SALTUS Probe Class Space Mission: Observatory Architecture and Mission Design

We describe the space observatory architecture and mission design of the SALTUS mission, a NASA Astrophysics Probe Explorer concept. SALTUS will address key far-infrared science using a 14-m diameter <45 K primary reflector (M1) and will provide unprecedented levels of spectral sensitivity for planet, solar system, and galactic evolution studies, and cosmic origins. Drawing from Northrop Grumman's extensive NASA mission heritage, the observatory flight system is based on the LEOStar-3 spacecraft platform to carry the SALTUS Payload. The Payload is comprised of the inflation control system (ICS), Sunshield Module (SM), Cold Corrector Module (CCM), Warm Instrument Electronics Module, and Primary Reflector Module (PRM). The 14-m M1 is an off-axis inflatable membrane radiatively cooled by a two-layer sunshield (~1,000 m2 per layer). The CCM corrects for residual aberration from M1 and delivers a focused beam to two instruments - High Resolution Receiver (HiRX) and SAFARI-Lite. The CCM and PRM reside atop a truss-based composite deck which also provides a platform for the attitude control system. The 5-year mission lifetime is driven by a two-consumable architecture: the propellant system and the ICS. The Core Interface Module (CIM), a multi-faceted composite truss structure, provides a load path with high stiffness, mechanical attachment, and thermal separation between the Payload and spacecraft. The SM attaches outside the CIM with its aft end integrating directly to the bus. The spacecraft maintains an attitude off M1's boresight with respect to the Sun line to facilitate the <45 K thermal environment. SALTUS will reside in a Sun-Earth halo L2 orbit with a maximum Earth slant range of 1.8 million km thereby reducing orbit transfer delta-v. The instantaneous field of regard provides two continuous 20-deg viewing zones around the ecliptic poles resulting in full sky coverage in six months.