Modeling contaminant outgassing and free molecular transport processes for the cryogenic SPHEREx observatory.

Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) is a Jet Propulsion Laboratory (JPL) and Caltech led mission to address goals of NASA's astrophysics division by investigating the origin of the universe, the evolution of galaxies and the abundance biogenic ices in the universe. It accomplishes these goals through near infrared all sky surveys of the entire celestial sphere collected using a passively cooled cryogenic telescope. The combination of cryogenic temperatures and a passive thermal subsystem lead to several unique water contamination issues which must be carefully mitigated by controlling the payload's temperature. As the SPHEREx mission is intended to investigate water and ices in the universe one of its primary wavelength bands of interest is where water molecules have a strong adsorption peak. Because of this, any water contamination within the instrument has a significant detrimental impact on the scientific data collected. In addition to the optical instrument's performance, water contamination negatively impacts the performance of the passive cryogenic thermal system. Excessive water contamination on the thermal system degrades its ability to cool the instrument. Because of the effects on the optical system and thermal system precise predictions of the outgassing contamination are needed for mission success. In this work a novel free molecular transport model for outgassing contamination is used to predict the accumulation of water during the cooldown and operation of the SPHEREx observatory. This model incorporates time and spatially resolved thermal data to calculate the outgassing, adsorption and desorption kinetics of contaminant molecules. This results from this new model provides high fidelity predictions of the outgassing accumulation on the sensitive surfaces of the SPHEREx observatory ensuring the performance of the optical and thermal systems required for mission success. [ABSTRACT FROM AUTHOR]