Influence of Outgassing and Desorption on Pressure in Spacecraft Cavities in Flight

This study investigated the influence of outgassing and desorption on pressure dynamics within spacecraft cavities during flight. As satellites ascend and position themselves, the ambient pressure decreases rapidly, while internal pressures in semi-enclosed cavities lag and can even increase due to heating of subsystems. This pressure behavior is attributed to the outgassing of internal materials and the further adsorption/desorption of outgassed species on cavities walls. The study combines ground experiments and physical modeling to predict these pressure variations, which are critical for operational decisions such as system start-ups and de-icing strategies. Experiments were conducted at CNES using a three-cavity mockup to simulate spacecraft conditions, with pressure measurements taken during material outgassing and cavity reheating. The results showed significant pressure differences and transients, particularly during temperature changes, indicating the role of desorption from cavity walls. Modeling efforts included both simple analytical approaches and more complex models incorporating adsorption and desorption phenomena. The simplest models provided a basic understanding but failed to capture transient behaviors accurately. Advanced models, including multi-energetic adsorption, better matched experimental data, highlighting the importance of considering the variety of adsorption sites and interaction energies. The findings underscore the need for accurate outgassing characterization and sophisticated modeling to predict and mitigate pressure-related issues in spacecraft cavities, ensuring reliable operation in space environments.