46th International Conference on Environmental Systems ICES-2016-157 10-14 July 2016, Vienna, Austria

JAXA’s X-ray Astronomy Mission ASTRO-H: Launch and First Month’s In-Orbit Thermal Performance

Naoko IWATA1 Japan Aerospace Exploration Agency, Sagamihara, Kanagawa, 252-5210 Tel: +81-50-3362-3592, Fax: +81-42-759-8068 E-mail: iwata.naoko@jaxa.jp

Takashi USUI2, Akihiko MIKI3, Mizuho IKEDA4 NEC Corporation

and

Yoh TAKEI5, Atsushi OKAMOTO6, Hiroyuki OGAWA7, Tadayuki TAKAHASHI8 Japan Aerospace Exploration Agency

In this study, the thermal performance evaluation results of JAXA’s X-ray astronomy mission ASTRO-H are presented. ASTRO-H was successfully launched on February 17, 2016 from Tanegashima Space Center using an H2A rocket. ASTRO-H houses four telescopes and six detectors. Each detector has its own radiator and heat pipes for heat dissipation. The most major mission will feature a soft X-ray spectrometer having four loop heat pipes (LHPs) for heat transport from two cryocoolers. Six fans have been mounted close to each cryocooler for ground cooling in the fairing just before the launch. Hard X-ray imagers (HXIs) are mounted on an HXI plate; this plate is expanded by 6.4 m via an extensible optical bench (EOB) in orbit to achieve the necessary focal length. The EOB was successfully expanded 11 days after the launch. Heat pipes appropriately functioned in orbit. The two LHPs for the compressors have been operated properly for more than one month Measured inflight temperatures agree well with predicted ones for an attitude condition.

Nomenclature BOL = Beginning Of Life CFRP = Carbon Fiber Reinforced Plastic EOB = Extensible Optical Bench EOL = End Of Life FM = Flight Model FOB = Fixed Optical Bench HCE = Heater Control Electronics HXI = Hard X-ray Imager HXT = Hard X-ray Telescope

1 Researcher, Research and Development Directorate, Research Unit 2 2 Assistant Manager, Space Technologies Department, Space Systems Division 3 Manager, Space Technologies Department, Space Systems Division 4 Engineering Manager, Space and Satellite Systems Department, Space Systems Division 5 Assistant Professor, Department of Space Astronomy and Astrophysics, Institute of Space and Astronautical Science 6 Senior researcher, Research and Development Directorate, Research Unit 2 7 Associate Professor, Department of Space Flight Systems, Institute of Space and Astronautical Science, Senior Member AIAA 8 Professor, Department of Space Astronomy and Astrophysics, Institute of Space and Astronautical Science JAXA = Japan Aerospace Exploration Agency LHe = Liquid Superfluid Helium LHP = Loop Heat Pipe LP = Launch Pad MLI = Multilayer Insulation SGD = Soft Gamma-ray Detector SNT = Santiago Ground Station STA2 = Second Spacecraft Test and Assembly building SXI = Soft X-ray Imager SXS-XCS = Soft X-ray Spectrometer X-ray Calorimeter Spectrometer SXT = Soft X-ray Telescope TKSC = Tsukuba Space Center TVT = Thermal Vacuum Test TMM = Thermal Mathematical Model TTM = Thermal Test Model USC = Uchinoura Ground Station UT = Universal Time UVC = Under-voltage Controller VAB = Vehicle Assembly Building

