Control-structures Interaction Test of the LACE Satellite

It is clear that additional experience and validation of Control Structures Interaction (CSI) techniques are needed in controlling the structural dynamics of flexible spacecraft. It is also clear that the effects of the space environment such as weightlessness dictate that this be done in space. Unfortunately, orbital tests are difficult to achieve because of the high cost of the test article, the launch into orbit, the instrumentation, and communication systems. The Low-power Atmospheric Compensation Experiment (LACE) Satellite has provided an opportunity to achieve a CSI test in space for very little cost. First, the CSI test rode piggy-back and did not interfere with the primary objective of LACE. Second, the novel technique of using ground based measurements of vibration of the orbiting satellite was employed. The LACE has a heavy central body to which is attached booms with lengths as long as 150 feet. The ground measurements were obtained using laser Doppler radar at the MIT Lincoln Laboratory Firepond Facility. The initial tests demonstrated the accuracy of the vibration measurements and obtained structural responses for enhancing the accuracy of the mathematical model of the structural dynamics. Germanium corner-cube retroreflectors attached to the central body and a boom deployed to 18 feet ensured a high strength return signal. Subsequent tests demonstrated the ability of an open-loop damper to attenuate the vibrations of the orbiting satellite. The LACE test results are important in contributing to the validation of a CSI technique, and demonstrating a novel ground measurement technique for orbital tests that is accurate but which has very low cost.