Mascons and the Engineering Excavation in Geologically Active Lunar Regions

1. Introduction

1.1 Overview: Lunar Mass Concentrations and Their Relevance to Excavation

Lunar mass concentrations (mascons) represent high-density anomalies embedded beneath major impact basins, first identified through Doppler tracking of Apollo-era orbiters and later confirmed in high resolution by NASA’s GRAIL mission (2011–2013). These anomalies, centered beneath maria such as Imbrium, Serenitatis, and Crisium, manifest as gravitational bullseyes that correspond to deep-seated subsurface density irregularities.

In terrestrial terms, these are not merely passive geophysical curiosities; they represent zones of anomalous subsurface behavior, critical for excavation design, load distribution, and structural anchorage. Mascons can increase local gravity by ~0.5%, cause measurable deflection of instruments, and distort subsurface stress fields. From an engineering standpoint, their presence changes excavation energy requirements, settlement behavior, and equipment loading assumptions.

1.2 Objectives: Linking Geophysical Anomalies to Construction Planning

This article provides technical guidance for excavation and subsurface construction within and around mascon-affected regions, with a focus on the Imbrium Basin. It integrates:

• Gravimetric data from legacy sources (Muller & Sjögren, 1968) and GRAIL.

• Geotechnical zoning (L1–L5 system, de Moraes 2025) applicable to mascon terrains.

• Subsurface structure hypotheses (mantle uplift, crustal differentiation, and cavities).

• Risk parameters relevant to mechanized excavation operations, foundation design, and spoil handling.

The aim is not merely academic. As Artemis-era lunar development expands, excavation contractors and system designers will require forward-looking frameworks that integrate subsurface geophysics into construction logistics and tool deployment plans.

1.3 Scope and Structure of the Article

This work focuses on Imbrium Basin as a case study due to its clear gravity anomaly, rich historical data, and potential utility for future lunar surface operations. The analysis will:

• Present historical gravity mapping and interpretations.

• Compare terrestrial excavation zoning systems to lunar adaptations.

• Highlight risk factors introduced by mascon gravity and subsurface heterogeneity.

• Recommend planning and equipment strategies for excavation feasibility.

Importantly, this article incorporates recent discoveries from the Lunar Reconnaissance Orbiter Camera (LROC), including tectonic features such as grabens and lobate scarps, which indicate that the Moon is not geologically inert. This has direct implications for excavation risk modeling, long-term stability, and hazard mitigation.

2. Historical and Modern Gravimetric Mapping

2.1 Early Discoveries: The 1968 Doppler Contour Maps

The first identification of lunar mascons came from Doppler tracking anomalies during the Lunar Orbiter missions in the 1960s. Muller and Sjögren (1968) produced the earliest contour maps of lunar gravity anomalies, revealing intense mass concentrations beneath major nearside maria. These anomalies were shown as concentric zones with positive gravity values exceeding +200 mGal in some regions—most notably in the Imbrium, Serenitatis, and Crisium basins.

The “bullseye” nature of the contours indicated dense subsurface structures, offsetting the expected gravitational gradient for a uniformly dense Moon. These early maps, though coarse by modern standards, became the foundation for later gravimetric studies and excavation-relevant models. Figure 2.1 presents a digitized overlay of the 1968 gravity contours across key mascon basins, including Imbrium.

Figure 2.1a - Lunar Gravity Map. Contour lines show gravity strength above mean value of the moon in units of 100 milligals. Imbrium exhibits a central +200 mGal anomaly surrounded by -100 mGal collars and an outer +30 to +50 mGal ring (Sjögren, 1968).

Figure 2.1.b - Maria Nomenclature all visible mascons in the near side of the Moon.

2.2 GRAIL Mission (2011–2013): High-Resolution Gravity Mapping

NASA’s GRAIL mission provided a transformational leap in lunar gravity understanding, delivering resolution improvements of over two orders of magnitude (Figure 2.2). GRAIL data confirmed and refined the earlier observations, revealing that mascons are characterized by:

• Central Positive Anomalies (~+300 mGal), consistent with uplifted mantle and mare basalt infill.

