorney, Agent or Firm: Pollock, Vande Sande &
Priddy
Parent Case Text
This application comprises a continuation-in-part of my prior
copending application Serial No. 29,111 filed May 13, 1960, for
"Satellite and Space Communications Systems," now abandoned.
Claims
Having thus disclosed our invention, what we claim as new and
desire to secure by Letters Patent of the United States
follows:
1. The method of communicating intelligence by radio waves between
at least two bodies in space in motion with respect to each other
where a first of said bodies includes an antenna having at least
one null orientation with respect to radio waves received from a
predetermined direction, said method comprising the steps of:
(a) transmitting the intelligence simultaneously via at least two
separate radio waves from at least two geographically widely
separated transmitting stations on said second body respectively
and with said stations having sufficient separation that the two
lines of sight from the location of said antenna on said first body
to each of said separated transmitting stations on said second body
form a finite angle therebetween which exceeds the angular cross
section of the antenna null;
(b) and responding at said first body in space only to strongest of
the several signals received from said transmitting stations on
said second body;
whereby said antenna on said first body can have at any time a null
orientation with respect to, at most, one of said radio waves and
said first body thereby continually receives said intelligence from
said second body.
2. The method of claim 1 in which the intelligence transmitted from
one of said transmitting stations is delayed by an amount causing
it to be in time and phase coincidence at said first body with the
intelligence received on said second body from the other of said
stations.
3. The method of claim 1 wherein said two separate radio waves
transmitted to said first body are on respectively different
nominal carrier frequencies.
4. The method of claim 1 in which the frequency of said radio waves
transmitted from the respective transmitting stations on said
second body is adjusted by an amount substantially equal and
opposite to the amount of Doppler frequency shift produced in said
wave as received on said first body.
5. The method of claim 1 in which the same intelligence is
transmitted from each of said transmitting stations on each of a
plurality of respectively different carrier frequencies all of
which are radiated in substantially the same direction toward said
first body but which travel over different propagation paths
because of the different refractions experienced by the
respectively different frequencies, whereby at least one of said
carrier frequencies from each said transmitting station is likely
to impinge upon said first body.
6. The method of claim 5 in which said first body radiates at least
one radio wave which is received by both said stations on said
second body, and said plurality of frequencies is radiated from
each said station on said second body in the direction of reception
of said one wave from said first body even though the line-of-sight
direction between said two bodies is constantly changing.
7. The method of communicating signal intelligence to a body in
space where said body includes a directional antenna having at
least one null orientation with respect to radio signals received
from any predetermined direction, the method comprising the steps
of:
(a) transmitting said intelligence simultaneously in the form of
modulated carried radio waves from at least two geographically
widely spaced stations whose spacing is sufficient in relation to
the distance of said body that said antenna can have a null
orientation with respect to at most one of said radio waves;
(b) and responding at said body in space to only the stronger of
the waves received from said two transmitting stations.
8. The method of claim 7 including the further steps for
transmitting intelligence from said body in space to said
transmitting stations which comprises:
(a) energizing said antenna with a radio carrier wave modulated
according to the intelligence to be transmitted from said body;
(b) responding at each said station to the signal transmitted from
said body;
(c) and connecting an output circuit which is common to both said
stations to the signal being received at each said station from
said body;
whereby said output circuit is substantially continuously energized
in response to a signal representing the intelligence transmitted
from said body in space.
9. The method of claim 7 including the further steps of
continuously orienting a transmitting antenna at each said station
to maximize the amplitude of the signal transmitted toward said
body.
10. The method of communicating intelligence to a space station
having an antenna which is at times disposed in a null orientation
with respect to a radio wave received from any predetermined
direction and comprising the steps of:
(a) transmitting simultaneously at least two carrier radio waves
each modulated according to the intelligence to be communicated to
said space station and with said waves emanating from stations
sufficiently widely spaced that said antenna can have a null
orientation with respect to at most one of said radio waves;
(b) delaying the modulation on at least one of said carrier waves
in accordance with the difference in the respective propagation
times of the modulations from their common source to said space
station to thereby cause the respective modulations on said waves
to be substantially in time coincidence when received at said space
station;
(c) and responding at said space station to the stronger of the two
carrier waves.
11. In a system for communicating intelligence via radio with a
body in space having a directional antenna that may at times be
null oriented with respect to a radio beam coming from any
particular direction, the combination comprising: first and second
transmitting means at geographically widely spaced locations for
transmitting carrier waves simultaneously to said body in space
with both said waves being modulated substantially simultaneously
according to the intelligence to be transmitted to said body, said
locations being so far separated that said directional antenna can
at any instant have a null orientation with respect to at most one
of the radio waves transmitted from said respective first and
second transmitting means, receiving means on said body
electrically coupled to said directional antenna and producing an
output signal only in response to the received carrier wave which
produces the greatest amplitude of signal in said directional
antenna, and output means connected to said receiving means and
being responsive to the demodulated output of said signal produced
by said receiving means.
12. The system of claim 11 in which means is coupled to each said
transmitting means to vary its frequency in response to the
continuously measured component of velocity of said body relative
to said transmitting location, whereby the carrier frequency
received at said body from any transmitting station is
substantially unvarying despite Doppler frequency shifts resulting
from the relative velocity between said body and the location of
said transmitting station.
13. The combination of claim 11 in which each said station includes
at least one antenna for radiating electromagnetic energy to said
body in space, and means is coupled to each said radiating antenna
to continuously orient said antenna with respect to said body,
whereby the maximum amplitude of radio wave is continually received
by said antenna on said body from each said station.
14. A system for communicating intelligence between the earth and a
space station having an antenna which may at times have a null
orientation with respect to radio waves received from any one
station on earth, the combination comprising: at least two stations
on earth each comprising transmitting and receiving means and being
sufficiently widely spaced that said antenna can have at most a
null orientation with respect to radio waves originating with one
of said stations but still permitting line-of-sight communication
between each said earth station and said space station, means at
each earth station for modulating a carrier frequency wave
transmitted from that station according to the intelligence to be
transmitted to said space station, means at said space station
including demodulator means responsive only to the strongest of the
carrier waves energizing said antenna, modulator means at said
space station for modulating a carrier wave according to the
intelligence to be transmitted to earth and energizing said antenna
with the resulting modulating carrier wave to radiate said wave
toward said earth stations, said receiving means including a
receiving antenna at each earth station, and means connected
electrically to each said receiving means at the respective
stations and being responsive to the intelligence transmitted by
said space station and being received by the associated receiving
means.
15. The system of claim 14 wherein both said transmitting and
receiving antennas at each earth station have directional
sensitivity, and each said station includes antenna control means
for orienting both receiving and transmitting antennas to have
their maximum sensitivity generally in the line-of-sight direction
with respect to said space station.
16. The combination of claim 15 wherein said antenna control means
for each said station includes means responsive to said receiving
means for orienting said receiving and transmitting antennas at the
respective station toward the direction from which the receiving
antenna receives the maximum energization from the signal
transmitted from said space station.
17. The method of communicating signal intelligence between two
widely spaced stations on earth via a body in space, comprising the
steps of transmitting from one of said stations simultaneously
different carrier frequency waves each modulated according to the
intelligence to be transmitted, receiving at said body in space the
several carrier waves impinging thereon, demodulating at said body
in space the strongest of the several received carrier waves to
thereby obtain a signal containing said intelligence, transmitting
from said body in space another carrier frequency wave modulated
according to said intelligence signal received from the strongest
carrier, and receiving and demodulating at the other of said
stations the modulated signal received from said body in space.
18. The method of claim 17 in which the signal from said body in
space may be transmitted on any one of a plurality of different
frequencies and the particular frequency selected at any instant is
the one which is closest to that on which said body is then
receiving the strongest signal from said one station.
19. The method of claim 18 in which an antenna at said other
station is directed to have its maximum sensitivity along the
direction from which said radio wave from said body in space is
received.
