Precise, fault-tolerant pointing using a Stewart platform

Presents a 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 evaluating 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-μrad rms pointing error