Precision Pointing Experiment

The objective of the Spice Program was to demonstrate improvement in precision pointing, tracking, and retargeting by integration of active isolation, active and passive structural control, advanced materials, active optics, and adaptive control. Experiments were carried out on a full-size and well- characterized precision test-bed that represented a space laser structure. in the Precision Pointing Experiment, an active control system that combined low authority local rate feedback and high authority global control was designed with the goal of achieving 50:1 attenuation of line-of-sight jitter in the 5- to 500-Hz band. The jitter was due to disturbances input at the base of the structure and at the simulated secondary mirror. A custom suite of optical sensors allowed determination of the line of sight of the structure. Proof mass actuators of unprecedented force and linearity were developed during this and preceding subtasks. A series of tests culminated with the attainment of repeatable attenuation of line-of-sight jitter by 75:1 in the band 5 to 500 Hz with little spillover into unmodeled structural modes or unregulated degrees of freedom. The control system proved to be robust, with gain margin greater than 1.75 demonstrated. Comparison of measure transfer functions with those calculated from the structural model used in the control system design showed that high controller performance does not require unreasonable structural model accuracy. (MM)