The X-ray Imaging and Spectroscopy Mission (XRISM) is an X-ray astronomy satellite successfully launched in September 2023. The satellite carries two X-ray telescopes with a focal length of 5.6 meters. One of these is Resolve, which consists of an X-ray Mirror Assembly (XMA) and a microcalorimeter array, providing a relatively narrow field of view (FoV) of 3.05 arcminutes squared. The other is Xtend, which consists of an XMA and an X-ray CCD camera, offering a large FoV of 38 arcminutes squared. Due to Resolve’s limited FoV, pointing accuracy is crucial for stable observation. The observation aimpoint, defined as the position on the focal plane where an on-axis target is located, was verified within a few arcseconds of the center of the array after the satellite’s boresight correction. It was also confirmed to be suitable, with no significant irreversible shift detected over approximately half a year. In the commissioning phase, all measurable requirements for pointing accuracy were confirmed to be met. The absolute pointing determination accuracies are less than 20 arcseconds for both instruments. The aimpoint shift and its temperature dependence were also assessed for each detector. The aimpoint shifts of both instruments in each observation have a good correlation on the X-axis, but not on the Y-axis in the detector coordinates. Resolve’s Y-axis shift clearly depends on the base panel temperature, on the order of a few arcseconds, which can be ignored for the absolute control accuracy and effective area. The sharp PSF core with an FWHM of approximately 10 arcseconds and arcsecond-scale relative determination accuracy enable Xtend to achieve good image reconstruction performance.
KEYWORDS: Space operations, Data processing, Photovoltaics, Equipment, Calibration, Source mask optimization, Information technology, Data archive systems, Satellites, X-rays
The X-Ray Imaging and Spectroscopy Mission (XRISM) is an international X-ray observatory developed by Japan Aerospace Exploration Agency (JAXA) and National Aeronautics and Space Administration (NASA) in collaboration with European Space Agency (ESA), successfully launched in September 2023. Since the early stage of the project, the XRISM science operations team (SOT) was organized independently of the spacecraft bus system and mission instrument development teams, having prepared for the in-orbit science operations to maximize the scientific outputs. During about half year for the initial operation phase after launch, operations for the mission instruments were started, and the quick-look and the pipeline processes were carried out by SOT in order to check the functions of the instruments. After transition to the nominal operation phase, we started the target observations in the performance verification phase, whose short and long-term observation plans are considered by SOT, including planning the target of opportunity observations. The information on the observation modes of the mission instruments and the status of the data processing is maintained collectively in database synchronized between JAXA and NASA. We also performed the performance verification and optimization activities which provide the well-calibrated data, appropriate tools, and analysis methods for the users and established a help desk that supports the XRISM data analysis. The publicly solicited observation for the guest observer will be started from August or September 2024. These daily science operations are being carried out by dedicated scientists belonging to JAXA in collaboration with the other SOT members, the mission operations team and the instrument teams. This paper will introduce the ground system for the XRISM science operations and report on the activities of the SOT from the launch to today and plans for future science operations.
KEYWORDS: Global Positioning System, Clocks, Vacuum, Temperature metrology, Data conversion, Calibration, Satellites, Data modeling, Space operations, Physics
We report the results from the ground and on-orbit verification of the XRISM timing system when the satellite clock is not synchronized to the GPS time. XRISM carries a GPS receiver which synchronizes the main satellite clock to the GPS time but in a rare case that the satellite fails to receive the GPS signal, the clock runs freely and its frequency changes depending on its temperature. In this case, we correct the time drift considering the temperature dependency of the clock frequency measured in advance. To confirm that the accuracy of the time assignment in the GPS unsynchronized mode satisfies the requirement (within a 350 us error in the absolute time, for the satellite bus system plus ground system), we have performed the ground and on-orbit tests. In the thermal vacuum test performed in 2022, we obtained the GPS unsynchronized mode data and the temperature versus clock frequency trend. Comparing the time values assigned to the data and the true GPS times when the data were obtained, we confirmed that the requirement was satisfied in the temperature condition of the thermal vacuum test. We also simulated the variation of the timing accuracy in the on-orbit temperature conditions, using the Hitomi on-orbit temperature data and the dependency of the timing error on the temperature gradient obtained in the thermal vacuum test. We found that the error remained within the requirement over ∼ 300000 s without any time calibration data. After the launch, we performed on-orbit tests in 2023 September and October as part of the bus system checkout. The temperature versus clock frequency trend was found to remain unchanged from that obtained in the thermal vacuum test and the observed time drift was consistent with that expected from the trend.
