The choice of test conditions in this study reflects the extreme environment of the lunar polar regions. Permanently shadowed regions at the poles never receive direct sunlight, and surface temperatures there remain low enough that water-ice can survive for billions of years even under ultrahigh vacuum, sublimating only very slowly. To replicate these conditions, samples were held at approximately 93 K while the probe itself was varied across a range from 83 K to 163 K. Maintaining such temperatures during mechanical testing is nontrivial, and the experimental design addressed this with careful thermal management, including thermally isolating components so that sensitive instrumentation such as the load cell remained near room temperature even while the probe tip was immersed in cryogenic conditions. This attention to thermal boundary conditions matters because the mechanical behavior of ice is strongly temperature dependent, and uncontrolled warming during a test could substantially distort the measured strength.

A central contribution of the work is its systematic comparison of four distinct icy regolith morphologies prepared from the same lunar highlands simulant. Ice-cemented samples are made by freezing liquid water into a granular mineral matrix, producing a material in which ice acts as a cement between particles, analogous to the way cement binds concrete. Pressure sintered samples instead combine granular ice and dry regolith compacted together, yielding a more granular, less cemented texture. Unsintered samples represent loosely mixed material, while vapor deposited samples simulate ice that has condensed directly from vapor onto cold regolith surfaces, a process thought to be relevant in permanently shadowed regions where ice may be deposited from transient atmospheres or impact-generated vapor. Because no in-situ observations have yet been made within a lunar PSR, the actual form of lunar ice remains unknown, and each of these morphologies represents a plausible candidate for what future missions may encounter.

The finding that microstructure dominates geotechnical behavior has significant implications for how the community interprets prior simulant studies. Previous research had already hinted at enormous variability: ice-cemented simulants showed sharp strength increases at critical ice contents of roughly 1 and 3 weight percent, and ice-enriched material above about 12 weight percent was reported to behave like hard rock or concrete with strengths exceeding 100 megapascals. In contrast, pressure sintered mixtures at 10 weight percent ice were far weaker, below 14 megapascals, and showed no abrupt strength transitions. The new controlled measurements confirm that even under identical ice contents, densities, and temperatures, different preparation methods can produce materials whose strengths differ by orders of magnitude. This means that the preparation recipe, not merely the ice content, controls mechanical response.

The quantitative trafficability results are particularly striking. When cone index gradients were corrected for lunar gravity and normalized to a common penetration depth, a vapor deposited sample containing 6.88 weight percent ice proved 3.92 times stronger than a pressure sintered sample with 8 weight percent ice, and even 1.23 times stronger than the upper bound of in-situ cone index values measured in the Descartes Highlands during Apollo 16. This comparison anchors the laboratory measurements to the only direct penetrometer data ever collected on the lunar surface, providing a useful reality check. It suggests that some icy morphologies could produce surfaces that are at least as firm as the dry regolith traversed by Apollo astronauts, which is encouraging for rover mobility planning in polar terrain.

The excavation energy results reveal a more nuanced picture, with opposing trends depending on morphology. For pressure sintered samples, the energy required per unit mass of excavated water fell from 0.35 joules per gram at 1 weight percent ice to 0.11 joules per gram at 30 weight percent, a 3.2-fold improvement in efficiency. This counterintuitive result arises because richer ice deposits contain proportionally more water per unit of material excavated, so the energy cost attributable to each gram of recovered water declines even if the material itself is somewhat harder to dig. For ice-cemented samples the trend runs in the opposite direction, with excavation energy climbing from 2.74 joules per gram at 1 weight percent to 143.03 joules per gram at 12 weight percent, a 52-fold increase. The cementing action of ice between mineral grains makes the material progressively harder to break apart, overwhelming the benefit of higher water content.

