GEO-X (GEOspace X-ray imager) is a small satellite mission to visualize the Earth’s magnetosphere through Solar Wind Charge eXchange (SWCX). SWCX is known as soft X-ray emissions generated by the charge exchange between highly charged-state heavy ions and neutral atoms in the Earth’s exosphere. The GEO-X satellite is aimed to be launched during the upcoming solar maximum around 2025-2027 and is planned to be injected to a low-latitude orbit which allows visualization of the magnetosphere from outside the magnetosphere. The satellite will carry a light-weight X-ray imaging spectrometer, dramatically improving the size and weight of those onboard past X-ray astronomy satellites.
We report a development status of a focal plane detector for the GEO-X (GEOspace X-ray imager) mission that will perform soft X-ray (≤2 keV) imaging spectroscopy of Earth’s magnetosphere from a micro satellite. The mission instrument consists of a microelectromechanical systems (MEMS) X-ray mirror and a focal plane detector. A sensor with fine positional resolution and moderate energy resolution in the energy band of 0.3 to 2 keV is required. Because the observing target is the magnetosphere around the day-side Earth, the visible-light background must be decreased by shortening the integration time for readout. To satisfy the above requirements, a high-speed X-ray CMOS sensor is being evaluated as a primary candidate for the detector. Irradiating the flight candidate sensor with monochromatic X-rays, we obtained the energy resolution of 205 eV (FWHM) at 6 keV by cooling the devices to −15°C. Radiation tolerance of the sensor, especially in terms of total dose effect, is investigated with 100 MeV proton. The amount of degradation of energy resolution is <50 eV up to 10 krad, which ensures that we will be able to track and calibrate the change of the line width in orbit.
GEOspace X-ray imager (GEO-X) is a small satellite mission aiming at visualization of the Earth’s magnetosphere by X-rays and revealing dynamic couplings between solar wind and the magnetosphere. In-situ spacecraft have revealed various phenomena in the magnetosphere. X-ray astronomy satellite observations recently discovered soft X-ray emissions originating from the magnetosphere. We are developing GEO-X by integrating innovative technologies of a wide field of view (FOV) X-ray instrument and a small satellite for deep space exploration. The satellite combines a Cubesat and a hybrid kick motor, which can produce a large delta v to increase the altitude of the orbit to about 30 to 60 RE from a relatively low-altitude (e.g., geo transfer orbit) piggyback launch. GEO-X carries a wide FOV (5 × 5 deg) and a good spatial resolution (10 arcmin) X-ray (0.3 to 2 keV) imaging spectrometer using a micro-machined X-ray telescope and a CMOS detector system combined with an optical blocking filter. We aim to launch the satellite around the solar maximum of solar cycle 25.
We propose an x-ray imaging system, multi-image x-ray interferometer module (MIXIM), with which a very high angular resolution can be achieved even with a small system size. MIXIM is composed of equally spaced multiple slits and an x-ray detector, and its angular resolution is inversely proportional to the distance between them. Here, we report our evaluation experiments of MIXIM with a newly adopted CMOS sensor with a high spatial resolution of 2.5 μm. Our previous experiments with a prototype MIXIM were limited to one-dimensional imaging, and more importantly, the achieved angular resolution was only ∼1 ″ , severely constrained due to the spatial resolution of the adopted sensor with a pixel size of 4.25 μm. By contrast, one-dimensional images obtained in this experiment had a higher angular resolution of 0.5″ when a configured system size was only ∼1 m, which demonstrates that MIXIM can simultaneously realize a high angular resolution and compact size. We also successfully obtained a two-dimensional profile of an x-ray beam for the first time for MIXIM by introducing a periodic pinhole mask. The highest angular resolution achieved in our experiments is smaller than 0.1″ with a mask-sensor distance of 866.5 cm, which shows the high scalability of MIXIM.