20. Means for communicating between two bodies in space having a
substantial radial velocity component therebetween resulting in a
substantial frequency shift in a a received radio wave as compared
to the frequency of the transmitted wave and comprising, receiving
and transmitting means at both said bodies with both transmitting
means transmitting normally on respectively different nominal
frequencies, first means at one of said bodies producing a first
signal having a value representative of the frequency transmitted
from the other of said bodies, means at said one body coupled to
said receiving means responsive to said first signal for producing
an output having at least one characteristic thereof which is
proportional to the Doppler difference in frequency between the
signal received at said one body from the other said body and the
signal transmitted from said other body, second means at said one
body producing a second signal having a value representative of the
pass-band of frequencies of the receiving means for the other of
said bodies, frequency-control means at said one body responsive to
said output and to said second signal for controlling the frequency
of the signal transmitted by said transmitting means from said one
body to differ from its said nominal frequency by an amount
substantially proportional to the amount of said Doppler frequency
difference, said frequency control means shifting the frequency
transmitted from said one body in a direction opposite to the
direction of the frequency shift in the signal received from the
other body, said receiving means on said other body being
responsive only within a pass-band that encompasses said nominal
frequency of said transmitting means at said one body.
21. Means for communicating between two stations in space having a
substantial radial velocity component therebetween such that a
radio wave transmitted from one station is received with a
substantial Doppler frequency shift at the other of said stations,
the combination comprising: first transmitting means of one of said
stations for transmitting a carrier wave on a fixed predetermined
frequency, first receiving means at said one station for receiving
carrier waves occurring within a predetermined pass-band, second
receiving means at the other of said stations receiving the carrier
frequency wave transmitted from said one station, first means at
said other station generating a signal representative of said fixed
predetermined frequency, control means coupled to said second
receiving means and responsive to said signal and being
distinctively controlled according to the frequency difference
between the carrier wave received from said one station and the
predetermined frequency transmitted from said one station, variable
frequency transmitting means at said other station operating at a
frequency range other than said fixed predetermined frequency, said
control means and said second means jointly varying the frequency
of the carrier wave transmitted by said variable frequency
transmitting means by an amount proportional to the frequency shift
of the carrier wave received from said one station to thereby cause
said carrier wave transmitted by said variable frequency
transmitting means to be received by said first receiving means
within said pass-band.
22. The method of communicating the same signal intelligence from
each of at least two transmitting stations on one body in space to
a receiving station on a second body in space comprising the steps
of:
transmitting carrier waves from both of said two stations to said
second body in space;
modulating each of said carrier waves with the signal intelligence
to be transmitted to said receiving station on said second body in
space;
measuring the difference in distance between each respective one of
said transmitting stations on said first body in space to said
receiving station on said second body in space;
and delaying the modulating signal intelligence to that
transmitting station which is nearer said body in space relative to
the same modulating signal intelligence for the other of said
transmitting stations and by an amount substantially equal to the
transmission time of said carrier wave in space over the distance
measured in the immediately preceding step;
whereby said signal intelligence is received at said receiving
station in substantial phase coincidence for both of said
transmitting stations.
23. A system for communicting electromagnetic intelligence signals
between bodies in space, said signals while being radiated between
said bodies being subject to space propagation phenomena including
spin fading, amplitude scintillation, frequency scintillation,
polarization fading, signal reflection, signal ducting, and signal
black-out, said system comprising, means on said one body including
a first directive antenna means transmitting a first signal in a
highly directive beam toward the other said body in space, and
signal direction finding means on said one body responsive to a
signal transmitted from said other body which is subject to said
space propagation phenomena .Iadd.substantially
.Iaddend..[.substationally.]. the same as said first signal for
.Iadd.continually .Iaddend..[.continuously.]. controlling the
direction of transmission of said directive antenna means in both
azimuth and elevation to maximize the intensity of signal reception
at said other body, said direction finding means including at least
one antenna means having a single axis of directivity and means
responsive to coincidence of said axis with the direction of signal
reception from said other body for controlling said directivity of
transmission.
24. The system of claim 23 in which said other body in space is a
satellite repeatedly orbiting about the earth's center.
25. The system of claim 23 in which said signal transmitted from
said other body is an intelligence signal.
26. The system of claim 23 in which said direction finding means
includes means for repeatedly moving said direction finding means
to bring its single axis of directivity into momentary coincidence
with said direction of energy reception from said other body in
space.
27. A system for receiving an electromagnetic intelligence signal
from a body in space, said received intelligence signal being
subject to space propagatiotn phenomena including spin fading,
amplitude scintillation, frequency scintillation, polarization
fading, signal ducting, and signal black-out, said system
comprising means including a first directive antenna means for
directionally receiving said signal from said body in space, and
satellite signal direction finding means responsive to a signal
from said body in space which is subject to said propagation
substantially the same as said received signal for continually
controlling the direction of reception of said first directive
antenna means in both azimuth and elevation to maximize the
intelligence signal received from said body in space, said
direction finding means including at least one antenna means having
a single axis of directivity and means responsive to coincidence of
said axis with the direction of signal reception from said body in
space for controlling said directivity of reception.
28. The system of claim 27 in which said body in space is a
satellite repeatedly orbiting about the earth's center.
29. The system of claim 27 in which the signal to which said
direction finding means responds is the same as said intelligence
signal received by said first directive antenna means.
30. The system of claim 27 in which said direction finding means
includes means for repeatedly moving said direction finding means
to bring its single axis of directivity into momentary coincidence
with said direction of energy reception from said other body in
space. .Iadd. 31. A system for communicating electromagnetic
intelligence signals between bodies in space, said signals while
being radiated between said bodies in space being subject to space
propagation phenomena including spin fading, amplitude
scintillation, frequency scintillation, polarization fading, signal
reflection, signal ducting, and signal black-out, said system
comprising,
means on said one body including a first directive antenna means
transmitting a first signal in a highly directive beam toward the
other said body in space,
means on said one body including a second directive antenna means
for directionally receiving a second signal from said other body in
space,
signal direction finding means on said one body responsive to a
signal from said other body which is subject to said space
propagation phenomena substantially the same as said first
transmitted signal and also substantially the same as said second
received signal for continually controlling the direction of
transmission of said first directive antenna means in both azimuth
and elevation to maximize the intensity of signal reception of said
first signal at said other body and for also continually
controlling the direction of reception of said second directive
antenna means in both azimuth and elevation to maximize the
intensity of reception of said second signal received from said
other body,
said direction finding means including at least one antenna means
having a single axis of directivity and means responsive to
coincidence of said axis with the direction of signal reception
from said other body for controlling said direction of transmission
of said first directive antenna means and also the direction of
reception of said second antenna means..Iaddend.
Description
This invention relates to methods and means for providing optimum
radio communications, or electromagnetic signalling, or
transmission and reception of data or other information or
intelligence between a ground station on or near the earth's
surface, and a space station travelling in accordance with Newton's
laws of motion in the first approximation, between space stations,
and among the various types of earth and space stations.
This invention comprises a major means for improvement of
moon-relay or other radio communication systems using reflections
of beamed signals from a planet or other astronomical body. An
additional purpose of this invention is to provide sufficient means
for tracking satellites so that the beams of radio energy emitted
from the earth station will continually illuminate the space
station in spite of the phenomena of refraction, bending,
scattering, and scintillation of the beamed energy, all of which
phenomena are due to nature processes more fully reviewed
below.
Furthermore, in addition to these natural processes, it is known to
us by careful study of radio signals received from many United
States and Russian satellites, that there occur serious
deficiencies in the reception and transmission of electromagnetic
energy between earth and space stations because of the spinning and
tumbling of such satellites and because of the non-isotropic nature
of antenna patterns, including both the simple dipole and more
complex structures. As a result of this spinning and tumbling,
large unwanted variations occur in the signal received at the space
station from a beam of uniform energy radiated by a ground station
and similarly, large unwanted variations occur in the reception by
a ground station of constant-amplitude signals radiated by space
stations. Thus, under normal conditions where space stations are
spinning or tumbling with respect to the direction of the
energy-transmission path to either an earth station or to another
space station, it has not been possible with previously known
techniques to maintain continuous signalling or transmission of
electromagnetic energy between such stations; it has only been
possible to have a series of discontinuous transmissions depending
upon the relative spinning or tumbling motions cited above.
An object of this invention is to provide continuous real-time
radio communications (including either transmission or reception of
data or other signals) between earth and space stations and between
two or more space stations.
