30 September 2004 Error modeling of multi-baseline optical truss: part II. Applications to SIM metrology truss field dependent error
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Abstract
The current design of the Space Interferometry Mission (SIM) employs a 19 laser-metrology-beam system (also called L19 external metrology truss) to monitor changes of distances between the fiducials of the flight system's multiple baselines. The function of the external metrology truss is to aid in the determination of the time-variations of the interferometer baseline. The largest contributor to truss error occurs in SIM wide-angle observations when the articulation of the siderostat mirrors (in order to gather starlight from different sky coordinates) brings to light systematic errors due to offsets at levels of instrument components (which include corner cube retro-reflectors, etc.). This is the external metrology wide-angle field-dependent error. Physics-based model of field-dependent error at single metrology gauge level is developed and linearly propagated to errors in interferometer delay. General formulation of delay error sensitivity to various error parameters is developed. The essence of the linear error model is contained in an errormapping matrix. A corresponding Zernike component matrix approach is developed in parallel with its advantages discussed. As a first example, dihedral error model is developed for the corner cubes (CC) attached to the siderostat mirrors. Average and worst case residual errors are computed when various orders of field-dependent terms are removed from the delay error. These serve as guidelines for arriving at system requirements given the error budget allocation. Highlights of the non-common vertex error (NCVE) model are shown as a second example followed by discussions.
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Liwei D. Zhang, Mark H. Milman, Robert E. Korechoff, "Error modeling of multi-baseline optical truss: part II. Applications to SIM metrology truss field dependent error", Proc. SPIE 5528, Space Systems Engineering and Optical Alignment Mechanisms, (30 September 2004); doi: 10.1117/12.557138; https://doi.org/10.1117/12.557138
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