Performance validation of passive radiant cryo-cooler for meteorological payload of INSAT-3D satellite through in-orbit data

INSAT-3D satellite built by ISRO carries Imager - advanced meteorological payload, wherein infra-red detectors are cooled to 90 K by means of passive radiant cooler. Heat load from detectors is around 20 mW. Passive radiant cooler works on the concept of staged radiator cooling. Imager cooler consists of three stages. Stages are designed such that successive stages have higher degree of isolation from the external loads and each stage is radiant to space. The first stage temperature is around 200 K, the second around 120 K and third stage is around 90 K. Infra-red detectors are mounted on the third stage. The in-orbit temperature and control heater power data over five years of Imager cooler of INSAT-3D validates its intended performance and shows insignificant degradation.