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DN-017 L: In situ measurement of particle velocity during lunar plume surface interaction (PSI) phenomena

The sizes, speeds and ejection angles of regolith blasted out by a lander's rocket plume, at different sites and for different lander types. Current predictions rest on Apollo regolith data plus engine models and "are insufficient". The SCALPSS cameras captured stereo imagery of Blue Ghost's landing, and "similar imaging suites could be used" for comparison. It is named in the Moon Base Users Guide (near-term), under two challenges, landing and "Small cargo return" (Data gaps spreadsheet, DN-017 L; Users Guide, p. 12).

Quotations below are from row DN-017 L of the data gaps spreadsheet unless marked otherwise. ADD Rev C's Appendix E prints the same record as a table, and it matches the row field for field, the SCALPSS paragraph under "Current state of data" included (ADD Rev C, p. 281).

Description

"Characterize the lunar regolith ejected by rocket exhaust plumes interacting with the lunar surface at different sites and under different plume conditions (i.e. lander types). During final descent and landing, material may be lofted toward the landing vehicle and/or ejected away. As material leaves the influence of the exhaust plume, and given the lack of a substantial lunar atmosphere, it will travel on a trajectory dictated by those initial conditions."

Data utility (white paper, Table Two): "To enable better modelling of the interactions between landers and surface regolith to mitigate risk of damage to hardware" (ACR25 data-gaps white paper, p. 3).

Need driver and data type

  • Need driver: Lunar Surface Induced Environment Characterization
  • Data type: In Situ Measurement

Target measurement parameters

"Regolith particle sizes, speeds, and angles of ejection caused by rocket exhaust interacting with the lunar regolith."

Current state of data

"Modeling reports for preliminary site comparisons have been generated using regolith data gathered during Apollo coupled with engine performance data. Plume surface interaction is a complex phenomenon, and current estimates are insufficient to accurately predict the behavior of regolith and its effects on vehicle performance. SCALPSS instrument suite successfully captured stereo imagery during Blue Ghost's final descent and soft landing. Similar imaging suites could be used to provide comparative data for different lander configurations and lunar terrain types."

Impact if data is unavailable

"Increased uncertainty in risk to landing vehicle and surrounding assets caused by debris strike or the "sandblasting", abrasive effects of ejected material. Increased uncertainty to scientific operations near the landing site, as the probability of surface alteration caused by ejected material may not be well constrained. Inability to determine PSI effects during landing and ascent events, including vehicle and hardware lunar dust loading. Inability to predict visibility expectations for spacecraft during ascent and landing. Inability to determine effectiveness of radar and range finding hardware, particularly those used during landing and ascent events."

Benefits if data is available

"Understanding and characterization of this will translate to vehicle hardware which is better designed to withstand the effects of PSI during ascent and landing events and mitigate the risk of damage to this hardware. Increased confidence in ejecta hazard analyses that affect the landing vehicle and nearby assets. Tighter design constraints for protection from hazards/operating conditions. Better understanding of induce landing environment to inform lunar surface science goals."

Traceability

  • Objectives: SE-07 LM, LI-05 L, TH-03 L (codes as printed; the sheet gives no titles)
  • Segment: Human Lunar Return (HLR): "The M2M segment during which the data is needed, but not necessarily when it is collected" (Data gaps spreadsheet, Key sheet). A segment is not a Moon Base phase.

Priority

None. The spreadsheet has no priority field, and the Users Guide calls the data-gap list "not comprehensive or prioritized" (Users Guide, p. 11).

