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The Soft X-Ray Telescope (SXT) is an instrument on the International X-Ray Observatory (IXO). Its flight mirror assembly (FMA) has a single mirror configuration that includes a 3.3 m diameter and 0.93 m tall mirror assembly. It consists of 24 outer modules, 24 middle modules and 12 inner modules. Each module includes more than 200 mirror segments. There are a total of nearly 14, 000 mirror segments. The operating temperature requirement of the SXT FMA is 20°C. The spatial temperature gradient requirement between the FMA modules is ±1°C or smaller. The spatial temperature gradient requirement within a module is ±0.5°C. This paper presents thermal design considerations to meet these stringent thermal requirements.

The Swift mission Burst Alert Telescope (BAT) Detector Array thermal control system includes two propylene loop heat pipes (LHPs), eight ammonia constant conductance heat pipes (CCHPs), a radiator that has AZ-Tek's AZW-LA-II low alpha white paint, and precision heater controllers that have adjustable set points in flight. The Power Converter Box (PCB) and Image Processor Electronics (IPE) boxes (a primary and a redundant) of the BAT have Z93P white paint radiators. Swift was successfully launched into orbit on November 20, 2004. The spacecraft (S/C) was placed into a safehold mode on August 10, 2007 after an anomaly on inertial reference unit (IRU) #3. It was returned to inertial pointing on August 16 and instrument power up followed. This paper presents a thermal assessment of the BAT instrument thermal control system (TCS) shut down and recovery as a result of the S/C safehold mode. The recovery required starting up the LHPs manually.

On Day 97, 2005, a temperature excursion of the Burst Alert Telescope (BAT) loop heat pipe (LHP) #1 compensation chamber (CC) caused this LHP shut down. It had no impact on the 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 have been nominal. 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 -50°C or colder most of the time. The CCD temperature meets the main objective of pinpointing GRB afterglow positions. With these anomalies overcome, the Instrument Module (IM) thermal control system (TCS) is nominal during the first 2.5 years in flight.

The Burst Alert Telescope (BAT) instrument of the Swift mission consists of a telescope assembly, a Power Converter Box (PCB), and a pair of Image Processor Electronics (IPE) boxes (a primary and a redundant). The telescope assembly Detector Array thermal control system includes eight constant conductance heat pipes (CCHPs), two loop heat pipes (LHPs), a radiator that has AZ-Tek's AZW-LA-II low solar absorptance white paint, and precision heater controllers that have adjustable set points in flight. The PCB and IPEs have Z93P white paint radiators. Swift was successfully launched into orbit on November 20, 2004. This paper presents a thermal assessment of the BAT instrument thermal control system during the first six months in flight.

A heritage wine-rack thermal/mechanical design for the nickel-hydrogen batteries was the baseline at the Land-sat-7 Preliminary Design Review. An integrated thermal and power analysis of the batteries performed by the author in 1994 revealed that the maximum cell-to-cell gradient was 6.6°C. The author proposed modifying the heritage wine-rack design by enhancing heat conduction from cells to cells, and from cells to battery frame. At the 1995 Intersociety Energy Conversion Engineering Conference (IECEC), the author presented a paper on methods of modifying the wine-rack design [1]. It showed that the modified wine-rack option, which uses a metallic filler, could reduce the maximum cell-to-cell temperature gradient to 1.3°C, and could also reduce the maximum cell temperature by as much as 8°C. That design concept was adopted by the Landsat-7 Project Office, and a design change was made at the Critical Design Review.

The Enhanced Thematic Mapper Plus (ETM+) Main Electronics Module (MEM) power supply heat sink temperature is critical to the Landsat-7 mission. It is strongly dependent on the thermal louver design. A lower power supply heat sink temperature increases the reliability of the MEM, and reduces the risk of over heating and thermal shutdown. After the power supply failures in ETM+ instrument thermal vacuum tests #1 and #2, the author performed detailed thermal analyses of the MEM, and proposed to reduce the louver set points by 7°C. At the 1998 Intersociety Energy Conversion Engineering Conference (IECEC), the author presented a paper that included results of thermal analysis of the MEM. It showed that a 7°C reduction of the louver set points could reduce the maximum power supply heat sink temperature in thermal vacuum test and in flight to below 20°C in the cooler outgas mode and in the nominal imaging mode, and has no significant impact on the standby heater duty cycle [1].

