Lunar Poles Research Articles

Lunar-Derived Propellants for Fueling Mars-Bound Spacecraft in Cis-Lunar Space

The conventional method to send payloads to Mars is by direct trans-Mars injection (TMI) from LEO. NASA is considering an alternative of fueling large Mars-bound cargo transfer vehicles in cis-lunar space with propellants derived from the Moon by in situ propellant production (ISPP) prior to trans-Mars injection from cis-lunar space. A large team of investigators developed an Evolvable Lunar Campaign (ELC) that defined its strategic objective as follows: "The ELC strategic objective is commercial mining of propellant from lunar poles where it will be transported to lunar orbit to be used by NASA to send humans to Mars." Unfortunately, sending Mars-bound vehicles to cis-lunar space prior to trans-Mars injection saves little mass in LEO, unnecessarily includes lunar ISPP, which is costly, complex, and risky, and at the bottom line, has no benefits. The problem is that the amount of propellant needed to go from LEO to cis-lunar space is roughly comparable to the amount of propellant used for direct TMI from LEO, so the lunar-derived propellants only offset a small amount of propellant used to augment Mars Orbit Insertion and Entry, Descent, and Landing, and the amount of propellant required in LEO is almost the same in both cases. The initial mass in low Earth orbit (IMLEO) is not reduced much by utilizing lunar ISPP. At the bottom line, sending Mars-bound MCTV to cis-lunar space adds complexity, cost, and risk and provides essentially no benefits.

Temporary atmospheres produced by human activities on the Moon

Outgassing from materials, whether through the ascent/descent stages of lunar vehicles, airlock depressurizing, rover or astronaut suit outgassing, may cause an effect of unwanted accumulation of volatiles at the surface and exosphere. This is especially important at (or proximal) to permanently shadowed regions (PSRs) at the lunar poles. Herein, we provide estimates of expected outgassing from various human-landed objects on the Moon, including backpacks, airlocks, rovers, landers, trash and mining operations. Astronaut suits produce some level of oxygen outgassing (Helou et al., 2022), which may transport and condense in these PSRs, even in micro- cold traps (Glavin et al., 2010).We estimate the outgassing from drill mining and trash-to-gas conversion assuming a specific technology is operating. These outgassing systems can create local, temporary atmospheres in the vicinity (∼100 km radius) of the sources. The atmosphere may be particularly high within meters of the source. To obtain column densities for these temporary atmospheres, we first bracket ranges for the gas number loss as a function of time. We then derive the maximum distance traveled and the time the released molecules remain in the exosphere for a single ballistic hop, assuming the molecules are ejected from the surface of the object at its surface temperature. In some cases, such as the astronaut backpack and the rover, the temperature is that of the source. Given this information, an average and peak local exospheric density and column density can be estimated. We find that backpacks, airlock releases, and the Starship lander can create relatively high-density local atmospheres, with local near-lander outgassing water densities exceeding 107/cm3. This local water exosphere is over 106 times greater than the LADEE-derived lower limit of the natural water exosphere at ∼3/cm3. Thus, the anthropogenic temporary water exosphere will likely dominate the environment near the lander, making an assessment of the natural exospheric water environment difficult.

Topography‐Enhanced Ultra‐Cold Trapping at the LCROSS Impact Site

AbstractSmall topographic features below the resolution of existing orbital data sets may create “micro ultra‐cold traps” within the larger permanently shadowed regions that are present at the lunar poles. These ultra‐cold traps are protected from the major primary and secondary illumination sources, and thus would create surfaces that are much colder than lower‐resolution temperature maps would indicate. We examine this effect by creating a high resolution (1 m pix−1) terrain map based on upscaled data from the Lunar Orbiter Laser Altimeter. This map is illuminated by scattered sunlight and infrared emissions from sunlit terrain, which are then run through a thermal model to determine temperatures. We find that while most of the terrain experiences maximum temperatures around 50 K, there are a number of 1–30 m‐scale ultra‐cold traps with maximum temperatures as low as 20–30 K. By comparing our modeled ultra‐cold trapping area to volatile abundances measured by Lunar Crater Observation and Sensing Satellite (LCROSS), we reveal a diverse environment where the surficial abundances necessary to explain the LCROSS results are strongly dependent on precisely where the impact occurred.

