Abstract: Control of an active three-axis multiple-wheel attitude control system is provided with a bias momentum to achieve stiffness about the pitch axis. With this stiffness, the system overcomes the inherent inability of a zero momentum system employing the sun as its yaw reference to be provided with this yaw reference during the periods encompassing satellite high noon and midnight (i.e., approximate coalignment of the sun line and the local vertical). The satellite attitude is normally maintained by angular momentum exchange developed by three or more reaction wheels positioned on the satellite. The control mechanism is arranged to provide net angular momentum in the pitch axis wheels to achieve the momentum bias or stiffness along the pitch axis, whereas the time average of the angular momentum about the roll and yaw axes is substantially zero.

Abstract: Spacecraft nutation caused by applying propulsive forces to a spacecraft along an axis which does not pass through the spacecraft's center of gravity is eliminated by a signal responsive control system which operates the propulsive forces for a predetermined time period which corresponds to an integral number of nutation periods.

Abstract: A pair of reaction motors or thrusters connected to spin-stabilized spacecraft are used to reorient spacecraft attitude without affecting spacecraft velocity. The spacecraft reaction motors are arranged to produce a couple in response to an attitude reference signal without applying a spacecraft velocity changing force to the spin-stabilized spacecraft.

Abstract: The orientation maneuver of a bias momentum stabilized spacecraft is achieved without the need of attitude determination by sensors and gyros and the like and without the conventional spin-down and spin-up procedures. The spacecraft is provided with a momentum wheel mounted in perpendicular relation to the axis of maximum moment of inertia. The wheel is initially de-energized during the time the spacecraft is initially launched from the ground launching platform until it is desired to orient the spacecraft in the final orbit. The momentum wheel, when energized from zero rotation to increasing rotation speeds, causes the rotation of the spacecraft from spinning about the maximum moment of inertia axis to an axis parallel to the momentum wheel axis with the final convergence of the wheel axis to the momentum vector being effected by energy dissipation in a nutation damper.