During the radiative cooler cool-down phase of the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) instrument thermal vacuum test #3, the coldest temperature that the cold focal plane array (CFPA) achieved was 89.5 K. The cold stage/CFPA temperature decreased from 315 K to 89.5 K in 80 hours. In the spacecraft and instrument integrated thermal vacuum test, the cold stage/ CFPA temperature decreased from 315 K to 86.9 K in 80 hours, and was still decreasing at a rate of 0.1 K/hr when the cool-down was terminated. The cool-down was faster, and a colder CFPA temperature was obtained. In flight, the cooler cool-down was even faster, and colder. The cold stage/CFPA temperature decreased from 315 K to 89.7 K in 33 hours, and was still decreasing at a rate of 1 K/hr when cool-down was terminated at 89.7 K.

There was a thermal anomaly of the landsat-7 Enhanced Thematic Mapper Plus (ETM+) radiative cooler cold stage during the cooler outgas phase in flight. With the cooler door in the outgas position and the outgas heaters enabled, the cold stage temperature increased to a maximum of 323 K when the spacecraft was in the sunlight, which was warmer than the 316.3 K upper set point of the outgas heater controller on the cold stage. Also, the outgas heater cycled off when the cold stage was warming up to 323 K. A corrective action was taken before the attitude of the spacecraft was changed during the first week in flight. One orbit before the attitude was changed, the outgas heaters were disabled to cool off the cold stage. The cold stage temperature increase was strongly dependent on the spacecraft roll and yaw. It provided evidence that direct solar radiation entered the gap between the cooler door and cooler shroud.

The thermal design and the instrument thermal vacuum (T/V) test of the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) instrument were based on the Landsat-4, 5 and 6 heritage. The ETM+ scanner thermal model was also inherited from Landsat-4, 5 and 6. The temperature predictions of many scanner components in the original thermal model had poor agreement with the spacecraft and instrument integrated sun-pointing safehold (SPSH) thermal balance (T/B) test results. The spacecraft and instrument integrated T/B test led to a change of the Full Aperture Calibrator (FAC) motor stack “solar shield” coating from MIL-C-5541 to multi-layer insulation (MLI) thermal blanket. The temperature predictions of the Auxiliary Electronics Module (AEM) in the thermal model also had poor agreement with the T/B test results. Modifications to the scanner and AEM thermal models were performed to give good agreement between the temperature predictions and the test results.

The original thermal design of the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) scanner was inherited from Landsat-4, 5 and 6 at the instrument Critical Design Review (CDR). The ETM+ Auxiliary Electronics Module (AEM) and Full Aperture Calibrator (FAC) are new components and had no heritage thermal design at the CDR. More than a year after the CDR, the Landsat-7 program was transferred from the U.S. Air Force to the National Aeronautics and Space Administration (NASA). NASA added the sun-pointing safehold mode which has significant thermal impacts on the instrument. The temperature predictions for the scanner were much colder than the survival temperature limits in the sun-pointing safehold cold case. This paper presents thermal solutions to the cold survival problems. The solutions have no major impacts on the program cost and schedule.

National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) requires the maximum analytical temperature limit for solar array drive (SAD) slip rings to be 50°C based on previous flight programs. With the baseline thermal control, the Landsat-7 peak slip ring temperature prediction significantly exceeded the requirement. The initial options of changing the slip ring assembly shaft material from titanium to aluminum or filling the hollow center of the titanium shaft with copper could reduce the slip ring temperature significantly. However, they have high technical risks and significant impacts on the program cost and schedule. This paper presents low-risk and low-cost thermal changes to reduce the peak slip ring temperature prediction to below 50°C.