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: A four-axis gyro stabilized inertial reference system. The system comprises a nested gimbal configuration, which includes a platform and three successively larger and concentrically disposed inner, middle and outer gimbals and an outer casing. The platform and inner, middle and outer gimbals are each configured to permit rotation about an associated axis with that axis being perpendicular to the corresponding axis of the neighboring gimbal or platform. The system further includes a platform stabilizing means for maintaining the platform in a substantially fixed spatial orientation, independent of the spatial orientation of the outer casing and over a predetermined range of angular rates.

Abstract: A reactionless drive system is disclosed comprising in combination a base, a torquer mechanism, the stator portion of which is affixed to the counter-rotational inertia member and accepting control signals from sources external to the system. A rotatable member, coupled to the torquer, is driven in a first direction. A torque compensator consisting of stator and rotor members is coupled between the base and the first mentioned rotatable member in one instance, and to an oppositely rotating member in another instance. All the foregoing components act together to maintain angular momentum of the system during its operative mode to a value of substantially zero. An electronic subsystem is provided which senses the angular velocities of the rotating members and provides a feedback signal to the torque compensator.

Abstract: In a strapped-down gyroscope space vehicle attitude control system, a method and apparatus are provided for gyro drift and input axis misalignment error compensation employing a sun and a star tracker and preselected vehicle calibration maneuvers. During the preselected maneuvers using the sun and a star as external references, the outputs of two-axis strapped-down gyroscopes nominally aligned with the optical axis of the sun and star trackers are measured. The measured outputs provide gyro drift calibration, roll, pitch and yaw axis scale factors and values corresponding to the degree of nonorthogonality between the roll axis and the pitch and yaw gyro input axes and the nonorthogonality of the roll and pitch axes relative to the yaw axis. With the calibration data so obtained stored in a special purpose digital computer, the vehicle is then rolled and yawed through precomputed angles as modified by the calibration data to acquire a target without further recourse to external references.

Abstract: A system for autonomously unloading accumulated angular momentum on space craft reaction wheels in the attitude control systems with external torques generated by the interaction of spacecraft magnetic dipoles with the earth's magnetic field.An onboard computer receives reaction wheel speed information, wheel speed threshold and geomagnetic latitude information and controls magnetic dipoles that will create a spacecraft torque and desaturate reaction wheels in a closed loop system.

Abstract: Three-axis attitude control of a substantially zero momentum satellite is achieved by a control system which includes three mutually orthogonal reaction wheels and a fourth backup reaction wheel. The backup wheel is mounted on an axis which is skewed with respect to the axes of the three mutually perpendicular wheels. Spacecraft attitude is normally maintained by torques developed by the mutually orthogonal wheels. If one and only one of the orthogonal wheels should fail to correct the attitude error on its associated axis, the backup wheel is caused to rotate and develop a torque to maintain spacecraft attitude.

Abstract: An attitude control system for a substantially zero momentum spacecraft is arranged to minimize the attitude errors during periods of reaction wheel speed reversals. Wheel speed is sensed by a suitable device such as a tachometer or Hall elements. Spacecraft three axis attitude is sensed by suitable sensors such as sun sensors, star sensors, gyroscopes or earth horizon sensors. A control network is provided to generate the wheel torque commands necessary to maintain proper three axis attitude. During periods of wheel speed reversal, the control network includes appropriate compensation terms and corrections to the wheel torque command.

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.