On the reachability and genesis of water ice on the Moon

Understanding the reachability of water ice by future in-situ experiments near the lunar poles is crucial for supporting growing exploration plans and constraining the uncertainties on its genesis and distribution. To achieve this objective, we perform a thorough three-dimensional mapping of the distribution of water ice in the lunar polar regions (70° onward), integrating radar, optical, and neutron detector observations from the Lunar Reconnaissance Orbiter mission (LRO). Our analysis reveals ∼5-to-8-fold larger expanse of subsurface water ice (∼1-3 m depth) compared to surface water ice (up to 1 m depth) for the north and south poles, respectively. Our investigation cannot rule out the possibility of deep-seated water ice deposits in the lunar poles that remains beyond the detection capabilities of existing instruments on LRO. Moreover, we find that the extent of water ice in the northern polar region (∼1100 ± 74 km2) is twice that in the southern polar region (∼562 ± 54 km2). Our mapping also suggests that the dichotomous latitudinal distribution and the antipodal longitudinal distribution of water ice are likely driven by Mare volcanism and preferential cratering. We provide additional evidence that outgassing during Imbrian volcanism was probably the primary source of subsurface water ice in the lunar poles, which favors larger expanse over meteoritic sources.

Modeling and analysis for volatile characteristics of lunar water ice

Lunar water ice resources are important space assets for human survival and sustainable living on the Moon. Detection data indicates that the permanently shadowed regions at the lunar poles contain water ice resources. The efficiency of in-situ extraction of lunar water ice resources depends on its volatile characteristics. In the context of extraction and utilization of water ice resources in the permanently shadowed regions, the sublimation and diffusion processes of lunar water ice are investigated by combining the theory of pure ice sublimation with the fractal theory of porous media. On this basis, a volatilization model for lunar water ice is established to examine the effect of temperature, relative density, and water content on the volatile behaviors of lunar water ice. The findings of this study can provide technical and theoretical support for the in-situ exploration, extraction, and utilization of lunar water ice resources and offer insights into the existence and distribution of lunar water ice resources.

Low‐temperature thermal and physical properties of lunar meteorites

AbstractLunar meteorites are the most diverse and readily available specimens for the direct laboratory study of lunar surface materials. In addition to informing us about the composition and heterogeneity of lunar material, measurements of their thermo‐physical properties provide data necessary to inform the models of the thermal evolution of the lunar surface and provide data on fundamental physical properties of the surface material for the design of exploration and resource extraction hardware. Low‐temperature data are particularly important for the exploration of low‐temperature environments of the lunar poles and permanently shadowed regions. We report low‐temperature‐specific heat capacity, thermal conductivity, and linear thermal expansion for six lunar meteorites: Northwest Africa [NWA] 5000, NWA 6950, NWA 8687, NWA 10678, NWA 11421, and NWA 11474, over the range 5 ≤ T ≤ 300 K. From these, we calculate thermal inertia and thermal diffusivity as functions of temperature. Additionally, heat capacities were measured for 15 other lunar meteorites, from which we calculate their Debye temperature and effective molar mass.

Review of energy supply techniques for ice in-situ thermal mining in lunar permanently shadowed regions

The Moon's polar regions have abundant water ice resources. The mining and utilization of lunar polar water ice could serve as a propellant and survival resource for human exploration of deep space. The concept of thermal mining has been proposed to extract water ice resources. There are advantages and disadvantages to different mining methods. The energy problems faced by in situ resource utilization on the Moon are of great concern. The electrolysis of water and the heating of weathered layers require a continuous supply of energy. Wired energy transfer at the lunar poles would be very costly for launching conductors from Earth to the Moon. Wireless energy transfer technology is also well-developed today and has promising applications in the energy supply of lunar thermal mining. This paper describes the different methods of thermal mining and the various ways of supplying energy using solar energy for thermal mining.

Opportunities and limits of lunar gravitational-wave detection.

A new era of lunar exploration has begun with participation of all major space agencies. This activity brings opportunities for revolutionary science experiments and observatories on the Moon. The idea of a lunar gravitational-wave detector wasalready proposed during the Apollo programme. The key characteristic of the Moon is that it is seismically extremely quiet. It was also pointed out that the permanently shadowed regions at the lunar poles provide ideal conditions for gravitational-wave detection. In recent years, three different detector concepts were proposed with varying levels of technological complexity and science potential. In this paper, we confront the three concepts in terms of their observational capabilities based on a first more detailed modelling of instrumental noise. We identify important technological challenges and potential show-stoppers. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades (part 2)'.

