In-Space No-Vent Fill Operations for Cryogenic Propellants

Pressurization of a cryogenic propellant tank during a no-vent fill operation was evaluated using computational fluid dynamics (CFD) simulations, comparing validated results in standard earth gravity (1g) with reduced gravity (low-g) in-space predictions. Modeling low-g conditions for cryogenic fluid management (CFM) operations and understanding how they differ from ground conditions is critical for supporting ongoing and future space missions under the Artemis Program. Long-term storage and conditioning of cryogenic propellants is a difficult task that requires multiple developing technologies, testing for which is typically only feasible in standard gravity conditions. CFD modeling with validated tools provides additional insights on how these operations may differ in flight-like conditions. In the case of no-vent fill (NVF) operations, ground testing has been used to validate various modeling approaches, including nodal models and CFD. However, under low-g conditions less data is available and the simplified models and tools for 1g become unreliable. CFD still provides meaningful insights here, showing additional propellant mixing can occur that accelerates energy transfer and phase change. For the parameters evaluated in this analysis, it was found that 1g conditions tend to be conservative for modeling pressure rise from NVF operations. Additional consideration should be given for buoyancy effects due to inflow temperature, which can drive 1g predictions into over-conservatism.