Reference Concept • Pre-Operational Capability

Regolith Mechanics Head (RMH)

A requirements-style definition of a minimal, repeatable in-situ geotechnical capability that should precede mobility-dependent lunar surface activities (rovers, repeated traffic, anchoring, drilling, and emplacement).

What this page is

This is a neutral definition of a minimal “RMH-class” investigation: a compact, rover- or lander-hosted capability for measuring regolith mechanical behavior at operational scale. It is not a product announcement, not a solicitation, and not a claim of planned development.

Geotechnical, not geology Design parameters, not inference Mobility risk reduction Repeatable test recipe
Core idea: before vehicles, traffic, or structures depend on lunar ground behavior, that behavior should be measured directly in the wheel/footing interaction zone.
Regolith Mechanics Head (RMH) block diagram: actuator spine to load pad or penetration cone to engineering data products.

Why this capability is needed

As lunar missions move from one-off demonstrations to sustained surface activity, a practical operational gap becomes more consequential: quantified regolith mechanics at the scale mobility systems actually interact with.

  • Mobility risk is often driven by unknown load–sinkage and shear behavior, not by lack of rugged hardware.
  • Terrain “looks safe” is not a substitute for measured bearing capacity, compaction response, and strength gradients.
  • Repeated traffic changes the ground. First-pass performance can differ materially from tenth-pass performance.

Scope of application

RMH-class characterization should precede or accompany:

  • Sustained rover operations and long traverses
  • Heavy or repeated surface traffic (logistics loops, staging areas, routes)
  • Anchoring, drilling, and emplacement activities
  • Construction-adjacent operations and site preparation
  • Operations in poorly constrained terrain (e.g., polar regions, heterogeneous slopes)

RMH-class characterization complements science payloads; it is focused on operational mechanics rather than compositional discovery.

Measurement objectives

Primary (minimum) objectives

  • Measure load-dependent sinkage under controlled normal force
  • Estimate bearing capacity and stiffness proxies from load–sinkage response
  • Measure penetration resistance vs depth across the wheel-interaction zone
  • Quantify disturbance / compaction sensitivity via pre/post measurements

Recommended (mission-dependent)

  • Correlate slip with tractive force via a simple reaction load reference (tether/push)
  • Capture environmental context (temperature shallow profile, surface texture documentation)
  • Replicate tests at multiple micro-sites to bound variability and uncertainty
Success criterion: outputs are directly usable by rover and surface-ops engineers (plots + tables), not only raw telemetry or qualitative descriptions.

Functional requirements (requirements-style)

ID Function Requirement
RMH-F-001 Normal load testing The system shall apply controlled normal force to the regolith surface and measure resulting deformation (sinkage) as a function of load.
Load–sinkage
Bearing proxy
Compaction
RMH-F-002 Penetration profiling The system shall measure penetration resistance continuously as a function of depth to a minimum depth representative of the wheel/footing interaction zone.
0–30 cm class
Layering
Strength gradient
RMH-F-003 Disturbance sensitivity The system shall support repeat measurements at disturbed and undisturbed locations to quantify changes in mechanical response due to traffic or loading.
Pre/post
First-pass vs repeated-pass
RMH-F-004 (recommended) Traction correlation When paired with a reaction load reference, the system should enable correlation of wheel slip with tractive force to generate drawbar pull vs slip relationships.
Traction envelope
Slip limits
RMH-F-005 Time synchronization The system shall timestamp all measurements and synchronize with rover state data (pose, wheel speed, IMU where available) to support reconstruction of test conditions.
Engineering traceability

Note: quantitative thresholds (forces, depths, accuracies) are mission- and platform-dependent and should be set by the mobility and surface-ops requirements of the host system.

Conceptual device elements

  • Actuator spine: a single linear actuation axis suitable for both surface loading and penetration tasks
  • Load interface: footpad / plate with known area (optionally two areas to capture scale sensitivity)
  • Penetration interface: cone or rod for shallow profiling
  • Sensor set (minimum): force, displacement/depth, timestamps
  • Optional: reaction load measurement (tether/push), shallow temperature, context imaging
Design bias: reduce part count and qualification burden. A single actuator and limited toolfaces often provide the best reliability-to-information ratio.

Minimal test recipe (one-site, one-sol class)

  1. Baseline penetration profiles at 2–3 micro-sites (depth resistance vs depth)
  2. Load ramp test (incremental or continuous) to produce a load–sinkage curve
  3. Repeat loading at the same point to observe compaction response
  4. Post-disturbance penetration to quantify strength/density change
  5. Optional traction runs with reaction reference to map drawbar pull vs slip

This recipe is intentionally compact: it prioritizes engineering-usable parameters over broad exploratory mapping.

Data products

RMH-class investigations should deliver a small set of standardized outputs suitable for mobility modeling and trafficability assessment:

Plots (minimum set)

  • Load vs sinkage (with repeat cycles where performed)
  • Penetration resistance vs depth (multiple micro-sites)
  • Pre/post disturbance comparison (delta curves)

Tables (minimum set)

  • Test metadata: location, timestamps, instrument configuration
  • Derived proxies: stiffness/bearing indicators, layer depth markers
  • Uncertainty bounds or observed variability across micro-sites
Engineering usability requirement: a mobility team should be able to plug outputs into a model or spreadsheet without bespoke interpretation.

Ballpark cost (ROM)

Order-of-magnitude cost for a flight-qualified RMH-class investigation payload (excluding rover/lander bus and launch) typically falls in:

  • $7M–$12M for minimal load + penetration + disturbance capability
  • $12M–$22M with traction correlation (reaction reference), higher autonomy, and additional operational maturity

These ranges are planning-grade estimates intended for early architecture budgeting and discussion, not vendor quotes.

Where it fits in mission planning

  • Precursor step before committing to sustained mobility routes or surface logistics loops
  • Input to site selection for repeated operations (staging, roads, pads, anchors)
  • Complements compositional payloads by addressing mechanical uncertainty
  • Improves design margins and reduces conservatism driven by unknown terrain behavior
Framing: as surface operations scale, measured regolith mechanics becomes an enabling capability rather than an optional add-on.

Relationship to mission risk

Absence of RMH-class measurements prior to sustained mobility or construction-adjacent operations constitutes a known operational risk, including unexpected sinkage, traction loss, immobilization, or overloading of mobility systems.

RMH-class characterization reduces epistemic uncertainty; it does not eliminate all risk and does not replace disciplined operational constraints.

Standardization potential

Standardizing RMH-class investigations across missions enables cross-site comparability and accumulation of empirical lunar geotechnical datasets. Over time, this reduces the need to “relearn” terrain behavior and supports better-grounded design and operational margins.