U.S. patent application number 16/439302 was filed with the patent office on 2019-09-26 for space-based tethered communications antenna array.
The applicant listed for this patent is The Charles Stark Draper Laboratory, Inc.. Invention is credited to Adam J. Greenbaum, Bradley A. Moran, Robert D. Tingley.
Application Number | 20190296425 16/439302 |
Document ID | / |
Family ID | 67394045 |
Filed Date | 2019-09-26 |
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United States Patent
Application |
20190296425 |
Kind Code |
A1 |
Greenbaum; Adam J. ; et
al. |
September 26, 2019 |
Space-Based Tethered Communications Antenna Array
Abstract
A space-based phased antenna array provides one- or
two-dimensional beam steering, yet is compact upon launch and does
not require gravity to maintain its shape or orientation. An
exemplary antenna array includes a central satellite and at least
three peripheral satellites. Each peripheral satellite is
mechanically connected to the central satellite by an extendible
tether. At launch, the tethers are retracted, so the peripheral
satellites are close to, or within, the central satellite. Once in
position, the central satellite rotates and extends the tethers,
thereby deploying the peripheral satellites in a planar radial
pattern. Multiple antenna elements, some disposed on each tether,
collectively form a planar phased array that can be electronically
beam steered in two dimensions. The antenna array may relay
signals, such as between local companion satellites or planet-based
stations, and earth. Linear versions, with as few as two tethered
satellites, are beam steerable in one dimension.
Inventors: |
Greenbaum; Adam J.;
(Brookline, MA) ; Moran; Bradley A.; (Concord,
MA) ; Tingley; Robert D.; (Waltham, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Charles Stark Draper Laboratory, Inc. |
Cambridge |
MA |
US |
|
|
Family ID: |
67394045 |
Appl. No.: |
16/439302 |
Filed: |
June 12, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15227446 |
Aug 3, 2016 |
10367254 |
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16439302 |
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62206644 |
Aug 18, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01Q 21/22 20130101;
H01Q 3/36 20130101; H01Q 21/062 20130101; H01Q 3/24 20130101; H01Q
1/087 20130101; H01Q 1/288 20130101; H04B 1/40 20130101 |
International
Class: |
H01Q 1/28 20060101
H01Q001/28; H04B 1/40 20060101 H04B001/40; H01Q 21/22 20060101
H01Q021/22; H01Q 3/24 20060101 H01Q003/24 |
Claims
1. An antenna array, comprising: a central hub; at least three
flexible extendible tethers attached to the central hub; at least
three peripheral satellites, each peripheral satellite being
attached to the central hub by a respective associated one of the
tethers; wherein: the antenna array has a first mode and a second
mode; in the first mode, each tether is retracted, such that the
peripheral satellite associated therewith is disposed within 2
meters of the central hub; and in the second mode, the central hub
is configured to rotate about an axis and the tethers are extended,
thereby deploying the peripheral satellites radially away from the
central hub a distance greater than 2 meters, such that the
peripheral satellites orbit the central hub in a plane
perpendicular to the axis and each tether is taut; the antenna
array further comprising: a plurality of antenna elements disposed
along the tethers, such that at least two antenna elements are
disposed along each tether; and a phaser coupled to the plurality
of antenna elements and configured to beam-steer a lobe of a
radiation pattern of the plurality of antenna elements in two
dimensions.
2. An antenna array according to claim 1, wherein, in the second
mode, centripetal forces, caused by orbiting of the peripheral
satellites about the central hub, extend and tension the
tethers.
3. An antenna array according to claim 1, wherein the phaser is
configured to alter phasing of the plurality of antenna elements in
synchrony with rotation of the central hub.
4. An antenna array according to claim 1, further comprising: a
second antenna; a radio-frequency receiver having an input coupled
to the second antenna and having an output; and a radio-frequency
transmitter having an input coupled to the output of the receiver
and having an output coupled to the phaser, wherein the receiver is
configured to receive signals via the second antenna and the
transmitter is configured to relay the signals via the plurality of
antenna elements.
5. An antenna array according to claim 1, further comprising: a
second antenna; and a radio-frequency transceiver coupled to the
second antenna and to the phaser, wherein the transceiver is
configured to receive first signals via the second antenna and
relay the first signals via the plurality of antenna elements.
6. An antenna array according to claim 5, wherein the transceiver
is further configured to receive second signals via the plurality
of antenna elements and relay the second signals via the second
antenna.
7. An antenna array according to claim 1, wherein the central hub
comprises at least one spool configured to extend the at least
three tethers.
8. An antenna array according to claim 1, wherein each peripheral
satellite comprises a respective spool configured to extend the
tether associated with the peripheral satellite.
9. An antenna array according to claim 1, wherein each tether
comprises a respective optical fiber communicably coupled between
the phaser and the at least two antenna elements disposed along the
tether
10. An antenna array, comprising: a central hub configured to
rotate about an axis; at least three tethers attached to the
central hub and configured to extend radially away from the central
hub; at least three peripheral satellites, wherein each peripheral
satellite is: (a) attached to the central hub by a respective one
of the tethers, (b) configured to be spaced apart from the central
hub and tension the respective one of the tethers and (c)
configured to orbit the central hub in a plane perpendicular to the
axis; a plurality of antenna elements disposed along the tethers,
such that at least two antenna elements of the plurality of antenna
elements are disposed along each tether; and a phaser coupled to
the plurality of antenna elements and configured to beam-steer a
lobe of a radiation pattern of the plurality of antenna elements in
two dimensions.
11. An antenna array according to claim 10, wherein centripetal
forces, caused by orbiting of the peripheral satellites about the
central hub, extend and tension the tethers.
12. An antenna array according to claim 10, wherein the phaser is
configured to alter phasing of the plurality of antenna elements in
synchrony with rotation of the central hub.
13. An antenna array according to claim 10, further comprising: a
second antenna; a radio-frequency receiver having an input coupled
to the second antenna and having an output; and a radio-frequency
transmitter having an input coupled to the output of the receiver
and having an output coupled to the phaser, wherein the receiver is
configured to receive signals via the second antenna and the
transmitter is configured to relay the signals via the plurality of
antenna elements.
14. An antenna array according to claim 10, further comprising: a
second antenna; and a radio-frequency transceiver coupled to the
second antenna and to the phaser, wherein the transceiver is
configured to receive first signals via the second antenna and
relay the first signals via the plurality of antenna elements.
15. An antenna array according to claim 14, wherein the transceiver
is further configured to receive second signals via the plurality
of antenna elements and relay the second signals via the second
antenna.
16. A method for receiving or transmitting radio-frequency signals
in outer space, the method comprising: providing a central hub in
outer space; rotating the central hub about an axis; extending at
least three flexible tethers radially from the central hub, a
respective peripheral satellite being attached to each of the
tethers, thereby deploying the peripheral satellites radially away
from the central hub, such that the peripheral satellites orbit the
central hub in a plane perpendicular to the axis and each tether is
taut between the central hub and the respective peripheral
satellite, each tether having at least two antenna elements
disposed thereon, the antenna elements of all the tethers
collectively forming an antenna array; and automatically phase
adjusting signals delivered to or received from the antenna array
to beam-steer a lobe of a radiation pattern of the antenna array in
two dimensions.
17. A method according to claim 16, wherein extending the at least
three flexible tethers radially from the central hub comprises
using centripetal forces, caused by orbiting of the peripheral
satellites about the central hub, to extend and tension the
tethers.
18. A method according to claim 16, further comprising altering
automatically phasing of the plurality of antenna elements in
synchrony with rotation of the central satellite.
19. A method according to claim 16, further comprising: providing a
second antenna mechanically coupled to the central hub; providing a
radio-frequency receiver mechanically coupled to the central hub,
an input of the receiver being communicatively coupled to the
second antenna; providing a radio-frequency transmitter
mechanically coupled to the central hub, an input of the
transmitter being communicatively coupled to an output of the
receiver and an output of the transmitter being communicatively
coupled to the antenna array; receiving a signal via the second
antenna and the receiver; and relaying the signal via the
transmitter and the antenna array.
