Geoscience Laser Altimetry System (GLAS) Loop Heat Pipe Anomaly and On Orbit Testing

Abstract

The Geoscience Laser Altimetry System (GLAS) is the sole instrument on the ICESat Satellite. On day 230 of 2003, the GLAS Component Loop Heat Pipe (CLHP) entered a slow circulation mode that resulted in the main electronics box reaching its hot safing temperature, after which the entire instrument was turned off. The CLHP had a propylene working fluid and was actively temperature controlled via a heater on the compensation chamber. The slow circulation mode happened right after a planned propulsive yaw maneuver with the spacecraft. It took several days to recover the CLHP and ensure that it was still operational. The recovery occurred after the entire instrument was cooled to survival temperatures and the CLHP compensation chamber cycled on a survival heater. There are several theories as to why this slow circulation mode exhibited itself, including: accumulation of Non-Condensible Gas (NCG), the secondary wick being under designed or improperly implemented, or an expanded (post-launch) leak across the primary wick. Each of these is discussed in turn, and the secondary wick performance is identified as the most likely source of the anomalous behavior. After the anomaly, the CLHP was controlled to colder temperatures to improve its performance (as the surface tension increases with lower temperature, as does the volume of liquid in the compensation chamber) and only precursor pulses occurred later in the mission. After GLAS's last laser failed, in late 2009, a decision was made to conduct engineering tests of both LHPs to try and duplicate this flight anomaly. The engineering tests consisted of control setpoint changes, sink changes, and one similar propulsive Yaw maneuver. The only test that showed any similar anomaly precursors on the CLHP was the propulsive maneuver followed by a setpoint increase. The ICESat Satellite was placed in a decaying orbit and ended its mission on August 30, 2010 in Barents Sea.

Comparative study of two loop heat pipes using R134a as the working fluid

“…Compared with traditional heat pipe, significant structural improvement has been made for LHP, mainly including the local installment of porous wick, the employment of inverted evaporator as well as the separation of liquid/vapor transport lines. These structural improvement effectively overcomes the inherent drawback of conventional heat pipe such as small heat transfer capacity, weak antigravity capability and unfavorable flexibility in installment, enabling LHP to be a more universal and advanced heat transfer device [10][11][12][13][14][15]. Its long distance heat transport capability and flexibility in packaging as well as strong antigravity operation show obvious advantages over traditional heat pipes [16][17][18][19][20][21][22][23][24][25][26][27].…”

Effect of evaporator tilt on a loop heat pipe with non-condensable gas

“…However, degradation of LHP performance has been found in practical spacecraft application [9][10][11]. The non-condensable gas (NCG) produced during the operation of LHP was believed to be responsible for the performance degradation and lifespan issues of LHP [12].…”

Experimental study on the supercritical startup of cryogenic loop heat pipes with redundancy design

“…Several years ago, operation anomaly also occurred for a loop heat pipe applied in the thermal control system of the Geoscience Laser Altimetry System on the ICESat Satellite [33]. Therefore, it is quite necessary to adopt the redundancy design to improve the operation reliability and realize a long life operation.…”