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MAM (Micro-Arcsecond Metrology Testbed), is a dedicated systems-level testbed that combines the major SIM (Space Interferometry Mission) subsystems including laser metrology, pointing, and pathlength control. The testbed is configured as a modified Michelson interferometer for the purpose of studying the white-light (science or guide stars) fringe measurement processes. This paper will compare the performance of various algorithms using the MAM data, and will aid in our recommendation of how the SIM flight system should process the science and guide interferometer data. The experiment measures optical pathlengths via the white-light phase and infrared (IR) laser metrology. The variance of phase differences between white light and metrology is directly related to our accuracy in relative optical pathlength measurements. The full aperture He-Ne laser served as a proxy to measure the optical path reference for white light in the system prior to the installation of SAVV (Sub-Aperture Vertex-to-Vertex3) 1.3 um laser metrology. In this simplified configuration, analysis of the white-light detected on the CCD and the He-Ne light detected on the photodiode was providing us with the phase differences between the two. In general, MAM data are subject to random noise, e.g. shot noise and vibration, and systematic noise, e.g. drifts and cyclic errors, from instruments and detectors. Our noise floor in phase (or pathlength) difference measurements is determined by analysis of both the 111 aperture He-Ne laser light and white light fringe detected on the CCD4. Several fringe estimation algorithms have been developed and tested with the MAM data. Preprocessing procedures for fringe data have also been developed in conjunction with estimation algorithms to further enhance the fidelity of data',2. The performance improvements are quantified with respect to a baseline algorithm, which is the least-squares fitting solution5. The adopted performance metrics are long-time modified Allan variance6 and short-time chop variance7. The algorithms recommended to SIM are based on the improvements and sensitivity studies from MAM data analysis.

Dependence of the micro-arcsecond metrology (MAM) testbed performance prediction on white light algorithm approach