Abstract
Recently, JAXA initiated the study of a new type of earth observation satellite which can select observation areas by changing the attitude of the satellite. Because this kind of satellite requires a high-torque attitude control system, a control moment gyro (CMG) is considered as an actuator candidate. The maximum torque produced by a CMG can be dozens of times the torque produced by a reaction wheel. Because the torque vector of a CMG changes according to the gimbal angle, careful consideration must be given to singularity configurations. In the singularity configurations, the compound torque vector from CMGs is restricted to two dimensions even in typical four-skew redundant CMG configurations. For that reason, a satellite loses tri-axial attitude control capability. Many researchers of CMG singularity avoidance problems have studied this problem and created various CMG steering logics. We must verify CMG control logics not only through numerical simulation but also through experimentation by using CMG hardware to develop satellite-mounted CMGs. Since 2005 we have studied CMG singularity avoidance logic in numerical simulations using Matlab/Simulink. Then in 2006 we started developing CMG Software Evaluation Equipment . We developed an air bearing that comprises a ball and a saucer to demonstrate tri-axial free motion like that of a satellite in orbit. This ball floats in the saucer with air and rotates freely on three axes. An aluminum square pipe is attached over the air bearing as a balance. Four CM Gs are mounted on one side of the balance. The MPU, the gyro, and the battery are mounted on the other side of the balance. Furthermore, we are developing a CMG Test Bed for use as ground test equipment to perform the Dynamic Close Loop Test with CMG EM and Attitude and Orbit Control System (AOCS) Hardware. An especially ambitious undertaking is to mount experimental electronic devices in a ball to eliminate the limit (roll, pitch, yaw). The ball must be large. And we produced aluminum hemispheres with a radius of2000 mm.