20. A method according to claim 16, further comprising: providing a
second antenna mechanically coupled to the central hub; providing a
radio-frequency transceiver mechanically coupled to the central hub
and communicatively coupled to the second antenna and to the
antenna array; receiving first signals via the second antenna and
the transceiver; and relaying the first signals via the transceiver
and the antenna array.
21. A method according to claim 20, further comprising: receiving
second signals via the antenna array and the transceiver; and
relaying the second signal via the transceiver and the second
antenna.
22. A method according to claim 20, wherein extending the at least
three flexible tethers comprises paying out the at least three
flexible tethers from the central hub.
23. A method according to claim 20, wherein extending the at least
three tethers comprises, for each of the at least three tethers,
paying out a respective one of the at least three flexible tethers
from the peripheral satellite attached to the tether.
24. A non-transitory computer-readable medium encoded with
instructions that, when executed by a processor, establish
processes for performing a computer-implemented method of receiving
radio-frequency signals in outer space, the processes comprising: a
process configured to rotate a central hub about an axis; a process
configured to extend at least three flexible tethers radially from
the central hub, a respective peripheral satellite being attached
to each of the tethers, thereby deploying the peripheral satellites
radially away from the central hub, such that the peripheral
satellites orbit the central hub in a plane perpendicular to the
axis and each tether is taut between the central hub and the
respective peripheral satellite, each tether having at least two
antenna elements disposed thereon, the antenna elements of all the
tethers collectively forming an antenna array; and a process
configured to automatically phase adjust signals delivered to or
received from the antenna array to beam-steer a lobe of a radiation
pattern of the antenna array in two dimensions.
25. A non-transitory computer-readable medium according to claim
24, wherein the process configured to extend the tethers is
configured to extend and tension the tethers using centripetal
forces caused by orbiting of the peripheral satellites about the
central hub.
26. A non-transitory computer-readable medium according to claim
24, the processes further comprising a process configured to
automatically alter phasing of the plurality of antenna elements in
synchrony with rotation of the central hub.
27. A non-transitory computer-readable medium according to claim
24, wherein: a second antenna is mechanically coupled to the
central hub; a radio-frequency receiver is mechanically coupled to
the central hub, an input of the receiver is communicatively
coupled to the second antenna; a radio-frequency transmitter is
mechanically coupled to the central hub, an input of the
transmitter is communicatively coupled to an output of the receiver
and an output of the transmitter is communicatively coupled to the
antenna array; the processes further comprising: a process
configured to receive a signal via the second antenna and the
receiver; and a process configured to relay the signal via the
transmitter and the antenna array.
28. A non-transitory computer-readable medium according to claim
24, wherein: a second antenna is mechanically coupled to the
central hub; and a radio-frequency transceiver is mechanically
coupled to the central hub and communicatively coupled to the
second antenna and to the antenna array; the processes further
comprising: a process configured to receive first signals via the
second antenna and the transceiver; and a process configured to
relay the first signals via the transceiver and the antenna
array.
29. A non-transitory computer-readable medium according to claim
28, the processes further comprising: a process configured to
receive second signals via the antenna array and the transceiver;
and a process configured to relay the second signal via the
transceiver and the second antenna.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 15/227,446, filed Aug. 3, 2016, titled "Space-Based
Tethered Communications Antenna Array," which claims the benefit of
U.S. Provisional Pat. Appl. No. 62/206,644, filed Aug. 18, 2015,
titled "Tethered Antenna Array for Space-to-Ground and
Space-to-Space Communications Links," the entire contents of each
of which are hereby incorporated by reference herein, for all
purposes.
TECHNICAL FIELD
[0002] The present invention relates to antennas and, more
particularly, to phased arrays of antenna elements tethered to
satellites and spun in outer space.
BACKGROUND ART
[0003] Phased arrays of antenna elements are commonly used in radar
and other applications in which a direction of an incoming radio
frequency (RF) signal needs to be ascertained or in which an RF
signal needs to be transmitted in a particular direction. One or
more receivers, transmitters or transceivers are electrically
connected to an array of antenna elements via feed lines, such as
waveguides or coaxial cables. Taking a transmitter case as an
example, the transmitter(s) operate such that the phase of the
signal at each antenna element is separately controlled. Signals
radiated by the various antenna elements constructively and
destructively interfere with each other in the space in front of
the antenna array. In directions where the signals constructively
interfere, the signals are reinforced, whereas in directions where
the signals destructively interfere, the signals are suppressed,
thereby creating an effective radiation pattern of the entire array
that favors a desired direction. The phases at the various antenna
elements, and therefore the direction in which the signal
propagates, can be changed very quickly, thereby enabling such a
system to be electronically steered, for example to sweep over a
range of directions.
[0004] According to the reciprocity theorem, a phased array of
antenna elements can be used to receive signals preferentially from
a desired direction. By electronically changing the phasing, a
system can sweep over a range of directions to ascertain a
direction from which a signal originates, i.e., a direction from
which the signal's strength is maximum, or to electronically steer
a phased array toward a transmitting antenna and away from
interference (noise) sources.
[0005] Phased arrays are physically large, relative to wavelengths
of signals transmitted and/or received by the arrays. Many phased
arrays are also massive. Consequently, launching phased arrays into
outer space, or constructing such arrays in space, is difficult or
impossible with current launch vehicles and space construction
techniques.
SUMMARY OF EMBODIMENTS
[0006] An embodiment of the present invention provides an antenna
array. The antenna array includes a central hub and at least three
flexible extendible tethers attached to the central hub. The
antenna array also includes at least three peripheral satellites.
Each peripheral satellite is attached to the central hub by a
respective associated one of the tethers.
[0007] The antenna array has a first mode and a second mode. In the
first mode, each tether is retracted, such that the peripheral
satellite associated with the tether is disposed within about 2
meters of the central hub.
[0008] In the second mode, the central hub is configured to rotate
about an axis. Also in the second mode, the tethers are extended,
thereby deploying the peripheral satellites radially away from the
central hub a distance greater than about 2 meters. The peripheral
satellites orbit the central hub in a plane perpendicular to the
axis. Each tether is taut.
[0009] The antenna array also includes a plurality of antenna
elements. The antenna elements are disposed along the tethers. At
least two antenna elements are disposed along each tether. A phaser
is coupled to the plurality of antenna elements to beam-steer a
lobe of a radiation pattern of the plurality of antenna elements in
two dimensions.
[0010] In some embodiments, in the first mode, each tether is
retracted, such that the peripheral satellite associated with the
tether is proximate the central hub, and in the second mode, the
tethers are extended, thereby deploying the peripheral satellites
radially away from the central hub.
[0011] In some embodiments, in the first mode, each tether is
retracted, such that the peripheral satellite associated with the
tether is disposed less than a first predetermined distance (such
as about 0.5, 1, 2, 3 or 4 meters) of the central hub, and in the
second mode, the tethers are extended, thereby deploying the
peripheral satellites radially away from the central hub at least a
second predetermined distance (such as about 0.5, 1, 2, 3 or 4
meters).
[0012] In the second mode, centripetal forces, caused by orbiting
of the peripheral satellites about the central hub, may extend and
tension the tethers.
[0013] The phaser may be configured to alter phasing of the
plurality of antenna elements in synchrony with rotation of the
central hub.
[0014] The antenna array may also include a second antenna and a
radio-frequency receiver. The radio-frequency receiver may have an
input coupled to the second antenna. The radio-frequency receiver
may also have an output. The antenna array may also include a
radio-frequency transmitter. The radio-frequency transmitter may
have an input coupled to the output of the radio-frequency
receiver. The radio-frequency transmitter may have an output
coupled to the phaser. The radio-frequency receiver may be
configured to receive signals, via the second antenna, and the
transmitter may be configured to relay the signals, via the
plurality of antenna elements.
