Double-offset Cassegrain telescopes for the Ultraviolet Type Ia mission concept

Our understanding of cosmology is shaped by type Ia supernovae (SNe Ia), the runaway thermonuclear detonations of white dwarfs via accretion from a companion star. The nature of this companion star is highly debated, with disparate models explaining the currently available SNe Ia data. Critical ultraviolet (UV) signatures of SNe Ia progenitors are only observable within the first few days post-detonation. We present the instrument design of the Ultraviolet Type Ia (UVIa) Supernova Mission, a proposed SmallSat to make early UV observations of SNe Ia. UVIa conducts simultaneous observations in three photometric channels: far-UV (1500 to 1800 Å), near-UV (1800 to 2400 Å), and Sloan u-band (3000 to 4200 Å). UVIa employs two 80-mm double-offset Cassegrain UV telescopes and a similar 50-mm u-band telescope, imaging onto three Teledyne e2v CIS120-10-LN complementary metal-oxide semiconductor (CMOS) detectors. The UV detectors are delta-doped for enhanced sensitivity, with custom metal-dielectric filters providing further in-band efficiency and red light rejection. The UV optics utilize multi-layer coatings, defining the UV bandpasses and providing additional red light rejection. The instrument design achieves high UV sensitivity (21.5 mag AB) and superior red light rejection (<10−5 throughput), allowing UVIa to make early observations of SNe Ia while serving as a pathfinder for future UV transient telescopes.