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The science objectives of increasingly ambitious space missions require meeting stringent contamination requirements. The process of outgassing under vacuum exposure is often a primary source of spacecraft molecular contamination. Materials, such as cabling insulation and structural adhesives, evolve molecules that can be transported to and deposit on contamination -sensitive surfaces. Such deposition can negatively impact spacecraft performance : contaminant films may compromise scientific observations made by optical instruments, and may degrade the efficiency of radiators or solar arrays. The design of spacecraft and their mission operations is informed by contamination modeling, an engineering discipline combining empirical data and established science principles. Empirical data obtained from short-duration ASTM E1559 testing is used to determine outgassing rates from source materials. Scaling laws, based on Fick's law of diffusion and Arrhenius factors to account for temperature variations, are used to extrapolate outgassing test data to mission conditions and durations. Outgassing contamination transport processes in vacuum are modeled as free molecular transport using a view factor formulation. Data from a thermo-gravimetric assessment performed at the conclusion of the ASTM E1559 test is used to estimate contamination condensation on spacecraft surfaces. Examples describing the contamination model — incorporating source outgassing, free molecular transport, and condensation onto spacecraft surfaces—are presented. [ABSTRACT FROM AUTHOR]

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]