[0015] The antenna array may also include a second antenna and a
radio-frequency transceiver. The radio-frequency transceiver may be
coupled to the second antenna and to the phaser. The
radio-frequency transceiver may be configured to receive first
signals, via the second antenna, and relay the first signals, via
the plurality of antenna elements.
[0016] The transceiver may be further configured to receive second
signals, via the plurality of antenna elements, and relay the
second signals, via the second antenna.
[0017] The central hub may include at least one spool configured to
extend the at least three tethers.
[0018] Each peripheral satellite may include a respective spool
configured to extend the tether associated with the peripheral
satellite.
[0019] Another embodiment of the present invention provides an
antenna array. The antenna array includes a central hub rotating
about an axis and at least three tethers attached to the central
hub. The at least three tethers extend radially away from the
central hub. The antenna array also includes at least three
peripheral satellites. Each peripheral satellite is spaced apart
from the central hub by at least about 2 meters. Each peripheral
satellite is attached to the central hub by a respective one of the
tethers. The respective one of the tethers is taut. Each peripheral
satellite orbits the central hub in a plane perpendicular to the
axis.
[0020] The antenna array also includes a plurality of antenna
elements. The antenna elements are disposed along the tethers. At
least two antenna elements are disposed along each tether. A phaser
is coupled to the plurality of antenna elements to beam-steer a
lobe of a radiation pattern of the plurality of antenna elements in
two dimensions.
[0021] Centripetal forces, caused by orbiting of the peripheral
satellites about the central hub, may extend and tension the
tethers.
[0022] The phaser may be configured to alter phasing of the
plurality of antenna elements in synchrony with rotation of the
central hub.
[0023] The antenna array may also include a second antenna and a
radio-frequency receiver having an input coupled to the second
antenna. The radio-frequency receiver may have an output. The
antenna array may also include a radio-frequency transmitter having
an input coupled to the output of the receiver. The radio-frequency
transmitter may have an output coupled to the phaser. The receiver
may be configured to receive signals, via the second antenna, and
the transmitter may be configured to relay the signals, via the
plurality of antenna elements.
[0024] The antenna array may also include a second antenna and a
radio-frequency transceiver coupled to the second antenna and to
the phaser. The transceiver may be configured to receive first
signals, via the second antenna, and relay the first signals, via
the plurality of antenna elements.
[0025] The transceiver may be further configured to receive second
signals, via the plurality of antenna elements, and relay the
second signals, via the second antenna.
[0026] Yet another embodiment of the present invention provides a
method for receiving or transmitting radio-frequency signals in
outer space. The method includes providing a central hub in outer
space and rotating the central hub about an axis. At least three
flexible tethers are extended radially from the central hub. A
respective peripheral satellite is attached to each of the tethers.
Extending the tethers thereby deploys the peripheral satellites
radially away from the central hub. The peripheral satellites orbit
the central hub in a plane perpendicular to the axis. Each tether
is taut between the central hub and the respective peripheral
satellite. Each tether has at least two antenna elements disposed
on it. The antenna elements of all the tethers collectively form an
antenna array. Signals delivered to, or received from, the antenna
array are phase adjusted to beam-steer a lobe of a radiation
pattern of the antenna array in two dimensions.
[0027] Extending the at least three flexible tethers radially from
the central hub may include using centripetal forces to extend and
tension the tethers. The centripetal forces may be caused by
orbiting of the peripheral satellites about the central hub.
[0028] Phasing of the plurality of antenna elements may be altered
in synchrony with rotation of the central satellite.
[0029] A second antenna and a radio-frequency receiver may be
provided. The second antenna and the radio-frequency receiver may
be mechanically coupled to the central hub. An input of the
radio-frequency receiver may be communicatively coupled to the
second antenna. A radio-frequency transmitter may be provided. The
radio-frequency transmitter may be mechanically coupled to the
central hub. An input of the transmitter may be communicatively
coupled to an output of the receiver. An output of the transmitter
may be communicatively coupled to the antenna array. A signal may
be received via the second antenna and the receiver. The signal may
be relayed via the transmitter and the antenna array.
[0030] A second antenna and a radio-frequency transceiver may be
provided. The second antenna and the radio-frequency transceiver
may be mechanically coupled to the central hub. The radio-frequency
transceiver may be communicatively coupled to the second antenna
and to the antenna array. First signals may be received via the
second antenna and the transceiver. The first signals may be
relayed via the transceiver and the antenna array.
[0031] Second signals may be received via the antenna array and the
transceiver. The second signal may be relayed via the transceiver
and the second antenna.
[0032] Extending the at least three flexible tethers may include
paying out the at least three flexible tethers from the central
hub.
[0033] For each of the at least three tethers, extending the tether
may include paying out a respective one of the at least three
flexible tethers from the peripheral satellite attached to the
tether.
[0034] An embodiment of the present invention provides a
non-transitory computer-readable medium. The medium is encoded with
instructions. When executed by a processor, the instructions
establish processes for performing a computer-implemented method of
receiving radio-frequency signals in outer space. The processes
include a process configured to rotate a central hub about an axis.
A process is configured to extend at least three flexible tethers
radially from the central hub. A respective peripheral satellite is
attached to each of the tethers. Extending the tethers thereby
deploys the peripheral satellites radially away from the central
hub. The peripheral satellites orbit the central hub in a plane
perpendicular to the axis. Each tether is taut between the central
hub and the respective peripheral satellite. Each tether has at
least two antenna elements disposed on it. The antenna elements of
all the tethers collectively form an antenna array. A process is
configured to phase adjust signals delivered to, or received from,
the antenna array to beam-steer a lobe of a radiation pattern of
the antenna array in two dimensions.
[0035] The process configured to extend the tethers may be
configured to extend and tension the tethers using centripetal
forces caused by orbiting of the peripheral satellites about the
central hub.
[0036] The processes may include a process configured to alter
phasing of the plurality of antenna elements in synchrony with
rotation of the central hub.
[0037] A second antenna and a radio-frequency receiver may be
mechanically coupled to the central hub. An input of the receiver
may be communicatively coupled to the second antenna. An input of
the radio-frequency transmitter may be communicatively coupled to
an output of the receiver. An output of the transmitter may be
communicatively coupled to the antenna array.
[0038] A process may be configured to receive a signal via the
second antenna and the receiver. A process may be configured to
relay the signal via the transmitter and the antenna array.
[0039] A second antenna and a radio-frequency transceiver may be
mechanically coupled to the central hub. The radio-frequency
transceiver may be communicatively coupled to the second antenna
and to the antenna array. A process may be configured to receive
first signals, via the second antenna and the transceiver. A
process may be configured to relay the first signals via the
transceiver and the antenna array.
[0040] A process may be configured to receive second signals via
the antenna array and the transceiver. A process may be configured
to relay the second signal via the transceiver and the second
antenna.
[0041] Another embodiment of the present invention provides an
antenna array. The antenna array includes a first satellite and a
flexible extendible tether. The antenna array also includes a
second satellite attached to the first satellite by the extendible
tether. The antenna array has a first mode and a second mode.
[0042] In the first mode, the tether is retracted, i.e., the first
satellite is disposed within about 2 meters of the second
satellite.
[0043] In the second mode, the first and second satellites are
configured to rotate about an axis and extend the tether. Extending
the tether deploys the first and second satellites radially away
from each other a distance greater than about 2 meters. The first
and second satellites orbit in a plane perpendicular to the axis.
While the first and second satellites orbit, the tether is
taut.
[0044] A plurality of antenna elements is disposed along the
tether. A phaser is coupled to the plurality of antenna elements to
beam-steer a lobe of a radiation pattern of the plurality of
antenna elements.
[0045] In some embodiments, in the first mode, the tether is
retracted, such that the first satellite is disposed less than a
first predetermined distance (such as about 0.5, 1, 2, 3 or 4
meters) of the second satellite, and in the second mode, the tether
is extended, thereby deploying the first and second satellites
radially away from each other at least a second predetermined
distance (such as about 0.5, 1, 2, 3 or 4 meters).
