Geoscience Laser Altimetry System (GLAS) On-Orbit Flight Report on the Propylene Loop Heat Pipes (LHPs)

The Geoscience Laser Altimetry System (GLAS) instrument which is the sole instrument on ICESat was launched on January 12, 2003. GLAS utilizes the very first actively controlled propylene Loop Heat Pipes (LHPs) as the core of its thermal system that are tightly controlled (to +/− 0.1°C.) The LHPs started quickly when the Dale Ohm starter heaters were powered and have started, as designed, several additional times in the mission. The low control heater power and on‐orbit tight temperature control appear independent of gravity effects when comparing ground testing to flight data. The use of coupling blocks was also unique to these LHPs. Their application reduced control heater power by reducing the subcooling from the radiator. The effectiveness in reducing subcooling of the coupler blocks decreased during flight from ground testing, but internal thermal isolation in the compensation chamber between the subcooled returning liquid increased in flight resulting in no net increase in control heater power versu...