Another important feature of this invention is to provide a
preferred means for maintaining such continuous real-time
communications in spite of various adverse natural or man-made
environmental phenomena by using a particular frequency band of
electromagnetic radiation. We have found that the use of other
higher or lower frequency bands causes sufficient bending,
absorption, scattering, or other distortions and degradation of the
signals to require at best an excessive amount of electrical power
for transmission and, at worst, result in an inability to maintain
communications.
Still another feature of this invention relates to the use of
several pluralities of geographically widely-separated stations,
the separation of the stations in each plurality being measured in
terms of hundreds or thousands of miles and which are linked by the
communications system of our invention. For the purpose of
describing this invention a plurality of ground stations situated
on the earth's surface will be used, but it is nevertheless a part
of our invention that one or more of the geographically
widely-separated stations used in this system will be established
on the moon or other planets, planetoids, or satellites, and
therefore, in the context of this invention, the expression
"geographically widely-separated" is to be taken as not limited to
points on the earth's surface, but in fact is intended to include
specifically any combination of location on the earth's surface,
natural plants or planetoids, and man-made space stations.
This feature of the invention overcomes the large-amplitude
variations caused by the spinning and tumbling of a space station
with respect to the ray path to any other station. Furthermore, it
ensures that upon the transmission of a signal from one of these
stations it will be received at any other station after a lapse of
time sufficient only for the electromagnetic energy to travel from
one station to the other. Thus, if a plurality of signals is
radiated, each signal comprising the same intelligence and each
transmitted from a different one of the widely-separated stations,
the reception of these signals will commence as soon as the
radiated energy has reached the intended receiving station and the
reception of the intelligence will go on continuously as long as
the receiving station is illuminated by at least one of the
plurality of transmitting stations. Conversely, if the reception of
an intelligence signal by the plurality of stations is desired,
this reception will commence as soon as the energy reaches one
station having its antenna oriented to intercept sufficient energy
from the passing electromagnetic wave and will continue as long as
at least one of the plurality of receiving stations is receiving
the radiated signal. In the case of ground stations on the earth's
surface and space stations, which are earth satellites, the period
of continuous reception from any one station might vary from a few
minutes for an earth satellite in a polar orbit to continuous
operation for an earth satellite in the approximately 22,000 mile
stationary equatorial orbit.
These and other objects and features of this invention will be more
readily understood from the following detailed description of a
preferred embodiment, which is shown in the accompanying
illustration and drawings. However, before proceeding to this
detailed description, the general organization of this invention,
as described above, will be more fully indicated in drawings and by
further description.
In the drawings:
FIG. 1A diagrammatically illustrates one arrangement for providing
communications between earth and space stations;
FIG. 1B is a block diagram showing in greater detail the components
of the system of FIG. 1A;
FIG. 2 illustrates certain characteristics of the directional
antenna employed by a space station;
FIG. 3 illustrates a system of communications between two earth
stations via a passive space station reflector such as the
moon;
FIG. 4 is a block diagram illustrating a multichannel communication
system between two stations in space, one of which may be on the
earth's surface;
FIG. 5 illustrates one form of directional finding equipment which
may be employed in the systems of our invention;
FIG. 6 illustrates certain geometrical considerations involved in a
determination of distances;
FIG. 7 is a block diagram illustrating apparatus for automatically
controlling the delay applied to signals to compensate for
differences in transmission times over widely different signals
paths;
FIG. 7A illustrates apparatus for controlling the relative delays
of respective modulating signals to compensate for differences in
transmission time over widely different signal paths, such
apparatus not having the automaticity of the apparatus of FIG.
7;
FIG. 8 graphically illustrates some of the factors involved in
correcting for Doppler frequency shifts; and
FIG. 9 illustrates apparatus providing for the automatic control of
frequency to compensate for Doppler shift.
FUNCTION OF SYSTEM COMPONENTS
FIG. 1A illustrates diagrammatically one aspect of our invention.
The system illustrated provides for real time communications from
one location to another on the earth surface via a space station S.
It is assumed that the two earth locations are so widely separated
that direct communications between them are not practicable but
that the two locations are not so widely spaced as to make it
impossible for each of them to communicate with space station S. It
should be understood that, although the two locations, i.e., the
one including stations A and B and the other including stations A'
and B', are both shown as being located on the earth's surface,
this is by no means necessary for the practice of our invention
which also comprehends, as previously stated, communications
between space stations, from the earth to a space station and then
to a second space station, and all other such configurations.
In FIG. 1A, it is shown that the stations A and B (or A' and B') at
each communications location are connected by a communications
network, the primary purpose of which is to permit transmission or
reception of the same intelligence signal by either of the two
stations. Thus, we contemplate that an intelligence signal to be
transmitted from one earth location to the other may be transmitted
simultaneously from both stations A and B on respective frequencies
f.sub.ta and f.sub.tb, and, furthermore, that both these stations A
and B may, at times, simultaneously receive signals from the space
station on respective frequencies f.sub.ra and f.sub.rb.
In FIG. 1B we have shown in greater detail the system organization
of the appratus for stations A and B at one of these locations.
The two ground stations A and B may be separated from each other by
a distance of several hundred miles along the earth's surface.
Space station S both receives from and transmits to stations A and
B in real time, as shown below. In FIG. 1B, the input signal which
is to be transmitted from the earth to space station S is applied
to modulate 3 which modules transmitter 4 and delivers the
radio-frequency output of the transmitter 4 to a controllable
directional antenna 5 located at station A. This antenna 5 is
controlled by a three-dimensional radio-direction-finder 6, which
is located at or sufficiently close to station A so that the
direction from antenna 6A for direction finder 6 to the space
station S is within the limits of the beam widths of both the
transmitting antenna 5 and receiving antenna 20. Thus, to a first
approximation, the same azimuth and elevation bearings from station
A to space station S apply for the radio-direction-finder antenna
6A, the transmitting antenna 5 and the receiving antenna 20.
The direction finder 6 detects the radio transmissions emitted from
space station S on a radio frequency f.sub.ra and continuously
determines the angular directions of azimuth and elevation bearings
used to control both the transmitting antenna 5 and the receiving
antenna 20. Thus, the output signals of the direction finder 6,
which contain the angular information required for positioning
antennas 5 and 20 are applied to the respective antenna directors 7
and 19. Antenna director 7 positions antenna 5 in the direction
required to illuminate the satellite S with the radio-wave energy
carrying the signals or modulation connected to modulator 3.
Antenna director 19 similarly positions the receiving antenna 20 in
the direction required to receive maximum output from radio
emissions from the space station S.
The input signals connected to modulator 3 are also transmitted
over a ground-to-ground communications system to modulator 11 at
station B. In the same manner as previously described for station
A, this signal modulates a transmitter 12, and the radio-wave
output energy from the transmitter is connected to a controllable
directional antenna 13. This controllable directional antenna 13
and a directional receiving antenna 24 are, in a similar manner to
that described for station A, controlled by antenna directors 23
and 15 respectively, both of which are operable from output signals
from direction finder 14 connected to direction-finder antenna 14A.
Directional bearings from station B to space station S are
determined by radio-direction-finder 14, which through the antenna
directors 15 and 23 illuminates the space station S with radio-wave
output energy from transmitter 12 and positions the receiving
antenna 24 to receive maximum output from radio emissions from
station S.
In this manner, each of the ground stations used in this embodiment
of our invention continuously illuminates the space station S with
its radio beam for the period of time that the space station S is
within view of stations A and B. Now let f.sub.ta designate the
frequency of signals in the transmitted radio beam from station A
and f.sub.tb the frequency of the signals in the radio beam from
station B. As previously indicated, the distance between stations A
and B measured along the earth's surface is measured in hundreds or
even thousands of miles. Thus, at any instant, the points
comprising stations A, B, and S constitute a triangle of which one
angle is ASB, designated as .alpha..sub.AB. This angle
.alpha..sub.AB measures the difference in direction between the
radio beams arriving at space station S from ground stations A and
B. Similarly, if additional system stations were established at
additional geographical locations either on the earth, or moon, or
other planet or planetoid, or space station, it is clear that the
beam from each of these additional stations would illuminate the
space station S from a different direction, as seen from the space
station, thus generating additional angles .alpha..sub.BC,
.alpha..sub.AC, et cetera, depending upon the plurality of stations
used. Now let us consider reception of these multiple beams at
space station S.
