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 have been developing an ultra-lightweight Wolter type-I X-ray telescope fabricated with micro electro mechanical systems (MEMS) technologies for GEO-X (GEOspace X-ray Imager) mission.
GEO-X will aim global imaging of the Earth's magnetosphere using X-rays.
The telescope is our original micropore optics which is light in weight (~5 g), compact with a short focal length (~250 mm), and has a wide field-of-view (~5 deg x 5 deg).
In this talk we show developed assembly processes to meet the requirements of the GEO-X mission and the telescope's X-ray imaging performance as an engineering model with this method.
We have been developing an ultra-lightweight Wolter type-I x-ray telescope fabricated with MEMS technologies for GEO-X (geospace x-ray imager) which is an 18U CubeSat (∼20 kg) to perform soft x-ray imaging spectroscopy of the entire Earth’s magnetosphere from Earth orbit near the moon. The telescope is our original micropore optics which possesses lightness (∼15 g), a short focal length (∼250 mm), and a wide field of view (∼5 ◦ × ∼5 ◦ ). The MEMS x-ray telescope is made of 4-inch Si (111) wafers. The Si wafer is firstly processed by deep reactive ion etching such that they have numerous curvilinear micropores (20-µm width) whose sidewalls are utilized as X-ray reflective mirrors. High-temperature hydrogen annealing and chemical mechanical polishing processes are then applied to make those sidewalls smooth and flat enough to reflect X-rays. After that, the wafer is plastic-deformed into a spherical shape and Pt-coated by plasma atomic layer deposition (ALD) process to focus x-rays with high reflectivity. Finally, we assemble two optics bent with different curvatures (1000- and 333-mm radius) into the Wolter type-I telescope. Optimizing the annealing and polishing processes, we found that the optic achieves an angular resolution of ∼5.4 arcmins in HPW. This is comparable with the requirement for GEO-X (∼5 arcmins in HPD at single reflection). Our optic was also successfully Pt-coated by a plasma-enhanced ALD process to enhance x-ray reflectivity. Moreover, we fabricated an STM telescope and confirmed its environmental tolerances by conducting an acoustic test with the H-IIA rocket qualification test level and a radiation tolerance test with a 100 MeV proton beam for 30 krad equivalent to a 3-year duration in the GEO-X orbit.
We are developing a novel Bragg reflection x-ray polarimeter using hot plastic deformation of silicon wafers. A Bragg reflection polarimeter has the advantage of simple principle and large modulation factor but suffers from the disadvantage of a narrow detectable energy band and difficulty to focus an incident beam. We overcome these disadvantages by bending a silicon wafer at high temperature. The bent Bragg reflection polarimeter have a wide energy band using different angles on the wafer and enable focusing. We have succeeded in measuring x-ray polarization with this method for the first time using a sample optic made from a 4-inch silicon (100) wafer.
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.
The super DIOS mission is a candidate of Japanese future satellite program after 2030’s and this scientific concept has been approved to establish an ISAS/JAXA research group. The main aim of the super DIOS is a x-ray survey to quantify of baryons, over several scales, from the circumgalactic medium around galaxies, cluster outskirts to the warm-hot intergalactic medium along the large cosmic structure by detections of the redshifted emission lines from OVII, OVIII and other ions, for investigating the dynamical state of baryons, including energy flow and metal cycles, in the universe. The super DIOS will have a resolution of 15 arcseconds and 3 kilo-pixels of transition edge sensor (TES) and its micro-wave SQUID multiplexer read-out system. This performance resolves most contaminating x-ray sources and reduces the level of diffuse x-ray background after subtracting point-like sources. The technical achievements of on-board cooling system reached by the Hitomi (ASTRO-H) and XRISM for microcalorimeter provide baseline technology for Super DIOS. We will also have a large scale collaborations with multi wave-length survey projects such as optical and radio survey observations.
LiteBIRD has been selected as JAXA’s strategic large mission in the 2020s, to observe the cosmic microwave background (CMB) B-mode polarization over the full sky at large angular scales. The challenges of LiteBIRD are the wide field-of-view (FoV) and broadband capabilities of millimeter-wave polarization measurements, which are derived from the system requirements. The possible paths of stray light increase with a wider FoV and the far sidelobe knowledge of -56 dB is a challenging optical requirement. A crossed-Dragone configuration was chosen for the low frequency telescope (LFT : 34–161 GHz), one of LiteBIRD’s onboard telescopes. It has a wide field-of-view (18° x 9°) with an aperture of 400 mm in diameter, corresponding to an angular resolution of about 30 arcminutes around 100 GHz. The focal ratio f/3.0 and the crossing angle of the optical axes of 90◦ are chosen after an extensive study of the stray light. The primary and secondary reflectors have rectangular shapes with serrations to reduce the diffraction pattern from the edges of the mirrors. The reflectors and structure are made of aluminum to proportionally contract from warm down to the operating temperature at 5 K. A 1/4 scaled model of the LFT has been developed to validate the wide field-of-view design and to demonstrate the reduced far sidelobes. A polarization modulation unit (PMU), realized with a half-wave plate (HWP) is placed in front of the aperture stop, the entrance pupil of this system. A large focal plane with approximately 1000 AlMn TES detectors and frequency multiplexing SQUID amplifiers is cooled to 100 mK. The lens and sinuous antennas have broadband capability. Performance specifications of the LFT and an outline of the proposed verification plan are presented.
We are developing an x-ray imaging spectrometer for Super DIOS satellite mission, a future x-ray observatory, planned by JAXA, to be launched in 2030’s. Super DIOS will reveal the nature of the missing baryon in the warm-hot intergalactic medium because of its fine energy and angular resolution, large effective area and large field of view. A main detector on-board Super DIOS consists of a transition-edge sensor (TES) microcalorimeter array of over 30,000 pixels working at a temperature below 100 mK and it poses a considerable technical difficulty to the readout. A microwave superconducting quantum interference device (SQUID) multiplexing is promising technique and expected to achieve a large scale readout of more than 30,000 pixels. We describe our development of a 40-channel microwave SQUID multiplexer with low-noise characteristics∗ and a demonstration of simultaneously reading out 40-pixel TESs. Finally, we discuss a future prospect and a feasibility of reading out an array of more than 30,000 pixels.
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