A 600 m2 array of 6.5 m telescopes at the lunar pole.

The proposed lunar telescope for optical and infrared astronomy aims at very large aperture, 600 m2, at a fundable cost. It comprises an array of 18 separate telescopes, each of 6.5 m aperture. The 200 m diameter array will be located within 1/2° (15 km) of a lunar pole on approximately level ground, with a perimeter screen deployed to provide shade and cooling to cryogenic temperature. The 500 m diameter screen will allow unobscured access down to 8° elevation. All 18 telescopes will reflect light into a central beam combiner to form a single image covering wavelengths from 0.4 µm to 10 µm. The initial instrument complement will include high-resolution and multi-object spectrographs to exploit the single combined field of view of two arcminute diameter, with the diffraction limited resolution of 6.5 m aperture. Scientific applications include the search for molecular biosignatures in transiting exoplanets, and the study of galaxy evolution using red-shifted spectra to beyond z = 10. The array cost, including delivery to the Moon by SpaceX Starship for installation using lunar base infrastructure, is around $10 billion, similar to that of the 25 m2 JWST. To test the concept, first a single prototype 6.5 m unit would be operated at the lunar south pole. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades (part 2)'.

Additive manufacturing of hydrogel-based lunar regolith pastes: A pathway toward in-situ resource utilization and in-space manufacturing

Additive Manufacturing (AM), combined with efficient in-situ resource utilization, has the potential to enable sustained presence on the Moon through in-situ production and replacement of construction blocks, engineered parts, and devices in the lunar terrain. As an initial step toward realizing this vision, this work proposes a new material formulation utilizing lunar regolith simulants (LHS-1), water, and a hydrophilic hydrogel-forming polymer (Pluronic F127) to produce a hydrogel-based lunar regolith paste suitable for material extrusion AM. This formulation enables the use of water as another potential lunar in-situ resource for the first time in the literature, considering the recent confirmation of large quantities of water-ice in the shadowed craters around the lunar poles and the presence of water on the sunlit surface of the Moon. To systematically investigate the viability of the proposed hydrogel-based lunar regolith material feedstock and the application of material extrusion AM, this work introduces a three-stage design of experiment (DOE) framework to achieve two fundamental objectives. First, the viable range of lunar regolith simulant in the hydrogel-based material formulation is identified using a categorical quality evaluation of single and multi-layer material depositions. Second, the material printability window is established in terms of printing speed and extrusion rate for different viable material compositions through hierarchically designed experiments. The observed porosity of the sintered parts decreased with increasing regolith content in the material composition, while the density and compressive strength increased with higher regolith content. For material compositions consisting of 25–40 vol% regolith simulants, the observed porosity of the sintered parts decreased from 6.4 to 2.18 %, their density increased from 0.78 to 0.89 g/cm3, and their average compressive strength ranged between 0.68 and 1.32 MPa. Finally, the printability of the material was demonstrated by producing various prototype hand tools and lab-scale construction blocks with varying geometrical complexities. This work represents a crucial step toward in situ resource utilization and sustainable in-space manufacturing, sets the stage for future investigations, and the introduced DOE driven framework offers a pathway toward systematically identifying the optimal material compositions and the corresponding process parameters to enable high-quality prints.

Development of icy regolith simulant for lunar permanently shadowed regions

The lunar poles are thought to contain vast ice deposits that could be beneficial to future space exploration efforts. However, it is not well characterized how water ice content affects regolith and dust physical properties. In order to develop suitable technologies that can operate safely in the cryogenic regolith, testing should be conducted in simulated regolith. We present a new production method for lunar permanently shadowed regions (PSRs) icy regolith simulant. We build on an existing lunar highlands simulant, by adapting it for lunar poles, where water ice might be present in PSRs. We have demonstrated a production concept using controllable simulant and water flow rates to make granular icy simulant with variable water ice content. We found that with this production method, icy simulant has a porosity of 0.6 to 0.7, that persists even after dehydration.

