Mr. Michael Farey Profile

Michael Farey

at NGC – Aeronautics Systems

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Proceedings Article | 27 September 2016 Presentation + Paper

Data veracity checks for the alignment of the JWST optical telescope element

Josh Levi, Tiffany Glassman, Mike Farey, Till Liepmann

Proceedings Volume 9951, 995104 (2016) https://doi.org/10.1117/12.2236360

KEYWORDS: James Webb Space Telescope, Optical alignment, Optical components, Metrology, Adaptive optics, Interfaces, Mirrors, Finite element methods, LIDAR, Optical fabrication

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Alignment of the James Webb Space Telescope (JWST) Optical Telescope Element (OTE) requires a multitude of demanding and exacting dimensional and positional measurements. Many of the alignment requirements are in the range of hundreds of microns over significant distances (up to 8 m) on a flexible structure, which creates stringent accuracy demands on the alignment measurements. Furthermore, to optimize the performance of the system, the telescope is aligned to a relatively small (<1 m) structure in the center, creating the potential for coordinate system errors. Measurements have been performed using laser trackers (predominantly), photogrammetry, coordinate measurement machine (CMM), and laser radar instruments. Measurements from different instruments/ stations are combined and processed within SpatialAnalyzer (SA) commercial software using the Unified Spatial Metrology Network (USMN) feature. While this approach should yield the best possible accuracies (hopefully in the tens of microns range), our experience has been that there can be significant errors in the data based on the details of how SA is set up and how the measurements are conducted. As a result of our experience, we have developed analytical tools and processes that allow us to test the data veracity in near real time using, for example, Excel spreadsheet calculations. These tools combine measurements made at various levels of assembly, measurements of cross check points, and finite element analysis to determine the correlated and uncorrelated discrepancies in the measured data. This provides a detailed understanding of systematic and random measurement errors and has allowed us to quickly uncover issues with placement, measurement, and modeling, as well as to quantify our measurement performance.

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