I. Introduction STRO-H observes black holes and clusters of galaxies using a set of instruments with the highest energy A resolution ever achieved and a four-decade range from soft X-rays to gamma rays.1 The development of ASTRO-H started in 2008. The flight model (FM) system integration test campaign, including a thermal vacuum test (TVT), was conducted in 2014 and 2015 in JAXA’s Tsukuba Space Center (TKSC). FM spacecraft was transferred to JAXA’s Tanegashima Space Center via land and sea. ASTRO-H was launched on February 17, 2016 using an H2A rocket after approximately two months of flight operation. Following JAXA’s custom, ASTRO-H was named after it was successfully launched. Its name, “Hitomi,” generally means “eye” in Japanese, specifically the pupil or entrance aperture of the eye. To avoid confusion, it is referred to as “ASTRO-H” in this study. ASTRO-H was injected into an approximately circular orbit of orbital height 575 km and inclination 31° (Fig. 1). As shown in Fig. Figure 1. Artist’s orbital ASTRO-H 2, any attitude within 0–30° relative to the y axis can be attained with in approximately circular orbit. a limit on the range determined by the incidence angle of sunlight on telescopes. ASTRO-H is a three-axis-stabilized spacecraft. The construction of ASTRO-H is shown in Fig. 3. There are four telescopes on the top of the fixed optical bench (FOB): two hard X-ray telescopes (HXTs)2 and two soft X-ray telescopes (SXTs). Two star trackers are also mounted on the top of the FOB to satisfy the need to precisely control directions for observations. Two science instruments for detecting soft X-rays, i.e., the soft X-ray spectrometer X-ray calorimeter spectrometer (SXS-XCS)3 and soft X-ray imager (SXI)4, are mounted on the base plate, which is an octagonal plate of 3-m diameter. Eight side panels are mounted on the base plate, one per edge. The side panel on the +X-direction edge shown in Fig. 2 is designated as side panel #1, and remaining panels are designated as side panels #2–#8 in a counterclockwise direction from #1. Soft gamma-ray detectors (SGDs)5 are symmetrically mounted on the outer sides of side panels #1 and #5. Hard X-ray imagers (HXIs)6 are mounted on the HXI plate; this plate is expanded to 6.4 m in orbit via the extensible optical bench (EOB) to achieve the necessary focal length. The Figure 2. Coordinate system of ASTRO-H.

2 International Conference on Environmental Systems

total length of ASTRO-H before the launch is 8.2 m and that in orbit is 14 m. Six solar panels are mounted on the outer side of side panel #3. Total power generation is below 3500 W. Total mass is below 2700 kg. After the launch and deployment of the solar array paddle, bus components and mission instruments, including the cooling system of the SXS-XCS, were powered up, and then, the operational test of the SXS was conducted. Finally, the EOB was successfully expanded and the critical operation phase was completed in February 29, 2016.

II. Thermal Design To achieve desired science objectives such as high- energy resolutions and sensitivities, the most important requirements for the thermal control system are as follows: 1) The minimization of the thermal distortion of the spacecraft structure to satisfy the need to precisely control the direction for a stable observation of celestial bodies along the optical axes of telescopes. 2) Science instruments should be maintained within Figure 3. Construction of ASTRO-H. their required temperature range. All plates, including the base plate, three plates of the FOB, and side panels, are made of aluminum honeycombs and carbon fiber reinforced plastic (CFRP) skins with a very low coefficient of thermal expansion. Truss tubes of the FOB are also made of CFRP. The entire structure above side panels is covered with multilayer insulation (MLI) to isolate the FOB from the external thermal environment. Furthermore, the exterior surfaces of each plate and truss tube of the FOB are covered with aluminized polyester film to minimize radiation coupling among adjacent components. These features are designed to minimize the temperature gradients of the FOB. The exterior of the EOB is covered with a one-sided aluminized polyimide film to minimize its temperature gradients. This is because the pointing accuracy of an HXI would be strongly impacted by thermal distortion in the EOB. The film is folded before the launch and expanded accordion style with the EOB in orbit. Most bus components are mounted on side panels. The components’ heat is dissipated by radiators (silverized Teflon) placed on the exterior of side panels. Each instrument has a surface of high IR emissivity (black paint) to equalize the internal temperature. For the same purpose, the interior surfaces of side panels are bare CFRP skins. All sensors, i.e., SXS-XCS, SXI, SGD, and HXI, have their own radiators for heat dissipation. Heat is transported via heat pipes using ammonia (NH3) as the working fluid. All heat pipes are dual channels or two single channels for redundancy. The heaters attached on the bus components, mission instruments, and heat pipes to satisfy their temperature requirements are controlled by Heater Control Electronics (HCE) except for the heaters controlled by mission instruments. Two heaters and temperature sensors are attached on a specified part to be controlled for redundancy. The set point of the redundant heater and temperature sensor is lower than that of the primary heater and temperature sensor so that only the primary heaters turn on normally. Besides, more than 50 temperature sensors are also attached on the bus components, mission instruments, and panels just to measure their temperature. Three HCEs are mounted on ASTRO-H, one is used only for the bus components and mission instruments on HXI plate and other two are used for those mounted on the part other than HXI plate. The former is defined as HXI-HCE and Figure 4. SXS-XCS thermal control system. the latter are defined as HCE-A and

