Telecommunications – Carrier wave repeater or relay system – Portable or mobile repeater
Reexamination Certificate
1999-03-03
2001-08-14
Urban, Edward F. (Department: 2683)
Telecommunications
Carrier wave repeater or relay system
Portable or mobile repeater
C455S013200, C455S430000, C701S013000
Reexamination Certificate
active
06275677
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to satellite control systems and, more particularly, to a method and apparatus for managing the configuration of a fleet of satellites in low earth orbit.
Satellite communications systems which comprise one or more communications satellites that travel about the globe in non-geosynchronous orbits and one or more ground stations located in various regions of the world are known. A given satellite and a given ground station can connect to each other to effect communications when they are in view of each other. However, they generally will not be able to communicate properly unless they are configured to operate according to the same communications protocol.
Different communications protocols are used in different regions of the world. A ground station located in a particular region is configured to operate according to that region's communications protocol. Since the satellites are contemplated to fly over, and communicate with, ground stations in different regions, it is important that the satellites can be reconfigured, on-the-fly, according to the local communications protocols of the regions they fly over and the ground stations located therein.
Direct command control systems whereby a satellite can be reconfigured by executing commands transmitted to the satellite from a ground station are known. However, in some systems, the satellites are receptive to such direct commands from some, but not all, ground stations. For example, a satellite may be receptive to direct command by ground stations located in the United States, but not those located in other parts of the world.
In situations where a satellite needs to adopt only two protocols throughout its orbit, one for use when flying over the command-receptive region and another for all other regions it flies over, the foregoing limitation would not present a significant obstacle to operation. The satellite could simply be reconfigured for the required protocol as it approached and departed from the command-receptive region.
In practice, however, it is likely that a satellite's orbit will take it over several different regions using several different protocols while the satellite is out of sight of, and therefore cannot receive commands from, a ground station in a command-receptive region. To accommodate such situations, the satellite must be reconfigurable by means other than direct control in order to maximize its availability as it travels throughout its orbit.
One known method for reconfiguring a satellite by means other than direct control involves using known information about the satellite's orbit to calculate which regions it will be flying over at which times, and to thus determine which communications protocol it must be configured for at a particular time. This information can be used to generate a command set which can be uploaded to the satellite from a ground station in a command-receptive region. The satellite's on-board computing facilities can then execute the appropriate command set at the appropriate time to reconfigure the satellite, as needed, as it travels throughout its orbit.
While the foregoing method is effective, it requires that the times that the satellite will enter and exit the regions of interest be precalculated on the ground and uploaded to the satellite. Based on the limited computing and storage resources on board the satellite and on other factors, such information generally needs to be calculated and uploaded to the satellite regularly. It may be necessary to upload hundreds of time-based command sets to each satellite every day. This places a significant burden on the ground control staff and hardware, as well as on the limited computing and storage resources on board the satellite. Furthermore, the command upload process is subject to error. The greater the number of commands that must be uploaded, the greater the potential for errors to occur.
Accordingly, it would be desirable to provide a method and apparatus by which a satellite can reconfigure itself autonomously to adopt the local communications protocol of the regions it flies over, which places a minimal burden on the satellite hardware and control staff.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method and apparatus by which a satellite can efficiently reconfigure itself to adopt a predetermined communications protocol based on its current geographical position.
A satellite ground controller specifies a region on the globe where a particular communications protocol configuration is required by denoting a point on the earth's surface and a radius defining a circle around that point. This data is uploaded to the satellite from a ground station from which the satellite can receive commands. A computer on-board the satellite stores the data defining the region in the form of a dot product derived from the point and radius described above.
Using a global positioning system (GPS) unit or other on-board apparatus for determining geographical position, the satellite monitors its geographical position at regular intervals. Also at regular intervals, the satellite's on-board computer calculates a dot product of a vector from the Earth's center to the point defining the center of the region (for which a particular communications protocol configuration is required) and a vector from the Earth's center to the satellite's current geographical position. The computer compares the stored, regiondefining dot product to the satellite-position dot product at regular intervals. Based on the comparison, the computer determines whether or not the satellite is within the defined region. If the computer deems that the satellite has entered the defined region, it executes a command set which configures the satellite to operate with the defined region's communications protocol. When the satellite exits the defined region, another command set is executed, returning the satellite to a default configuration, or to a configuration supporting the communications protocol of an adjoining defined region.
In another embodiment of the invention, the regions are global areas defined in terms of, for example, latitude and longitude, rather than as circular areas. Data, such as latitude and longitude coordinates, defining such regions are be stored on-board the satellite. The satellite's computer compares the stored data to regularly obtained data defining the satellite's position. If the computer deems that the satellite has entered the defined region, it executes a command set which configures the satellite to operate with the defined region's communications protocol. When the satellite exits the defined region, another command set is executed, returning the satellite to a default configuration, or to a configuration supporting the communications protocol of an adjoining defined region.
The method and apparatus of the present invention can be applied to a fleet of satellites, as well as to a single satellite. Furthermore, each satellite can store data defining a predetermined number of regions. The satellite's on-board computer can compare the data defining the satellite's current location to the data defining the defined regions at regular intervals, and can execute a command set to configure the satellite to operate with the protocol of the defined region over which it is flying at a particular time.
In an embodiment of the invention, a satellite has plural facilities for receiving and transmitting data. A first set of transmitting and receiving equipment can be configured according to the communications protocol of a first region and can communicate with a ground station therein. Simultaneously, a second set of transmitting and receiving equipment can be configured according to the communications protocol of a second region and can communicate with a ground station therein.
REFERENCES:
patent: 5109346 (1997-10-01), Wertz
patent: 5187805 (1993-02-01), Bertiger et al.
patent: 5574660 (1996-11-01), Die
Jackson Blane J.
Jennifer & Block
Orbcomm Global, L.P.
Urban Edward F.
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