Space Systems/loral, LLC

David J Wirthman

John Scott Higham

Thomas J Holmes

Peter Y Chu

Michel B Baylocq

David L Cielaszyk

For a switching of a magnitude of system gain in the driving of a load by a control system, a method of inhibiting formation of switching transients has a step of distinguishing between an estimate of a plant state, such as the attitude of a spacecraft, and an integral control state which allows the control system to provide actuation in response to long term disturbances, such as solar pressure, in operation of the system. In the case of a feedback configuration to the system with controller in a forward branch and an estimator in a feedback branch, a loop error signal serves to drive an actuator of the load via the controller. The method includes a further step of evaluating a portion of a controller input signal which is exclusive of an integral control state and which comprises a difference between a desired state and an estimate of the plant state. The evaluation step enables observation of an occurrence of a magnitude of the difference which falls within a range of values satisfying a criteria of minimal effect on the actuator. There is a further step of switching a value of the gain during the occurrence. Also, concurrently with the switching step, there is a scaling of an amplitude of the integral state by a factor inverse to a ratio of switched gain values.

Transient-free gain switching within error threshold

A low cost, fuel efficient solution to the problem of avoiding high yaw errors in communications satellites after station keeping maneuvers is achieved by adding a selectable function to the LTMM controller which allows it to calculate roll momentum based on measured yaw attitude error data from the yaw DIRA. The so calculated roll momentum is used to trigger roll unloads, which will reduce the yaw attitude error. This solution has the advantages that: it maintains yaw attitude error within the pointing budget; the fuel penalty is negligible; it can be made fully automatic; it can be disabled and not used; and, it requires only a very small addition to the firmware.

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Mountain View, CA, United States of America

David J Wirthman