3 International Conference on Environmental Systems

HCE-B. Exceptionally, one temperature sensor connected to HCE-A is mounted on HXI plate to measure its temperature during EOB extension as all the electronics including HXI-HCE are planned to be turned off at that time. Total heat dissipation from SXS-XCS, which has six cryocoolers mounted on the exterior of the liquid superfluid helium (LHe) dewar, is 290 W. Figure 4 shows the SXS-XCS thermal control system. Approximately one-third of total heat dissipation is radiated from the LHe dewar surface to deep space, and remaining heat is transported to SXS-XCS’s radiator via heat pipes. Four loop heat pipes (LHPs) are mounted on two shield coolers (two cold heads and two compressors) that are mounted on the middle shell of the LHe dewar to transport their dissipated heat to heat pipes. Two LHPs, SC-A-CMP and SC-B-CMP, are mounted on the two compressors of the shield coolers, and other two LHPs, SC-A-CHD and SC-B-CHD, are mounted on their coldheads, as shown in Fig. 5. Condensers of the two LHPs for SC-A-CMP and SC-B-CHD share one cold Figure 5. Four LHPs for SXS-XCS. plate, and other LHPs share another cold plate. A heater is attached to an evaporator on each LHP for start-up. A heater is also attached to the vapor line of each LHP so that the vapor forces the liquid to the reservoir to aid in LHP start-up. Temperature sensors are attached to the evaporator, vapor line, and liquid line of each LHP. There are three heat pipes (length: 3 m) on each SXS-XCS radiator so that heat dissipation is evenly distributed over the entire radiator. Four other cryocoolers are mounted on the aft dome of the dewar. Heat dissipated from two cryocoolers is transported to the heat pipes by two thermal straps. Heat dissipated from other two is directly radiated to deep space and conducted to the LHe dewar. Conceptual details of the thermal designs of other science instruments are described in a previous study.7

III. Thermal Vacuum Test of Flight Model The thermal design was verified by thermal balance tests of a thermal testing model (TTM) in 2012 in a thermal vacuum chamber (solar simulator) in TKSC.8 The proto-FM spacecraft structure and FOB were provided to TTM, while the thermal dummies of bus components and mission instruments were used instead of the FM. Some aspects of the thermal design were changed after the TTM thermal balance tests to satisfy the thermal requirements and to address other factors.9 The thermal design was finally verified by a thermal balance test using the FM in June 2015 in the same thermal vacuum chamber in TKSC. The main objective of the test was to Figure 6. Thermal vacuum test configuration. verify the spacecraft’s electrical function in the thermal vacuum environment. The test configuration same as that of the TTM thermal balance test shown in Fig. 6 was adopted. The HXI plate is enclosed by IR panels because it is situated besides the main spacecraft structure beyond the solar illumination range. HXT and SXT are not mounted because they are highly sensitive to contamination such as the gases emitted from the spacecrafts and chamber shrouds . Liquid helium was stored in the SXS-XCS LHe dewar, and the evaporated helium gas was evacuated outside of the chamber. TVT phases are shown in Table 1. Four thermal balance tests, including two worst cold cases and two worst hot cases, were conducted. Thermal environment conditions of the two worst hot cases were identical. During the HOT- A mode, primary (A-side) bus components operated and redundant (B-side) ones did not; in the HOT-B mode, only the redundant components operated. The nonredundant mission instruments operated throughout the thermal balance test except the COLD-2 mode. The COLD-2 mode simulated the worst cold case in an anomaly mode, i.e., under- voltage controller (UVC) condition that occurs when the battery voltage drops below the nominal voltage of 36 V. It was decided that only bus components and cryocoolers of SXS-XCS would operate in case of the UVC condition. Almost all instruments and components were turned on again to increase their temperature after the COLD-2 mode. Some bus components that were planned to be turned on during descent after the launch were operated during repressurization to verify their electrical performance under various pressure conditions.