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0046] Embodiments of the invention will be more fully understood
by referring to the following Detailed Description of Specific
Embodiments in conjunction with the Drawings, of which:
[0047] FIG. 1 is a schematic perspective view of an antenna array,
according to an embodiment of the present invention.
[0048] FIG. 2 is a schematic cut-away top view of the antenna array
of FIG. 1 in a compact mode, according to an embodiment of the
present invention.
[0049] FIG. 3 is a schematic perspective view of the antenna array
of FIGS. 1-2, once tethers have been fully payed out and the
antenna array is in a fully deployed mode, according to an
embodiment of the present invention.
[0050] FIG. 4 is a schematic side view of a portion of one tether
of FIGS. 2-3, according to an embodiment of the present
invention.
[0051] FIG. 5 is a schematic block diagram of a phaser
interconnected to antenna elements on one tether of the antenna
array of FIGS. 1-4, according to an embodiment of the present
invention.
[0052] FIG. 6 is a two-dimensional radiation pattern (antenna
pattern) of a hypothetical dipole antenna, according to the prior
art.
[0053] FIG. 7 is a two-dimensional radiation pattern (antenna
pattern) of a hypothetical dipole antenna, with a reflecting
element, according to the prior art.
[0054] FIG. 8 is a schematic side view of portions of one tether of
FIGS. 1-3, according to another embodiment of the present
invention.
[0055] FIG. 9 is a perspective illustration of a portion of one
tether of FIG. 8, according to an embodiment of the present
invention.
[0056] FIG. 10 is a hypothetical two-dimensional radiation pattern
of a linear phased array of FIG. 8, according to an embodiment of
the present invention.
[0057] FIG. 11 is a schematic top view of the tether of FIG. 8,
according to an embodiment of the present invention.
[0058] FIG. 12 is a schematic perspective view of the antenna
array, fully deployed, of FIGS. 1-3, 8, 10 and 11, according to an
embodiment of the present invention.
[0059] FIGS. 13, 14 and 15 are schematic block diagrams of signal
distribution architectures for the antenna array of FIGS. 1-3, 8
and 10-12, according to respective embodiments of the present
invention.
[0060] FIG. 16 is a schematic block diagram illustrating a signal
relay station configuration of the antenna array of FIGS. 1-3, 8
and 10-15, according to an embodiment of the present invention.
[0061] FIGS. 17 and 18 are schematic block diagrams illustrating
operations performed, in various combinations, by the antenna array
of FIGS. 1-3, 8 and 10-16, according to embodiments of the present
invention.
[0062] FIG. 19 is a schematic block diagram illustrating
components, combinations of which make up various embodiments of
the present invention and may perform all or some of the operations
and functions described with reference to FIGS. 17 and 18,
according to embodiments of the present invention.
[0063] FIG. 20 is a schematic cut-away top view of an antenna
array, similar to the antenna array of FIG. 1, but according to an
alternative embodiment of the present invention.
[0064] FIG. 21 is a schematic top view of an antenna array, similar
to the antenna array of FIG. 20, according to another alternative
embodiment of the present invention.
[0065] FIG. 22 is a schematic top view of a linear antenna array
that includes two peripheral satellites connected to each other by
a tether, according to yet another embodiment of the present
invention.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0066] In accordance with embodiments of the present invention,
methods and apparatus are disclosed for space-based phased antenna
arrays that provide two-dimensional beam steering, yet are compact
upon launch and do not rely on gravity to maintain their shapes. An
exemplary antenna array includes a central satellite and at least
three peripheral satellites. Each peripheral satellite is
mechanically connected to the central satellite by an extendible
tether. At launch, the tethers are retracted, i.e., not extended,
so the peripheral satellites are close to, or even within, the
central satellite. However, once the antenna array is inserted into
orbit or another desired trajectory, the central satellite rotates
and extends the tethers, thereby deploying the peripheral
satellites in a planar radial pattern. Multiple antenna elements
are disposed on each tether, and collectively all the antenna
elements form a planar phased array that can be electronically beam
steered in two dimensions.
[0067] In some alternative embodiments, each peripheral satellite
pays out its own tether, rather than the central satellite paying
out all the tethers. Some embodiments omit the central satellite
and, instead, merely bind together central ends of the tethers. In
some embodiments, the peripheral satellites are equipped with
thrusters and use the thrusters to reposition themselves to
reorient the antenna array, without necessarily retracting the
tethers. Yet other embodiments include only two tethered satellites
in each array, thereby providing spinning one-dimensional (linear)
phased antenna arrays that can be beam steered in one
dimension.
[0068] FIG. 1 is a schematic perspective view of an antenna array
100, according to an embodiment of the present invention. The
antenna array 100 includes a central satellite 102 (also referred
to herein as a "central hub") and at least three peripheral
satellites, represented by peripheral satellites 104, 106 and 108.
Although ten peripheral satellites 104-108 are shown in the
embodiment of FIG. 1, other numbers, larger or smaller than ten, of
peripheral satellites 104-108 may be used.
[0069] At launch, the antenna array 100 should be compact, so as to
fit within a payload compartment of a launch vehicle. Currently,
the largest available launch vehicles have launch fairings on the
order of 5 or 6 meters in diameter, limiting the size of payload
objects to this size. The antenna array 100 has two modes: a
compact mode and a fully deployed mode. FIG. 1 shows the antenna
array 100 in the compact mode. In the compact mode, the peripheral
satellites 104-108 are close to the central satellite 102. In the
embodiment of FIG. 1, each peripheral satellite 104-108 is at least
partially disposed within a corresponding recess, represented by
recesses 110, 112 and 114, in the central satellite 102.
[0070] Once the antenna array 100 is inserted into orbit or another
desired trajectory, the central satellite 102 rotates, as indicated
by arrow 116, about an axis 118. FIG. 2 is a schematic cut-away top
view of the antenna array 100 in the compact mode. The central
satellite 102 may include a reaction wheel 200, thrusters,
represented by thrusters 202, 204 and 206, or any other suitable
station-keeping device. Turning the reaction wheel 200 as indicated
by arrow 208, or firing the thrusters 202-206 as represented by
arrows 210, causes the central satellite 102 to rotate, as
indicated by arrow 212. Alternatively, the launch vehicle can
impart the rotation 212 when the antenna array 100 is ejected from
the payload compartment (not shown). Other well-known methods may
be used to initiate the rotation 212 of the central satellite
102.
[0071] As noted, in the compact mode, the peripheral satellites
104-108 are close to the central satellite 102, such as within 2 or
3 meters of the central satellite 102. Each peripheral satellite
104-108 is mechanically coupled to the central satellite 102 by a
respective flexible tether, represented by flexible tethers 214 and
216. In the first mode, the tethers 214-216 are wound on respective
spools, represented by spools 218 and 220. However, once the
central satellite 102 begins to rotate 212, centripetal forces urge
the peripheral satellites 104-108 radially away from the central
satellite 102, as represented by arrows 222 and 224.
[0072] "Flexible" here means the tethers 214-216 can bend laterally
sufficiently to be wound on the spools 218-220, without appreciable
damage to the tethers 218-220, by forces generated by the spools
218-220 and respective motors (not shown) that drive the spools.
However, the tethers 214-216 should have limited longitudinal
stretchability, to maintain total length in use, and length between
antenna elements, so as to maintain phase relationships among the
antenna elements. The tethers 214-216 may be made of, or include, a
suitable aramid fiber, such as Kevlar aramid fiber available from
E. I. du Pont de Nemours and Company, or any other suitable
material. Optionally, a phaser (described herein) may adjust the
phasing to compensate for changes in lengths of the tethers 214-216
and/or between the antenna elements, as the tethers 214-216
longitudinally stretch or shrink.
