Innovations in Modeling Cryogenic Propellant Phase Change for Long Duration Spaceflight

Cryogenic propellants are going to be the cornerstone for effective future human space exploration. These propellants need to be stored and maintained at really low temperatures for a long duration. Accurate phase change modeling is necessary for characterizing the thermal state of future cryogenic propellant tanks and for designing systems to alleviate the self pressurization problem. Better understanding about how to properly store and manage cryogenic propellants would help greatly with In-Situ Resource Utilization (ISRU) strategies for future missions to Mars and further. Predicting the fluid flow, heat transfer, and phase change mass transfer in long term cryogenic storage using CFD models is greatly affected by our understanding of the accommodation coefficient. The kinetically limited phase change model governed by the Hertz-Knudsen-Schrage equation is the model of choice for such calculations. The value of the accommodation coefficient required for the model is unknown for cryogenic propellants. Even in the case of water, the value of the accommodation coefficient has been found to vary over three orders of magnitude based on 80 years of measurements. Experiments specifically built to study accommodation coefficient are needed to estimate the value of the accommodation coefficient and understand some of the uncertainties surrounding these models.