Abstract: A method for operating an orbiting spacecraft includes the steps of (a) changing a mass distribution of the spacecraft from a first mass distribution for setting a first principal moment of inertia of the spacecraft along a first axis approximately equal to a second principal moment of inertia of the spacecraft along a second axis, thereby minimizing a gravity gradient torque about a third axis; (b) performing a desired activity while the gravity gradient torque about the third axis is minimized; and (c) resetting the mass distribution back to the first mass distribution at a completion of the desired activity. The spacecraft includes a plurality of solar array panels, and the step of changing is accomplished by varying a position of at least two of the solar array panels away from a sun-pointing configuration. Also disclosed is a method for stabilizing the spacecraft to resist a rotation about an axis by varying the positions of solar array panels.

Abstract: A system and method employ a sensing of the attitude or orientation of a spacecraft for correcting the orientation of a line of sight of an instrument carried by a spacecraft to compensate for a transient perturbation in the attitude of the spacecraft. The instrument may be a microwave antenna for communicating with a station on the earth, or a camera for viewing the earth. The transient perturbation in the orientation, such as may be caused by the firing of a thruster of the spacecraft, is extracted from a measurement of the spacecraft orientation, such as the orientation relative to the earth. The line of sight of the instrument is reoriented by injection of an incremental orientation equal and opposite to the transient perturbation. The application of the incremental orientation can be accomplished in mechanical fashion, in the case of an antenna mechanically mounted to the spacecraft, and electrically, as in the case of a phased array antenna carried by the spacecraft.