In FIG. 2 there is shown a dipole antenna 16 at space station S.
This antenna is aligned so that the angle .beta..sub.A exists
between the axis of the dipole and the beam f.sub.ta of radio-wave
energy received from ground station A. Similarly, angles
.beta..sub.B, .beta..sub.C, et cetera, exist between the axis of
the dipole and the other beams, f.sub.tb, f.sub.tc, et cetera,
illuminating the space station S. Now it is well known that a
dipole has induced in it a maximum radio frequency voltage when the
direction of the electric field of the incident electromagnetic
wave is parallel to the length of the dipole. Furthermore, as the
direction between the incident electric field of a wave passing the
space station S changes from one in which the space station dipole
is parallel to the field and becomes one in which the space station
dipole 16 becomes perpendicular to the electric field of the
passing wave, the induced signal in the dipole will drop to zero.
Therefore, as space station S spins or tumbles in its orbit, these
changes in its attidue with respect to the oncoming beam from any
single station, such as station A, will cause large changes in the
signal induced in the dipole and thus in the space station received
signal.
A space station antenna 16 has a null direction, that is one in
which minimum signals are received, and at times the null of the
space station antenna 16 will be coincident with the direction of
one of the beams illuminating the space station and, therefore, a
minimum or no signal will be received from that station. However,
since our invention insures that signals bearing the same
modulation will be arriving at the satellite or space station S
substantially simultaneously from substantially different
directions, which difference in directions exceeds the null width
of the space station antenna, there will always be energy available
from at least one of the beams illuminating the space station S
when it happens that the null direction of the space station dipole
(or other antenna) coincides with the direction of a particular one
of the illuminating beams. Therefore, as this invention shows, the
use of two or more beams arriving simultaneously from different
directions overcomes the lack of an isotropic radiator or
equal-amplitude antenna pattern extending over the 4.pi. sperical
radians denoting all directions extending outward from space
station S.
Continuing with the system description, the frequencies f.sub.ta
and f.sub.tb bearing the same modulations induce voltages in dipole
16 at the space station S. Since, at any instant of time, only one
of the illuminating frequencies f.sub.ta, f.sub.tb, et cetera, can
be in the null of the receiving antenna pattern, signals are
continuously induced in the receiving antenna and fed from the
receiving antenna 16 to a receiver 17 which provided the real-time
reception of signals continuously at the space station S as long as
signals are being sent by the ground stations A, B, et cetera.
Transmission from space station S to the earth is by a transmitter
18 at the space station, which radiates energy simultaneously
towards a plurality of earth stations; namely stations A, B, et
cetera. Since, as explained above and shown in FIG. 2, stations A,
B, C, et cetera lie in different directions from space station S,
then at such times as the null pattern of the antenna at space
station S lies in the direction of a particular one of the
plurality of ground stations, thus affording that particular
station a minimum or even unusable signal, the other ground
stations do not lie in the null of the space station antenna
pattern and will receive stronger and usable signals. Thus, it is
seen that no matter when radio emissions are radiated from the
space station S, there will at most be only one ground station
which lies in the null of the space station antenna and, therefore,
the ground part of this system will receive and transmit to the
ground control point signals or other intelligence, as previously
defined above, from space station S. These signals will, of course,
be received by the remainder of the plurality of ground stations
whose locations are such, that, at any instant, they do not lie in
the null of the space station antenna.
Now referring to FIG. 1B, the radio-direction-finder 6, whose
antenna 6A has detected the signals from space station transmitter
18 and determined the direction of the space station S with
reference to earth station A, controls antenna director 19 to
orient receiving antenna 20 so as to align the receiving antenna
beam along the ray path at station A of the received radio wave
f.sub.ra from space station S. The received energy is connected to
receiver 21 which receives and demodulates the incoming signal and
delivers the demodulated output to a signal combiner 22. In a
similar fashion, the radio-directional-finder at station B is
connected to control antenna direction 23 to align the beam of
receiving antenna 24 in the direction of the received energy
f.sub.rb. This received energy is connected to receiver 25 and
demodulated. The resulting signal is applied over a communications
channel from station B to station A. The output of this channel is
then connected to signal combiner 22, and the combined output (that
from receiver 21 at station A and that from receiver 25 at station
B) is made available as a system output.
The earth system input signal terminal and output signal terminal,
therefore, comprise the system ground terminals of this real-time
satellite and space communications system. To these terminals may
be connected a telephone, teletypewriter, computer, or other device
or combinations of such devices depending upon the intelligence
which it is desired to transmit to and receive from space station
S. Furthermore, since this system may have separate input and
output terminations at both the earth control station and at space
station S (as shown, more particularly, in FIG. 4), it is possible,
but not necessary, to transmit one type of intelligence from the
ground to the space station and another type of intelligence
simultaneously from the space station to the ground. Therefore, in
addition to having described a system for continuous real-time
communication between the earth and space stations, and between
earth stations via a space station, we have described a system
which transmits on a continuous basis, different kinds of
intelligence for each direction of transmission. In particular,
with an unmanned space station, it would be expected that
telegraph, teletype, computer signal, or other coded commands would
be transmitted to the space station in order to affect or control
its position in space, its attitude, or to start, stop, or control
various functions of the apparatus carried in the space station,
including the function of control of ejection of material from the
space station; whereas transmission from such an unmanned space
station would give indication of receipt and execution of such
control functions and would telemeter data observed at the space
station on either its own functions or on its environment or in
connection with other experiments.
The next functional aspect of this invention describes a method and
means for obtaining an improvement of transmission of signals to
the moon or other planet. It is clear that as the distance of the
space station S increases from the earth, a point will be reached
at which it will be necessary to use an earth-moon communications
system at the internal communication systems of our invention. That
is, Station A will be on the earth and the other stations B, C, et
cetera, will be on the moon and other planets. Furthermore, such an
improvement may be used in moonrelay systems for providing more
effective transmission of signals from earth to earth stations via
moon relay.
In FIG. 3 is shown a system for communicating between widely spaced
earth stations via reflections from a moon or other passive
reflection. It should be noted, however, that this system is not to
be considered as limited to one in which the stations are
necesarily on the earth, since one or more of the stations may be
on a space station at a great distance from the earth. In the
system of FIG. 3, transmission of signals takes place from a
multi-channel transmitter 28 and steerable directional antenna 29
aimed at the earth's moon M. In this system the transmitter 28
generates and the antenna 29 radiates a plurality of radio
frequencies, for example, f.sub. 1, f.sub. 2, f.sub. 3, f.sub. 4
each of which by virtue of their frequency separation, is bent to a
different degree in passing from the earth's surface through the
atmosphere and ionosphere which surrounds the earth. Each frequency
f.sub. 1 --f.sub. 4 is modulated by modulator 28A in accordance
with the signal to be transmitted. By using this multi-frequency
type of radiation, a spreading can be obtained in the effective
beam width so that it can be made several times greater than that
necessary to cover either the whole of the moon's surface or a
specific part thereof (for example, the first Fresnel zone).
It is known to use that signals received from space stations appear
to come at varying times from positions ahead of, behind, or to one
side of the true bearings at that instant from the earth's
position. This is due to both systematic deviations caused by
refractive effects, and random variations caused by natural changes
in the electron density of the ionosphere. These natural changes
are due to solar radiation, ion recombination, ionization,
ionospheric winds, and other natural phenomena. The total effect of
all these conditions causes the received beam to vary continuously
to a greater or lesser extent from the true bearing from earth to
the space station. In a similar fashion, these and other natural
phenomena (tropospheric effects) will affect any radio wave aimed
from the earth in the direction of the earth's moon or other
planet. Now as the radiated energy in frequencies f.sub. 1, f.sub.
