Methods for correlating autocollimation of theodolites and coordinate metrology in spacecraft systems

Abstract

This paper will discuss the details of the metrology associated with the integration and testing of spacecraft systems and scientific instruments at the NASA Goddard Space Flight Center (NASA GSFC). Specifically, this paper will outline the process for correlating theodolite autocollimation measurements with theodolite coordinate triangulation measurements, laser tracker coordinate measurements, photogrammetry camera system, and other coordinate measurement techniques. For theodolite autocollimation data, NASA GSFC developed a Microsoft Excel-based spreadsheet program to calculate the transformation matrices from reference cube pointing directions into spacecraft coordinates defined by physical features. The autocollimated image return from the mirrored faces of the reference cubes are measured relative to each other and define unit vectors that point in the direction perpendicular to the cube face surface. The roll, zenith, pitch, and yaw are calculated from the direction cosines of the unit vectors that define the directional pointing rotations around coordinate axes. The theodolite-based pointing vectors are then transformed to the spacecraft coordinate system. The Brunson Spatial AnalyzerTM coordinate measuring software program is used to analyze data from theodolites using triangulation on target positions, a laser tracker coordinate measuring system, a photogrammetry system or any other coordinate measuring system. All the coordinate data is tied into theodolite coordinate data by measuring common targets. To correlate theodolite autocollimation on cube faces to the point coordinate location data, one must first measure the test object with the Spatial AnalyzerTM theodolite triangulation coordinate system. From coordinate features, a spacecraft coordinate system is defined by the blueprint design. One of the Spatial AnalyzerTM theodolites is used as the primary reference for the auto-collimation measurements. This ties together the coordinate target point locations to the pointing directions of mirrored surfaces of cubes.