Attitude reacquisition of a gravity-gradient control-moment-gyro stabilized spacecraft
Clark E. Stohl, Bruce E. LeRoy, United States. National Aeronautics and Space Administration, Lewis Research Center
National Aeronautics and Space Administration, 1970 - Science - 29 pages
Impulsive or time-decaying disturbances of sufficient magnitude will cause a gravitygradient control-moment-gyro stabilized spacecraft to tumble. A procedure for operating a thruster system by ground command to perform reacquisition was functionally designed and evaluated on an analog computer. When the disturbance has ceased, an on-board thruster system is used to aline the total angular momentum vector of the spacecraft in an orientation that allows the control-moment gyros to damp all spacecraft motion into a single axis. For a spacecraft in a Sun-synchronous orbit, a procedure was found to shorten the time for attitude reacquisition by using a solar array for crude attitude information.
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alined analog computer analog simulation shows angular momentum vector attitude orientation attitude reacquisition axis system body axes body rates bring the pitch CMG gimbal angles CMG's column matrix cone to negative coning conditions control-moment gyros control-moment-gyro gimbal control-moment-gyro rotor damped to zero despin direction cosines error Euler equations force the yaw Gimbal stops gravity gradient gravity-gradient CMG gravity-gradient torques ground command impulse KCMG minimum kinetic energy misalinement moment-gyro moments of inertia mounting angles negative pitch cone negative pitch rate negative pitch torque negative yaw cone nonzero on-board thruster system orbit angular rate Orbit eccentricity Positive pitch cone principal body pulse pure negative pitch quaternion rad/sec rate to zero reacquisition procedure roll and yaw roll rates sec Figure Semimajor axis SERT II mission SERT II spacecraft solar array solar panels Solar pressure spacecraft to tumble Stiction Stohl Sun-synchronous orbit telemetry thruster shutdown thrusting torques due yaw axis