Precise, fault-tolerant pointing using a Stewart platform

This paper presents a novel precision pointing strategy. The principal contribution is the development of a fault-tolerant control which allows active pointing to continue despite multiple failures. A six-axes active platform is utilized to reject disturbances from a vibrating base to a precision payload. A decentralized controller is proposed which converts desired rotations into corresponding strut lengths via a decoupling transformation. The decoupling approach allows for simple single-input-single-output compensator design and for the incorporation of fault-tolerant strategies. The proposed strategy was evaluated on the microprecision interferometer testbed (a full-scale model of a future spaceborne optical interferometer) at the Jet Propulsion Laboratory; Pasadena, CA. Experimental pointing results demonstrate 50 dB of disturbance rejection at low frequency. In the laboratory ambient disturbance environment, this corresponds to a 1-mu rad rms pointing error.