• Intermediate Negative Collars (~–100 mGal), suggesting crustal thinning and isostatic overshoot.

• Outer Positive Rings (~+30 to +50 mGal), resulting from compression zones at the basin margins.

Imbrium’s mascons in particular was shown to possess a deeply rooted high-density core with a total anomaly width exceeding 1,000 km. This level of resolution enables stratified excavation feasibility assessments based on gravity gradient transitions, as later interpreted in de Moraes (2025) L1–L5 zoning models.

Figure 2.2 - GRAIL image of the Moon showing variations in the gravity fields.

2.3 Gravimetric Interpretation for Excavation planning

For excavation planners and contractors, the gravimetric data must be translated into practical consequences. Key takeaways include:

• Subsurface Density Modeling: Mascons are associated with uplifted denser materials (e.g. partially melted mantle rock) and high-density mare basalts (ρ ~3.3 g/cm³), in contrast with the Moon’s average crustal density (~2.9 g/cm³). Some estimates suggest local density peaks reaching 8.7 g/cm³, possibly due to iron-rich intrusions.

• Excavation Resistance: Higher subsurface density directly increases cutting tool resistance, particularly for L2–L4 layers in the de Moraes zoning system.

• Stability Gradient: The outer positive rings (~+30 to +50 mGal) may offer more favorable excavation conditions compared to the central cores or negative collars, due to lesser gravitational distortion and shallower density transition zones.

Table 2.3 summarizes these relationships for contractors considering mechanized excavation equipment deployment, anchoring systems, or spoil removal planning in mascon terrains.

Table 1. Excavation-Relevant Gravimetric Characteristics in Mascon Zones (GRAIL-Based)

Feature	Gravity Anomaly	Approx. Radius (km)	Geotechnical Implication
Central Mascon Core	+200 mGal	0–300	High excavation resistance, dense infill, strong gravity pull
Negative Collar	–100 mGal	300–600	Stress shadow zone, increased differential settlement risk
Outer Compression Ring	+30 to +50 mGal	600–1000	Transitional zone, moderate density, feasible for L2–L3

3. Subsurface Structure of Mascon Basins

3.1 Stratigraphic Architecture of Imbrium and Similar Basins

Lunar mascons basins such as Imbrium are not uniformly layered. Instead, they are characterized by a concentric and stratified structure resulting from impact-induced deformation and post-impact volcanic infill. GRAIL-based models and seismic reinterpretations reveal the following sequence beneath mare plains:

1. Regolith Layer (2–8 m thick): Fine-grained, impact-fragmented material with variable cohesion and porosity. Often underlain by an immature brecciated transition zone.

2. Basaltic Mare Layer (~1–3 km thick): Dense, iron- and titanium-rich basalt infill deposited post-impact. Density ~3.2–3.4 g/cm³.

3. Uplifted Mantle Material: In the central regions of mascons, mantle material is believed to be uplifted toward the surface, reducing crustal thickness by up to 20 km (Zhao et al., 2021).

These subsurface features contribute directly to increased rock competence, elevated stresses, and discontinuous excavation zones, each critical for equipment design and zone classification.

3.2 Crustal Thinning and Mantle Uplift in Imbrium

According to GRAIL and previous Apollo seismic reanalysis, the Imbrium Basin exhibits crustal thinning from the global average of ~50 km to as little as ~25–30 km in its central mascons zone. The missing crust is compensated by uplifted denser mantle rock, explaining the persistent +200 mGal anomalies observed.

This crustal configuration creates a transition zone (Figure 3.2), where excavation projects may encounter a sharp gradient in rock properties:

• Shallower depth to competent bedrock

• Abrupt increase in UCS and density with depth

• Heterogeneous zones due to faulting, stress relics, and lava intrusions

Figure 3.2 - Conceptual cross-section of the Imbrium Basin showing regolith, basaltic infill, fractured crust, and uplifted mantle beneath the mascon (adapted from GRAIL inversion models).