4 International Conference on Environmental Systems

Two hundred and seventy-six flight temperature sensors (including 106 redundant Table 1. TVT phases. sensors) were mounted on the spacecraft; more than 400 thermocouples were attached for the TVT. The thermal balance criterion was “less than 0.3°C/h,” the same as the TTM thermal balance test. Almost all temperature change rates settled at less than 0.2°C/h in the thermal balance state. Most heat pipes, including the 3-m-long vertical heat pipes mounted on the SXS-XCS radiator, operated in an appropriate manner, but one failed to operate during the TTM thermal balance test. Some LHPs did not operate or stopped operating during this test. The operational status of LHPs is shown in Table 2. All start-up heaters were kept turned on during the HOT-B mode to ensure that LHPs operated until thermal equilibrium was attained because it was assumed that there would be insufficient heat entering the evaporators of LHPs for coldheads to start or maintain operation. Nominal heat dissipations of a compressor and coldhead are 35 W and 15 W, respectively. After the HOT-B mode, the start-up heater turned on only when LHP operation was attempted at the beginning of each thermal balance test. The LHPs for the coldhead and compressor (SC-B-CMP) stopped Table 2. SXS-XCS LHPs status on each test mode during the COLD-2 mode for about 40 hours. The temperature of the outer surfaces of the LHe dewar during the COLD-2 mode became lower than that during the COLD-1 mode. It is assumed that the SC-B-CMP LHP cannot maintain sufficient heat input as more of compressor’s heat dissipation flowed into the colder dewar. The following are expected from the abovementioned test results: 1) LHPs for coldheads may not remain in operation without start-up heaters, and 2) LHP for the SC-B-CMP may shut down in case of the UVC condition if a start-up heater does not turn on. Based on the TVT results, there is no major error in the thermal design of the spacecraft. The thermal mathematical model (TMM) is correlated with the test results to improve its accuracy so that the difference between the predicted and measured temperatures is less than 5°C. Some parameters of conductive couplings, node divisions, and MLI configurations were revised. It makes the TMM improved and the the difference between the predicted and measured temperatures decreased about 10 degC at maximum.

IV. Thermal Analysis System thermal analyses Table 3. Analysis cases. were performed using the adjusted TMM. The number of nodes of the TMM for the bus system is 22,770, which includes SXS-XCS and SXI radiator and heat pipes nodes. The total number of TMM nodes is 38,323, of which 15,553 are subsystems, including mission instrument interface TMM nodes. Thermal Desktop (version 5.5) was used as the simulator. 5 International Conference on Environmental Systems