These opposing trends carry direct consequences for the economics of lunar water extraction. In-situ resource utilization concepts that envision mining polar ice to produce propellant, drinking water, and oxygen depend on favorable energy budgets for excavation and processing. If lunar ice occurs predominantly in sintered, granular, or vapor deposited forms, the study’s results suggest that excavation may be considerably more economical than many hardware development programs have assumed, since tests based on ice-cemented simulants would have systematically overestimated the resistance that mining equipment must overcome. Conversely, if substantial fractions of polar ice are genuinely cement-like, excavation energy demands could be far higher than optimistic projections. Because the true morphology is unknown, mission planners face a wide envelope of possible outcomes, and this work helps bound that envelope with quantitative data.

The implications extend to the validation of flight hardware. Robotic excavators, drills, and mobility systems destined for the lunar poles are typically qualified against simulant beds in terrestrial laboratories. If those beds are made with ice-cemented recipes, the hardware will be tested against a material that may be far stronger than what it actually encounters, leading to over-engineered systems with unnecessary mass and cost. On the other hand, hardware validated only against weak sintered simulants could fail catastrophically if it encounters cemented ice. The authors’ observation that ice-cemented simulants, rocks, and concrete analogues may be unsuitable as general-purpose proxies for all icy regolith morphologies therefore challenges a widespread practice in the field and argues for morphology-specific testing campaigns matched to the best available scientific estimates of how lunar ice actually forms.

The study also addresses strategic knowledge gaps formally identified by the International Space Exploration Coordination Group, including the geotechnical characteristics and accessibility of permanently shadowed regions, the form and distribution of frozen polar volatiles, and trafficability across the lunar surface. Missions such as the Volatiles Investigating Polar Exploration Rover and the crewed Artemis program will operate in precisely the environments where these uncertainties matter most, traversing and sampling terrain whose mechanical properties cannot yet be observed directly. Quantitative laboratory measurements of the kind reported here provide a bridge between remote sensing indications of ice and the engineering parameters, such as bearing capacity and excavation resistance, that determine whether wheels will sink, slip, or find firm purchase.

Methodologically, the work demonstrates the value of miniature cone penetration testing as a compact, information-rich technique for cryogenic simulant characterization. The apparatus described, combining a small stainless steel cone with a low-capacity load cell mounted on a universal test machine, achieves sufficient precision to resolve differences between morphologies while remaining simple enough for routine laboratory use. The inclusion of a thermocouple within the hollow cone tip allows probe temperature to be monitored and controlled independently of sample temperature, an important capability given that probe-sample friction and ice deformation behavior both depend on temperature. Calibration against a certified reference load cell further strengthens confidence in the absolute values reported.

Looking forward, the results suggest several productive avenues for the field. First, confirming the morphology of lunar ice through in-situ measurements, whether by penetrometers on future rovers or by sample return from polar regions, would dramatically narrow the uncertainty in excavation and mobility predictions. Second, extending this experimental framework to other volatiles, such as carbon dioxide ice, and to mixtures of multiple ices, would broaden its applicability to other cold solar system bodies including Mars, comets, and the moons of the outer planets. Third, relating cone index measurements to full-scale excavation forces and wheel-soil interaction models would help translate these laboratory parameters into mission-level engineering requirements. In the meantime, the demonstration that icy lunar regolith may be easier to excavate and traverse than previously thought offers a cautiously optimistic outlook for the emerging economy built around lunar polar resources, while reminding the community that the ground truth beneath the shadows remains one of the most important open questions in planetary exploration.

Subject of Research: Trafficability and excavatability of icy lunar regolith simulants quantified using cone penetration

Article Title: Trafficability and excavatability of icy lunar regolith simulants quantified using cone penetration

Article References: Ricardo, D., Hodgkinson, J., Rhamdhani, M. A., & Brooks, G. (2026). Trafficability and excavatability of icy lunar regolith simulants quantified using cone penetration. Space and Planetary Resources, 2(1), Article 9. https://doi.org/10.1007/s44461-026-00015-w

Image Credits: AI Generated

DOI: 10.1007/s44461-026-00015-w

Keywords: Trafficability, excavatability, lunar, regolith, simulants, quantified, cone, penetration, scientific research

