Modeling Characterization of Smoke Particle Transport and Fate in Lunar Gravity

Spacecraft fires present one of the most dangerous scenarios threatening crew safety for future lunar and deep space missions. Spacecraft fire detection strategies are challenged by transport phenomena unique to reduced gravity environments. To date, spacecraft fire detection studies have focused on microgravity systems, but, as NASA plans to return to the Moon, more research is needed to evaluate optimal fire detector placement in lunar gravity. This placement must consider a balance between the buoyant flow towards the ceiling due to lunar gravity and the cabin air filtration. Here, we present results from a study to evaluate smoke particle transport from an early-stage fire in lunar gravity. This model, built in COMSOL Multiphysics, combines turbulent flow, heat transfer, and particle transport from a simulated material overheating (pre-flame) event under varied temperature conditions. Particle velocities are tracked in lunar gravity and compared to results from terrestrial gravity calculations to evaluate timescales for buoyant transport. Results suggest that in lunar gravity, small (~1 µm) particles travel upward at velocities similar in magnitude to average air velocities on the ISS. However, maximum smoke plume velocities are dependent on fuel configuration and location, and smoke particle transport must be evaluated considering particle properties like size, density, and morphology. Finally, we consider a hypothetical ventilation strategy with a low-velocity forced flow applied from ceiling air supplies to floor air returns. Under the tested conditions, the upward flow of a buoyant lunar smoke plume may enable strategic placement of smoke detectors on ceilings of future lunar spacecraft cabins depending on the cabin ventilation velocity, air filtration, and habitat design.