We have been developing ultra-lightweight Wolter type-I X-ray telescopes fabricated with MEMS technologies for GEO-X (GEOspace X-ray imager) which is a small satellite mission to perform soft X-ray imaging spectroscopy of the entire Earth’s magnetosphere. The telescope is our original type of micropore optics and possesses lightness (∼5 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 first processed by deep reactive ion etching, which has numerous curvilinear micropores (a 20-μm width) whose sidewalls are utilized as X-ray reflective mirrors. High-temperature hydrogen annealing and chemical mechanical polishing processes are 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 a plasma atomic layer deposition process to focus X-rays with high reflectivity. Finally, we assemble two optics bent with different curvatures (1000- and 333-mm radii) and complete the Wolter type-I telescope. We optimized each process and conducted an X-ray irradiation test to assemble the full-processed optics into an EM telescope for the GEO-X mission, which enabled to complete the telescope to achieve an angular resolution of ∼4.8 arcmin in FWHM in the assembled telescope. We report on our latest development status and the X-ray imaging performance of the GEO-X EM telescope.
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.
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 silicon foil X-ray optics using a hot plastic deformation process for future astronomical observations. Our foil mirror is made of a 0.3-mm thick silicon wafer and is plastically deformed into a high-accurate conical shape with a curvature radius of ~100 mm. The angular resolution we evaluated using a test sample mirror was ~32 arcseconds in the best region. We have also successfully coated a platinum film on the foil mirror using the atomic layer deposition process. In this talk, we report on the fabrication method and the X-ray imaging capability of our silicon foil X-ray optics.
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.
GEO-X (GEOspace X-ray imager) is a 50 kg-class small satellite to image the global Earth’s magnetosphere in X-rays via solar wind charge exchange emission. A 12U CubeSat will be injected into an elliptical orbit with an apogee distance of ∼40 Earth radii. In order to observe the diffuse soft X-ray emission in 0.3-2 keV and to verify X-ray imaging of the dayside structures of the magnetosphere such as cusps, magnetosheaths and magnetopauses which are identified statistically by in-situ satellite observations, an original light-weight X-ray imaging spectrometer (∼10 kg, ∼10 W, ∼10×10×30 cm) will be carried. The payload is composed of a ultra light-weight MEMS Wolter type-I telescope (∼4×4 deg2 FOV, <10 arcmin resolution) and a high speed CMOS sensor with a thin optical blocking filter (∼2×2 cm2 , frame rate ∼20 ms, energy resolution <80 eV FWHM at 0.6 keV). An aimed launch year is 2023-25 corresponding to the 25th solar maximum.
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