Cryogenic testing of detector alignment of the Fine Guidance Sensor for the James Webb Space Telescope

Abstract

The development of the James Webb Space Telescope (JWST) is an international collaboration led by NASA in partnership with the European Space Agency and the Canadian Space Agency (CSA). The Canadian contribution to the mission is the Fine Guidance Sensor (FGS). The FGS-Guider images two fields of view onto two detectors. For testing, Optical Ground Support Equipment telescopes are used to simulate the image from the Observatory's Optical Telescope Element. The FGS Engineering Test Unit (ETU) comprises 2 functioning Guider channels: one fully functional channel with a Teledyne H2RG HgCdTe 5 micron cutoff detector, and another with an H2RG multiplexer in place of a detector. This paper reports on the results of cryogenic vacuum testing of the alignment of the final ETU instrument configuration. Images at ambient (from the H2RG multiplexer) and at cryo (from detector and H2RG multiplexer) were analysed to determine best focus and FGS field of view at cryogenic temperatures. The ETU test results for best focus, tip/tilt of focal planes, field of view location and size are well matched to the budgets and predictions and meet requirements for the FGS-Guider.