Hughes Electronics Corporation

The Boeing Company

Paul D Williams

Jeremiah O Salvatore

Grant Wang

Loren I Slafer

Michael F Barsky

Thomas M Tanner

Steve Franklin

Christopher D Olsen

Wendy Wang

Troy D Wallace

Joseph M Allard

Pat Cazeau

George B Semeniuk

A spacecraft with a reaction wheel system can be autonomously safed by setting the solar wings to continuous tracking, determining a slew rate vector based on the total angular momentum, and slewing the spacecraft using the slew rate vector until commanded to stop autonomous safing. When the total angular momentum of the spacecraft to large to be handled by rotisserie, then the spacecraft is reoriented to align a suitable rotation vector with the system momentum. In a typical application, the spacecraft has a reaction wheel assembly with four wheels arranged to form a right regular pyramid. Two reaction wheels on opposite edges of the pyramid form a first pair and the two remaining reaction wheels forming a second pair. The slew axis of rotation is found by determining as a selected pair the first pair if either reaction wheel in the second pair is inoperative, otherwise determining as the selected pair the second pair and determining as the slew axis of rotation the normalized projection of the axes of rotation of the selected pair onto the base. The slew direction is determined by the sign of the total angular momentum component along the slew axis of rotation.

Safing mode for high momentum states in body stabilized spacecraft

A Stationkeeping Mode for a spacecraft having a gimballed momentum wheel for attitude control in which the stationkeeping is divided into short duration open-loop stationkeeping maneuvers to correct orbital errors, and interlaced with closed-loop momentum management operations to manage momentum stored in the momentum wheel. The sequence of open-loop pulses are spaced to deadbeat a given dominant flexible motion of the spacecraft. Between and during the thruster pulses, the gimbaled momentum wheel is maintained in the closed-loop feedback control using gyro sensor or other inertial reference measurements. Limitations on the range of the momentum storage device and its torque capability are minimized by combining the maneuver thruster pulses with pulses from other thrusters, or by reducing the fire time of one of the maneuver thrusters, to minimize momentum buildup. Thus, thrusters are used for changing orbital velocity and managing momentum through open-loop pulsing with closed-loop momentum refinement, and the momentum storage device controls the attitude with closed-loop attitude feedback.

Stationkeeping method utilizing open-loop thruster pulses and closed-loop authority limited momentum storage devices

The attitude of a spacecraft is controlled during an eclipse without the dependence on auxiliary power by configuring the spacecraft so that it will receive solar power after solar eclipse is passed. The spacecraft is then oriented with respect to a sun line. The spacecraft is then spun so that it maintains a desired angular momentum throughout the eclipse and provides passive stabilization of the attitude. After the eclipse has passed, the spacecraft power is restored and the spacecraft attitude is detected. All spacecraft units are then powered up and thereafter, normal on-station attitude is re-established and normal spacecraft operations are established.

Method and apparatus for using a momentum bias to provide spacecraft attitude stabilization during an eclipse

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Paul D Williams