Experimental Verification of Vibration Reduction in Flexible Spacecraft Using Input Shaping

Abstract

The performance of many spacecraft can be improved by using closed-loop control and command-shaping techniques. However, because little information exists about the operation of controlled structures in zero gravity, it is dife cult for designers to anticipate and place cone dence in the on-orbit performance of their ground-based control designs. To address this issue, the middeck active control experiment was conducted aboard the Space Shuttle Endeavor in March of 1995. The results of the command shaping experiments implemented during the mission are presented, and guidelines forusing command shaping to suppress unwanted vibration in e exible space structures are proposed. HE combination of stringent performance specie cations and lightly damped structural modes makes the effective operation of many space systems vulnerable to vibration. To attack this problem, closed-loop control and open-loop command-shaping techniques are often enlisted. However, with only ground-based testing available prior to on-orbit implementation, uncertainty about zerogravity(0-g) behavior can hamper the success of these 0- g control designs. The Massachusetts Institute of Technology (MIT) middeck activecontrolexperiment (MACE)isaSpaceShuttlee ightexperiment designed to expose critical issues associated with the design of controllers and shaped commands for 0 g. As part of this experiment, data were collected from a e exible structure on-orbit, and results illustrated that both the control and command-shaping strategies employed on the test article could effectively reduce problematic vibration. Additionally, as a result of careful ground-based modeling efforts, predictions of 0- g behavior were accurate enough to achieve high-performance control and command shaping without on-orbit redesign. After introducing the MIT MACE project and the MACEcommand-shaping efforts, this paper presents the results from a specie c subset of the mission experiments: the MACE input shaping tests. Based on these results, key points are summarized and conclusions are drawn.