Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Aeronautical vehicle
Reexamination Certificate
2000-06-06
2001-11-13
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Aeronautical vehicle
C244S158700, C244S164000, C455S012100
Reexamination Certificate
active
06317661
ABSTRACT:
BACKGROUND
The present invention relates generally to satellites, and more particularly, to a methods for controlling the orbit of an inclined, eccentric, geosynchronously orbiting satellite.
The assignee of the present invention manufactures and deploys communication satellites that orbit the Earth in geosynchronous orbit. In particular, certain satellites are to be located in inclined, eccentric geosynchronous orbits.
More particularly, the satellites must maintain their orbits within a certain tolerance in order to maintain constellation integrity. The stationkeeping strategy for the satellites requires that no maneuvers be performed in the operational zone while yaw steering is being performed, because due to the rotating s/c body, the thrusters are not properly aligned with the desired thrust vector.
In order to meet this constraint, all the major stationkeeping maneuvers must take place in the two periods per year coinciding with orbit normal attitude operations. During these periods, all required stationkeeping maneuvers must be performed while observing the primary and derived requirements.
It would therefore be desirable to have methods that provides the ability to controlling the orbit of such an inclined, eccentric geosynchronously orbiting satellite. Accordingly, it is an objective of the present invention to provide for improved methods for controlling the orbit of an inclined, eccentric, geosynchronously orbiting satellite.
SUMMARY OF THE INVENTION
To accomplish the above and other objectives, the present invention provides for methods that control the orbit of an inclined, eccentric geosynchronous satellite by maintaining its perigee location while simultaneously preventing a reference point on the orbit from moving too far relative to a normal position over the Earth. Doing this also changes the semimajor axis of the orbit, which when perturbed away from the geosynchronous value, creates a drift rate relative to the Earth.
To correct the argument of perigee and maintain the prescribed tolerance on ground track position, several maneuvers must be performed to control the drift rate. The relationship between maximum allowable velocity change and time between maneuvers is defined by the required correction to the argument of perigee and the allowable motion of the reference point.
A first exemplary method comprises the following steps. An estimate of the current orbit parameters is determined. The desired change to the orbit is determined. N points on the orbit are located which allow the desired orbit correction to be achieved. The velocity changes to be performed at each of the N points which achieve the orbit correction is determined. If the velocity changes cause the longitude deadband to be exceeded, the method
10
further comprises the step of increasing the value of N and repeating the above steps.
In the method, the orbit has a period of substantially one day, and the orbit has substantially repeating ground track. The reference point may be the sub-satellite longitude at the instant the satellite is at any given true anomaly between 0° and 360° (e.g., perigee or apogee). The reference point may also be a sub-satellite longitude at the instant the satellite is at any given argument of latitude between 0° and 360° (e.g., ascending node). The number of orbits allowed between the two maneuvers in a given pair may be selectable (which impacts the allowable velocity change). The orbit inclination is preferably greater than 7 degrees.
REFERENCES:
patent: 5855341 (1999-01-01), Aoki et al.
patent: 6019318 (2000-02-01), Cellier et al.
patent: 6089507 (2000-07-01), Parvez et al.
Bruno Michael J.
Kemper Brian
Pervan Sherry
Cuchlinski Jr. William A.
Float Kenneth W.
Marc-Coleman Marthe
Space Systems Loral, Inc.
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