2, f.sub. 3, and f.sub. 4 is kept aimed in the direction of the
moon (using, if neccessary, an ephemeris of the moon to obtain the
direction of the moon from station C and control antenna director
29A) the beamed energy will illuminate the moon, or the specific
portion thereof desired, by these transmitted frequencies. Because
of the ray bending and scintillation effects mentioned above, at
different instants of time, one of the above radio frequencies will
provide both optimum illumination of the moon and maximum reflected
signal from the moon M to earth station D. Thus the strength of the
received signal at station D depends largely at any instant of time
upon the following:
(a) that frequency which most effectively illuminates the moon, or
the desired portion thereof;
(b) that frequency most effectively reflected by the moon;
(c) ionospheric and tropospheric effects in the regions between the
moon M and stations C and D respectively.
From the above, it is clear that a directional antenna 30 located
at station D and pointed in the direction of the moon M by
direction finder 30A which is responsive to the moon-reflected
energy will receive fluctuating energy from the various frequencies
f.sub. 1, f.sub. 2, f.sub. 3, and f.sub. 4 as a function of time.
The antenna delivers the collected energy to a multi-channel
receiver 31 which responds to the strongest carrier present,
demodulates this signal and delivers this signal to station D, thus
accomplishing transmission of information or signal from station C
to station D. Since the same modulation is used simultaneously on
all the carrier frequencies f.sub. 1, f.sub. 2, f.sub. 3, and
f.sub. 4, it is unimportant which of these frequencies carries the
information at any instant and continuous communications are
thereby maintained. It is clear, however, that for frequencies
sufficiently low to be affected by the ionosphere, the use of a
single frequency is insufficent to maintain continuous
communications and that an optimum system requires a multiplicity
of frequencies. Transmission in the reverse direction from station
to station C is carried out in a similar fashion.
By substituting a space station S for the moon M in the
multi-frequency communications system just discussed, it is
possible to obtain a variation of the above system for space
station use. Under certain circumstances, such as the availability
of a space station, with controllable antennas, whose nulls will
always be directed away from the earth, this variation may be used
as a single earth station to satellite or space station system;
whereas if the above does not apply, the variation may be used in
combination with our multi-station earth to space station
communication system described above.
Referring to FIG. 4, radio frequency energy generated at a
plurality of radio frequencies f.sub. 1, f.sub. 2 and f.sub. 3 by
transmitter 32 is radiated by a beamed antenna 33 in the direction
of the path of space station S. Each transmitted frequency is
modulated by modulator 44 according to the signal to be
transmitted. As indicated above, at some time when the space
station comes into the beam of antenna 33, one of the frequencies
f.sub. 1 through f.sub. 3 will be received with the greatest
intensity by antenna 34 at the space station S. The received
radio-frequency energy is connected to the receiver 35 which
identifies which of the frequencies f.sub. 1 through f.sub. 3 is
the strongest and causes the space station transmitter 37 to
radiate a signal on a frequency which is sufficiently close to the
frequency received from the earth so that the principle of
reciprocity along the transmission path is maintained. Under this
condition, the frequency f.sub. s emitted from the space station S
will be received at the earth station F with sufficient intensity
to provide a useable signal.
The multichannel receiver 35 produces a separate output signal for
each of its several channels corresponding, respectively, to the
frequencies f.sub. 1 -f.sub. 3. The amplitude of the signal
appearing on any one channel is dependent upon the amplitude of the
corresponding signal and, conceivably, one or more channels may
produce zero output if antenna 34 receives no signal on the
corresponding frequency.
Each of the separate outputs of receiver 35 is applied to a level
monitor which may, for example, be of the type shown in Patent
1,823,739, issued September 15, 1931. Such a level monitor
comprises a plurality of amplitude responsive circuits which are
selectively operated in accordance with the amplitude of input
signal applied to the level monitor. Thus, the output of any one of
these level monitors shown in FIG. 4 may comprise a plurality of
relays, each of which is operated from its normal condition only
when the input signal applied to the level monitor exceeds a
predetermined corresponding value. Thus, the conditions of these
relays for any one level monitor indicate at each instant the level
of the input signal applied thereto. It is well known in the art
how the contacts of the various relays for each of the level
monitors 35A--35C may be connected to comprise what is termed a
channel selector 36 which, in effect, determines which of the
several level monitors is receiving the highest amplitude of input
signal, thereby effectively also determining which of the signals
f.sub. 1 -f.sub. 3 is then being most effectively received by
antenna 34 and determining also which of the several possible
output frequencies of transmitter 37 is closest to that of the
strongest received frequency in order that reciprocity in return
transmission to earth station S will be obtained.
This feature of our invention has to do with the selection from
among a plurality of available radio frequencies that frequency for
which at any instant of time the best propagation condition between
earth and space stations occurs. The emitted signal on frequency
f.sub. s from space station S is received at earth station F by a
radio-direction-finder 38 whose rotating antenna 38A is responsive
to the f.sub. s signal and which, through antenna directors 39 and
39A point the receiving antenna 40 and the transmitting antenna 33,
respectively, in the direction of the energy received on frequency
f.sub. s.
Operation of the radio-direction-finder 38 completes a closed loop
energy system consisting of the following:
(1) Transmission from station F on a multi-frequency basis;
(2) Reception of the optimum frequency at space station S;
(3) transmission from space station S on a frequency f.sub. 5
sufficiently close to the received optimum frequency for
reciprocity to hold;
(4) Reception of frequency f.sub. s of the direction-finder antenna
38A.
Operation of this closed loop system on continuous realtime basis
is contingent upon the following:
(a) Either the space station or its antenna is stabilized in such a
manner that the null of the space stations antenna never lies in
the direction from the space station S to the ground station F.
(b) As propagation or other conditions change, the optimum
frequency will vary among those selected and available for use at
earth station F. Furthermore, from the plurality of frequencies
available at the ground station F, these will be a similar number
of frequencies f.sub. s1, f.sub. s2, et cetera, available at the
space station.
When the above-mentioned closed loop energy system has been
established and the earth station F receiving antenna 40 has been
aligned to maximize collection of the incoming radio-frequency
energy on frequency f.sub. s, this energy is coupled from receiving
antenna 40 to multi-channel receiver 41 which then provides an
intelligence signal output. Signals which are to be transmitted
from space station S to earth station F may be generated at the
space station itself or may be received from another earth or space
station for direct retransmission to station F. Alternatively, such
signals may be stored at station S for later relay to station F
when communications are established as evidenced by the presence of
an output from space station receiver 35 in response to one or more
of the frequencies f.sub. 1 -f.sub. 4. Whatever the source of the
signal, it is applied as a modulating input to transmitter 37 which
then transmits on the selected one of the frequencies f.sub. 1
-f.sub. 4. In this manner two-way communication is established and
maintained on a continuous basis between earth station F and space
station S. As mentioned above, it should be noted that this feature
of our invention applies to the stablishment of continuous two-way
communications with space stations which have been stabilized in
their attitude, or provided with other means for keeping their
antenna or antennas so oriented that they can maintain a continuous
radiation of energy in the direction of the path to the ground
station on the earth's surface.
The final part of this description of system functions relates to
our discovery of a method and means for obtaining optimum
performance of the two following system functions, each of which is
part of our invention.
(1) Communications;
(2) Tracking and position location.
Although each of these aspects is related to the frequency
scintillations observed from both earth satellites and solar
satellite transmissions, the optimum frequency bands for each
function are not the same. In fact, our discovery leads us to the
conclusions that the optimum band of frequencies for precision
tracking and position location of earth satellite's and space
stations from the surface of the earth is included within and is a
relatively small part of that frequency band, which is optimum for
communications between stations on the earth's surface, as
described above, and earth satellite or space stations. Based upon
recent experimental recordings of earth satellite and space probe
signals, it now has become clear to us that the lowest radio
frequency suitable for earth to earth satellite or earth to space
station communications lies at a sufficiently high ratio frequency
so that frequency scintillations of the received signal are
negligible. Because of effects of the ionosphere, these frequency
scintillations do not become negligible until the transmitted
frequency is greater than 500 mc./s. On the other hand,
trophospheric inhomogeneities also create amplitude scintillations,
which degrade the received signals at frequencies greater than
4,000 mc./s. From the above, it is clear that to obtain
satisfactory and reliable communications between the earth and
earth satellites and space stations, it is necessary, for optimum
conditions, which include the avoidance of frequency scintillations
caused by the ionosphere and amplitude scintillations caused by the
troposphere, to use a particular band of radio frequencies. Our
method consists of radiating signals for this purpose in the
frequency band of 500 mc./s to 4,000 mc./s.
