Liquid helium Dewar for one meter mirror testing

Abstract

The NASA Ames Research Center has developed a baseline design for a One Meter Cryogenic Optical Test Facility (OMF) incorporating a liquid helium Dewar for cryogenic optical testing of one-meter-class mirrors, principally the Space Infrared Telescope Facility (SIRTF) primary mirror. The primary requirements for the test facility are as follows: (1) the facility must be capable of interferometrically testing any mirror, positioned face-up or face-down, with a diameter less than 1.5 meters and a radius of curvature from 1.5 to 5.5 meters; (2) the facility must achieve and maintain, for 24 hours, a mirror temperature of 4 K with a maximum radiative heat load of less than 500 mW to the mirror, using stored liquid helium and liquid nitrogen; (3) the facility must include a vibration-isolated metrology structure between the test mirror and an external interferometer, and (4) the facility must be operated by two persons and a test, starting from the mounting of a mirror to the removal of a mirror, must be conducted within one week.