Optical stimulus for the calibration of the Ultraviolet and Optical Telescope (UVOT) for SWIFT

Abstract

The Ultraviolet and Optical Telescope (UVOT) is one of the three astronomical instruments onboard the SWIFT spacecraft. The optical calibration of this instrument, which was done prior to integration to the SWIFT spacecraft optical bench, is key to determine if UVOT will meet its science objectives. In this paper, we describe the optical ground support equipment (GSE) used for the calibration of UVOT. These tests, which were carried out in the Diffraction Grating Evaluation Facility (DGEF), at NASA Goddard Space Flight Center, required building an optical stimulus. We report the radiometric measurements of all the optical components used in putting together this stimulus. This includes a vacuum collimator with a Cassegrain design, a Pt/Cr-Ne light source, a complete set of neutral density filters spanning 6 orders of magnitude in transmission levels, a set of narrow-band filters matching the center of each of the six bands of UVOT, a set of pinholes of various sizes, flat fielding diffusers, and a set of parabolic mirrors.