Microsatellite array and related method

• US 6,002,360 A
• Filed: 03/07/1997
• Issued: 12/14/1999
• Est. Priority Date: 03/07/1997
• Status: Expired due to Fees

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: TRW Inc. (Northrop Grumman Corporation)
• Inventors: Evans, Christopher T., Shah, Atul, Wolcott, James L.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US08/813,127
• Time in Patent Office: 1,012 Days
• Field of Search: 342/352, 342/353, 342/354, 342/368, 342/371, 342/372, 342/375, 455/12.1, 455/13.1, 455/13.2
• US Class Current: 342/354
• CPC Class Codes: H01Q 1/288 Satellite antennas
• CPC Class Codes: H04B 7/18576 Satellite systems for providing narrowband data service to fixed or mobile stations, e.g. using a minisatellite, a microsatellite for selecting H04W

Abstract

A communication relay having a large number of free-flying, self-powered miniature spacecraft (10M) that cooperate to form a large antenna array with sufficient aperture and gain to focus transmit and receive beams much more accurately than in conventional satellite communication relays. The miniature spacecraft, or microsatellites, fly in a single constellation (10) but are allowed to drift in relative position because no rigid structure is provided to restrain their relative movement. Operation as a large phased-array antenna system is achieved by providing for accurate measurements of the microsatellite positions in real time. In one disclosed form of the array, a control satellite (20) conditions the microsatellites (10M) to form receive and transmit beams in desired directions. Received uplink signals are transmitted over communication crosslinks (42) to the control satellite (20), which forwards signals back to the microsatellites after conditioning them to form a transmit beam when forwarding the signals on as a downlink, transmission. A constellation (10) of microsatellites of the type disclosed may also be used as a deep-space communication relay, or as a radio-telescope.

Claims

1. A method for communicating from one ground-based transceiver to another using a satellite communication relay operating at ultra-high frequencies, and wavelengths up to approximately one meter, the method comprising the steps of:

conditioning a large number of free-flying, structurally independent, cooperative transponders to function cooperatively as a single phased-array antenna with a receive beam directed toward a transceiver that is ready to transmit an uplink signal, wherein the transponders are moving in adjacent but independent orbits as a single constellation of satellites and each transponder has faces and multiple antennas installed in the multiple faces;

transmitting the uplink signal from the transceiver to all of the transponders acting in cooperation as a single phased-array antenna;

receiving the uplink signal at the transponders;

conditioning the transponders to function cooperatively as a single phased-array phased array antenna with a transmit beam directed toward a destination; and

transmitting a downlink signal from the transponders acting in cooperation as a single phased-array antenna, to the destination transceiver;

wherein the receive beam and the transmit beam provide independent and simultaneous uplink and downlink paths;

wherein the transponders are sufficiently numerous and widely spaced to provide a large antenna aperture and relatively narrow receive and transmit beams that permit reuse of transceiver frequencies in different locations;

and wherein the steps of conditioning the transponders includes

periodically determining the locations of the individual transponders by detecting their angular positions and ranges with respect to a number of special-purpose satellites in known orbits,

interposing a selected time delay for uplink signals received at each transponder and for downlink signals transmitted from each transponder, wherein the time delays are computed using phased-array antenna principles and based on the locations of the transponders and the intended direction of the receive and transmit beams,

detecting the orientation of each transponder, and

applying antenna selection signals to each transponder, based on its detected orientation, to select the antennas in each transponder that provide for maximum transponder antenna gain for the uplink and downlink signals, and for signals transmitted and received over the communication crosslinks.

2. A method as defined in claim 1, and further comprising:

transmitting the delayed uplink signals over communication crosslinks from the transponders to a focal station orbiting with the transponders;

receiving multiple, coherently combined uplink signals at the focal station;

demodulating the received uplink signals at the focal station; and

identifying the destination transceiver from the demodulated uplink signals;

wherein the conditioning steps are effected by transmitting control signals from the focal station to the transponders over the communication links.

3. A satellite communication relay system, comprising:

a plurality of self-powered, cooperating microsatellites launched into adjacent obits such that they move generally together in a constellation but are free-flying and structurally independent of each other, wherein each microsatellite has at least one elemental antenna and two signal delay circuits for processing signals received and transmitted, respectively, through the elemental antenna;

at least one command satellite launched into an orbit adjacent to the orbits of the microsatellites, for controlling the microsatellites to function in cooperation as a single very large phased array antenna, the command satellite including a control system operative to condition the microsatellites to function as a receiving phased-array antenna having a receive beam directed toward a ground-based transceiver capable of transmitting a communication message containing an intended destination code, and to condition the microsatellites to function simultaneously as a transmitting phased-array antenna having a transmit beam directed toward a second transceiver that is the intended destination of the communication message;

a plurality of communication crosslinks between the control satellite and the microsatellites, for transmission of signals to determine the locations of the microsatellites, for transmission of communication signals for use in the transmit beam and derived from the receive beam, and for transmission of control signals to select appropriate signal delays in the microsatellites, to effect steering of the transmit and receive beams; and

a plurality of maneuverable satellites launched into orbits generally adjacent and parallel to those of the microsatellites, the maneuverable satellites providing optical beams that provide a frame of reference from which the microsatellites can determine their respective orientations,

wherein the receive beam and the transmit beam provide independent and simultaneous uplink and downlink paths;

and wherein each microsatellite has multiple faces and multiple elemental antennas installed in the faces, and also includes an antenna switch operable based on microsatellite orientation determined from the frame of reference provided by the maneuverable satellites, the antenna switch being operable to select an optimum antenna for each of three functions of the microsatellite, including receiving a receive beam component, transmitting a transmit beam component and communicating over one of the communication crosslinks.

4. A satellite communication relay system as defined in claim 3, wherein the receive beam and the send beam are transmitted at ultra-high frequencies, with a wavelength as long as approximately one meter.

5. A satellite communication relay system as defined in claim 3, wherein:

microsatellite orientation is determined from the maneuverable satellites, which transmit antenna switching signals to the microsatellites based on orientation determination.

6. A satellite communication relay system as defined in claim 3, wherein:

microsatellite orientation is determined in each individual microsatellite and appropriate antenna switching signals are generated internally.