A Turn By Turn Combined Wheel-Torquer Actuated Attitude Control System for Space Capsule Recovery Experiment (SRE)

Abstract

This paper describes a novel attitude control system for the Spacecraft Recovery Experiment. The objective of the attitude control system is to stabilize and maintain the pointing of each of the three axes of SRE-II spacecraft within a pre-defined specification. The specification is based on the requirement projected by the payload. In this design, two axes are controlled by actuating magnetic torquers and one axis is controlled by actuating a reaction wheel. The magnetic torquer based control loop uses the Earth’s magnetic field for producing the torque. The magnetic torquers have to control the two axes and also maintain the momentum of the wheel within the safety limits. Due to the cross axes action of the torquer based control, each magnetic torquer produces a control component as well as a disturbance component which makes the control challenging. Also the control torque cannot be produced in the direction of the instantaneous magnetic field thus rendering the system as an under-actuated system. The present design is based on the allocation of the control action in a turn by turn fashion and the decision is based on the attitude error and the availability of the magnetic field, thus yielding an optimum design within the limitations imposed by the system.