Integrated Thermal Deformation Modeling and Measurement of Space Optical Systems

A computational and experimental study of the thermal, response and thermally induced deformation of a circular plano mirror (101.6 mm in diameter) undergoing mW heat loading was performed to verify the capability to model the response of a representative imaging optic on the Space Interferometry Mission (SIM) spacecraft. Novel state of the art experimental and computational techniques provided milliKelvin and picometer precision in temperature and deformation prediction and experimental measurement. Mirrors of two different substrates, initially at ambient temperature, were subjected to nominal thermal loading profiles of three 5 hour steps of 12 mW, 54 mW, and 295 mW respectively, representing flight-like and overdrive thermal disturbance conditions. The experimental setup measured milliKelvin level temperature changes using the mKTMS (milliKelvin Temperature Measurement System) instrument and picometer level deformation responses using the CoPHI (Common Path Heterodyne Interferometer) instrument. I-deas/TMG was used to generate an integrated model to predict milliKelvin level temperature changes of the mirror and picometer level deformation responses of the mirror surface. This paper focuses on the thermal modeling and correlation to thermal experimental data of the optical system. Comparison between experimental results and computational models for the thermal aspects of the test show good agreement for the two test mirror materials, fused silica and Zerodur. In particular for the flight-like regime of primary interest, agreement between the experimental temperatures and computational thermal results was within 14%.