Validation of the image-distortion robustness to thermal deformation of the JASMINE telescope

We are promoting conceptual design and the validation study of the telescope on board the Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE). Precise correction of image distortion, which is a key technical challenge for astrometry, may be complicated by the time variation of point spread function centroids caused by thermal deformation of the telescope due to changing thermal condition in orbit. To assess this effect, we conducted a Structural Thermal Optical Performance analysis. After correcting image shifts and magnification changes, the time variation of the distortion in the second or higher orders was found to be approximately 1 nm RMS, corresponding to 50 μarcsec RMS in position angle. The time stability is insufficient to achieve the mission requirement of annual parallax estimation with a precision better than 40 μarcsec. This demonstrates the necessity of the correction of time-varying distortions in the second order during post processing.