Ultra-lightweight X-ray telescope fabricated with multiple MEMS technologies for GEO-X mission

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.