[0073] To enter the second (fully deployed) mode, the central
satellite 102 pays out the tethers 214-216 from the spools 218-220.
FIG. 3 is a schematic perspective view of the antenna array 100,
once the tethers 214-216 have been fully payed out and the antenna
array 100 is in the second mode. Ends of the tethers 214-216 close
to the central satellite 102 ("proximal ends of the tethers
214-216") are mechanically attached to the central satellite 102.
Thus, the peripheral satellites 104-108 orbit the central satellite
102, as indicated by arrows, such as arrow 300, at a fixed distance
from the central satellite 102. As used herein, "orbit" means to
follow a curved path about a point, including a moving point, not
necessarily under force of gravity. Thus, the meaning of "orbit"
includes following a curved path about a point as a result of being
tethered to, or near, the point. In the fully deployed mode, the
tethers 214-216 are held taut by the centripetal forces mentioned
above.
[0074] As used herein with respect to the tethers 214-216, "taut"
means under tension. Once the spinning antenna array 100 reaches a
steady state, including the peripheral satellites 104-108 reaching
stable respective distances from the central satellite 102, the
tethers 214-216 are relatively straight along their respective
lengths, although the tethers 214-216 may vibrate and may have
sharp bends at points where the tethers 214-216 meet the central
satellite 102 and/or the peripheral satellites 104-108. Each tether
214-216 has a resonant frequency, and the tethers 214-216 may
vibrate at their respective resonant frequencies, such as in
response to stimulation by atmospheric drag, solar pressure, jitter
in the reaction wheel 200, etc. In addition, the tethers 214-216
may be slightly deformed from a perfectly straight line by
atmospheric drag, solar pressure, etc. As used herein with respect
to the tethers 214-216, "straight" means extending linearly between
the central satellite 102 and a peripheral satellite 104-108,
except for possible displacements due to vibrations, bends where
the tether 214-216 meets the central satellite 102 or the
peripheral satellite 104-108 and slight deformations due to
atmospheric drag or solar pressure.
[0075] When fully deployed, each tether 214-216 may be as short as
about 1 meter to as long as several kilometers. The length of a
fully deployed tether 214-216 may be selected, at least in part,
based on the wavelength of signals to be received and/or
transmitted by the antenna array 100 and/or size and/or number of
antenna elements desired to be disposed along each tether 214-216.
The length of each tether 214-216 is limited primarily by strength
of the tether 214-216 and the orbital speed of the peripheral
satellites 104-108 about the central satellite 102.
[0076] As the tethers 214-216 are payed out and the peripheral
satellites 104-108 are deployed progressively radially further from
the central satellite 102, the orbital speeds (angular velocities)
of the peripheral satellites 104-108 decrease to conserve angular
momentum. The rotation speed (angular velocity) of the central
satellite 102 may be decreased, to match the decreased orbital
speeds of the peripheral satellites 104-108. Other details of
deploying a rotating system of tethered satellites, although in the
context of optical interferometers, are described by Ph. Claudin,
et al., in "A Concept of Deployable Tethered Interferometer,"
Proceedings of the ESA Colloquium on Targets for Space-based
interferometry, Beauliu, France, Oct. 13-16, 1992, the entire
contents of which are hereby incorporated herein, for all purposes.
Further details of deploying a rotating system of tethered
satellites, although in the context of optical interferometers,
such as damping of tether oscillations, are described by Enrico C.
Lorenzini in "Participation in the Analysis of the
Far-Infrared/Submillimeter Interferometer," Annual Report #1, NASA
Grant NNG04GQ21G, for the period 1 Sep. 2004 through 30 Jun. 2005,
July 2005, the entire contents of which are hereby incorporated
herein, for all purposes.
[0077] The antenna array 100 may include other components, such as
solar panels, exemplified by solar panel 302. The solar panels 302
may be used to generate electricity to operate components of the
antenna array 100, such as motors (not shown) that turn the
reaction wheel 208 (FIG. 2) and the spools 218-220, as well as a
phaser and transmitters and/or receivers that are described herein.
Only one solar panel 302 is shown in FIG. 3. However, additional
solar panels may also be disposed on the remaining peripheral
satellites 104-108. Total masses disposed at ends of the tethers
214-216 opposite the central satellite 102 should be at least
approximately equal, so angular momentums of the radial "arms" of
the antenna array 100 are at least approximately equal. Solar
panels (not shown) may be disposed on the central satellite
102.
[0078] The antenna array 100 may include a suitable navigation,
guidance and control system (not shown) to control the reaction
wheel 200, thrusters 202-206, etc. to initially orient the central
satellite 102 so the axis 118 extends in a desired direction, such
as toward a distant transmitting and/or receiving station.
Orienting the central satellite 102 so the axis 118 extends in the
desired direction may be more easily done before the peripheral
satellites are deployed than after they are deployed. Then,
periodically or occasionally, the navigation, guidance and control
system may make suitable adjustments to the orientation of the
antenna array 100 as needed, such as to correct for drift of the
antenna array 100 in space. The antenna array 100 may be reoriented
toward a different transmitting or receiving station, such as by
retracting the tethers 214-216 and then using the reaction wheel
200 and/or thrusters 202-206, etc. to reorient the central
satellite 102 toward a new target. Then, the peripheral satellites
104-108 may again be deployed by extending the tethers 214-216.
[0079] At least two antenna elements, represented by antenna
elements 304, 306, 308, 310, 312 and 314, are disposed on each
tether 214-216. Optionally, antenna elements may be disposed on the
peripheral satellites 104-108, as exemplified by antenna element
316. Similarly, optionally, antenna elements may be disposed on the
central satellite 102, as exemplified by antenna elements 318 and
320. Collectively, all the antenna elements 304-314, 316 and
318-320 on all the tethers 214-216, on the peripheral satellites
104-108 and on the central satellite 102 form a phase antenna array
and are collectively referred to herein as a "plurality of antenna
elements disposed along the tethers."
[0080] As noted, in a phased antenna array, phases of signals
deliver to, or received by, the antenna elements are individually
controlled to electronically steer the phased array in a desired
direction. The central satellite 102 includes a phaser 322 that
controls phases of the signals delivered to, or received by, the
plurality of antenna elements 304-314, 316 and 318-320.
[0081] FIG. 4 is a schematic side view of a portion of one tether
214, according to an embodiment of the present invention. Three
dipole antenna elements 400, 402 and 404, are shown disposed along
the portion of the tether 214, although other types of antenna
elements may be used and/or other numbers of antenna elements may
be disposed on the tether 214. The antenna elements 400 and 402 are
separated by a distance S. Other adjacent pairs of antenna elements
may be separated by distances S, or some or all other adjacent
pairs of antenna elements may be separated by other distances. The
separation distance(s) should be taken into account in the design
of the phaser 322 (FIG. 3), as would be appreciated by a
practitioner skilled in the art of phased antenna arrays.
[0082] In the embodiment of FIG. 4, each antenna element 400-404 is
communicatively coupled to a transmitter, a receiver or a
transceiver, represented by devices 406, 408 and 410. The
transmitters, receivers or transceivers 406-410 are coupled to the
phaser 322 (FIG. 3), such as via optical fibers, wires, coaxial
cables or other suitable cabled or cable-less interconnections,
represented by interconnections 412. The phaser 322 sends signals
via the interconnections 412 to the transmitters, receivers or
transceivers 406-410, and the devices 406-410 use the signals to
control phasing of signals the devices 406-410 transmit or receive
via the respective antenna elements 400-404.
[0083] The interconnections 412 may be individual or grouped, i.e.,
a separate interconnection 412 may extend from the phaser 322 to
each transmitter, receiver or transceiver 406-410, as shown
schematically if FIG. 5. Alternatively, a separate interconnection
412 may extend from the phaser 322 to each subset of devices
406-410, or a single interconnection 412 may extend from the phaser
322 to the first transmitter, receiver or transceiver 406, and the
interconnection 410 may then "daisy-chain" through the first device
406 and each subsequent device 408-410.
