Patent ID: 7246775

Claim:
An on-board autonomous orbit transfer system for transferring a spacecraft from an initial orbit to a target orbit, the system comprising: attitude sensors; an inertial measurement unit; a GPS receiver for receiving externally produced GPS signals and outputting GPS position data signals; control actuators for controlling spacecraft momentum and spacecraft thrust in response to received torque commands; a control processing system configured to operate repetitively during the transfer of the spacecraft from the initial orbit to the target orbit, the control processing system being comprised of: orbit determination logic configured to receive GPS position data signals from the GPS receiver and to generate current orbit elements data; thrust trajectory generation logic configured to receive the current orbit elements data from the orbit determination logic and to generate an updated inertial thrust trajectory vector by propagating a set of estimated final orbit elements data from the current orbit elements data, generating a set of orbit error elements based on a difference between the estimated final orbit elements data and target orbit elements data corresponding to the target orbit, updating a co-state vector (λ) based on the orbit error elements and generating the updated inertial thrust trajectory vector based on the updated co-state vector (λ); target frame generator logic configured to receive the updated inertial thrust trajectory vector and to generate an updated target inertial reference frame such that a nominal thrust direction is parallel to the updated inertial thrust trajectory vector when the spacecraft body axes are aligned with the updated target inertial reference frame; attitude and rate error generator logic configured to receive current attitude and rate information based on signals from the attitude sensors and the inertial measurement unit, and to generate current spacecraft attitude and rate errors with respect to the updated target inertial reference frame; attitude and momentum controller logic configured to receive the current spacecraft attitude and rate errors and a reaction wheel momentum error, and to generate updated torque commands for attitude and momentum control of the spacecraft; and torque distribution logic configured to receive the updated torque commands and to distribute the updated torque commands to the control actuators for controlling the attitude and momentum of the spacecraft to align the spacecraft body axes with the updated target inertial reference frame.