LAPYUTA Key Technology：Development of High-Reflectivity Ultraviolet Mirrors
Jan. 15, 2026 | Aerospace Project Research Associate, ISAS people
ENOKIDANI Umi / Dept. of Solar System Sciences, ISAS
Research Summary
LAPYUTA (Life-environmentology, Astronomy, and PlanetarY Ultraviolet Telescope Assembly) is a proposed Japanese high-precision ultraviolet space telescope that aims to understand the “habitability of environments in space” and the “origins of structures and materials.” LAPYUTA will be the successor to the Extreme ultraviolet spectroscope for Exospheric Dynamics (HISAKI, SPRINT-A (2013–2023)) which is the world’s first space telescope dedicated to planetary observations equipped with an extreme ultraviolet spectroscope. The development for LAPYUTA began around 2018 with the goal of launching in the 2030s (Figure 1). By continuously observing planets such as Mars, Venus, and Jupiter over long periods, HISAKI revealed the behavior of planetary gases that had long remained mysterious. Regarding Jupiter, as our understanding of the gases around the planet improved, new questions arose about its interactions with its moons and about the activity of those moons. To solve these remaining mysteries, LAPYUTA will improve upon both the sensitivity and spatial resolution of HISAKI by two orders of magnitudes. Taking advantage of this higher performance, LAPYUTA will also perform astronomical observations of extrasolar planets, galaxies, neutron star mergers*1, and supernova explosions. One of the telescope’s main scientific goals is the discovery and spectroscopic study of Earth-like exoplanets with atmospheres similar to our own, marking the beginning of a new era of ultraviolet astronomy in space.
I am developing the mirrors and diffraction gratings*2 used inside LAPYUTA’s observation instruments to achieve higher sensitivity. Figure 2 shows a cross-sectional view of LAPYUTA, illustrating the layout of the telescope and its instruments. LAPYUTA has a 60 cm-diameter primary mirror. Light from a celestial object is focused by the primary and secondary mirrors and then enters the instrument section. The instrument section contains a medium-dispersion spectrograph, a high-dispersion spectrograph, a UV slit imager, and a fine-guidance sensor (on the back side of the cross-section in Figure 2). Each instrument includes multiple mirrors and diffraction gratings to reflect and disperse the incoming light as desired. In the far-ultraviolet wavelength range of 110 – 190 nm, where LAPYUTA observes, transmissive optics such as prisms cannot be used. Therefore, all optical elements are reflective, like mirrors. Traditionally, the reflectivity of far-UV mirrors has been only about 80% for every single reflection, which means that after three reflections, half of the incoming light is lost. Thus, improving mirror reflectivity is essential for higher sensitivity. We use aluminum (Al), which has high reflectivity in the far-UV, as the mirror material. Aluminum is vacuum-deposited*3 onto a polished glass substrate. However, aluminum reacts quickly with oxygen, forming an oxide layer that lowers reflectivity. To prevent this oxidation, a protective coating is deposited on top of the aluminum layer in a vacuum. Our team has been optimizing the deposition conditions for both the aluminum and protective layers by producing mirrors under various conditions, measuring their reflectivity, and feeding the results back into the fabrication process (Figure 3, left). This summer, we finally achieved 90% reflectivity in our prototype mirrors—a major step that would increase LAPYUTA’s overall optical efficiency by 1.4 times. Our next goal is to apply this improved coating to the actual mirrors and diffraction gratings to be installed in LAPYUTA (Figure 3, right). We already have many coated gratings ready, so please stay tuned to more updates from our research.
This coating technology, developed to increase LAPYUTA’s sensitivity, will also contribute to NASA’s Habitable Worlds Observatory (HWO) project, which aims to launch in the 2040s. HWO is a 6-meter-class space telescope that will observe across wavelengths from ultraviolet to near-infrared. Its main goal is the direct observation of Earth-like exoplanets within habitable zones, seeking signs of extraterrestrial life. That day when we detect signs of extraterrestrial life may not be too far in the future. Japan is also preparing to contribute to HWO by developing instrument concepts and key components for possible inclusion in the observatory.
Both LAPYUTA and HWO are planned for launch after the 2030s. Developing a space telescope takes many years and involves many stages, so it is never too late to join. If you are interested, please consider joining the development team and working together to build the next generation of space telescopes!
Terminologies
- *1 Reflectance spectroscopy : technique that identified the composition and properties of a surface by measuring how it reflects light at different wavelengths.
- *2 Space weathering : Space weathering encompasses physical and chemical processes that alter the surface of bodies without atmospheres under the influence of solar wind, micrometeorites, and cosmic radiation.
- *3 Vacuum deposition : A technology in which a substance such as a metal is evaporated in a vacuum and the vaporized substance is deposited on the surface of a substrate to form a thin film.