[0084] In some embodiments, the devices 406-410 are power
amplifiers (for transmitting) or low-noise amplifiers (for
receiving), and the interconnections 420 carry RF signals to or
from the phaser 322 or another circuit, such as a transmitter or a
receiver (not shown), between the antenna elements 400-404 and the
phaser 322 or following the phaser 322. The phaser 322 may control
phasing of the transmitter or receiver. Alternatively, the devices
406-410 merely RF-couple the antenna elements 400-404 to the
interconnection(s) 412, without amplification. In these cases, the
phaser 322 generates and/or detects RF signals or a suitable
transmitter, receiver or transceiver, disposed in the central
satellite 102, is coupled to the phaser 322. The interconnection(s)
412 may, but need not, provide or contribute to mechanical strength
of the tether 214.
[0085] FIG. 6 is a two-dimensional radiation pattern (antenna
pattern) 600 of a hypothetical dipole antenna 602, as known in the
prior art. The radiation pattern indicates strength of a signal
radiated by the antenna 602 in various directions or, by the
reciprocity theorem, sensitivity of the antenna 602 to signals
received from various directions. The strength or sensitivity is
indicated by lengths of representative arrows, and the directions
are indicated by directions of the representative arrows. The locus
of tips of arrow heads of all possible direction arrows, which in
this case is two loops 604 and 606, is the radiation pattern. An
ideal dipole antenna has a three-dimensional radiation pattern
resembling a torus. The two loops 604 and 606 in FIG. 6 represent a
cross-sectional view, taken in the plane of the drawing, of such a
torus.
[0086] As shown in FIG. 7, disposing a reflecting antenna element
700 one-quarter wavelength (.lamda./4), or any odd integral
multiple thereof, from the dipole element 602 reflects signals,
thereby effectively folding the torus in half and theoretically
doubling the radiation pattern in a direction 702 opposite the
reflecting element 700, as known in the prior art. (Only the main
lobe of the radiation pattern is shown in FIG. 7. Side lobes are
omitted for clarity.)
[0087] FIG. 8 is a schematic side view of portions of the tether
214, according to another embodiment of the present invention.
Three dipole antenna elements 400-404 are shown disposed along a
portion of the tether 214, as in FIG. 4. Other types and/or numbers
of antenna elements may be used. A respective reflecting antenna
element, represented by reflectors 800, 802 and 804, is disposed
one-quarter wavelength, or an odd integral multiple thereof, from
each antenna element 400-404 to increase radiation and/or
sensitivity of the antenna elements 400-404 on a side opposite the
reflectors 800-804. Alternatively, rather than attaching separate
reflectors 800-804, the tether 214 may be made of, or coated with,
a suitable metallic material that reflects RF signals, and the
antenna elements 400-404 may be spaced apart from the tether 214
one-quarter wavelength, or an odd integral multiple thereof.
[0088] The tether 214 may have another suitable cross-sectional
shape, such as circular, ellipsoidal or rectangular. To prevent
twisting of the tether 214 about a longitudinal axis thereof, or to
restore the tether 214 to an untwisted state, the tether 214 may be
made of, or include, a shape-memory material, such as a
shape-memory alloy or a shape-memory polymer. Optionally, the
tether 214 may have a curved cross-sectional shape, as shown in
FIG. 9, similar to the cross-sectional shape of some
self-supporting tape measures.
[0089] Returning to FIG. 8, the set of antenna elements 400-404
disposed along the tether 214 forms a linear (one-dimensional)
phased array. By adjusting phases of signals sent to, or received
from, the antenna elements 400-404, relative to each other, this
linear phased array can be electronically steered in one dimension.
Exemplary directions in which the linear phased array can be
steered are indicated by arrows 806, 808, 810 and 812, all of which
are in the plane of the drawing. FIG. 10 is a hypothetical
two-dimensional radiation pattern of the linear phased array of
FIG. 8. (Only the main lobe of the radiation pattern is shown in
FIG. 10. Side lobes are omitted for clarity.) Arrow 1000 indicates
an exemplary range over which the linear phased array can be
electronically steered.
[0090] While FIG. 8 is a schematic side view of portions of the
tether 214, FIG. 11 is a schematic top view of the tether 214,
i.e., a view from the central satellite 102. Although the linear
phased array of antenna elements 400-404 on the tether 214 can be
electronically steered within the plane of FIG. 8, as shown in FIG.
11, directionality, indicated by arrow 1100, of the linear phased
array of a single tether 214 is fixed and cannot be electronically
steered in the plane of FIG. 11.
[0091] However, as shown schematically in FIG. 12, with addition of
more tethers and their attendant antenna elements, the plurality of
antenna elements 304-314, 316 and 318-320 forms a two-dimensional
array of antenna elements, which can be electronically steered in
two orthogonal dimensions 1200 and 1202. Prior art space-based
two-dimensional phased arrays require constellations of
disconnected, likely separately launched, satellites, where each
satellite includes one linear array of antenna elements, as
described by Philip G. Tomlinson, et al., in "Space-Based Tethered
Array Radar (STAR)--A Distributed Small Satellite Network," Second
Annual AIAA/Utah State University Conference on Small Satellites,
Sep. 19-21, 1988, the entire contents of which are hereby
incorporated by reference herein, for all purposes.
[0092] Ascertaining and maintaining distances among the individual
satellites and distributing signals among the disconnected
satellites, which are both required to operate a phased array, are
difficult in the Tomlinson system. Furthermore, each Tomlinson
linear array must be deployed in a gravitation gradient field, such
as in orbit around a planet, to maintain its attitude, relative to
other linear arrays in the constellation. Thus, Tomlinson's system
is not usable for interplanetary space flight or for deployment at
Lagrange points.
[0093] In contrast, due to tension in the tethers 214-216 created
by rotation of the antenna array 100, embodiments of the present
invention operate essentially as rigid systems and do not require
gravitational fields. Thus, once in the fully deployed mode,
distances among the antenna elements 304-314, 316 and 318-320
remain constant, thereby solving the distance problems inherent in
the Tomlinson system. Furthermore, all the components of the
presently disclosed antenna array are attached together by tethers,
facilitating communication via wires or optical fibers between the
phaser 322 and the antenna elements 304-314, 316 and 318-320,
whereas Tomlinson must use wireless communication, with its
attendant power, interference and licensing issues.
[0094] FIG. 13 is a schematic diagram illustrating interconnection
of the plurality of antenna elements 304-314, 316 and 318-320 on
all the tethers 214-216 and 1300 to the phaser 322 via respective
interconnections, such as interconnections 412, 1302 and 1304,
according to one embodiment. As discussed herein, in other
embodiments, other interconnection architectures may be used, such
as daisy chains. As shown in FIG. 13, a transmitter, receiver or
transceiver 1306 is connected to the phaser 322 to generate or
receive RF signals that the phaser 322 then processes, i.e.,
adjusts phases of, for distribution to the plurality of antenna
elements 304-314, 316 and 318-320.
[0095] Alternatively, as shown schematically in FIG. 14, the phaser
322 may provide phase control signals to one or more transmitters,
receivers or transceivers, exemplified by devices 1400, 1402, 1404
and 1406, and these devices may generate and/or receive RF signals
and couple to respective antenna elements 304-314 on the respective
tethers 214-216 and 1300. FIG. 15 schematically illustrates yet
another architecture, in which the phaser 322 sends phase control
signals via the interconnects, represented by interconnect 412,
1302 and 1304, to transmitters, receivers or transceivers,
represented by devices 406-410, on the various tethers 214-216 and
1300, and the devices 406-410 RF couple directly to antenna
elements 304-314.
