A modification of the optical design for the SOLAR-C EUVST instrument: design performance, sensitivity analysis, optical alignment, and optical error budget

SOLAR-C is a Japanese solar physics mission with contributions from the United States and European countries. It features the EUV High-Throughput Spectroscopic Telescope (EUVST) for EUV spectroscopy in a wide temperature range (10^4–10^7 K). The optical system’s innovation omits an aperture filter, using only a 28 cm off-axis parabolic primary mirror and a diffraction grating assembly composed of two different gratings, resulting in an effective area ten times larger than the Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode. This design offers exceptionally high spatial (0.4 arcseconds) and temporal (1 second) resolutions for EUV-UV imaging spectroscopy across a broad wavelength range (170–212 Å, 464–522 Å, 558–610 Å, 719–847 Å, 928–1043 Å, 1115–1221 Å) within a 100×100 arcsecond field of view. A trade-off study focusing on manufacturability successfully eased the specifications of one grating. This presentation reports the latest optical design, optical alignment policy, sensitivity analysis result, and the current spatial resolution error budget plan.