Jet-Induced Cratering of a Granular Surface with Application to Lunar Spaceports

Abstract

The erosion of lunar soil by rocket exhaust plumes is investigated experimentally. This has identified the diffusion-driven flow in the bulk of the sand as an important but previously unrecognized mechanism for erosion dynamics. It has also shown that slow regime cratering is governed by the recirculation of sand in the widening geometry of the crater. Scaling relationships and erosion mechanisms have been characterized in detail for the slow regime. The diffusion-driven flow occurs in both slow and fast regime cratering. Because diffusion-driven flow had been omitted from the lunar erosion theory and from the pressure cratering theory of the Apollo and Viking era, those theories cannot be entirely correct. IntroductionDuring the Apollo and Viking programs there was considerable research into the blast effects of launching and landing on planetary regoliths. That work ensured the success of those missions but also demonstrated that soil erosion or cratering will be a significant challenge for other mission scenarios. For example, the high-velocity spray of eroded soil will pose a serious challenge when we attempt to land multiple spacecraft within short distances of one another on the Moon. We have relevant experience because the Apollo 12 Lunar Module landed 155 meters away from the deactivated Surveyor 3 spacecraft. Portions of the Surveyor were returned by the Apollo astronauts to Earth for analysis. It was found that the surfaces had been sandblasted and pitted and that its openings had been injected with grit from the high-speed spray [Cour-Palais 1972]. This treatment is not acceptable for functional spacecraft.

Two-fluid modeling of cratering in a particle bed by a subsonic turbulent jet

“…However, for the case of a jet impinging downward onto a bed of particles, which is relevant to landing spacecraft, the motion of the particle phase was neglected and only the single-phase fluid (liquid or gas) was simulated. In particular, experimental studies demonstrated that when a turbulent, subsonic jet impinges onto a particle bed in atmospheric conditions, a crater is produced (details available elsewhere, e.g., [30][31][32][33]). However, previous computational fluid dynamics simulations were used to study the flow patterns in horizontal scour holes by modeling a jet impinging into a solid wall shaped as a crater (i.e.…”

Numerical study of jet-induced cratering of a granular bed: Effect of gravity

“…Five cratering regimes have been identified, including Diffused Gas Eruption (DGE) [3] Diffused Gas Explosive Erosion (DGEE) [4], Bearing Capacity Failure (BCF) [5], Diffusion Driven Flow (DDF) [2] and Viscous Erosion (VE) [6].This significantly improves our knowledge of thiscrateringprocess. However, at this stage of development, the particle-scale flow characteristics and forces governing cratering of a granular bedare difficult to measure.…”

“…In addition, experimental studies are sometimes expensive, particularly in studying the effect of gravity (by flying an aircraft through parabolic trajectories), which is critical to the landing and launching of aerospace equipments (e.g. rocket and spacecraft) on different planetary regolith [2,7]. In principle, these problems can be overcome by numerical simulations.…”

“…For example, itcan improve the safety of hydraulic structure [1], and prevent visibility reduction and lower hazard to personnel and equipment in aerospace by reducing particles entertained in air [2]. Therefore, understanding underlying the mechanisms andquantifying the effects of pertinent variables are important.…”

“…Xu et al [10] and Feng et al [11] developed a twodimensional (2-D) CFD-DEM to study the formation of a cavity -a type of crater -due to the lateral flow of gas into a granular bed. Recently, Metzger et al [2] studied gas flow within a crater by a CFD model. On the other hand, Haehnel et al [12] used the Lattice Boltzmann method, coupled with DEM, to study the 2-D gas-solid flow, and also observed the formation of a planar crater when a jet impinges on a granular bed.…”