The analyses were performed for 45 cases (categorized in Table 3.) A wide range of spacecraft attitudes to both the Sun and Earth was simulated for the analysis of extremes of hot and cold. Two contingency (i.e., abnormal operation) cases were considered. In the first case, the spacecraft loses the Sun and searches for it using the reaction control system. The spacecraft rotates 0.5°/s around its X and Z axes. The second case is the UVC condition. Almost all instruments except essential bus components and SXS-XCS cryocoolers are turned off during the UVC condition, and as a result, a 10°C uncertainty for the TMM is demanded by ASTRO-H thermal design criteria. This has not changed from previous development phases, even after TMM predictions were correlated with TVT results. In the simulation, it was found that the predicted temperatures of almost all components satisfy the thermal design criteria. As the results of SXS-XCS LHPs operation during TVT, the conductances of the two LHPs for the coldheads (SC-A-CHD and SC-B-CHD) are set 0 W/K for worst hot analyses. Predicted temperatures of coldheads and compressors are 10°C lower than the maximum allowable temperature of 40°C even if their heat dissipation reaches maximum at the cryocooler failure mode. The conductance of the SC-B-CMP LHP is set at 0 W/K for the UVC analysis; this caused the predicted temperature of the SC-B-CMP to reach 36°C, which is below the maximum allowable temperature of 40°C. This result does not satisfy the thermal design criteria, but it is agreed that this result does not impact the mission as compressors are automatically turned off by the autonomous function of the space management unit in orbit when compressor temperatures exceed 40°C. Table 4 shows the predicted temperatures of main parts and components of ASTRO-H from the worst hot (named as HOT-1 case) flight analysis. The measured and predicted temperature of TVT HOT-A mode are also shown in Table 4. Thermal mathematical model are considerably correlated and the TVT mode simulate the flight condition well. Note that the TVT conditions such as the spacecraft attitude against the solar are similar to the flight analysis conditions, but not exactly same.

Table 4. Results of flight analysis and TVT.

TVT (HOT-A) Flight analysis (HOT-1) ΔT (measured - Parts/components measured [℃] predicted [℃] predicted [℃] predicted) [℃] FOB/top plate 12 10 2 2 Side panel #1 18 18 0 15 Component A on side panel #1 11 13 -2 14 Side panel #2 28 28 0 24 Component B on side panel #2 24 22 2 16 Side panel #3 26 27 -1 25 Side panel #4 23 26 -3 23 Component C on side panel #4 17 18 -1 16 Side panel #5 21 23 -2 26 Component D on side panel #5 8 6 2 12 Component E on side panel #7 17 17 0 18 Side panel #6 3 3 0 -1 Side panel #8 5 4 1 5 Base plate 0 2 -2 4 EOB -5 -1 -4 2 HXI plate 20 13 7 27

V. Ground Operation before Launch ASTRO-H was underwent final assembly in the Second Spacecraft Test and Assembly building (STA2) at Tanegashima Space Center. Performance testing was conducted for both the heat pipes and LHPs in STA2 to check that they had not been damaged during transportation, and that they operated properly. It was confirmed by using the flight and nonflight heaters that each heat pipe operated. It took several iterations for LHPs to operate, but eventually all four LHPs operated properly. ASTRO-H was then moved to the Spacecraft and Fairing Assembly building to have the fairing installed. After fairing installation was complete, ASTRO-H was transferred to the Vehicle Assembly Building (VAB) and it was integrated to the H2A rocket. LHe was poured into the SXS-XCS LHe dewar though the access window of the fairing in VAB. The rocket was transferred to the Launch Pad (LP) from VAB about 12 h before the liftoff.