3.3 Implication for Zoning and Excavation Strategy

The L1–L5 zoning model proposed by de Moraes (2025) aligns with this geophysical understanding:

Zone	Approx. Depth (m)	Material Characteristics	Excavation Notes
L1	0–1	Loose regolith, high porosity, thermal cycling	Suitable for blade excavation, berms
L2	1–3	Compacted regolith or vesicular basalt cap	Requires rippers, shallow trenchers
L3	3–10	Denser basalt flows, cooling fractures	Mechanized excavation or rotary percussion required
L4	10–30	Layered basalt/mare with increasing UCS	Feasible with segmental excavation & support
L5	>30	Fractured crust or uplifted mantle	Typically, infeasible without heavy drilling/muck removal systems

In mascons centers like Imbrium, the L4–L5 transition may occur earlier (i.e., at shallower depths), compressing usable excavation layers and increasing tool wear and energy requirements.

Recent observations from LROC and the Lunar Reconnaissance Orbiter have confirmed the presence of lobate scarps and grabens within or near mascon regions, indicating ongoing contractional and extensional tectonics (Figures 3.3a and 3.3b). These movements are believed to be caused by internal cooling and mascon-related stress redistribution.

• Implication: Structural systems and excavation plans must consider potential strain accumulation and micro-faulting.

• Risk: Long-term displacement could affect anchoring systems, trench integrity, and underground stability.

Figure 3.3a - Graben and Pyroclastics in SW Mare Humorum. [NASA/GSFC/Arizona State University]

Figure 3.3b - Lobate Scarps are not large, but they tell us much about how hot the Moon was when it was born and its ongoing thermal evolution. Image width is about four kilometers. [NASA/GSFC/Arizona State University]

It is important to highlight that the message here is that excavations in the mascons regions is not merely a matter of regolith thickness but also subsurface heterogeneity, mantle proximity, and tectonic instability. This directly informs excavation system selection, support design and risk classification.

4. Engineering Risks and Planning Parameters for Contractors

4.1 Gravitational Anomalies and Structural Loads

Mascons regions like Imbrium exhibit localized gravitational highs of up to +0.5% due to subsurface density anomalies. This increased gravitational acceleration (~1.626 m/s² versus the lunar average of 1.62 m/s²) has the following engineering implications:

• Increased Dead Loads: Structures bear higher self-weight. For example, foundation pressures on slabs may be underestimated if mascon-adjusted g-values are not applied.

• Differential Stress Fields: The gravity gradient may cause non-uniform vertical loading, increasing the risk of tilt, rotation, or settlement differentials for surface and shallow subsurface installations.

• Soil–Structure Interaction: Excavations and footings in these regions must account for denser bearing strata, potentially reducing compliance but increasing brittleness.

Contractor Guidance: Adjust all geotechnical design parameters to reflect local gravity. Avoid flat-foot foundation assumptions for mass-sensitive installations (landers, tanks, processing skids).

4.2 Excavation Tool Selection and Wear

As shown in Section 3, the shallow basaltic sequences and uplifted crustal/mantle materials in mascon zones lead to significant excavation resistance. Tool selection must consider:

• Abrasion Index: High-density basalt increases tool wear (drums, bits, picks).

• Thermal Shock: Extreme temperature swings coupled with hard rock increase fracture unpredictability during cyclic excavation.

• Load and Torque Requirements: Penetrating L3–L4 zones demands machinery capable of sustained high torque and percussion loading.

Table 4.2 below shows the adapted zoning framework and the recommended excavation methods.

Table 4.2 - Recommended Excavation Methods by Lunar Zone (Mascon Regions)

Zone	Recommended Excavation Tools
L1	Bucket blades, lightweight dozers, articulated backhoe rippers
L2	Compact trenchers with reinforced tines, oscillating cutting heads, impact rippers
L3	Rotary-percussive drills, anchored coring units, teleoperated hammer drills
L4	Sequential rotary-percussive drilling with staged mucking; early thermal or microwave assistive methods
L5	Not feasible without multi-phase operations: staged blasting, directed thermal fracture, or laser ablation (future tech, >2040s)

Note: All excavation tool recommendations are provisional and adapted for mascon-region conditions where high-density anomalies, fractured crust, and uncertainty in subsurface mechanical behavior prevail. No tunnel boring machines (TBMs) are currently feasible for zones L3–L5 due to lunar logistics, payload capacity, machine design, lack of real-time geomechanical feedback, and uncertain in-situ support requirements. Support methods are not included; if structural support becomes necessary, estimated bolting or anchoring systems would need to be reassessed within the next two to three decades based on in-situ findings and material behavior under lunar stress regimes.

