Thermal propellant management devices for CubeSat cold gas propulsion

CubeSat cold-gas propulsion increasingly relies on two-phase, self-pressurizing propellants stored in conformal tanks. However, state-of-the-art propellant management strategies for these systems result in significant inefficiencies in volume or power management, limiting the total Δ V budget and the mission lifetime. These challenges highlight the need for a more compact propellant management approach. The VAporization for PrOpellant Repositioning (VAPOR) experiment investigates the feasibility of repositioning an ullage gas bubble of R-236fa using thermally-induced phase change in various propellant management devices (PMDs). These devices utilize a heat source to vaporize propellant near the outlet, inducing pressure-driven bubble condensation in colder regions of the tank. Capillary structures are integrated to retain vapor near the heater and promote bubble coalescence, facilitating extraction and routing to thrusters. Building upon iterative designs across two parabolic flight campaigns, six thermocapillary PMDs are evaluated, culminating in three thermal start basket architectures. Patch heater PMDs initiate ullage generation in under 1 s and sustain the highest boiling rates, whereas sponge-based start baskets exhibit an average initiation time of 6 . 9 ± 1 . 3 s with more modest ullage generation. All capillary structures successfully capture the generated vapor. Collectively, results establish thermocapillary PMDs as a compact alternative to conventional two-tank systems for CubeSat cold-gas propulsion.