Integrated dynamics and controls modeling for the Space Interferometry Mission (SIM)

Integrated dynamics and controls modeling provides confidence in the design of complex optomechanical space systems before integration and launch. This paper discusses the underlying process for modeling and analysis based on linear time-invariant systems theory in the frequency domain. Results are presented for the Space Interferometry Mission. Performance predictions are made for phasing as represented by optical pathlength difference (OPD) metrics and pointing given by wavefront tilt (WFT) metrics for one science and two guide star interferometers. The disturbance source is reaction wheel induced jitter caused by flywheel and bearing imperfections. Results are obtained for a broadband and a narrowband disturbance analysis, critical modes and wheel speed determination modal sensitivity analysis and isoperformance analysis. The findings suggest that the critical frequency region for SIM is in the range from 160-190 Hz with both optics and attitude control loops closed. It appears that a reduction in wheel disturbance by 30% would have a similar effect that an increase in optical control bandwidth from 100 to 180 Hz