Herschel Space Telescope: Optical test and model correlation

Subsequent to the cyrogenic optical testing of the 3.5 m silicon carbide ESA Herschel Space Telescope, a discrepancy between the prediction and measurement of the telescope back focal length was identified. Efforts to resolve this discrepancy involved both improvements to modeling and more thorough examination of the optical test techniques. The most significant input to modeling was the use of extremely precise cryogenic strain measurements. The optical test methods were extensively analyzed for accuracy, sensitivity, and systematic errors. Model results, error budgets, test results, and conclusions will be presented and discussed.