Aeronautics and astronautics – Spacecraft – Spacecraft formation – orbit – or interplanetary path
Reexamination Certificate
1999-01-14
2001-07-31
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Spacecraft
Spacecraft formation, orbit, or interplanetary path
C455S012100
Reexamination Certificate
active
06267329
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to satellite-based communication systems and, more particularly, to a satellite-based communication system that uses a medium earth orbit communication satellite constellation.
BACKGROUND OF THE INVENTION
In satellite based communication system, employing multiple relay satellites, it is often required to communicatively link at least two of the satellites in order to facilitate global communication between stations located, for example, on opposite sides of the earth. These relay satellites typically reside in synchronous orbit at an altitude of approximately 22,300 miles. The long distances between these synchronous orbit satellites can impose costs relating to the high powered transmissions and the large antennas required to support the links between these satellites.
The use known types of lower altitude relay satellite systems can also involve drawbacks. By example, longer altitude relay satellites can suffer from discontinous inter-connections and also may provide only limited coverage.
Therefore, it is desirable to provide a satellite relay communication system which is located at a lower altitude than synchronous orbit, and which thus shortens the communication range while providing nearly global coverage U.S. Pat. No. 5,439,190, issued to Horstein et al., discloses a satellite-based cellular transcommuniations system employing a constellation of telecommunications satellites in medium earth orbit. The system provides multibeam radio frequency communications links for for worldwide cellular telephone service. The satellites are placed in a plurality of inclined orbits about the earth. The orbital characteristics are tailored to maximize, by example, the coverage area of the satellites, while minimizing propagation time delays and the number of beam-to-beam satellite-to-satellite handovers. The Horstein patent discloses additional features which are said to eliminate beam-to-beam and satellite-to-satellite handovers, thereby proposing a reduction in the likelihood of dropout.
U.S. Pat. No. 5,422,647, issued to Hirshfield et al., discloses a communications satellite payload for providing efficient communications between user devices, such as hand held cellular telephones, and terrestrial gateways. The satellite payload simultaneously supports a plurality of independent antenna beams on both the uplink and downlink for user devices employing full duplex communications. The satellite payload is carried by one satellite of a plurality of such satellites in a low earth orbit (LEO) constellation.
Another patent of interest to this invention is U.S. Pat. No. 5,448,623, issued to Wiedeman et al. This patent discloses a wireless telephone system capable of servicing a roaming wireless telephone user. The system includes, by example, a plurality of terrestrial communications links, at least one orbiting satellite, and at least one terrestrial-based gateway. The system operates by effecting communication between a terrestrial wireless telephone end user transceiver apparatus and a terrestrial communications link via a single relay satellite. The gateway effects ultimate decision on linking cooperation with a network database to effect hand-off from a first orbiting satellite to a second orbiting satellite.
OBJECTS OF THE INVENTION
It is a first object of this invention to provide a Medium Earth Orbit (MEO) communication satellite system comprising N satellite subconstellations, wherein each of the N satellite subconstellations comprises a respective plurality of cross-linked satellites for relaying communications between a terrestrial node and at least one mission platform.
It is a second object of this invention to provide a Medium Earth Orbit (MEO) communication satellite system comprising N satellite subconstellations, wherein satellites from respective ones of the N satellite subconstellations are cross-linked on a continuous basis in order to avoid problems associated with dropping and reeacquiring satellite cross-links.
It is a third object of this invention to provide a Medium Earth Orbit (MEO) communication satellite system comprising N satellite subconstellations, wherein at least one satellite from respective ones of the N satellite subconstellations is always within view of a terrestrial node.
It is a fourth object of this invention to provide a Medium Earth Orbit (MEO) communication satellite system comprising satellite subconstellations, wherein at least one satellite from respective ones of the N satellite subconstellations is always within view of at least one mission platform, located within the coverage area served by the system.
It is a fifth object of this intention to provide a Medium Earth Orbit (MEO) communication satellite system that provides nearly global coverage.
It is a sixth object of this invention to provide a Medium Earth Orbit (MEO) communication satellite system for relaying a communication between a terrestrial node and at least one terrestrial-based or airborne platform in a manner that minimizes the number of satellite cross-links required to be traversed in order to complete the communication.
Further objects and advantages of this invention will become apparent from a consideration of the drawings and ensuing description.
SUMMARY OF THE INVENTION
The foregoing and other problems are overcome and the objects of the invention are realized by a Medium Earth Orbit (MEO) communication satellite system, and by a method for providing communications between a terrestrial node and at least one user terminal (also referred to as a “mission platform”) via a MEO satellite constellation. The MEO communication satellite system comprises a MEO satellite constellation, a terrestrial node, and a plurality of mission platforms. The MEO satellite constellation comprises a plurality of satellites that are uniformly arranged in at least two subconstellations P
1
and P
2
. The satellite of each subconstellation follow a circular or nearly circular orbit. In a preferred embodiment of the invention, there are, three satellites located in subconstellation P
1
and three satellites located in subconstellation P
2
. All of the satellites are located at about the same altitude between approximately 5,000 and 10,000 nautical miles. The satellites are thus in continuous motion with respect to a point on the surface of the earth. The subconstellations P
1
and P
2
are both located in an equatorial plane. Individual ones of the satellites within subconstellation P
1
are offset from each of two adjacent satellites of subconstellation P
2
, and individual ones of the satellites within subconstellation P
2
are offset from each of two adjacent satellites of subconstellation P
1
, by a co-longitudinal angle (&thgr;) of approximately 60°. The MEO satellite constellation provides continuous coverage between approximately 70° N Latitude and 70° S Latitude for terrestrial-based mission platforms. The MEO satellite constellation also provides total coverage for satellites located at all latitudes above altitudes of approximately 150 nautical miles.
According to one aspect of the invention, satellites located it subconstellation P
1
are cross-linked on a continuous basis, forming a “ring” configuration. Similarly, satellites located in subconstellation P
2
are cross-linked on a continuous basis, also forming a “ring” configuration. By leaving the satellites in the respective subconstellations P
1
and P
2
cross-linked in this manner, problems associated with the dropping and reacquiring of cross-links between satellites are avoided.
Each satellite has a data reception and transmission system which enables the satellite to connect to the terrestrial node, the mission platforms, and to other satellites that are located within a same subconstellation as the satellite. The data reception and transmission system includes, by example, a communications controller, a communications processor, and a plurality of sets of steerable antennas. According to another embodiment of the invention, laster telescopes, optical transmitters, and optical
Barefoot Galen L.
Loral Aerospace Corp.
Perman & Green LLP
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