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Proceedings Paper

Optical alignment of the Global Precipitation Measurements (GPM) star trackers
Author(s): Samuel Hetherington; Dean Osgood; Joe McMann; Viki Roberts; James Gill; Kyle McLean
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Paper Abstract

The optical alignment of the star trackers on the Global Precipitation Measurement (GPM) core spacecraft at NASA Goddard Space Flight Center (GSFC) was challenging due to the layout and structural design of the GPM Lower Bus Structure (LBS) in which the star trackers are mounted as well as the presence of the star tracker shades that blocked line-of-sight to the primary star tracker optical references. The initial solution was to negotiate minor changes in the original LBS design to allow for the installation of a removable item of ground support equipment (GSE) that could be installed whenever measurements of the star tracker optical references were needed. However, this GSE could only be used to measure secondary optical reference cube faces not used by the star tracker vendor to obtain the relationship information and matrix transformations necessary to determine star tracker alignment. Unfortunately, due to unexpectedly large orthogonality errors between the measured secondary adjacent cube faces and the lack of cube calibration data, we required a method that could be used to measure the same reference cube faces as originally measured by the vendor. We describe an alternative technique to theodolite autocollimation for measurement of an optical reference mirror pointing direction when normal incidence measurements are not possible. This technique was used to successfully align the GPM star trackers and has been used on a number of other NASA flight projects. We also discuss alignment theory as well as a GSFC-developed theodolite data analysis package used to analyze angular metrology data.

Paper Details

Date Published: 10 September 2013
PDF: 16 pages
Proc. SPIE 8844, Optical System Alignment, Tolerancing, and Verification VII, 884406 (10 September 2013); doi: 10.1117/12.2024558
Show Author Affiliations
Samuel Hetherington, NASA Goddard Space Flight Ctr. (United States)
Dean Osgood, Qinetiq North America (United States)
Joe McMann, Qinetiq North America (United States)
Viki Roberts, Qinetiq North America (United States)
James Gill, Qinetiq North America (United States)
Kyle McLean, Qinetiq North America (United States)

Published in SPIE Proceedings Vol. 8844:
Optical System Alignment, Tolerancing, and Verification VII
José Sasián; Richard N. Youngworth, Editor(s)

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