Aspera payload design overview: UV SmallSat mission to detect and map warm-hot halo gas around the nearby galaxies

Aspera is a NASA-funded UV SmallSat mission designed to detect and map warm-hot phase halo gas around nearby galaxies. The Aspera payload is designed to detect faint diffuse O VI emission at around 103.2 nm, satisfying the sensitivity requirement of 5×10⁻¹⁹ erg/s/cm²/arcsec² over 179 hours of exposure. In this manuscript, we describe the overall payload design of Aspera. The payload comprises two identical co-aligned UV long-slit spectrograph optical channels sharing a common UV-sensitive microchannel plate detector. The design delivers spectral resolution R ∼ 2,000 over the wavelength range of 101 to 106 nm. The field of view of each channel is 1 degree by 30 arcsec, with an effective area of 1.1 cm². The mission is now entering the payload integration and testing phase, with the projected launch-ready date set for late 2025 or early 2026. The mission will be launched into low-Earth orbit via rideshare.