In-flight performance of ASTER cryocooler

The advanced spaceborne thermal emission and reflection radiometer (ASTER) was one of the mission instruments selected by NASA to fly on the EOS-AMI spacecraft. The EOS-AMI (Terra) spacecraft was launched from Vandenberg Air Force Base, December 18th, 1999. The ASTER consists of a visible and near-infrared radiometer (VNIR), a short-wave infrared radiometer (SWIR) and a thermal infrared radiometer (TIR). Two cryocoolers are required to cool down the infrared detectors for the SWIR and the TIR. Two cold plates act as a heatsink for each compressor unit and maintain in temperature in the range between 20 °C and 25 °C by a capillary- pump heat-transfer system (CPHTS). Therefore, environmental temperature conditions are the same for the two compressor units. While the TIR expander unit is thermal controlled by a local radiator with a heat pipe, the SWIR expander unit employs radiative cooling for thermal control. The performance of ASTER cryocooler was evaluation to operate normally, based on the data obtained in the functional checkout in orbit. The SWIR cryocooler cools the detector to the operating temperature of 77 K in the cooldown time of 22 minutes. The TIR cryocooler cools the detector to the operating temperature of 80 K in the cooldown time of 23 minutes. The temperature of each detector was stabilized in the allowable temperature range. A clear image was obtained in the initial checkout of each radiometer in their observation mode. Although about four years passed before the launch, after each cryocooler was completed, it was clear that the performance requirements for the ASTER cryocooler in orbit were satisfied. After the initial checkout, operation of the radiometer will proceed to the normal observation phase. Long-term data will be acquired on the cooldown performance and power consumption (or motor current) under normal operating conditions for each cryocooler, and they will also be evaluated on the detector temperature and temperature stability in this phase.