Spacecraft attitude control by combination of various torquers

Abstract

This article addresses designing an implementable control law for spacecraft attitude manoeuvre using a combination of torque generating devices such as reaction wheels (RWs), magnetic torquers (MTs) and control moment gyros (CMGs). A compact equation of motion of a spacecraft installed with the torquers is derived. The singularity problem of CMGs is investigated by using a simple and practical virtual actuator methodology proposed in this article. A mixed control law is established for fine attitude control of an agile spacecraft manoeuvre. The control law allocates control torque to CMGs and RWs adequately to satisfy the control purpose. In the control torque allocation, the saturation problem of RWs is also addressed. Furthermore, a strategy for momentum restoration of CMGs by MTs to avoid singularity is suggested.

Keywords:

• control moment gyros
• singularity avoidance
• virtual actuators
• magnetic torquers
• aerospace control
• least square methods

Acknowledgements

The authors acknowledge several anonymous reviewers for their suggestions on improving this article, in particular one reviewer who provided useful and constructive suggestions. This research was supported by NSL (National Space Lab, S10801000123-08A0100-12310) program through the Korea Science and Engineering Foundation funded by the Ministry of Education, Science and Technology.