6 International Conference on Environmental Systems

The SXS-XCS cryocoolers were turned on immediately after the rocket was positioned on the LP and were kept operating for 75 min before liftoff to minimize the evaporation of LHe and temperature increase inside the LHe dewar. As mentioned above, each cryocooler temperature should be lower than the maximum allowable temperature of 40°C when in operation. The ambient temperature in the fairing was maintained at around 16°C by the air conditioner. Six fans are mounted on the LHe dewar to cool down the cryocoolers because both the computational fluid dynamics and thermal testing results showed that the fans are required to keep the temperature within the allowable temperature range at LP.10 Each fan is 80 mm × 80 mm × 15 mm. The maximum airflow per fan is 1.1 m3/min. The air velocity produced by the fans is approximately 5 m/s 50 mm from the fan. The fans were turned on simultaneously when the cryocoolers powered on, and turned off 45 min after the cryocoolers turned off, i.e., 30 min before the liftoff. The fans were kept operating after the cryocoolers stopped operating in order to cool the cryocoolers’ compressors to below 20°C by liftoff because of the temperature requirement of vibration-isolation systems for the compressors. Passive vibration isolators were mounted between the four compressors and the LHe dewar to prevent the transmission of micro- vibrations caused by the compressors.11 The temperature of the isolators should be within the range of 15°C–25°C at second engine ignition, Figure 7. Temperature profile of shield coolers and i.e., 400–800 second after liftoff. The temperature LHe Dewar outersurface before launch. profiles of two compressors of the shield coolers (SC-A-CMP and SC-B-CMP), coldheads of the shield coolers (SC-A-CHD and SC-B-CHD), and the LHe dewar outer surface are shown in Fig. 7. Note that the cooler driver was turned off and these temperature measurements finished as planned 10 min before the fans are stopped. The compressor and coldhead temperatures finally decreased to below 20°C just before temperature measurement was stopped.

VI. In-Orbit Checkout Phase The H2A rocket lifted off at 8:45 Universal Time (UT), February 17 and ASTRO-H was injected into the planned orbit. The temperatures of the components and mission instruments were measured and controlled by the heaters by HCE during the launch; HCE was not turned off before the liftoff, while the SXS-XCS cooler driver. The data transmitted from ASTRO-H was received at Santiago Ground Station (SNT) at 9:30 (UT) and showed that the spacecraft was in good health. The four LHPs were started up the same day so that the shield cooler could be operated in nominal conditions and heat dissipated as soon as possible. The bus components and SXS-XCS instruments were powered up in the next 10 days and the EOB was extended. ASTRO-H had been in a stable condition since its liftoff. However, suddenly the communication with ASTRO- H failed on March 26 and it has been not recovered yet up to now (April 28 2016). Here the four topics are reported: A) the heat pipes and LHP operation, B) temperature change of HXI plate during EOB extension, C) the spacecraft temperature evaluation after EOB extended, and D) communication anomaly.

A. Heat Pipes and LHPs operation The temperature measurement results indicated that the heat pipes were operating properly. The start-up operations for LHPs were initiated in the second communication operation via SNT 2 h and 24 min after liftoff. The orbit of ASTRO-H limits the length of the communications window to approximately 10 min. Communication operations were conducted from two ground stations, SNT in Chili and Uchinoura (USC) in Japan. The communication time comes one by one alternately between SNT and USC in one orbit. For the LHP start-up, the vapor line heaters were turned on for 1 min, and then were turned off; the start-up heaters were turned on simultaneously. The start-up heaters were turned on for 8 min and then automatically turned

7 International Conference on Environmental Systems

off. This serial start-up operation was also taken for the LHPs whenever the performance tests were conducted on ground including TVT. ALL the LHPs successfully started up at the first operation in the second SNT communication operation (SNT #2). Figure 8 shows SC-A-CMP LHP temperature profile including the start-up operation in SNT #2 that started at 11:13:56 (UT) and finished 11:22:56 (UT) on 17 February. The same start-up operation was also automatically done in the next USC communication operation (USC #2) at 12:10 (UT) 17 February because it was already planned. It was confirmed that all the LHPs were operating during USC #2. Then the cryo-cooler power was increased from about 20 W to 50 W in USC #2. The two LHPs for the compressors have been operated properly for more than one month until the communication anomaly happened on March 26 from the launch.

Figure 8. Temperature profile of the SC-A-CMP LHP in SNT #2 on 17 Feburuary.

