PLUME-SURFACE INTERACTIONS

When landing or taking off from a planetary surface, spacecraft engines shoot out gas plumes at kilometers per second that impinge on the loose soil under them. The resulting plume-surface interactions (PSI) entrain soil grains and launch them in all directions at supersonic velocities, and can also gouge out meters-deep craters beneath the spacecraft. In the past, landers have been small and have never landed near existing infrastructure, but newer landers are up to 25Å~ larger than the Apollo Lunar Module and are intended to land in the same place multiple times to build up bases or cities. Plume-surface interactions pose a significant risk to equipment around the lander and to the lander itself, possibly resulting in mission failure and crew loss without mitigation efforts. NASA and private companies have run supercomputer simulations for plume-surface interactions on the larger Starship and Blue Moon landers, but have not released any of the data publicly, nor disclosed how much PSI adds to the overall risk estimated for loss of crew.

Plume-surface interactions can be mitigated by changes to the vehicles and by preparing the surface by constructing a hardened landing/launch pad and possibly a surrounding berm. So far, the only mitigation being implemented for NASA’s Moon to Mars campaign is the extra thrusters on Starship placed higher on the vehicle, which are still expected to scour the surface out to 10 km away from the landing point. There is no backup plan if uncrewed demo landings of the Human Landing System vehicles show that plume-surface interactions pose an unacceptably high risk.