Space Systems/loral, LLC

Ford Aerospace & Communications Corporation

John A Lehner

Thomas J Holmes

Donald W Gamble

Christopher D Rahn

Kenneth L Lebsock

A satellite stabilization system compensates for the destabilizing torque introduced by solar radiation pressure by the emplacement of tabs of material angled relative to the back surfaces of the antenna reflectors to intercept solar rays. The material of the tabs interacts with the solar radiation in substantially the same manner as the interaction of the material on the back surface of each antenna reflector to produce a radiation pressure and consequential increment in a torque about an axis of the satellite. Each of the tabs is constructed in the manner of a plate or disk, and is attached by means of a spring mount to the back surface of one of the reflectors. The reflectors are angled relative to each other, as well as to a body of the satellite which holds feeds for illuminating the reflectors, for directing beams of radiation from the feeds towards the earth. Due to the angulation of the reflectors to each other, the total solar energy incident upon a pair of of the reflectors is generally unequal, this resulting in a net torque from the solar radiation pressure which tends to rotate the satellite. By virtue of the angulation of the tabs relative to the reflectors, an increased amount of solar radiation is received by the reflector which is angled away from the sun's rays, thereby to equalize the torque from both of the reflectors.

Satellite stabilization system

The present invention is a method and apparatus to control a pointing trajectory of an aim point with respect to one or more targets for a momentum bias spacecraft in an orbit inclined relative to an equatorial geosynchronous orbit wherein the spacecraft is provided with an onboard computer capable of using orbit information available to the spacecraft and spacecraft hardware to move the aim point according to a predetermined tracking model which may be either time-varying or invariant. The tracking model allows the controller to remove short-term nutational and long-term orbit rate dynamical disturbances, beyond simple-order sinusoidal functions having a single frequency.

Method and apparatus for inclined orbit attitude control for momentum

Disclosed is a method and apparatus estimating yaw error and roll and yaw disturbance torques from measured roll error and yaw momentum on a continuous on-orbit basis in an orbiting satellite. The information thus obtained can be used to continuously correct for the yaw error by means of, for example, activating a magnetic torquer. Two control loops are used in this invention, a fast loop to damp nutations by changing momentum wheel speed, and a slow loop of the Luenberger observer variety. The latter is a yaw error correction loop which also serves to unload yaw momentum. The satellite in which the invention was first incorporated is of the type having three momentum wheels, all situated in the plane orthogonal to the roll axis. In normal operation, two wheels, each having major momentum component along the pitch axis and minor momentum component along the yaw axis, are operable. A third backup wheel aligned along the yaw axis becomes operable only in the eventuality that one of the primary wheels suffers a breakdown during the life of the satellite. The slow speed yaw loop is used to adjust a magnetic coil torquer. It can be implemented in a number of forms including a hard-wired analog form or a digital computer with certain constant scaling factors programmed into the memory of the computer.

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Sunnyvale, CA, United States of America

John A Lehner