The initial architecture and controller design for a small satellite is proposed, using a two degree of freedom gyroscope on a two axis stabilized platform for pointing and estimating the spacecraft body angular rates, with a second gyro mounted on the spacecraft which measures the third spacecraft body rate component. The spacecraft configuration includes a three axis reaction wheel assembly and a large aperture optic fixed to the spacecraft which must be commanded to acquire an Earth-fixed target. The stable platform and optical payload have the same line of sight, and the approach developed was to command the platform as a free body to line its unit target vector line of sight with its line of sight; the spacecraft then is commanded to follow the platform and maintain the angular displacement between the platform and spacecraft near null. The platform controller is designed using nonlinear feedback to linearize and decouple the input/output mapping using the target unit vector direction cosine components as the controlled variables which are controlled in a linear manner by use of a fixed-time optimal controller. The spacecraft then follows the platform rate commands by commanding the reaction wheel assembly based on the commanded rates to the stable platform and a platform motion compensation feedforward command which regulates the angular displacement between the platform and spacecraft. The computed torque to the reaction wheels is accomplished by a nonlinear controller which linearizes and decouples the basic rigid body equations of motion where the controlled variables are the angular rates of the spacecraft.
High Accuracy Attitude Control of a Spacecraft Using Feedback Linearization
1992
150 pages
Report
No indication
English
Astronautics , Satellite attitude , Altitude controllers , Feedback , Angles , Apertures , Artificial satellites , Configurations , Displacement , Equations of motion , Gyroscopes , Inertia , Line of sight , Mapping , Models , Nonlinear systems , Optics , Payload , Platforms , Rates , Simulation , Spacecraft , Stabilized platforms , Targets , Tensors , Time , Torque , Uncertainty , Variables , Vision , Wheels , Theses
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