High-Resolution Receiver for the Single Aperture Large Telescope for Universe Studies

The High-Resolution Receiver (HiRX) is one of two instruments of the Single Aperture Large Telescope for Universe Studies (SALTUS), a mission proposed to NASA's 2023 Astrophysics Probe Explorer. SALTUS employs a 14 m aperture, leading to a 16-fold increase in collecting area and a factor of 4 increase in the angular resolution with respect to the Herschel Space Telescope. It will be radiatively cooled to <= 45 K and has a planned duration of >5 years. HiRX consists of four bands of cryogenic heterodyne receivers with a high sensitivity and high spectral resolution, being able to observe the gaseous components of objects across the far-IR. HiRX is going to detect water, HD, and other relevant astrophysical lines while resolving them in velocity. HiRX covers the following frequency ranges: Band 1 from 455 to 575 GHz, Band 2 from 1.1 to 2.1 THz, Band 3 from 2.475 to 2.875 THz, and Band 4 for both 4.744 and 5.35 THz. Bands 1 to 3 contain single, high-performance mixers. Band 4 consists of an array of seven hexagonally packed pixels, where the central pixel operates as a heterodyne mixer. Band 1 utilizes superconducting-insulator-superconducting mixers (SIS), whereas Bands 2 to 4 use superconducting hot electron bolometers (HEB) mixers. The local oscillator (LO) system uses frequency-multiplier chains for Bands 1 and 2, and quantum cascade lasers for Bands 3 and 4. Autocorrelator spectrometers are used to process the intermediate frequency (IF) signals from each science band, providing instantaneous frequency coverage of 4 to 8 GHz for Band 1 and 0.5 to 4 GHz for Bands 2 to 4. SALTUS will also fly a chirp transform spectrometer system for high spectral resolution observations in Band 1.