Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Aeronautical vehicle
Reexamination Certificate
2000-03-17
2001-11-06
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Aeronautical vehicle
C244S158700
Reexamination Certificate
active
06314344
ABSTRACT:
BACKGROUND
The present invention relates generally to spacecraft orbit maintenance systems, and more particularly, to an automated spacecraft orbit compensation system designed for a geosynchronous (GEO) satellite.
The assignee of the present invention manufactures and deploys spacecraft that orbit the Earth. Most stationkeeping is performed with a human operator which results, in substantial manpower costs when the stationkeeping is performed frequently. U.S. Pat. Nos. 5,528,502 and 5,687,084 entitled “Satellite Orbit Maintenance System” disclose an automated orbit-maintenance system which is located on-board a spacecraft.
More particularly, U.S. Pat. Nos. 5,528,502 and 5,687,084 entitled “Satellite Orbit Maintenance System” disclose techniques for maintaining a satellite in an assigned Low Earth Orbit (LEO) without control or intervention from the ground. Autonomously obtained navigational data provide a measurement of the actual orbit in which the satellite is traveling. So long as the measured orbit conforms to a desired orbit to within a preselected tolerance, periodic corrections of equal magnitude are made to the satellite's velocity, based on a prediction of the effect of atmospheric drag on the orbit.
Measurement of the orbit is made by observation of the time that the satellite passes a reference point in the orbit, such as by crossing the ascending node. If the measured orbit departs from the desired orbit by more than the preselected tolerance a velocity correction of a magnitude different from the one based on prediction is applied to the satellite.
For a decaying orbit, the magnitude of the velocity correction is increased above the correction value based on prediction. For a rising orbit, the magnitude of the velocity correction is decreased below the value based on prediction. It may be reduced to zero in low earth orbit (LEO) if the prediction shows that the atmospheric drag will bring the measured orbit back within the preselected tolerance range.
Accordingly, it is an objective of the present invention to provide for an improved automated spacecraft orbit compensation system that is not located on-board a spacecraft, and does not rely on natural perturbations to bring the measured orbit back within a preselected tolerance range. The present invention is also geared toward GEO rather than LEO satellites.
SUMMARY OF THE INVENTION
To accomplish the above and other objectives, the present invention provides for an improved automated spacecraft orbit compensation system and method that maintains a spacecraft in a desired orbit. The present spacecraft orbit compensation system and method is automated to minimize human intervention.
The automated spacecraft orbit compensation system includes apparatus for determining the current orbit, apparatus for determining the duration and location of orbital thruster firings to correct the orbit, and apparatus for communicating between the satellite and the ground. Each of the apparatus are located at a ground station.
More particularly, an orbit determination system is coupled between an antenna and the planning system The orbit determination system generates the current orbit estimate, while the planning system comprises a process that computes a thruster bum plan for the following N days. A transmitter is coupled between the planning system and the antenna. The transmitter is used to transmit the orbit and burn plan information to a control processor on-board the spacecraft. The control processor fires thrusters on the spacecraft to control the orbit of the spacecraft. The entire process is repeated at regular intervals (less than N), computing a new orbit and uploading the new thruster burn plan each time.
The method generates an estimation of the current orbit. The estimated orbit is used to compute a thruster burn plan for the following N days. The thruster burn plan is uploaded to the spacecraft. The above steps are repeated at regular intervals (generally every day, but always less than N).
There are various methods of estimating the orbit. One way is through a modified version of conventional ranging. Ranging antennas generate data indicative of the range of the satellite from the antenna. In addition, spacecraft telemetry from the last bum is also collected. A filter or sequential batch process is used to estimate the orbit from the last orbit estimate, the range data, and the telemetry. The burn can also be estimated if desired. Using the spacecraft telemetry reduces the amount of range data required and enhances the accuracy of the orbit.
Since the process is repeated at regular and frequent intervals, the thruster burn plan can be computed in a manner similar to a feedback control system. Orbit errors can be corrected gradually over the span of several days rather than corrected all at once. This allows for a more robust system that minimizes the amount of propellant used.
The present invention results in substantial manpower savings over human-operated systems. Unlike U.S. Pat. Nos. 5,528,502 and 5,687,084, the present invention does not require the system to be located on the spacecraft which has several advantages. For example, non-flight hardware can be used which provides better performance at a lower cost, and allows for hardware maintenance/repair and easy software updates.
REFERENCES:
patent: 5109346 (1992-04-01), Wertz
patent: 5528502 (1996-06-01), Wertz
patent: 5687084 (1997-11-01), Wertz
patent: 5992779 (1999-11-01), Gamble et al.
patent: 5992799 (1999-11-01), Gamble et al.
patent: 6023291 (2000-02-01), Kamel et al.
patent: 6142423 (2000-11-01), Wehner
Higham John S.
Sauer Birgit
Cuchlinski Jr. William A.
Float Kenneth W.
Marc-Coleman Marthe
Space Systems Loral, Inc.
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