4.3 Stress Redistribution and tectonic Reactivation

Recent LROC findings confirm that grabens and lobate scarps traverse multiple mascons basins (Figure 4.3a and 4.3b), including Imbrium. These features are indicative of:

• Recent Moonquakes (<50 Ma)

• Residual Stress Fields tied to cooling and mascon rebalancing

• Brittle Tension Zones that could intersect excavations at unpredictable orientations

This reactivation potential demands conservative support system design, especially for:

• Subsurface structures (storage caverns, tunnels)

• Anchored installations (masts, tanks)

• Utility corridors (cables, pipes under regolith)

Figure 4.3a - Evidence that the moon is being pulled apart forming features called graben. Displacements of up to 10 m have been inferred along fault scarps. [NASA/GSFC/Arizona State University]

Figure 4.3b - Sketch of graben feature showing that the moon is not shrinking. NASA.

Contractor Guidance: Apply rock mass classification methods with high safety factors; consider displacement monitoring even for shallow installations.

4.4 Risk-Based Zoning Summary for Contractors

To support rapid planning, the table below consolidates excavation risk levels by depth, based on GRAIL-informed mascon characteristics:

Table 4.4 - Provisional Risk Class for Mascon Context

Zone	Typical Depth	Risk Class (Mascon Context)	Key Concerns
L1	0–1 m	Low	Dust ejection, thermal cycling
L2	1–3 m	Moderate	Tool wear, regolith variability
L3	3–10 m	High	High UCS, excavation-induced stress shifts
L4	10–30 m	Very High	Crustal heterogeneity, stress reactivation
L5	>30 m	Prohibitive (Current Tech)	Mantle uplift, seismic risk, untested methods

Contractor Guidance: Construction planning must map target facilities against excavation zones. Zoning dictates not only tools and support systems but also risk tolerances and mitigation budgets.

5. Design Recommendations and Excavation Methodologies for Mascon Sites

5.1 Engineering Context for Mascon Excavation

Lunar construction in mascons regions, particularly in high-density basins like Imbrium, requires adaptive engineering strategies underpinned by partial data, uncertain in-situ conditions, and elevated subsurface gravity. Unlike terrestrial projects where geomechanical models are supported by core data and in-situ testing, excavation design on the Moon is fundamentally constrained by:

• Absence of representative samples across depth and lateral extent

• Limited knowledge of regolith-megaregolith interface geometry

• Unknown jointing, stress anisotropy, and thermomechanical history

Note: This document assumes highly limited ground truth data availability and prioritizes remote-sensing-based reconnaissance (GPR, AVG) for input into initial designs. All excavation operations must be preceded by reconnaissance campaigns and iterative updates.

Design Principle: The presence of uplifted mantle or dense basaltic infill within L3–L5 demands excavation planning based on rock mass response, not regolith models.

5.2 Recommendations for Design Application

• Use Ground Penetrating Radar (GPR) and Absolute Vector Gravimetry (AVG) for identifying layering, voids, and density anomalies.

• Develop probabilistic excavation models based on geophysical inversion rather than deterministic borehole data.

• For L1–L2 zones, apply geogrid-like reinforcement mats beneath structural pads to distribute load in variable density regolith.

• Recommend layered compaction by dozing cycles where possible, using vibro-blades to test load-bearing resistance dynamically.

• Rock bolts or dowels may improve local stability in L3–L4 where fractured basalt or uplifted megaregolith is encountered.