B. Temperature Change of HXI plate during EOB extension As mentioned in “ Thermal Design” section, the heaters of the bus components, mission instruments (HXI-S), and heat pipes are turned off during EOB extension because HXI-HCE is supposed to be turned off just before the extension. According to the transient thermal analysis results, predicted temperatures of some bus components on HXI plate and HXI-S decrease gradually and exceed their minimum allowable temperature when ASTRO-H goes round twice without heater control by HXI- HCE. It was decided to complete EOB extension in two rounds at most, if not the extension is temporarily suspended so that HXI-HCE is turned on and the bus components and HXI-S are heated up. It was also found that two bus components should be heated up prior to the extension, otherwise the temperatures become lower than their minimum allowable temperature range. The extension was started at USC #2 on 29 February. The extension operation was continued till Figure 9. Temperature profile of HXI plate during EOB the next two communication time, SNT #2 and USC extension on 29 February. #3. The HXI-HCE was turned on and the heater control was started after EOB extension operation was stopped temporarily in USC #3. The heater control by HXI- HCE kept for about 30 minutes and then HXI-HCE was turned off in the beginning of the next communication

8 International Conference on Environmental Systems

operation SNT #3 to restart EOB extension. EOB extension successfully completed and immediately HXI-HCE was turned on again during SNT #3. Figure 9 shows the temperature change of HXI plate measured by HCE-A during EOB extension operation. The HXI plate temperature was decreased linearly from USC #2 to USC #3 as not only the heater control by HXI-HCE was suspended but also it was exposed to the deep space while it was enclosed by the lower part of the spacecraft before the extension. As Fig. 8 shows, the temperature of the HXI plate was decreased 17 degC in one orbit. The measured temperature change agrees the predicted temperature change well. It was found that all the measured temperature of the bus components, mission instruments, and heat pipes on HXI plate are within their allowable temperature range when HXI-HCE was turned on in USC #3 and SNT #3.

C. Spacecraft temperature evaluation According to the temperature and heater duties, no problems with the thermal control system had arisen till the communication anomaly occurred on March 26. The differences between the measured temperature in orbit after the EOB was expanded and the predicted temperatures are shown in Table 5 for the typical parts of the spacecraft. The analysis for the worst cold case is used for the comparison because the actual orbital thermal optical property is assumed to be beginning of life (BOL) conditions. Regarding to the thermal optical properties, the end of lihe (EOL) conditions are used for the worst hot analyses and the BOL conditions are used for worst cold analyses. Note that the attitude of the spacecraft is the same but the actual orbital heat input, such as the solar intensity, is higher than the analysis condition. The measured temperatures shown in Table 4 are the parts where the temperatures were not controlled by the heaters. Almost all temperature differences are within the 5°C range. The TMM agrees well with the actual thermal design so far, but the temperatures were evaluated just for one case in the checkout phase. It is necessary to evaluate the TMM for more cases, with various spacecraft attitudes, after all mission instruments are turned on.

Table 5. Differences between the measured temperatures and predicted ones. the typical component is indicated in alphabet instead of its own name. There are no temperature sensors nearby the components on the side panel #3. There are no components on side panels #6 and #8. Parts/components ΔT (measured - predicted) [℃] FOB/top plate 2 Side panel #1 0 Component A on side panel #1 0 Side panel #2 4 Component B on side panel #2 3 Side panel #3 4 Side panel #4 0 Component C on side panel #4 -1 Side panel #5 2 Component D on side panel #5 4 Component E on side panel #7 -3 Side panel #6 0 Side panel #8 1 Base plate -2 EOB 2 HXI plate 3

D. Communication anomaly ASTRO-H completed the critical operation phase with the successful extension of EOB and started the initial functional verification of the instruments on February 29 2016. The spacecraft was in a stable condition and the thermal control systems operated normally. However, the communication with ASTRO-H failed from the start of its

9 International Conference on Environmental Systems

operation originally schedulled at 7:40 (UT) March 26 2016. After one-month effort to recover the communication, JAXA concluded that ASTRO-H’s functions cannot be restroed again on April 28.

