Abstract: Position control methods are described for satellites and spacecraft for controlling transition from thruster control to momentum wheel control in a three-axis stabilized spacecraft. Transition from a high-bandwidth, high-torque thruster-controlled stationkeeping (SK) mode to a low bandwidth, low torque momentum wheel On-Orbit Mode is carried out. Usually a unique threshold entry method to automatically initiate the transition mode at the point with the most favorable dynamics. Also, the disclosed method eliminates the use of nutation in conjunction with a deadbeat thruster sequence to correct the spacecraft attitude to improve pointing performance and significantly shorten the time spent in the transition mode.

Abstract: A system for achieving spacecraft camera (1, 2) image registration comprises a portion external to the spacecraft and an image motion compensation system (IMCS) portion onboard the spacecraft. Within the IMCS, a computer (38) calculates an image registration compensation signal (60) which is sent to the scan control loops (84, 88, 94, 98) of the onboard cameras (1, 2). At the location external to the spacecraft, the long-term orbital and attitude perturbations on the spacecraft are modeled. Coefficients (K, A) from this model are periodically sent to the onboard computer (38) by means of a command unit (39). The coefficients (K, A) take into account observations of stars and landmarks made by the spacecraft cameras (1, 2) themselves.