Limitations:

• Unknown joint persistence and aperture

• No data on in-situ stress field or thermal cycling impact

• Dust abrasion may degrade tensioning components over time

Exclusions and cautions:

• Grouting is not recommended as a design assumption. It relies on pressure delivery, material injection, and bonding behavior unverified under vacuum and thermal extremes.

• TBMs are excluded from baseline design unless robust field trials confirm compatibility with vacuum, dust, and power constraints.

  
  

Table 5.2 - Excavation Decision Support Matrix

Criterion	Recommended Methodology	Justification
No in-situ samples	GPR + AVG + conservative tool specs	Avoid overdesign or premature failure
High-density crustal zone	Avoid L5; use stepped cuts in L4	Stress amplification from mascon gravity field
Variable regolith thickness	L1–L3 zoning with embedded sensors	Manage transition zones with adaptive tool control
Dust-rich, thermally active	Modular shielding + short cycle ops	Reduce dust-induced tool degradation and thermal fatigue

6. Terrestrial Analogues and Lessons for Mascon Excavation

6.1 Relevance of Earth-Based Excavation Models

While lunar conditions are fundamentally distinct, characterized by ultra-low gravity, vacuum, thermal cycling, and absence of in-situ water, the experience from terrestrial subsurface construction in high-stress, dense rock massifs can provide partial analogues for excavation planning in mascon regions. These analogues are particularly relevant for L3 and L4 zones within uplifted mare basalts or megaregolith where excavation control, overbreak risk, and structural response are critical.

Projects with comparable excavation difficulties include:

Terrestrial Reference Site	Geotechnical Condition	Relevance to Lunar Mascons
Headrace Tunnels in Hydropower Projects (worldwide)	Dense volcaniclastic rock under high overburden	Analogous to uplifted mare basalt under residual thermal stress
Alps Base Tunnel (Switzerland)	Highly fractured crystalline rock and fault zones	Cautionary lessons in faulting, convergence, and rock support design
Himalayan Tunneling Projects	Mixed face conditions and highly variable lithology	Emulates abrupt transitions within megaregolith
Canadian Shield Mines	Deep mining in competent Archean granites	Useful for rock bolt behavior and dry excavation stability

6.2 Key Lessons from Earth-Based Engineering Practice

1. Excavation Stability in Dense, Brittle Rock

   a. Terrestrial experience in dense, high-RQD crystalline rock emphasizes pre-splitting techniques and staged advance cycles. These are adaptable to L4 operations where uplifted basalt layers may present competent but brittle excavation faces.

   b. Early overbreak control and face mapping protocols should be adapted using robotic photogrammetry and radar imaging post-blast or cut.

   
   

2. Support Systems and Rock Reinforcement

   a. Rock bolts are effective in stabilizing medium-stress excavation sections but require anchor point verification, which is impossible without pull testing in lunar conditions. Extrapolations from the Canadian mines show bolt pattern effectiveness drops significantly when stress directions are unknown.

   b. Lessons from hydropower tunnels recommend modular support segments, tensioned across known discontinuities. This supports development of prefabricated reaction rings for lunar trench and tunnel portals.

   
   

3. Instrumentation and Monitoring

   a. Terrestrial precedent underscores the need for continuous monitoring of deformation and convergence. For the Moon, remote sensing arrays, including LIDAR, radar, and thermal anomaly mapping, must substitute for in-situ gauges.

   b. Real-time dust flow observation, as developed for high-risk Alpine drill headings, can inform design of robotic inspection protocols on the Moon.

   
   

4. Logistics, Cyclic Loading, and Maintenance

   a. Extreme temperature variation, such as those faced in permafrost tunnels in northern Russia, correlate with lunar thermal cycling and inform the selection of thermal insulators and joint protection.

   b. Low-cycle fatigue observed in mountaintop infrastructure has shown that composite liners and segmental shells must be rated beyond elastic limits for reliability in fluctuating thermal-gravity environments.