For tracking and position location purposes, and especially where
precision tracking from the earth's surface is required, as it is
in our real-time communications system, the transmission
requirements are more severe than for signalling. For precision
tracking, it is essential to operate in a frequency range where
neither disturbances caused by turbulence of the transmission
medium refractive effects, scatter and variations due to
inhomogeneities, and the effects of frequency scintillations are
sufficient to distort the received signals, or cause sufficient
variations in delay of the received signal to the point where the
tracking or location systems yields large errors or fails. This
means that the refractive index of the media should, for the
frequency chosen, be as close as possible to a value of unity (the
free space value), and furthermore, this value should be most
uniform along the entire ray path. According to our discoveries,
based on frequency scintillation data, these features can be best
approximated by radio transmissions in the frequency range of
650-1050 mc./s. Within this frequency range, centered about an
optimum value in the neighborhood of 850 mc./s., the received
signals and radio-wave emissions are least affected by the
undesirable effects of both the ionosphere and the trophosphere.
Our method of minimizing tracking and position-location errors,
therefore, consists of using emitted and received radio waves for
such purposes in the frequency band of 650-1050 mc./s. These uses
include both the position location of earth satellites and other
space stations as well as the tracking of such objects.
Furthermore, it is a feature of our discovery and invention of this
method that in position tracking and position location systems in
which there is much difficulty caused by radiowave propagation
phenomena, we use an optimum value of approximately 850 mc./s.
A further feature of our invention is the provision of means within
the system for equalizing the time of transmission of the
modulations from the various stations A, B, et cetera, so that
these modulations or modulated signals will arrive simultaneously,
within accpetable time limitations, at the satellite or space
station. Since the modulated signal or radio wave from each of the
stations A, B, et cetera must in general travel a different
distance from the radio transmitter for that station, to the space
station or satellite, it is then, under some circumstances,
necessary to provide suitable time delays in the transmission
system for each of the transmitting stations and adjust these time
delays so that the modulated signals arrive simultaneously at the
space station. Means for providing the necessary time delays will
be included in the detailed description.
Another feature of our invention is the provision within the system
for varying the radio frequencies transmitted from each of the
stations A, B, et cetera, to the satellite or space station from
the nominal value of assigned radio frequency. This means of
variation is necessary to assure that the earth satellite or space
station receiver will simultaneously receive radio emissions from
each of station A, B, et cetera, within its pass band of radio
frequencies. It is easily seen that at times the satellite will be
approaching station A while receding from station B and under these
circumstances the transmissions from station A must be reduced in
frequency by an amount approximately equal to the Doppler shift
from station A and the transmissions from station B must be
increased by an amount approximately equal to the Doppler shift B.
The result of controlling these transmissions in this manner will
be to maintain transmissions to the earth satellite or space
station within a narrower tolerance of pass band and thus provide
the possibility of enhanced receiver sensitivity and reduced
interference. For the return signal, since the satellite or space
station is operating one transmitter, it is necessary that each of
the receiving stations adjust its frequency of reception so as to
maintain optimum reception of the incoming signal.
While for earth satellite communications, these Doppler effects are
not particularly large, nevertheless, they are important. Also, in
the case of space stations, which will operate at increasingly
higher speeds, it is neccesary to take care of the relativistic
effects on the Doppler shift. That these shifts in radio frequency
can become appreciable compared to our present ideas and
considerations bearing on the use of radio frequencies is seen from
the fact that the factor involved is the following: ##EQU1## where
v is the velocity of the vehicle, c is the velocity of propagation,
and the term is the relativistic effect. For an operating frequency
of 1,000 mc./s., a vehicle travelling at 5 miles/sec. has a maximum
Doppler shift of about 25 kc./s. If the vehicle's speed increases
to 20,000 miles/sec., then the maximum Doppler shift due to its
motion will be about 100 mc./s., and the increase in this shift due
to the relativistic effect is another 5.0 mc./s. Where the ground
controlled system is required to communicate with more than one
earth satellite or space station, the same considerations above
apply, and it is necessary to so operate the system that each of
the earth satellite or space stations receives signals of such
frequencies that they will appear within the pass band of the
satellite or space station receiver.
Detailed description of special features
As shown in FIG. 1B, direction finders 6, 14 are used to control
both the azimuth and elevation of transmitting antennas 5,13 and
receiving antennas 20, 24 respectively. One means by which one of
these angles, i.e., azimuth or elevation, can be determined, will
now be described.
Obviously, similar apparatus may be employed to determine
elevation.
Referring to FIG. 5, the direction-finder consists of a rotating
dipole array having a null direction .Iadd.or axis of
directivity.Iaddend., i.e., a direction for which a minimum or zero
signal is received from the transmission to which the
direction-finder is tuned. The output of the direction-finder is
connected to a fast-acting sensitive relay 49. The receiver output
is adjusted so that as antenna 47 rotates, the contact C1 of relay
49 remains closed except for the short times intervals during which
the D.F. antenna is passing through its null position.
Now referring to the bottom of FIG. 5, there is shown an annular
ring 52 having a brush 53 which is connected by a slip ring contact
53A to ground. Inside this annular ring 52 is a conductive rotating
element 54 which is connected through a slip ring contact 54A to
the right-hand terminal of the winding of relay 50. Element 54 is
aligned in the direction of the null of the directional antenna 47,
i.e., it is rotatably aligned relative to some predetermined
reference by the same angle that the null of antenna 47 makes
relative to a given reference, angle .beta..sub.1, and then locked
in position. As antenna 47 is rotated by antenna rotator 48A,
servomotor 48B corespondingly rotates element 54.
The annular ring 52 is driven by a servomechanism 54B coupled
thereto and is rotated in synchronism with the transmitting antenna
so that the azimuth direction of element .Iadd.53.Iaddend. .[.54.].
relative to the predetermined reference coincides with the azimuth
direction of maximum gain of the transmitting antenna or relative
to its predetermined reference. As antenna 47 rotates, relay 49
normally remains closed except for the short time intervals when
antenna 47 is passing through its null position. Also, once each
revolution of the D.F. antenna, element 54 will contact brush 53,
thus bridging contact C2 of relay 50 and resulting in the
energization of relay 50 provided that contact Cl of relay 49 is
then in its normal, closed position. This bridging of contact C2
occurs irrespective of the current angular position of ring 52
which "follows" the transmitting antenna. When contact C2 is
bridged in this manner, relay 50 is energized and is thereafter
locked in closed position when its own front contact C2 closes.
This action also closes front contact C3 of relay 50 which then
energizes relay 51.
With start-stop switch 57 closed and reversing switch 58 set
manually for the desired direction of track of the transmitting
antenna mount, motor 59 will be energized, thereby rotating the
antenna through rotator 56. Whereas, brake 61 is energized when
relay 51 is dropped away and its back contact C4 is closed, clutch
61A is engaged when front contact C4 is closed. Thus, the
transmitting antenna rotator 56 is actuated by motor 59, thereby
slowly revolving the directional transmitting antenna.
Since relay 51 is a slow release relay, it will not drop out when
contact C1 of relay 49 opens and de-energizes relay 50 even though
relay 50 remains dropped away until the next succeeding contact
between element 54 and brush 53. Therefore, since relay 51 remains
picked up, the transmitting antenna, turns in the direction of the
satellite's orbit as selected by reversing switch 58.
As the transmitting antenna slowly turns, the synchronized turning
of annular ring 52 eventually causes it to reach a position where
brush 53 is in such a position that, some time during the interval
that relay 49 is dropped away as antenna 47 rotates into its null
direction, brush 53 makes electrical contact with element 54. In
other words, relay 49 opens and remains open during the entire time
that brush 53 and element 54 are in contact. Under this condition,
no circuit is completed to energize relay 50 for a time in excess
of the time of one revolution of antenna 47 so that relay 51
becomes deenergized, and the clutch mechanism 61A declutches while
brake 61 holds the transmitting antenna rotator 56 in the
then-attained direction. As the position of the satellite moves
into a different azimuth bearing, relay 50 resumes its operation in
the manner previously described and the antenna rotator 56 is thus
caused to track the satellite. Additional relays can obviously be
used to control a receiving antenna in the vicinity of the
direction-finder. Thus, it is possible to keep both the directional
transmitting antenna and the directional receiving antenna at each
of the stations pointed in the direction of the satellite or space
station.
