Thermal Assessment of Swift Instrument Module Thermal Control System and Mini Heater Controllers after 5+ Years in Flight

Abstract

From Day 325, 2004 (launch) through Day 101, 2010, there is a total of 3 anomalies on the Swift Instrument Module (IM) Thermal Control System (TCS). Two are concerned with the Burst Alert Telescope (BAT) loop heat pipe (LHP) heater circuits. On Day 90, 2010, the primary heater circuit of the BAT LHP #0 compensation chamber (CC) failed to power on by the Power Converter Box (PCB). It caused a rapid decrease in the CC temperature and activated its secondary heater circuit which had a 2oC lower heater controller set point. The 2oC difference in temperature set points between the LHP #0 CC and LHP #1 CC led to thermal instability in the entire LHP thermal system and Blocks. After the LHP #0 CC secondary heater controller set point was increased to that of LHP #1, thermal stability has been restored and the temperatures of the LHP thermal system and Blocks are nominal. On Day 97, 2005, a failure in temperature controllability of the BAT LHP #1 CC primary heater circuit caused temperature excursions that led to a LHP #1 shut down. It had no impact on Gamma Ray Burst (GRB) detection because LHP #0 was nominal. After LHP #1 was started up and its primary heat controller was disabled on Day 98, both LHPs had been nominal until Day 90, 2010. On Day 337, 2004, the X-Ray Telescope (XRT) thermo-electric cooler (TEC) power supply (PS) suffered a single point failure. The charge-coupled device (CCD) has been cooled by the radiator passively to -50oC or colder most of the time. The CCD temperature meets the main objective of pinpointing GRB afterglow positions. With these 3 anomalies overcome, the IM TCS is nominal after more than 5 years in flight. Redundancy in thermal control hardware and electronics boxes that supply power to thermal control hardware is highly recommended to prevent a mission single point failure.