6.3 Cautions When Applying Earth Analogues

Despite useful insights, lunar excavation must reject certain terrestrial assumptions:

Assumption (Earth)	Invalid for Lunar Use	Alternative Strategy
Gravity-based muck removal	No gravity-driven flow in 1/6 g	Vacuum-assisted conveyance or tethered carts
Grouted joint confinement	No pressure injection viable in vacuum	Mechanical interlock only; friction anchoring
Hydration-sensitive lithology	No pore pressure, no freeze-thaw dynamics	Friction and cohesion-based classification only

7. Risk Classes and Safety Factors in Mascon Excavation

7.1 Need for a Mascon-Specific Risk Framework

Excavation in lunar mascon regions demands a dedicated risk classification system, distinct from terrestrial frameworks. The elevated gravity anomalies, subsurface density heterogeneity, absence of ground truth data, and regolith–bedrock transitions lead to nonlinear excavation risks that conventional RMR, Q-system, or GSI charts cannot address without severe adaptation.

While terrestrial systems classify rock masses based on joint spacing, groundwater, and strength, the Moon presents dry, cohesionless, variable-gravity regolith overlying high-density impact melt and fractured basaltic crust, particularly in mascons basins such as Imbrium.

The following risk classification is adapted from de Moraes (2025) to reflect excavation complexity across L1–L5 zones in mascon settings:

Lunar Excavation Zone	Dominant Material	Risk Class	Key Risk Drivers	Recommended Mitigation
L1 – Surface Regolith	Loose, fine regolith	Low	Dust dispersion, rover slip, unstable shallow anchoring	Compacting, mass stabilization, surface anchoring
L2 – Graded Regolith	Coarser, semi-compacted	Moderate	Excavator sink-in, bearing capacity variability	Area-wide GPR/GRAIL-assisted zonation, pad design
L3 – Megaregolith	Brecciated basalt layers	High	Excavation face stability, tool wear, overbreak	Robotic inspection, bolting (with caveats), slower cycles
L4 – Impact Melt Sheet	Dense, fractured basalt	Very High	Face instability, flyrock (if mechanical or explosive used)	Partial perimeter pre-support, risk staging
L5 – Uplifted Mantle	Unknown; potentially peridotite	Uncertain/Extreme	Unknown mechanical properties, no excavation precedent	Avoid unless confirmed by in-situ seismic & gravimetric imaging

7.2 Safety Factors for Lunar Construction

Unlike Earth-based construction, where safety factors often range from 1.5–3.0 depending on consequence class, lunar excavation demands probabilistic and adaptive safety approaches, given the high uncertainty and data scarcity. Suggested values:

Application	Suggested Safety Factor (FS)	Notes
Foundation bearing on L2–L3	FS ≥ 2.0	Use lowest expected regolith strength value
Lining thickness in trench/tunnel (L3)	FS ≥ 2.5	To account for unverified jointing and unknown stress path
Rock bolt anchorage in L4	FS ≥ 3.0	No pull-out data; use only where rock integrity confirmed
Portal/reinforced cut faces (L3–L4)	FS ≥ 2.0	Include freeze–thermal cycle degradation assumptions

Note: These factors may be revised as Artemis-era field data is acquired. Until then, conservatism and modularity are essential for constructability.

Rationale for the provisional FS approach:

1. Foundation Bearing on L2–L3 (FS ≥ 2.0)

   This aligns with terrestrial practices in variable soils or weak bedrock, especially when no in-situ testing or load-settlement data is available. On the Moon, the heterogeneity of megaregolith and regolith composition justifies a minimum FS of 2.0, especially for critical loads (e.g., habitat bases, launch pads).

   
   

2. Lining Thickness in Trench/Tunnel (FS ≥ 2.5)

   Given:

   a. Unknown joint orientation and spacing

   b. Absence of in-situ stress data

   c. Thermal fatigue from day-night cycles

   d. Unknown seismic response (e.g., micrometeoroid impacts, moonquakes)

   Note: A factor of 2.5 for lining design is prudent, especially since failure would be catastrophic and repair options are limited.

   
   

3. Rock Bolt Anchorage in L4 (FS ≥ 3.0)

   Since:

   a. Pull-out capacity is unknown

   b. Fractured basalt may be anisotropic and poorly bonded

   c. Dust contamination can impact grout–rock interface (if used at all)

   d. Creep or thermal loosening could occur

   Note: Using FS ≥ 3.0 is conservative and appropriate, especially if static testing is unavailable before installation.