[0096] Returning to FIG. 12, as the antenna array 100 rotates 116
about the axis 118, the phasing of the plurality of antenna
elements 304-314, 316 and 318-320 may need to be changed. For
example, if the antenna array 100 is electronically aimed in a
direction other than along the axis 118, such as in a direction
indicated by arrow 1204, and the antenna array 100 rotates, the
phasing of each antenna element 304-314, 316 and 318-320 should be
changed in synchrony with the rotation, so as to maintain the
antenna array's radiation pattern favoring the direction 1204. The
phasing may be altered continuously or in discrete steps, such as
every 1.degree. of rotation 116 about the axis 118 or every second
in time.
[0097] As shown in FIG. 13, a gyro 1308 or other orientation sensor
may be coupled to the phaser 322 to provide a signal indicative of
orientation of the antenna array 100, i.e., angular position about
the axis 118, so the phaser 322 can appropriately alter the phasing
of signals sent to, or received from, the plurality of antenna
elements 304-314, 316 and 318-320, as the antenna array 100 rotates
about the axis 118. As used herein, "gyro" means a sensor that
measures orientation (attitude), regardless the physical principle
used to implement the gyro. For example, the gyro 1308 may be
implemented as one or more accelerometers, spinning wheels in a
gimbal mount, solid-state ring lasers, fiber optic gyroscopes
(FOGs), hemispherical resonator gyroscopes (HRGs) or any other
suitable device. In cases where the gyro 1308 is expected to drift
significantly enough to adversely affect accuracy of the phasing,
the gyro 1308 may be periodically or occasionally corrected, such
as according to data from a GPS receiver, star tracker, earth
horizon sensor or sun sensor.
[0098] An antenna array 100 as described herein may be used to
relay signals between an earth station and another satellite, or
between an earth station and a station on the moon or on another
planet. Similarly, the antenna array 100 may be used to relay
signals between two other satellites, particularly if one of the
satellites is proximate the antenna array 100, and the other
satellite is far from the antenna array 100. The antenna array 100
may be physically oriented such that the axis 118 is aimed
approximately at the distant station, be it on the earth, the moon,
another planet or a distant satellite, to send signals to and/or
receive signals from the distant station.
[0099] As shown schematically in FIG. 16, a second antenna 1600 may
be used to send and/or receive signals to and/or from a local
station, such as a station on a planet, about which the antenna
array 100 is in orbit, or a companion satellite. A first receiver,
transmitter or transceiver 1602 receives and/or transmits signals
using the second antenna 1600, and a second transmitter, receiver
or transceiver 1604 transmits and/or receives, i.e., relays, the
signals using the antenna array 100. The second antenna 1600 may be
mounted on the central satellite 102 and/or on one or more of the
peripheral satellites 104-108 (FIG. 3). The second antenna 1600 may
include antenna elements disposed on some or all of the tethers
214-216 (FIG. 3). The second antenna 1600 may be a phased array
antenna.
[0100] Optionally, the peripheral satellites 104-108 and their
corresponding tethers 214-216 may be drawn back toward the central
satellite 102 by the spools 218-220, such as to facilitate
re-orienting the axis 118 of the antenna array 100 toward another
station or to put the antenna array 100 in a "safe mode" to prevent
damage, such as from expected space weather or meteors.
[0101] FIG. 17 contains a flowchart that schematically illustrates
operations performed, in various combinations, by embodiments of
the present invention. At 1700, a central satellite, such as
central satellite (central hub) 102, is provided, such as by
launching the central satellite into space. The central satellite
should be configured for space flight. For example, components and
construction of the central satellite should be selected and
performed to withstand the vacuum and temperatures expected to be
encountered in space during a mission of the central satellite.
Alternative embodiments, such as embodiments discussed with respect
to FIGS. 20 and 21, may have central hubs with more or fewer
structures and/or capabilities than the central satellite 102
described with respect to FIGS. 1-3 and 12. At 1702, the central
satellite (central hub) is rotated about its axis, such as the axis
118.
[0102] At 1704, at least three flexible tethers, such as tethers
214-216 (FIG. 2), are extended radially from the central satellite
using centripetal forces caused by orbiting of the peripheral
satellites about the central satellite. The tethers 214-216 may be
payed out by the central hub 102, as described with respect to
FIGS. 1-3 and 12. Alternatively, as described with respect to FIGS.
20 and 21, the peripheral satellites may pay out the tethers
214-216. All such embodiments and operations are included within
the meaning of the phrase "extending a tether from the central hub"
and similar phrases, including in the claims.
[0103] A respective peripheral satellite, such as peripheral
satellites 104-108, is attached to each of the tethers. Extending
the tethers thereby deploys the peripheral satellites radially away
from the central satellite. The peripheral satellites orbit the
center of mass of the antenna array in a plane perpendicular to the
axis. The center of mass of the antenna array may or may not be
within the central satellite. Each tether is taut between the
central satellite and the respective peripheral satellite. Each
tether has at least two antenna elements disposed thereon. The
antenna elements of all the tethers collectively form an antenna
array.
[0104] At 1704, signals delivered to, or received from, the antenna
array are phase adjusted to beam-steer a lobe of a radiation
pattern of the antenna array in two dimensions. At 1708, signals
are read from a gyro or other attitude measuring device, such as an
inertial navigation system (INS), to ascertain a current rotational
position of the central satellite about the axis. At 1710, the
phases of the signals delivered to, or received from, the antenna
array are adjusted in synchrony with rotation of the central
satellite, i.e., to compensate for the current rotational position
of the central satellite. Control returns to 1708.
[0105] FIG. 18 contains a flowchart that schematically illustrates
other operations performed, in various combinations, by embodiments
of the present invention to relay signals, such as from a station
on a planet or a companion satellite to and/or from earth. At 1800,
a second antenna, such as the second antenna 1600 (FIG. 16), is
provided. The second antenna is mechanically coupled to the central
satellite.
[0106] At 1802, a first RF receiver, transmitter or transceiver is
provided. The first receiver, transmitter or transceiver is
mechanically coupled to the central satellite. If a first receiver
or transceiver is provided, an input of the first receiver or
transceiver is communicatively coupled to the second antenna to
receive RF signals via the second antenna. If a first transmitter
or transceiver is provided, an output of the first transmitter or
transceiver is communicatively coupled to the second antenna to
send RF signals via the second antenna.
[0107] At 1804, a second RF receiver, transmitter or transceiver is
provided. The second receiver, transmitter or transceiver is
mechanically coupled to the central satellite. If a second receiver
or transceiver is provided, an input of the second receiver or
transceiver is communicatively coupled to the antenna array to
receive RF signals via the antenna array, and an output of the
second receiver or transceiver is coupled to an input of the first
transmitter or transceiver.
[0108] If a second transmitter or transceiver is provided, an
output of the second transmitter or transceiver is communicatively
coupled to the antenna array to send RF signals via the antenna
array, and an input of the second transmitter or transceiver is
coupled to an output of the first receiver or transceiver.
[0109] At 1806, an RF signal is received via the second antenna and
the first receiver or transceiver. At 1808, the RF signal is sent
by the second transmitter or transceiver via the antenna array,
thereby relaying the RF signal, such as from a local satellite or
planet-based station to a distant earth.
[0110] At 1810, an RF signal is received via the antenna array and
the second receiver or transceiver. At 1812, the RF signal is sent
by the first transmitter or transceiver via the second antenna,
thereby relaying the RF signal, such as from a distant earth to a
local satellite or planet-based station.
[0111] Operations and functions described with reference to FIGS.
17 and 18, as well as other operations and functions described
herein, may be performed, in whole or in part, by a processor
executing instructions stored in a memory. Thus, portions of the
antenna array 100 may be implemented by a processor executing
instructions stored in a memory. FIG. 19 is a schematic block
diagram illustrating components, combinations of which make up
various embodiments of the present invention and may perform all or
some of the operations and functions described with reference to
FIGS. 17 and 18.
[0112] A processor 1900 is coupled via a bus 1902 to a memory 1904.
The memory 1904 stores instructions, and the processor 1900 fetches
and executes the instructions to perform functions and operations
described herein. The memory 1904 also stores read-only data, such
as tables, and read-write data, such as calculated phase
relationships, as needed by the processor 1900.