The one-way communications circuits 9 and 26 (FIG. 1B) may be
either radio or wire circuits when stations A and B are both on the
earth's surface and may be any commerical circuit, provided only
that they will transmit the modulations of the intelligence being
transmitted by the system and that their time delay variations do
not exceed one millisecond over a period of a few minutes. The
actual time delays of transmission of the modulations between
stations A and B must be compensated for in this system when the
system is one wherein the difference in distances between the space
station and the respective stations A and B is significant and when
the type of signal used is such that a given amount of delay
interferes with proper reception of the intelligence. More
specifically, fairly substantial differences in delay times can be
tolerated when voice communications are used; whereas, the same
amount of difference night very well prove troublesome when a
high-frequency pulse code is used. In providing such compensation,
the following will occur:
All modulations reaching stations A, B, C, et cetera will be
delayed the correct amount so that the modulated signals on
frequencies f.sub. ta, f.sub. tb, f.sub. tc, et cetera will reach
the satellite or space station simultaneously. This delay may be
measured in microseconds, milliseconds, seconds, or longer periods
of time and depends solely on the relative position of the
satellite and space station with reference to the earth and other
stations A, B, C, et cetera.
Apparatus which provides for the several modulating signals from
widely spaced transmitting stations to reach a space station
simultaneously is illustrated in FIG. 7A. The apparataus of FIG. 7A
comprises a modification of that shown in FIG. 1B.
More specifically, a variable time delay means is provided which is
interposed in the system between the source of the data signal to
be transmitted and the respective modulators of the several
stations from which the modulation is to be transmitted. Thus, the
data signal to be transmitted is shown in FIG. 7A as being fed to
the control center and from there via the respective selector
switches 120 and 121 to a magnetic tape delay device. From there,
the signal is applied to the station A modulator 3 (see FIG. 1B)
and also over the communications network to the Station B modulator
11.
Referring to the magnetic tape delay apparatus of FIG. 7A, this
comprises a magnetic tape which moves with a uniform velocity in
the direction of the arrow. A plurality of recording heads 122-127
is provided, three of these, i.e., recording heads 122, 124, 126
being associated with one longitudinal recording track, while the
others, i.e., 123, 125, 127 are associated with a different
recording track. The signal which is to be variably delayed prior
to being applied to the Station A modulator 3 is applied to a
selected one of the recording heads 122, 124, 126 through the
slectable switch contact 120. When the signal is recorded on the
tape by one of the recording heads 122, 124, 126 in accordance with
the then-selected position of switch 120, it is delayed by an
amount corresponding to the travel time of the tape from the
particular recording head then in use to the associated read head
128. The position of the read head 128 longitudinally along the
tape is adjustable by means of rotation of threaded shaft 129 which
is rotatable by means of a belt drive 130 from motor 131. To obtain
maximum delay, switch 120 is operated to the position shown so as
to provide maximum distance between the recording head 122 and read
head 128. To obtain close adjustment of the amount of delay
desired, read head 128 is adjusted in position to provide the
desired distance between the selected recording heads and a read
head 128. Where lesser amounts of delay are desired, switch 120 can
be moved to either of the other two positions shown to provide
thereby a shorter distance between the selected recording head and
read head 128.
The delay which is provided with respect to the signal applied to
the station beam modulator 11 is controlled in an entirely similar
manner. Thus, the switch 121 is operated to one of the several
positions shown in accordance with whether a large or a small
amount of delay time is required. Finer adjustment is secured by
properly positioning read head 133 by rotation of the corresponding
threaded shaft 132.
The amount of delay that should be provided for the signal having
the shortest propagation path to the satellite or space station
relative to any other signal transmitted from a geographically
widely spaced station to the same satellite or space station can
readily be determined empirically. Thus, it is not essential that
apparatus be provided to determine automatically the relative
distances and thus the relative delay times. In practice, the
desired relative delay of the several signals is quite readily
determined by monitoring the signal received from the space
station. If the received signal is garbled because of improper
phase relationships between the several signals received at the
space station, the relative relays are accordingly adjusted at the
ground station until the garbled condition disappears.
Apparatus which will automatically provide the proper relative
amounts of delay for the signals from stations A and B, for
example, to cause such signals to arrive simultaneously at a space
station is shown in FIGS. 6 and 7. The apparatus disclosed from the
automatic computation of the difference in distance between two
respective stations and the space station and the related apparatus
for determining the relative delays to be applied to the respective
signals transmitted from such stations to the space station
constitutes subject matter which was not disclosed in the parent
application Serial No. 29,111, filed May 13, 1960, and with respect
to which the present application is a continuation-in-part. It is
only by reason of the addition of the apparatus for providing this
automatic control of the relative delays that the present
application is termed to be a continuation-in-part.
Apparatus to automatically determine the proper relative amounts of
delay must of necessity receive data as to the relative distances
of the space station from each of the two stations A and B. FIG. 6
illustrates some of the geometrical considerations involved in the
determination of these distances.
In FIG. 6, S represents the space station and P the suborbital
point, i.e., the point on the earth's surface lying along the line
connecting space station S with the earth's center. A and B
represent, respectively, the locations of the earth's stations A
and B, and it is desired to determine the distances As and Bs, from
which there can be computed the transmission times of signals
between the respective stations A and B and space station S,
thereby permitting a computation of the difference in these times.
Once this difference is known, the signal having the shorter
transmission time may be suitably delayed so that it will arrive at
its destination simultaneously with the signal from the more
distant location.
By employing either a pair of direction finders at each of the
stations A and B similar to that shown in FIG. 5, there is made
available at each of the stations both azimuth and elevation angles
from that station to space station. In other words, referring to
FIG. 6, and angles PAB and PAS are known at station A, and
similarly, the angles ABP and PBS are known at station B. Since the
distance Ab is also known, the triangle ABP is fully determined,
and from this, there can be computed the length of AP and BP. With
these known, and recognizing that angles SPA and SPB are both right
angles, one can then see that triangles SPB and SPA are now fully
determined so that the distances SA and SB are known. Dividing each
of these distances by the speed of light, there is obtained the
time required to transmit from each of stations A and B to station
S, and a simple subtraction of these two times then determines the
amount of delay that should be applied to the signal from the
station which is then more remote from space station S to
compensate for the longer transmission time from that station to
the space station. In addition to this, variable delay circuit 109
in FIG. 7 may be provided with an appropriate delay, over and above
that provided as just described, to compensate for the transmission
delay incurred in transmitting the signal intelligence over the
communication circuit extending from the control center (see FIG.
1A) to station B.
FIG. 7 shows in block diagram form one form of apparatus which may
be used to carry out the aforementioned computations. Three
dimensional direction finders 100 and 101 are shown, one for each
of the stations A and B. Each direction finder produces two output
signals, one representing the elevation angle from that station to
the space station and the other representing the azimuth angle. The
azimuth angles at stations A and B are both supplied to a computer
102 which then determines the length of AP and BP which is readily
determined once these azimuth angles are provided to computer 102
since distance AB is fixed. One output of computer 102 which
represents the length of BP is supplied to a similar computer 103
which also receives an input signal representing the elevation
angle measured at space station B. With these two input parameters,
computer 103 can readily compute the distance DS and supply this
output signal to a divider 106. In a similar manner, computer 104
receives an input signal from computer 102 which represents the
length of AP. Computer 104 also receives an output from direction
finder 100 which represents the measured elevation at station A.
Provided with this information, computer 104 can readily compute
the distance AS and provide a corresponding output signal to
divider 105.