The XRISM is the newly born X-ray satellite led by JAXA and NASA in collaboration with ESA, aiming to perform high-resolution spectroscopy of many astronomical X-ray objects. In the era of multi-messenger astronomy, where observations are performed in various wavelengths and include neutrino and gravitational data, it is important for the observatories to assign precise time of photons. To achieve the science goals of the XRISM mission, an absolute timing accuracy of 1.0 ms is required for the Resolve. The timing system, including both onboard instruments and off-line data-processing tools, is designed to meet this requirement. Following the lessons of the previous X-ray mission of Hitomi, comprehensive list of items that affect the accuracy of the timing are listed together with the timing error budget. During the system design and verification phases on the ground, all elements are controlled and verified to be within the budgets at the component level. After the launch of the satellite on 7 September 2023, in the initial commissioning phase, the overall timing performance of the timing system is scheduled to be confirmed to satisfy the timing requirements using a millisecond pulsar. The XRISM spacecraft carries the GPS receiver and the timing system uses the GPS signals in the nominal operation mode. In this presentation, we summarize the detailed design of the timing system of the XRISM, and the results of the timing verification tests both on ground and in orbit in the nominal operation mode. Detailed results on the failure mode of the GPS receiver will be presented in another presentation.
The X-Ray Imaging and Spectroscopy Mission (XRISM) project at JAXA officially started in 2018. Following the development of onboard components, the proto-flight test was conducted from 2021 to 2023 at JAXA Tsukuba Space Center. The spacecraft was launched from JAXA Tanegashima Space Center on September 7, 2023 (JST), and onboard components, including the science instruments, were activated during the in-orbit commissioning phase. Following the previous report in 2020, we report the spacecraft ground tests, the launch operation, in-orbit operations, and the status and plan of initial and subsequent guest observations.
The X-Ray Imaging and Spectroscopy Mission (XRISM) is the successor to the 2016 Hitomi mission that ended prematurely. Like Hitomi, the primary science goals are to examine astrophysical problems with precise highresolution X-ray spectroscopy. XRISM promises to discover new horizons in X-ray astronomy. XRISM carries a 6 x 6 pixelized X-ray micro-calorimeter on the focal plane of an X-ray mirror assembly and a co-aligned X-ray CCD camera that covers the same energy band over a large field of view. XRISM utilizes Hitomi heritage, but all designs were reviewed. The attitude and orbit control system were improved in hardware and software. The number of star sensors were increased from two to three to improve coverage and robustness in onboard attitude determination and to obtain a wider field of view sun sensor. The fault detection, isolation, and reconfiguration (FDIR) system was carefully examined and reconfigured. Together with a planned increase of ground support stations, the survivability of the spacecraft is significantly improved.
The ASTRO-H mission was designed and developed through an international collaboration of JAXA, NASA, ESA, and the CSA. It was successfully launched on February 17, 2016, and then named Hitomi. During the in-orbit verification phase, the on-board observational instruments functioned as expected. The intricate coolant and refrigeration systems for soft X-ray spectrometer (SXS, a quantum micro-calorimeter) and soft X-ray imager (SXI, an X-ray CCD) also functioned as expected. However, on March 26, 2016, operations were prematurely terminated by a series of abnormal events and mishaps triggered by the attitude control system. These errors led to a fatal event: the loss of the solar panels on the Hitomi mission. The X-ray Astronomy Recovery Mission (or, XARM) is proposed to regain the key scientific advances anticipated by the international collaboration behind Hitomi. XARM will recover this science in the shortest time possible by focusing on one of the main science goals of Hitomi,“Resolving astrophysical problems by precise high-resolution X-ray spectroscopy”.1 This decision was reached after evaluating the performance of the instruments aboard Hitomi and the mission’s initial scientific results, and considering the landscape of planned international X-ray astrophysics missions in 2020’s and 2030’s. Hitomi opened the door to high-resolution spectroscopy in the X-ray universe. It revealed a number of discrepancies between new observational results and prior theoretical predictions. Yet, the resolution pioneered by Hitomi is also the key to answering these and other fundamental questions. The high spectral resolution realized by XARM will not offer mere refinements; rather, it will enable qualitative leaps in astrophysics and plasma physics. XARM has therefore been given a broad scientific charge: “Revealing material circulation and energy transfer in cosmic plasmas and elucidating evolution of cosmic structures and objects”. To fulfill this charge, four categories of science objectives that were defined for Hitomi will also be pursued by XARM; these include (1) Structure formation of the Universe and evolution of clusters of galaxies; (2) Circulation history of baryonic matters in the Universe; (3) Transport and circulation of energy in the Universe; (4) New science with unprecedented high resolution X-ray spectroscopy. In order to achieve these scientific objectives, XARM will carry a 6 × 6 pixelized X-ray micro-calorimeter on the focal plane of an X-ray mirror assembly, and an aligned X-ray CCD camera covering the same energy band and a wider field of view. This paper introduces the science objectives, mission concept, and observing plan of XARM.
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