Lisa W White

US Patent:

54002524, Mar 21, 1995

Filed:

Dec 22, 1992

Appl. No.:

7/994769

Inventors:

Fatima Kazimi - San Carlos CA
Lisa K. White - Menlo Park CA
Carl T. Plescia - Sunnyvale CA

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

B64G 126
G06F 1550

US Classification:

364434

Abstract:

A 3-axis stabilized spacecraft has primary and secondary attitude control thruster strings, thrusters in each string exerting roll, pitch and yaw torques. The primary and secondary thruster strings are similar and exhibit paired thrusters oriented on opposite sides of an East/West axis passing through the spacecraft. A stationkeeping input energizes the North or South thrusters to cause a maneuver of the spacecraft along a North/South axis, the thrusters effecting a perturbation in the spacecraft's attitude. An attitude control system energizes at least a primary string thruster to counteract the attitude perturbation, the thruster being oriented so as also to cause a change in the spacecraft's East/West orbit velocity. A processor is responsive to the change in East/West orbit velocity reaching a deadband limit value to deactivate the primary string thruster and to activate the secondary string thruster which exhibits a similar torque effect on the spacecraft as the primary string thruster but is oriented so as to cause an oppositely directed change in the spacecraft's East/West orbit velocity. The spacecraft further includes a system for enabling all primary and secondary thrusters that exert a force in one direction (i. e.

US Patent:

51249251, Jun 23, 1992

Filed:

Jan 16, 1990

Appl. No.:

7/464799

Inventors:

Donald W. Gamble - Menlo Park CA
Lisa K. White - Menlo Park CA
Thomas J. Kelly - Franklin OH
Ronald H. Bingaman - Davis CA

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

B64G 124

US Classification:

364459

Abstract:

A method for East/West stationkeeping of a geostationary satellite maintains the osculating value of longitude from exceeding a specified deadband for a specified drift period between maneuvers. In the planning, the mean longitude, the mean drift rate and the mean eccentricity vector are calculated and then maneuvers are executed to maintain the values below a magnitude such that the osculating longitude will be within the specified deadband over a specified drift period. The target conditions are achieved through a plurality of maneuvers which initiate a period of free drift which lasts for a specified number of days. During the free-drift period, longitude remains within its deadband, and no additional maneuvers are needed or are performed. The method has the advantage that it can take into account limitations on thruster on-time by allowing for a generalized number of stationkeeping maneuvers.