Both dividers 105 and 106 divide their respective input distance
signals by the constant factor representing the speed of light,
thereby making available by each divider a time signal t.sub.1 to
t.sub.2 which represents the time required for the transmission of
the signal between the respective stations A and B and space
station S. These two time signals t.sub.1 and t.sub.2 are applied
to a subtractor 107 which subtracts these two time signals from
each other and provides two separate outputs, one representing the
difference t.sub.1 minus t.sub.2 and the other representing the
difference t.sub.2 minus t.sub.1. If t.sub.1 is greater than
t.sub.2, the difference t.sub.1 minus t.sub.2 is a positive
quantity and subtractor 107 then provides an analog signal to
variable delay 108 which is proportional to this difference. Under
these circumstances, the output signal applied to variable delay
109 may be zero. On the other hand, if the interval t.sub.2 exceeds
interval t.sub.1, then the difference t.sub.2 minus t.sub.1 is a
positive quantity which is applied to variable delay 109, and delay
circuit 108 then receives zero input signal.
Signal source 110 represents the source of data signals to be
transmitted from stations A and B to space station S. The output of
signal source 110 is applied to both the variable delays 108 and
109 where they are selectively delayed in accordance with the time
signal input to each of these delay circuits before being applied
as input to the associated modulator 111 or 112. Assuming again
that t.sub.1 exceeds t.sub.2, this means that station A is more
remote from station S than station B and this means that the
transmissions from station B must be suitably delayed in accordance
with the difference t.sub.1 minus t.sub.2. Accordingly, the
different signal representing t.sub.1 minus t.sub.2 is applied to
delay circuit 108 to selectively control the delay of the input
signal to the modulator for station B. It will be obvious from the
foreging description that the Station A signal will be delayed by
variable delay 109 in a similar manner when station B is more
remote from space station S than is station A.
There remains one final effect with regard to the system shown in
FIG. 1A. This is the fact that the frequency of the received
signals received at the space station or earth satellite will
depend upon the Doppler-shift as well as the radiated frequency.
With the system shown in FIG. 1A, where a plurality of stations are
so disposed that their radio waves intersect at a substantial angle
upon reaching the earth satellite or space station, it is clear
that the Doppler shift will be different for each station.
Therefore, if each station transmits on the identical radio
frequency, the received signals will vary as the Doppler shift from
each station. Conversely, in order that each of the received
signals will have the same frequency at the earth satellite or
space station, it is necessary to transmit different frequencies
from stations A, B, C, et cetera. With frequencies of the order of
100 mc./s., the expected Doppler shifts are not great for earth
satellites, and the above is only of academic interest. However,
when frequencies of several thousand megacycles/sec. or even 850
mc./s. are used, the Doppler shifts observable on earth satellites
increase by a factor of about 10 times the shifts at 100 mc./s.
Furthermore, in the case of space probes, very must larger
frequency shifts may occur. In the case of earth satellites and
with stations A, B, . . . on the earth's surface, it is quite
possible for the satellite to be rapidly approaching one station
and receding from the other, which will cause the Doppler shifts to
be in opposite directions.
Now referring to FIG. 8, it is seen that for radiation of the
transmitters at stations A and B on the identical carrier
frequency, namely f.sub.ta and f.sub.tb, there will be two
different frequencies received at the space station. Each will vary
from the radiated frequency by the Doppler shift between that
station and the satellite. As the frequency of transmissions to
satellites increases and as the speeds of satellites increases,
then the Doppler shifts .DELTA. f.sub.a and .DELTA. f.sub.b
increase. Furthermore, with increasing speeds and frequencies, the
difference between the two signals received at the space station
will increase--up to the point at which either one or both of the
frequencies transmitted are outside of the pass band of the
receiver.
Now referring to FIG. 9, it is seen that by transmitting the
signals from stations A and B on different frequencies, which in
this particular illustration are shown as higher than the nominal
received frequency, it is possible to cause the two frequencies
received at the space station to approach each other and to
approach the frequency nominally assigned so that they will enter
the pass band of the space station receiver. Obviously, it is
possible to operate this system in such a manner that the
difference between the two frequenices, as shown in FIG. 8, may
approach any desired value. We do this as follows: The space
station transmits on a single frequency which for the rays f.sub.ra
and f.sub.rb in FIG. 1B is identical. Now because of the Doppler
shift, the frequency received at each of the stations A and B is
different. Knowing the assigned frequency of the space station and
measuring the received frequency independently at both stations A
and B, we determine the Doppler shift at each station. By adjusting
the transmitters at each station to that frequency indicated in
FIG. 8 for each station, it is thus possible to place the signals
received at the space station within the pass band of the space
station receiver at the assigned frequency.
Now referring to FIG. 9, it is a part of our invention to provide
in addition to the manual methods of shifting the earth-controlled
transmitter frequencies, an automatic method for accomplishing the
same shifts. In connection with the communications with earth
satellites, which pass over the observing stations at relatively
low altitudes compared to the altitude or distance to space
stations, the Doppler shift causes the frequency received from
ground or earth stations to change rapidly. In FIG. 9, a signal
voltage having a frequency shift f.sub.1 - f.sub.2 is applied to
the circuit shown. Isolating resistor 87 causes an essentially
constant current to flow through inductor 94. In a similar manner a
signal voltage of frequency f.sub.1 - f.sub.4 is applied through
isolating resistor 90 and causes an essentially constant current to
flow through inductor 95. Th signal voltage of frequencies f.sub.1
- f.sub.2 is obtained by beating in heterodyne circuit 115 the
signal received by receiver 113 from the space station, i.e.,
f.sub.1, with a precision oscillator 114 adjusted to the frequency
f.sub.2 of the transmitter the space station. The beat frequency
obtained is the Doppler shift resulting from relative motion
between the earth and space stations, which after suitable
amplification is applied to the circuit shown. Similarly, the
signal of frequency f.sub.3 - f.sub.4 is obtained by beating in
heterodyne circuit 119 the frequency of the transmitter 116 at this
same station with a precision frequency standard provided by
oscillator 117 which is adjusted to the nominal frequency within
the pass band of the satellite receiver.
The voltages generated across inductors 94 and 95 are rectified by
diodes 92 and 93 and then compared on the balancing network of
resistors 88, 89 and 91. Since the D.C. current resulting from the
signal f.sub.1 - f.sub.2 travels through resistor 91 in an opposite
direction to the D.C. current resulting from the signal f.sub.3 -
f.sub.4, when the network is balanced, the junction of resistors
88, 89, and 91 is at zero potential. The D.C. recording
potentiometer 96 detects any unbalance and actuates the variable
master oscillator 118 in such a direction as to cause the
transmitter frequency to vary from the nominal space receiver pass
band frequency by an amount equal to the Doppler shift. This
discussion of the method of operation assumes that the satellite
and ground stations are both operating on the same frequency and
that the value of resistors 88 and 89 is adjusted to maintain this
balance. Now it is a feature of our system and this circuit that by
adjusting resistors 88 and 89, it is possible with the apparatus of
FIG. 9 to use the signal f.sub.1 - f.sub.2 obtained from one
carrier frequency at the space station (for example 400 mc./s.) to
generate the correction of the transmitter frequency on a carrier
frequency other than that, f.sub.1, received from the space station
(for example 420 mc./s.) so that the frequency received by the
satellite receiver will have been compensated for the Doppler shift
in transmission at such other frequency and will fall within the
pass band of the space station receiver.
Another feature of our invention is the radiation from the space
station transmitter of a plurality of frequencies say f.sub.10,
f.sub.11, f.sub.12, . . . et cetera so related that when
transmitting to a plurality of ground stations, these ground
stations may maintain receivers tuned to a specific assigned
frequency and, as a result of the Doppler frequency shift, at least
one of the plurality of frequencies f.sub.10, f.sub.11, f.sub.12 .
. . , all of which are modulated with the same signal or
intelligence, will fall within the pass band of the specific radio
frequency to which these receivers are tuned. Obviously, the
Doppler frequency shift will vary independently at the plurality of
stations receiving these space station signals, that frequency of
the plurality of frequencies radiated by the space station, which
falls within the receiver pass band at station A, may be different
from that at stations B, C, et cetera. On the other hand, there may
be times for which the same frequency of the plurality f.sub.10,
f.sub.11, f.sub.12 . . . will provide satisfactory communications
with more than one of the earth-controlled receiving stations.
* * * * *