Space Systems/loral, LLC

Fatima Kazimi

John Scott Higham

Keith J Reckdahl

Yat Fai Leung

Tung Y Liu

Carl T Plescia

Lisa K White

A spacecraft having a body, one or more appendages coupled thereto, and a controller that implements methods that rotate the one or more flexible appendages to point it (them) towards the Sun to reduce spacecraft attitude pointing disturbances and improves spacecraft attitude pointing. The steps of the one or more appendages are timed to deadbeat the disturbance imparted to the spacecraft body. Timing of the appendage steps may be such that the periodic disturbances are phased to substantially cancel each other, or phased to decrease the magnitude of the net disturbance. The present invention also cancels solar array slew disturbances. The present invention cancels predictable disturbance torques before they produce a pointing error, improving the spacecraft pointing performance. The present invention predicts a disturbance torque exerted on the body due to the controller moving the one or more appendages, calculates a feedforward torque necessary for the controller to cancel the disturbance torque and includes the feedforward torque in the calculation of the total control torque applied to the body.

Spacecraft and appendage stepping methods that improve spacecraft attitude pointing and cancel solar array slew disturbances

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. East or West) for attitude control during limit cycling and during the North or South stationkeeping maneuver. The like directed thrusters both provide attitude stabilization and cause a predetermined change in orbit velocity.

Spacecraft East/West orbit control during a North or South

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Santa Cruz, CA, United States of America

Fatima Kazimi