We are developing an x-ray CMOS detector for the GEO-X (GEOspace x-ray imager) mission that will perform soft x-ray (≤2 keV) imaging spectroscopy of Earth’s magnetosphere using a micro satellite. The mission instrument consists of a MEMS x-ray mirror and a focal plane detector. For the latter, we need a sensor with fine positional resolution and moderate energy resolution in the energy band of 0.3 to 2 keV. Because we observe the day-side structure of the earth’s magnetosphere, visible-light background must be decreased by shortening the integration time for readout. To satisfy the above requirements, a high-speed x-ray CMOS sensor is being evaluated as a primary candidate for the detector. We adopt back-side illuminated sensors that have been originally developed for visible-light or UV imaging. The sensors have different specification in terms of the thickness of epitaxial wafer and specific resistance. Irradiating sensors with monochromatic x-rays from 55Fe, we obtained the energy resolution of 205 and 227 eV (FWHM) depending on the sensor type for single pixel events at 6 keV by cooling down the sensor to −15°C. On the other hand, we found that the pulse height of the events whose charges spread over multiple pixels are significantly lower than that of single pixel events in some chips. Then we selected the chips that shows better charge collection efficiency as flight candidate. Radiation tolerance of the sensor, especially in terms of total dose effect, is investigated with 100 MeV proton. The amount of dose ranges up to 100 krad depending on position in the sensor. In spite of the excessive dose compared with 10 krad/yr in the expected highly elliptical orbit, Mn Kα and Kβ are well resolved. The amount of degradation of energy resolution is less than 50 eV up to 10 krad, which ensures that we will be able to track and calibrate the change of the line width in orbit We also utilize multi-color x-rays to investigate spectroscopic performance in the energy band of 0.5 to 7 keV. Multiple lines below 1 keV are resolved and energy resolutions are evaluated as well as linearity performance.
We have developed a novel x-ray interferometer, multi-image x-ray interferometer module (MIXIM), comprised of a fine aperture mask and an x-ray detector. The angular resolution of this system can be improved with an increase of the distance between two components or a decrease of the aperture size. Although MIXIM has already achieved an angular resolution of less than 0.1” by applying the Talbot effect with a periodic multi-pinhole mask, there remains the issue that its low opening fraction of 1.3% decreases the effective area of the imaging system. Therefore, we newly introduced periodic coded aperture masks which have opening fractions of about 50% instead of the multi-pinhole mask. Conducting an experiment with a 12.4 keV parallel x-ray beam, we successfully demonstrated that the periodic coded aperture could form the self-image, and obtained the x-ray source profile with sub-arcsecond angular resolution by deciphering the coded pattern. The effective area increases about 25 times compared with the multi-pinhole mask by the introduction of the periodic coded aperture masks, which indicates that this novel method can be effective for addressing the problem.
Xappl is a software framework written in Python to build pre-pipelines for the X-Ray Imaging and Spectroscopy Mission (XRISM) scheduled to be launched in the Japanese fiscal year 2022. Xappl chains software tasks in the order specified in configuration files in the INI format, enabling us to reduce the telemetry data to First FITS Files, which originate datasets ready for analysis. Since the functionalities of Xappl are highly generalized, it is reusable for future missions. In this paper, we present the design of Xappl and report the developmental progress of the pre-pipeline for XRISM.
GEO-X (GEOspace X-ray imager) is a small satellite mission aiming at visualization of the Earth’s magnetosphere by X-rays and revealing dynamical couplings between solar wind and magnetosphere. In-situ spacecraft have revealed various phenomena in the magnetosphere. In recent years, X-ray astronomy satellite observations discovered soft X-ray emission originated from the magnetosphere. We therefore develop GEO-X by integrating innovative technologies of the wide FOV X-ray instrument and the microsatellite technology for deep space exploration. GEO-X is a 50 kg class microsatellite carrying a novel compact X-ray imaging spectrometer payload. The microsatellite having a large delta v (<700 m/s) to increase an altitude at 40-60 RE from relatively lowaltitude (e.g., Geo Transfer Orbit) piggyback launch is necessary. We thus combine a 18U Cubesat with the hybrid kick motor composed of liquid N2O and polyethylene. We also develop a wide FOV (5×5 deg) and a good spatial resolution (10 arcmin) X-ray (0.3-2 keV) imager. We utilize a micromachined X-ray telescope, and a CMOS detector system with an optical blocking filter. We aim to launch the satellite around the 25th solar maximum.
Xtend is a soft x-ray imaging telescope developed for the x-ray imaging and spectroscopy mission (XRISM). XRISM is scheduled to be launched in the Japanese fiscal year 2022. Xtend consists of the soft x-ray imager (SXI), an x-ray CCD camera, and the x-ray mirror assembly (XMA), a thin-foil-nested conically approximated Wolter-I optics. The SXI uses the P-channel, back-illuminated type CCD with an imaging area size of 31mm on a side. The four CCD chips are arranged in a 2×2 grid and can be cooled down to −120 °C with a single-stage Stirling cooler. The XMA nests thin aluminum foils coated with gold in a confocal way with an outer diameter of 45 cm. A pre-collimator is installed in front of the x-ray mirror for the reduction of the stray light. Combining the SXI and XMA with a focal length of 5.6m, a field of view of 38′ × 38′ over the energy range from 0.4 to 13 keV is realized. We have completed the fabrication of the flight model of both SXI and XMA. The performance verification has been successfully conducted in a series of sub-system level tests. We also carried out on-ground calibration measurements and the data analysis is ongoing.
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