The six proposed Metrics for Sustainability offer a framework that moves beyond vague aspirations toward measurable performance. Material circularity captures the proportion of materials that remain in productive use across a lunar settlement, providing a quantitative analogue to recycling rates on Earth but extended to include the recovery of volatiles from waste streams and the repurposing of hardware at end of life. Life-support energy performance reflects the efficiency with which a habitat sustains breathable atmospheres, potable water, and thermal regulation, all of which demand continuous power through the two-week lunar night when solar generation is unavailable. Agricultural output measures the capacity of a settlement to produce food locally, which reduces launch mass from Earth, improves diet freshness for crews, and buffers against supply chain interruption.

Social cohesion as a metric may appear unusual in an engineering context, yet the evidence from isolated, confined, and extreme environments on Earth consistently shows that interpersonal dynamics, governance structures, and habitat design strongly influence mission outcomes. Research into salutogenesis in space emphasises that wellbeing is not merely the absence of illness but the presence of factors that help crews thrive, including a sense of coherence, meaningful work, and environments that support psychological adaptation. The finding that only a small minority of surveyed respondents expressed willingness to live in very small space settlements underscores that perceived habitability and community size matter to real people, and that any long-term lunar presence must be designed with human factors as rigorously as with power systems or landing pads.

Supply chain resilience, the fifth metric, acknowledges that even a mature lunar settlement will remain connected to Earth through the exchange of specialised components, scientific instruments, and personnel. Resilience in this context means the ability to absorb shocks, whether geopolitical conflict disrupts international partnerships, economic downturns curtail budgets, or a launch failure removes a critical logistics node. A settlement that can fabricate more of its own spares through additive manufacturing, maintain buffer stocks of essential consumables, and operate degraded systems safely for extended periods scores higher on this metric than one dependent on just-in-time delivery from Earth.

The final metric, legal and governance frameworks, is perhaps the most consequential and the least technologically deterministic. The Outer Space Treaty of 1967 established foundational principles, including that space is free for exploration and use by all states and that celestial bodies are not subject to national appropriation, but it was written long before the prospect of commercial lunar resource extraction became plausible. Subsequent instruments, national legislation, and multilateral initiatives have begun to address gaps, yet substantial ambiguity remains regarding property rights in extracted resources, standards of environmental protection on the lunar surface, coordination of activities to avoid harmful interference, and mechanisms for dispute resolution. The paper’s argument that the Spacefaring scenario is most desirable partly depends on the existence of agreed norms that allow multiple actors to operate without conflict.

The four scenarios, Red Tape, Run for Resources, Restricted Operations, and Spacefaring, function as a foresight tool that illuminates how different combinations of governance and technical choices lead to divergent futures. In a Run for Resources world, competitive dynamics could produce rapid activity but also duplication, environmental degradation of scientifically valuable sites, and increased risk of accident or confrontation. Restricted Operations, by contrast, might protect the lunar environment through excessive caution while foreclosing the benefits that a sustained presence could deliver, including scientific discovery, economic development, and the demonstration of technologies needed for eventual Mars missions. The Spacefaring scenario emerges as preferable because it couples ambitious activity with cooperative governance and sustainable practice, treating the Moon as a place where humanity learns to live and work off-planet responsibly.

The staged model of lunar presence, moving from robotic reconnaissance through short-termSortie missions to long-term habitation and eventually something akin to a lunar village, provides a useful temporal scaffold for planning sustainability interventions. At the robotic stage, sustainability considerations centre on planetary protection and the avoidance of contamination at sites of scientific interest, such as permanently shadowed regions where water ice records billions of years of solar system history. Short-term missions introduce questions of landing site selection, traffic management, and the cumulative effects of repeated landings on regolith dynamics and the exosphere. Long-term habitation raises the full suite of circular economy challenges, including waste processing, radiation shielding through regolith construction, and the provisioning of agriculture under artificial light.

