Contamination Control of the SABER Cryogenic Infrared Telescope

The SABER instrument (Sounding of the Atmosphere using Broadband Emission Spectroscopy) is a cryogenic infrared sensor on the TIMED spacecraft with stringent molecular and particulate contamination control requirements. The sensor measures infrared emissions from atmospheric constituents in the earth limb at altitudes ranging from 60 to 180 km using radiatively-cooled 240 K optics and a mechanicallyrefrigerated 75 K detector. The stray light performance requirements necessitate nearly pristine foreoptics. The cold detector in a warm sensor presents challenges in controlling the cryodeposition of water and other condensable vapors. Accordingly, SABER incorporates several unique design features and test strategies to control and measure the particulate and molecular contamination environment. These include internal witness mirrors, dedicated purge/depressurization manifolds, labyrinths, cold stops, and validated procedures for bakeout, cooldown, and warmup. The pre-launch and on-orbit contamination control performance for the SABER telescope will be reviewed.