Moon Base relevance

The Users Guide names DN-017 L for two challenges (Users Guide, p. 12):

  • "Landing Safely and Accurately on the Lunar Surface" (headline challenge). Its knowledge challenge has two sentences: "Observe the lunar surface to identify surface blocks, such as rocks and craters; map surface topology; and characterize variance in gravitational fields to enable precise and safe landings." and "Characterize and predict the properties of a plume-surface interaction (PSI) event, including ejecta trajectory, particle size distribution, and resulting surface site alterations to evaluate impact risk to mission and nearby assets." The guide lists DN-001 L, DN-014 L, DN-002 L, DN-017 L and DN-018 L under both sentences together and does not say which sentence each serves. The challenge's technology half cites tech gap #1101, which wants landing systems that work "with induced PSI effects".
  • "Small cargo return": "Returning cargo from the lunar surface (e.g., scientific samples) requires a detailed understanding of how launch from the surface affects lunar regolith and nearby assets." Also cited: DN-018 L. No tech gap.

The guide ties its challenges to "near-term Moon Base development efforts": missions in phase one "offer opportunities to collect data and mature technologies to enable essential phase two and phase three capabilities" (p. 11). See Technology and knowledge challenges.

Phase 1 mission on the same subject (the wiki's link; no source pairs them): Blue Moon MK1 "Endurance" carries SCALPSS, which "will capture high-resolution imagery before, during, and after landing to study how rocket engine plumes interact with the lunar surface" (Moon Base Phases, "Blue Origin's Blue Moon Mark 1"). The spreadsheet itself names SCALPSS only for its Blue Ghost flight. See the data gaps index.

A Moon Base payload with no phase, same subject (the wiki's link): DISCO, selected through PRISM in September 2026, will study "how rocket exhaust disturbs the ground". The release gives no site and no lander (PRISM release, "DISCO").

SCALPSS on four more landings (the wiki's link). The four CLPS landings selected in June 2026 for late 2028, on Astrobotic, Firefly and Intuitive Machines landers, each carry SCALPSS, collecting data "from a variety of engine sizes, propellants, and landing locations" for "models to predict lunar dust erosion and ejecta characteristics". This gap asks for "different plume conditions (i.e. lander types)"; the release gives no sites or phase (June 2026 release; data gaps index).

Cargo return in the Ignition material (the wiki's link, by the name of the guide's challenge). The Moon Base Program's Ignition deck plans the return the guide's "Small cargo return" challenge is about. Its "Cargo Return" key mission is to "Return cargo from the lunar surface": "Initial demo in Phase 2"; "Phase 3: implement capability with mass goal of 500 kg"; "Uncrewed cargo return missions: Science returns; Critical hardware; Inspiration" (slide 34). Its habitation and logistics table has "Demo small cargo return" in Phase 2, and "Sustained small cargo return" and "Demo med/large cargo return" ("Goal: 500 kg") in Phase 3 (slide 62); one of Phase 3's goals is "Initial uncrewed mission cargo return capabilities" (slide 28) (Ignition deck 2, slides 34 and 62). The deck says nothing about how launch from the surface affects regolith and nearby assets, the guide's concern under this challenge, and this data gap's impacts include PSI effects "during landing and ascent events". Slides 34 and 62 word the 500 kg goal differently, as implementing the capability and as a demonstration (open question 83).

Ground tests on the same subject (the pairing is the wiki's; the article names no data gap). Langley is firing small engines (an ethane system of "about 100 pounds of thrust", later a hybrid motor of "around 35 pounds") into a bin of Black Point-1 regolith simulant in its 60-foot vacuum sphere, measuring "crater formation, angle and height of the ejecta sheet, spatial distribution of solid ejecta, and the speed of the regolith particles", with "a version of" the SCALPSS cameras, for Artemis IV "and develop a Moon Base" (plume tests article). These are this gap's speeds and angles, and the aim, "to improve predictive models", is its data utility, "better modelling". They are ground tests on simulant at small thrust, not the "In Situ Measurement" the gap's data type asks for. The article says the set-up can be changed to a Mars simulant and pressure, the subject of DN-005 M.

Sources

Data gaps spreadsheet, DN-017 L · ACR25 data-gaps white paper, p. 3 · Users Guide, pp. 11–12 · Moon Base Phases, "Blue Origin's Blue Moon Mark 1" · ADD Rev C, p. 281 · PRISM release · June 2026 release · Ignition deck 2, slides 28, 34, 62 · Plume tests article, Aug 2026