The lunar night deserves particular emphasis because it dominates the engineering envelope of any permanent presence. Fourteen days of darkness mean that solar power alone cannot sustain life support without substantial storage or complementary generation, and options such as fuel cells, nuclear surface power, and strategically sited solar arrays at peaks of near-eternal light near the poles are all under active investigation. Any sustainability metric on energy performance must therefore account for night survivability, not just daytime efficiency, because a settlement that cannot reliably endure the night cannot claim long-term resilience. The paper’s pragmatic definition of permanence, as continuing operations by successive crews with continuous robotic support where technology cannot yet fully overcome the night, reflects this reality honestly.

In-situ resource utilisation sits at the heart of the technical vision. The lunar poles are believed to host water ice within permanently shadowed craters, a resource that can yield drinking water, breathable oxygen, and, through electrolysis, hydrogen and oxygen propellant. Regolith itself can be sintered or bound into building elements, providing radiation shielding and thermal mass without importing construction material. Oxygen constitutes a large fraction of regolith oxides, and extraction processes ranging from hydrogen reduction to molten regolith electrolysis are being developed at increasing levels of maturity. Extending ISRU toward ISRU-wellbeing, as the paper proposes, is a novel conceptual move: it suggests that local resources should support not only survival but flourishing, informing habitat architecture, lighting design that mimics terrestrial circadian cues, and communal spaces that foster the social cohesion the metrics seek to measure.

The proposal that the metrics could eventually be embedded in legal, governance, and technical agreements between stakeholders mirrors the way terrestrial environmental standards migrate from voluntary frameworks into binding regulation and procurement requirements. A common measurement language would allow agencies, commercial operators, and researchers to benchmark performance, compare approaches, and identify trade-offs transparently. It could also support proportionate regulation, since rules calibrated to measurable sustainability outcomes are less likely to be either ineffective or punitive than rules drafted in the abstract. The recommended research agenda, which prioritises refining the metrics and soliciting feedback from diverse stakeholder groups, recognises that legitimacy depends on participation, and that frameworks imposed without broad consultation are unlikely to endure.

Connections across the three space domains reinforce the argument that lunar sustainability cannot be pursued in isolation. Launch activity on Earth generates emissions and affects communities near spaceports, so reducing launch mass through ISRU indirectly reduces terrestrial impacts. Orbital infrastructure, including stations that act as gateways for lunar missions, must itself be operated sustainably amid growing congestion and debris in Earth orbit, since a collision or debris-generating event could interrupt the logistics chain on which lunar operations depend. Conversely, technologies matured for the Moon, such as closed-loop life support, advanced recycling, and autonomous construction, have clear applications in orbital habitats and eventually in Mars missions, making lunar sustainability a proving ground for broader spacefaring capability.

Historical context strengthens the case for proactive rather than reactive governance. On Earth, many environmental harms were addressed only after damage became evident and costly, whereas the Planetary Boundaries framework exemplifies an attempt to define safe operating limits in advance. The Moon offers a rare opportunity to apply that lesson preemptively, before large-scale activity begins, because key decisions about landing sites, resource extraction methods, and heritage protection for sites like the Apollo landing areas are still being made. Whether future generations will judge humanity’s return to the Moon as sustainable will depend substantially on choices made in the present decade, and the framework of a Lunar Circular Economy with measurable metrics provides a concrete starting point for making those choices deliberately rather than by default.

Subject of Research: Developing a sustainable human lunar presence using space resources

Article Title: Developing a sustainable human lunar presence using space resources

Article References: Cernev, T., de Zwart, M., & Hessel, V. (2026). Developing a sustainable human lunar presence using space resources. Space and Planetary Resources, 2(1), Article 8. https://doi.org/10.1007/s44461-026-00014-x

Image Credits: AI Generated

DOI: 10.1007/s44461-026-00014-x

Keywords: Developing, sustainable, human, lunar, presence, space, resources, scientific research