[0113] A motor interface 1906 interconnects the bus 1902, and
therefore the processor 1900 and the memory 1904, to spool motors
1908 that drive the spools 218-220 (FIG. 2). The processor 1900
controls the spool motors 1908, such as to pay out or retract the
tethers 214-216. Similarly, if the antenna array 100 is equipped
with a reaction wheel, a second motor interface 1910 interconnects
the bus 1902 to a reaction wheel motor 1912. The processor 1900
controls the reaction wheel motor 1912 to start and stop rotation
116 of the central satellite 102, to control rotational speed of
the central satellite 102 and optionally to control attitude of the
central satellite 102. Some embodiments include more than one
mutually-orthogonally oriented reaction wheel, as known in the
art.
[0114] If the antenna array 100 is equipped with thrusters 1914, a
thruster controller 1916 interconnects the bus 1902 with the
thrusters 1914. The processor 1900 controls the thrusters 1914 to
start and stop rotation 116 of the central satellite 102, as well
as to control rotational speed and/or orientation of the central
satellite 102.
[0115] The phaser 322 is connected to the bus 1902. The processor
1900 controls the phaser 322, such as to specify phasing of signals
received from, or sent to, the plurality of antenna elements
304-314, 316 and 318-320 to electronically steer the antenna array
100. The gyro or other suitable sensor 1308 is coupled to the bus
1902 to provide the processor 1900 with a signal indicating the
real-time or near real-time rotational position of the central
satellite 102. In some embodiments, the processor polls or
otherwise queries the gyro 1308.
[0116] In embodiments where the antenna array 100 relays signals,
as discussed with respect to FIG. 18, a local link controller 1918
is coupled between the bus 1902 and the first receiver, transmitter
or transceiver 1920. In addition, a distant link controller 1922 is
coupled between the bus 1902 and the second transmitter, receiver
or transceiver 1924.
[0117] A suitable navigation, guidance and control 1926 may be
coupled to the bus 1902 to communicate with the processor 1900. The
navigation, guidance and control 1926 may receive correction
signals, as needed, from an external system, such as a global
positioning system (GPS) receiver, star tracker, earth horizon
sensor or sun sensor.
[0118] FIG. 20 is a schematic cut-away top view of an antenna array
2000, similar to the antenna array 100 of FIG. 1, but according to
an alternative embodiment. While in the antenna array 100, the
central satellite 102 pays out and retracts the tethers 214-216, in
the antenna array 2000, peripheral satellites pay out and retract
the tethers. Each peripheral satellite, represented by peripheral
satellites 2002, 2004 and 2006, includes a respective spool,
represented by spools 2008 and 2010. Each spool 208-2010 is driven
by a respective motor (not shown). Distal ends of the tethers
214-216 are wound on the spools 2004-2006, and proximal ends of the
tethers 214-216 are attached to the central satellite 2012 at
respective anchors, represented by anchors 2014 and 2016. In other
respects, the antenna array 2000 is structured and operates like
the other antenna arrays described herein.
[0119] FIG. 21 is a schematic top view of an antenna array 2100,
similar to the antenna array 2000 of FIG. 20, but according to
another alternative embodiment. While the antenna array 2000
includes a central satellite 2012, the antenna array 2100 does not
include a central satellite. Instead, proximal ends of the tethers
214-216 are bound together by a suitable clamp 2102 where a central
satellite would be located. The clamp 2102 forms a central hub.
[0120] In addition, each peripheral satellite, represented by
peripheral satellites 2104, 2106 and 2108, includes thrusters,
represented by thrusters 2110, 2112 and 2114. Each peripheral
satellite 2104-2108 uses its respective thrusters 2110-2114 to urge
itself away from the clamp (central hub) 2102 while paying out its
respective tether 214-216 and to initiate, change or stop the
rotation 212 of the antenna array 2100. In addition, the peripheral
satellites 2104-2108 collectively use the thrusters 2110-2114 to
reposition themselves relative to each other and to reorient the
antenna array 2100, without necessarily retracting the tethers
214-216. In other words, each peripheral satellite 2104-2108 may
fly to a new position, thereby reorienting the entire antenna array
2100.
[0121] The peripheral satellites 2104-2108 may be initially held
together, such as during launch and ejection from a launch vehicle,
by a frame or bracket 2116, as indicated by dashed line. The frame
or bracket 2116 may include a reaction wheel and/or thrusters (not
shown) to initially position and/or spin 212 the antenna array
2100, before the tethers 214-216 are extended. The frame or bracket
2116 may be deorbited after the peripheral satellites 2104-2108
deploy, i.e., after the tethers 214-216 are initially extended. In
other respects, the antenna array 2100 is structured and operates
like the other antenna arrays described herein.
[0122] Some embodiments include only two peripheral satellites,
thereby forming a linear (one dimensional) antenna array. FIG. 22
is a schematic top view of a linear antenna array 2200 that
includes two peripheral satellites 2202 and 2204 connected to each
other by a tether 2206. Such a linear antenna array 2200 is beam
steerable in one dimension, as discussed with respect to FIG. 10.
One or both of the peripheral satellites 2202 and 2204 include a
spool, represented by spools 2208 and 2210. The peripheral
satellites 2202-2204 may be initially held together, such as during
launch and ejection from a launch vehicle, by a frame or bracket
2116, as discussed with respect to the antenna array 2100 of FIG.
21. In other respects, the antenna array 2200 is structured and
operates like the other antenna arrays described herein.
[0123] Although aspects of embodiments may be described with
reference to flowcharts and/or block diagrams, functions,
operations, decisions, etc. of all or a portion of each block, or a
combination of blocks, may be combined, separated into separate
operations or performed in other orders. All or a portion of each
block, or a combination of blocks, may be implemented as computer
program instructions (such as software), hardware (such as
combinatorial logic, Application Specific Integrated Circuits
(ASICs), Field-Programmable Gate Arrays (FPGAs) or other hardware),
firmware or combinations thereof. Embodiments may be implemented by
a processor executing, or controlled by, instructions stored in a
memory. The memory may be random access memory (RAM), read-only
memory (ROM), flash memory or any other memory, or combination
thereof, suitable for storing control software or other
instructions and data. Instructions defining the functions of the
present invention may be delivered to a processor in many forms,
including, but not limited to, information permanently stored on
tangible non-writable storage media (e.g., read-only memory devices
within a computer, such as ROM, or devices readable by a computer
I/O attachment, such as CD-ROM or DVD disks), information alterably
stored on tangible writable storage media (e.g., floppy disks,
removable flash memory and hard drives) or information conveyed to
a computer through a communication medium, including wired or
wireless computer networks.
[0124] As used herein, outer space (or simply space) means at least
100 km (62 mi.) above earth sea level. While specific parameter
values may be recited in relation to disclosed embodiments, within
the scope of the invention, the values of all of parameters may
vary over wide ranges to suit different applications. Unless
otherwise indicated in context, or would be understood by one of
ordinary skill in the art, terms such as "about" mean within
.+-.20%.
[0125] As used herein, including in the claims, the term "and/or,"
used in connection with a list of items, means one or more of the
items in the list, i.e., at least one of the items in the list, but
not necessarily all the items in the list. As used herein,
including in the claims, the term "or," used in connection with a
list of items, means one or more of the items in the list, i.e., at
least one of the items in the list, but not necessarily all the
items in the list. "Or" does not mean "exclusive or."
[0126] While the invention is described through the above-described
exemplary embodiments, modifications to, and variations of, the
illustrated embodiments may be made without departing from the
inventive concepts disclosed herein. Furthermore, disclosed
aspects, or portions thereof, may be combined in ways not listed
above and/or not explicitly claimed. Embodiments disclosed herein
may be suitably practiced, absent any element that is not
specifically disclosed herein. Accordingly, the invention should
not be viewed as being limited to the disclosed embodiments.
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