Twin control moment gyros for small satellites.

Future spacecraft will, of necessity, require rapid rotational manouvreability or agility. Such rapid retargeting manoeuvres are often subject to the physical limits of actuators. Control Moment Gyros (CMGs) are employed as primary actuators because of their high torque control capability. A typical configuration used is the 4 Single-Gimbal Control Moment (4SGCMG) pyramid mounting arrangement [48]. In the 1960s researchers studied an arrangement of CMGs called Twin Control Moment Gyros (TCMGs) [6, 11,20]. At the time these configurations were considered unsuitable for large satellite platforms, and the 4SGCMG pyramid configuration became the most common arrangement. The research in this report revisits their work, to address the suitability of TCMGs to future small satellite missions. Candidate configurations of both SGCMG and TCMG arrangements are considered as possible replacements for the 4SGCMG pyramid configuration. The candidate configurations are compared m terms of torque capability, power consumed and mass and volume occupied. In this report the principles of Single-Control Moment Gyro and Twin-Control Moment Gyro operation are studied. The study of Euler's equations and controller principles lead to the implementation of an attitude control system in SIMULINK, for which results are compared with previous work [46]. The results of a sizing/selection process show that the 4SGCMG pyramid configuration performs the best all round in terms of torque developed, power consumed and mass and volume occupied. Of the candidate configurations the 6SGCMG pyramid configuration stands out as a possible replacement for the baseline configuration. Of the TCMG configurations the 3TCMG pyramid configuration is the most promising. It is recommended that the 3TCMG pyramid configuration is investigated further. If the total mass of this system could be reduced it could be a contender as a possible replacement for the 4SGCMG pyramid configuration