Fringe-tracking filters for space-based interferometers

The purpose of this research is to explore, from the point of view of nonlinear filtering, the feasibility of microarcsecond astrometry using space-based optical interferometers in typical disturbance environments. Two nonlinear estimators are developed to enable high precision estimates of the optical path difference (OPD) between the two starlight paths in a spaceborne optical interferometer. Focal plane fringe data measurements by either CCD (charge coupled device) or photon counting (PC) cells are processed by an Extended Kalman Filter (EKF)- based algorithm to yield the OPD estimate. Whereas the filter based on CCD cell measurements results in a straightforward implementation of an EKF, the filter utilizing PC cells requires some innovations before yielding to the EKF framework. Instead of using the photon arrival events as measurements, the filter measurements are taken to be the interarrival time between photons. The excellent results obtained with the PC filter are backed by intuition based on linear analysis results. Simulation studies show that as the CCD readout time is decreased, the performance of the CCD filter approaches that of the PC filter.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.