   
   

4. Portal/Reinforced Cut Faces (FS ≥ 2.0)

   This aligns with cut slope design on Earth under uncertain cohesion and groundwater effects. Even without water on the Moon, thermal stress cycling and gravity-induced slumping can initiate instability in steeper cuts, especially under heavy construction loads or mobile equipment traffic.

In the Imbrium Basin:

• L1–L2: Relatively uniform regolith thickness (2–8 m); safe for surface grading and ISRU pads if compacted.

• L3: Transition to megaregolith and fractured impact melt sheets begins. Tool degradation and face control dominate risk. GRAIL gravity highs and USGS slope maps should be cross-referenced.

• L4–L5: Potential mantle uplift zones under central mascon. Excavation not recommended without in-situ confirmation of stress regimes, material types, and thermal expansion coefficients.

8. Conclusions

Mascons regions present stratified and mechanically distinct excavation zones that require rigorous, phase-specific planning. The superposition of regolith, dense basaltic infill, and fractured, uplifted crust, confirmed by GRAIL-derived gravity anomalies and inversion models, demands that excavation strategies be zoned and methodologically tailored. In particular, the Imbrium Basin illustrates the necessity of adapting excavation techniques across variable material interfaces, with decreasing feasibility and increasing geotechnical uncertainty below the L3–L4 thresholds. At these depths, excavation faces elevated risks due to abrupt lithological transitions, elevated rock mass densities, unpredictable fracture networks, and unknown in-situ stress regimes.

In the absence of reliable mechanical sampling data from depths beyond the shallow regolith, early-stage excavation planning in mascon basins must rely heavily on geophysical methods, such as Ground Penetrating Radar (GPR), Absolute Vector Gravimetry (AVG), seismic refraction, and magnetometry. These tools will form the foundation for subsurface characterization, enabling preliminary hazard mapping and equipment selection. Until validated regolith and megaregolith profiles are obtained, all zoning classifications and excavation tool recommendations, such as those proposed in the provisional L1–L5 system (de Moraes, 2025), must be treated as conditional and subject to refinement.

Despite these challenges, the high structural coherence of mascons basins, particularly in their central uplifted regions, suggests that such locations may offer long-term geotechnical stability for embedded infrastructure, including subsurface habitats, storage facilities, and ISRU processing vaults. However, the feasibility of such integration depends entirely on the success of initial excavation efforts and on overcoming the early operational constraints imposed by material hardness, tool wear, dust propagation, and thermal cycling.

Proposed Application Pathways for Artemis and Commercial Missions

• Artemis III–IV: Surface operations in L1–L2 zones with teleoperated trenching tools.

• Artemis V–VI: Pilot tests of percussion drilling and robotic borehole imaging in L3 zones.

• Commercial cargo pads: Preferential siting over basaltic plains (Imbrium East).

• ISRU demo units: Deployment in regolith-rich L1 zones adjacent to mascon rims.

• Lunar bases (2035–2045): Structural emplacement in stabilized L2–L3 sectors.

9. References

1. Muller, P. M., & Sjögren, W. L. (1968). Gravity anomalies and mascons on the Moon. Science, 161(3842), 680–684.

2. GRAIL Mission Datasets (NASA/GSFC, 2013).

3. Hammond, P. E. (1972). Lunar tectonics and crustal evolution. NASA Technical Reports.

4. Carrier, W. D., Olhoeft, G. R., & Mendell, W. (1991). Physical properties of the lunar surface. In Lunar Sourcebook.

5. Canup, R. M., & Esposito, L. W. (1996). Accretion of the Moon from an impact-generated disk. Icarus, 119(2), 427–446.

6. de Moraes, R. (2025). The Moon Builders: Engineering the Lunar Subsurface. Space Geotech Publishing.

7. NASA/GSFC/Arizona State University. (2015). LROC WAC mosaic of the Imbrium Basin. Retrieved July 26, 2025, from https://lroc.sese.asu.edu