Thermal Evaluation of NASA/Goddard Heater Controllers on Swift BAT, Optical Bench and ACS

Abstract

The BAT D etector Module (DM) Blocks and loop heat pipes ( LHPs ) require h eater controllers wit h adjustable set points in flight and multiple control units per controller box. Also the LHP heater controller is required to meet the temperature set point offset and work -in -reverse requirements for the variable conductance heat pipe (VCHP) . No commerci ally available heater controller could meet these requirements. Therefore, heater controllers were developed at NASA Goddard Space Flight Center (GSFC) for the Swift mission. A fixed set point version of the BAT heater controllers was developed for the Opt ical Bench, Star Trackers and I nertial Reference Unit (IRU). A thermal evaluation of the heater controllers reveals that t he y meet the temperature set po int and tolerance requirements. The LHP heater controller tolerances are larger than the specification, possibly due to instability that is caused by the VCHPs. The LHP #1 primary heater controller circuit stuck on for about 40 minutes each on Day 091 and Day 097. It caused a large temp erature excursion on the LHP #1 compensation chamber ( CC ). Prior to the LHP #1 CC thermal anomaly on Day 091, the LHP #1 primary heater controller circuit controlled the CC temperature poorly. Due to limited flight telemetry data, it is not conclusive whether a heater controller failure , a pin -socket interconnect open circuit , or a faulty thermistor caused the heater circuit “stuck on”. The LHP #1 primary heater controller circuit has been disabled since Day 098. Only the LHP #1 redundant heater controller is used to control its CC temperature. Because the BAT LHPs and heater c ontrollers have redundancy, the LHP #1 heater controller circuit anomaly has no impact on gamma ray burst detection.