Numerical Modeling of Liquid Propellant Mass Transfer with Sloshing during On-Orbit Refueling

Key Contributions

• Addresses fundamental physics challenge of liquid propellant sloshing in partially filled tanks during orbital refueling
• Models behavior of UDMH (unsymmetrical dimethylhydrazine) propellant during chaser-target satellite docking
• Sloshing produces non-cooperative motion between chaser and target, complicating the refueling interface
• Provides numerical framework for predicting propellant behavior in microgravity transfer scenarios

Methodology

• Computational fluid dynamics (CFD) modeling of partially filled propellant tanks
• Simulates docking approach dynamics and resulting propellant slosh
• Accounts for microgravity effects on liquid surface tension and capillary behavior

Results

• Sloshing forces during docking can destabilize the refueling connection
• Tank fill level significantly affects slosh magnitude — partially filled tanks are most problematic
• Results inform design requirements for baffles, PMDs (propellant management devices), and approach velocity limits

Relevance to Current Programs

• Directly applicable to Orbit Fab / Astroscale GEO refueling demo (summer 2026)
• Informs SpaceX Starship propellant transfer architecture (cryogenic, larger scale)
• Supports design of future commercial refueling interfaces (RAFTI, GRIP)

Source: Numerical Modeling of Liquid Propellant Mass Transfer with Sloshing during On-Orbit Refueling — IEEE, 2024