Hughes Aircraft Company

James H Green

Loren I Slafer

Bernard C Soriano

A feedforward disturbance compensation system and method for use with a spacecraft that compensates for predictable disturbances exerted on the spacecraft. The invention comprises a model of the disturbance that is to be compensated, means for knowing when the disturbance will occur, and means for applying the feedforward compensation to the spacecraft in accordance with the model (a compensation profile). The present invention reduces pointing transients through the application of open-loop, feedforward compensation of actuators used to point the spacecraft. The shape of the feedforward profile is determined by an in-orbit test or is predicted by analytical means. For the in-orbit test case that compensates for an eclipse, for example, the spacecraft is flown through the eclipse once to determine the size and shape of the thermal shock disturbance and this information is stored in a spacecraft control processor. The application of the feedforward compensation is synchronized with the start and end of each day's eclipse. This may be achieved by sensing the change in battery discharge current that occurs in solar panels on the spacecraft, for example. On subsequent days, the invention anticipates the occurrence of the disturbance using the stored data. When the start or end of eclipse is detected, compensation for the expected disturbance is automatically applied to spacecraft actuators. The invention can also compensate for a large variety of known periodic disturbances other than thermal shock. These disturbances may be external or internal to the spacecraft. The present invention can also provide compensation by fine tuning the compensation magnitude and duration of the compensation, and is also applicable to both linear and nonlinear control systems.

Spacecraft disturbance compensation using feedforward control

A method of spacecraft attitude determination is proposed which calculates the bias between the usual two-cell and four-cell earth sensor measurements. During period of sun or moon interference, when the two-cell mode is selected, this bias is added to or subtracted from the two-cell measurements. This removes the step change in the calculated spacecraft roll and pitch angles when the switch is made between two and four cell modes and allows a substantially more accurate measurement to be obtained from a given sensor for the period of time for which interference would otherwise reduce sensor performance.

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Hermosa Beach, CA, United States of America

James H Green