Contingency Decontamination Utilizing Pointing Maneuvers for the Cryogenic SPHEREx Mission

The The Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) mission, a collaboration between NASA's JPL and Caltech, aims to conduct the first near-infrared all-sky spectral survey using a passively-cooled, cryogenic telescope in low-earth orbit. This mission addresses NASA's astrophysics goals by investigating the origin of the universe, the evolution of galaxies, and the abundance of biogenic ices. A significant challenge faced by SPHEREx is the management of water contamination, which can interfere with the wavelengths critical to its survey. Unique water contamination issues arise from the combination of cryogenic operating temperatures and the limited temperature control capabilities of passive cooling. In this work, we explore a novel approach to contingency decontamination of SPHEREx utilizing pointing maneuvers to mitigate water contamination risks. A comprehensive contamination model, previously developed to simulate the transport and accumulation of outgassed water on sensitive components of the SPHEREx payload, is extended and utilized to analyze contingency scenarios for the SPHEREx observatory decontamination. This model incorporates time and spatially resolved thermal data to predict the behavior of water outgassing under various operational conditions, ensuring a comprehensive molecular contamination simulation. The baseline decontamination strategy designed for SPHEREx employs decontamination heaters to control the thermal environment. During the cooldown phase, the heaters manage the temperature of optical surfaces to prevent excessive water accumulation. However, if the originally planned decontamination heaters fail, excess water contamination could be detrimental to the scientific return of the mission, effectively blinding the observatory from detecting water in the universe, a key biogenic molecule. In a contingency scenario, specifically timed pointing maneuvers must be performed to preferentially heat the optical elements. These maneuvers involve adjusting the spacecraft's orientation to expose the optical components to varying thermal environments, promoting the desorption of accumulated water. This approach was simulated with high fidelity, demonstrating its effectiveness in maintaining the required temperatures to meet water contamination requirements. The simulations showed that these pointing maneuvers can effectively reduce water contamination on the cryogenic surfaces, thus protecting the optical performance of the instrument. Through these high-fidelity simulations and the incorporation of pointing maneuvers, the SPHEREx mission can confidently mitigate water contamination risks in a contingency scenario. This ensures that, even under scenarios where the primary decontamination heaters fail, the SPHEREx mission can meet its scientific objectives.