Hughes Electronics Corporation

Hughes Aircraft Company

Stuart F Bockman

Douglas J Bender

Samir F Bassily

Bruce N Eyerly

Christopher M Cosner

John Joseph Anagnost

William L Burkett, Jr

Thomas F Brozenec

George N Young

William A Nakano

Kenneth R Obert

Tiffany Bowles

An agile steering control arrangement is provided for a spacecraft having a skewed scissor pair control moment gyro (SSP CMG) attitude control arrangement gimbaled with respect to the spacecraft body. The control arrangement includes a steering control process which converts arbitrary spacecraft boresight commands into spin torque and gimbal rate commands for a pair of spinning CMG. The steering control process generates suitable CMG torque commands based on requiring that the boresight nominally follow an arbitrary boresight trajectory described by required angular accelerations for the boresight together with one of various requirements on yaw motion. In this manner, a SSP CMG actuated spacecraft can be steered having tight boresight control while allowing a certain amount of error in yaw about the desired boresight. If spin motor capacities are exceed, new gimbal rates are determined based on saturation wheel spin torque.

Steering control for skewed scissors pair CMG clusters

A sun-referenced safe-hold control system for momentum-biased satellites employs a safe-hold processor responsive to a set of sun sensors to detect attitude errors of the solar wings. Safe-hold processor provides independent control logic which rotates the solar wings to ensure that sunlight is maintained incident on the solar wings to maintain solar power in the safe-hold mode. In addition, the safe-hold processor provides independent control of the momentum wheel to place the spacecraft body in a passively stable nutational state. Passive nutational stability inherent in a momentum-biased satellite about two axes of the spacecraft enables the safe-hold processor to actively control the spacecraft about only one of its axes. The spacecraft safe-hold control system increases the period in which spacecraft health is guaranteed by adding active, closed-loop control of the solar wings.

Sun-referenced safe-hold control for momentum biased satellites

A rigid panel solar array for a spacecraft. The layers of materials for the panels are selected and oriented to control the net coefficient of thermal expansion in the array's longitudinal direction. Some of the layers are discontinuous and softly coupled to the others by flexible adhesive materials. The panels are interconnected with hinge members which are positioned at appropriate locations and with appropriate degrees of freedom so that thermally induced transverse bending does not cause transverse motion of the center-of-mass of the panels.

Low disturbance solar array

A control system (40) and procedure (50) that uses repetitive control to control repetitive error sources such as result from the phenomenon of thermal shock experienced by a spacecraft (10). Repetitive control is a 'learning algorithm' that substantially eliminates errors in a stable control system (43) that performs highly repeatable tasks. The repetitive control system (40) and procedure (50) employs a repetitive signal generator (41) (G.sub.r), to store a sensed short-term error signal during each cycle and to process it to generate a signal that compensates for the error. The repetitive control system and procedure integrates (52) the error signal over several cycles, multiplies (53) the integrated value by a predetermined gain factor, and sums (54) it with the sensed error signal before the sensed error reaches the stable controller (43). An output filter (42), G.sub.f, which may be a multirate-sampling output filter, may be used to increase stability robustness of the repetitive control system (40) and procedure (50). The present repetitive control system (40) and procedure (50) substantially eliminates pointing error caused by thermal shock disturbance, for example. The repetitive control system (40) and procedure (50) 'learns' the errors that exist in the system and over several cycles, converges on a substantially exact compensation for these errors. Implementation of the present control system (40) and procedure (50) allows the spacecraft (10) to maintain precise pointing throughout an eclipse and thereby allow the spacecraft (10) to perform its mission despite the presence of thermal shock disturbances or errors caused by other repetitive error sources.

Repetitive control of thermal shock disturbance

A multi-loop control system for a gimballed antenna that employs devices for measuring both absolute line-of-sight (an autotrack receiver or beacon tracker) and relative angular position (a resolver). The control system uses both signals simultaneously, thereby increasing the performance and pointing accuracy capability. Two control loops operate simultaneously to provide for optimum performance. The first loop is an inner high-bandwidth control loop that uses the relative gimbal angle measurement to control pointing of the antenna along a precommanded profile. The inner loop may run alone to provide for coarse pointing. When available, the line-of sight measurement is used in a low-bandwidth outer loop to provide corrections to the command profile of the inner loop. Control logic is provided that allows switching between several control modes. By using the present invention, antenna tracking control performance is maximized, especially in the presence of attitude disturbances of a spacecraft or significant flexible interactions.

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Torrance, CA, United States of America

Stuart F Bockman