Abstract: In this paper the digital computer attitude determination and control system used in chinese returnable satellite for scientific exploration and technical experiments is described.The attitude determination algorithm and the jet control logic in phase plane are the major contents of this paper. The concept of quasi-steady gain matrix is introduced for periodic filtering system and a simplfied filtering algorithm has been developed. In the digital autopilot the variable step deadband control logic is developed and it remarkably improves the control quality. Some flight data are presented.The control system performed successfully in the flight test.

Key words: Digital control system, Attitude control, Spaceborne computer