Conclusions The thermal performances of the ASTRO-H satellite before and after the launch have been evaluated. The thermal control systems and TMM were verified by the TVT conducted about 8 months before the launch. The thermal analysis was performed for 45 cases with the updated TMM and it was confirmed that the predicted temperatures of almost all components satisfy the thermal design criteria and requirements. The temperature requirements of the SXS-XCS cryocoolers at LP could be met with six of the eight fans mounted on the LHe dewar for ground cooling. According to the orbital data, no problems about thermal control system have arisen in the three weeks since launch. The heat pipes are operating properly in orbit. Two LHPs for the coldheads stopped operating but it has not impacted the temperature of the cryocoolers; this was predicted by the TVT results. The measured (in- flight) temperatures agree well with the predicted values for the attitude condition attained after the EOB expanded.

Acknowledgments We deeply appreciate all other members in ASTRO-H team for their cooperation and support. We thank NIIPI corporation (FOB and EOB contractor), Mitsubishi Heavy Industries (SXI, SGD, and HXI contractor), Sumitomo Heavy Industries (SXS-XCS contractor), Nagoya University (HXT contractor), and the team members in the United States, Canada, and Europe. We especially appreciate IberEspacio and the European Space Agency for their contribution for the LHPs. We also thank Mitsubishi Heavy Industries (H2A rocket contractor) for a successful launch.

References 1Takahashi, T. et al. “The ASTRO-H mission,” Proceedings of SPIE meeting, Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray, edited by M. Arnaud, S. S. Murray, and T. Takahashi, Vol. 7732, 2010, pp. 77320Z 2Kunieda, H. et al. “Hard x-ray telescope to be onboard ASTRO-H,” Proceedings of SPIE meeting, Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray, edited by M. Arnaud, S. S. Murray, and T. Takahashi, Vol. 7732, 2010, pp. 773214 3Mitsuda, K. et al. “The High-Resolution X-ray Microcalorimeter Spectrometer System for the SXS on ASTRO-H,” Proceedings of SPIE meeting, Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray, edited by M. Arnaud, S.

S. Murray, and T. Takahashi, Vol. 7732, 2010, pp. 773211 4Tsunemi, H. et al. “Soft X-ray Imager (SXI) Onboard ASTRO-H,” Proceedings of SPIE meeting, Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray, edited by M. Arnaud, S. S. Murray, and T. Takahashi, Vol. 7732, 2010, pp. 773210 5Tajima, H. et al. “Soft Gamma-ray Detector for the ASTRO-H Mission,” Proceedings of SPIE meeting, Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray, edited by M. Arnaud, S. S. Murray, and T. Takahashi, Vol. 7732, 2010, pp. 773216 6Kokubun, M. et al. “Hard X-ray Imager (HXI) for the ASTRO-H Mission,” Proceedings of SPIE meeting, Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray, edited by M. Arnaud, S. S. Murray, and T. Takahashi, Vol. 7732, 2010, pp. 773215 7Iwata, N. et al. “Thermal Control Design of X-ray Astronomy Satellite ASTRO-H,” 42nd International Conference on Environmental Systems, San Diego, California, 2012, AIAA-2012-3579 8Iwata, N. et al. “Solar Simulation Tests of the X-ray Astronomy Satellite ASTRO-H,” 43rd International Conference on Environmental Systems, Vail, Colorado, 2013, AIAA-2013-3369 9Iwata, N. et al. “Thermal Control System of X-ray Astronomy Satellite ASTRO-H: Current Development Status and Prospects,” 44th International Conference on Environmental Systems, Tucson, Arizona, 2012, ICES-2014-285 10Nonomura, T. et al. “Thermal Condition of ASTRO-H under Air-cooled Environment before Launch,” Transactions of the Japan Society for Aeronautical and Space Science Aerospace technology Japan, Vol. 12, No. ists29, 2014, pp. To_4_1-To_4_10 11Yasuda, S. and Ishimura, K. “Method of Determming Specification for Transmissibility of Vibration Isolator for ASTRO-H Soft X-ray Spectrometer (SXS),” 43rd European Conference on Spacecraft Structures, Materials & Environmental Testing, Braunschweig, Germany, 2014

10 International Conference on Environmental Systems