Improved Orthorectification and Empirical Reduction of Topographic Effects in Monostatic Mini-RF S-band Observations of the Moon

The Miniature Radio Frequency instrument (Mini-RF) on the Lunar Reconnaissance Orbiter obtained widespread synthetic aperture radar observations of the Moon in the S band (12.6 cm), including nearly complete coverage at both lunar poles. The currently archived monostatic data have spatial offsets from the lunar reference frame, making them more difficult to compare to other data sets. To address this issue, we have developed a new algorithm for spatially controlling the Mini-RF S-band monostatic data set and orthorectifying these data onto lunar topography. Additionally, as the influence of incidence angle changes on radar observations is well known, we describe an empirical approach to account for variations in observation geometry and surface topography. Individual radar swaths and mosaics produced using this method more clearly show the variability in scattering behavior due to changes in lunar regolith properties and suppress some of the behavior arising from these topographic effects alone. Once these terrain effects are taken into account, we find that areas of permanent shadow at both poles have a higher median radar reflectivity than nonpermanently shadowed regions, but the polarization behavior of shadowed versus unshadowed areas is largely similar. The higher radar reflectivity in permanent shadow is likely the result of physical or compositional differences in these unique environments, though the precise cause remains uncertain. The results here illustrate how reducing the influence of topography and geometry effects in Mini-RF radar data may enable better characterization of lunar geologic units, regolith structure, and potential areas hosting volatile deposits at the lunar poles.

A Robust Fuel Cell Operating on Lunar Water Derived Fuels

The space proven fuel cell technology will likely play a crucial role in the upcoming expansion of human presence into the solar system. In particular, polymer electrolyte membrane (PEM) fuel cells excel due to their high power-density, low weight and their ability to operate on in-situ resource utilization (ISRU) based fuels. Hydrogen fuel and oxygen can be derived from lunar water, which is believed to be trapped in permanently shadowed craters on the lunar poles. However, Colaprete A. et al. found that H2S and NH3 as well as smaller quantities of other sulfur compounds and hydrocarbons are detected alongside the water ice. These compounds are well known fuel impurities which cause reversible yet also irreversible damage to the platinum catalyst and other components of the membrane electrode assembly (MEA). Commercially available fuel cells on the other hand require highly purified fuels with contamination levels in the low ppb region. Thus, these impurities pose a profound problem, even if only a fraction of them is carried onwards to the hydrogen fuel and oxygen. Subsequent intensive purification processes are costly and require large amounts of energy – a process which could render the whole approach useless.As mentioned before, H2S and other sulphur compounds adsorb strongly to the platinum metal and irreversibly degrade its catalytic activity until performance drops to unusably low levels. This effect is directly related to the amount of available catalyst, since a doubling of the platinum loading leads to a two-fold reduced degradation. We hypothesize that the resilience of a fuel cell can not only be improved by increasing the amount of platinum, yet also by using the available platinum more effectively. A lot of the platinum remains inactive within a fuel cell electrode due to different effects like excessive ionomer coverage or particle agglomeration. With the so-called platinum utilization parameter the obtained fuel cell performance is related to the total platinum weight and thus can be used to rate how effective platinum is used. In our recently published review, we found that electrospun electrodes have the highest platinum utilization out of all compared fuel cell electrode manufacturing methods. Furthermore, electrospun electrodes are reportedly less prone to other degradation mechanisms like Ostwald ripening. In this ongoing work, we aim to fabricate MEAs with fully electrospun electrodes and benchmark them against a commercial alternative. The electrodes will be operated with contaminated gases in half cell as well as full cell degradation experiments. The outcome of this research aims to support the exploration community in designing robust energy systems on the moon by investigating the effect of lunar contaminants on fuel cell systems.

Simulation of the temperatures in the permanently shadowed region of the Moon's south pole and data validation

The permanently shadowed regions (PSRs) at the lunar poles without direct solar illumination maintain low temperatures throughout the year, making them optimal environments for the preservation of water ice. This paper investigates the diurnal and seasonal temperature variations of the PSRs within craters at the lunar south pole. The craters de Gerlache, Shoemaker, Amundsen, and Wiechert E are selected to explore how latitudes and shapes impact PSR temperature. Using the ray tracing approach, the shadow effect of terrain on the scattered sunlight and thermal radiation is calculated. PSR temperatures are simulated with the one-dimensional heat conduction equation. The thermal emissivity of the lunar surface is studied. Simulations with anisotropic emissivity are closer to the Diviner data in PSRs than the simulations with isotropic emissivity. In addition, by comparing the simulations to the Diviner data, it is found that the thermal conductivity at the extremely low temperatures in PSRs might be lower than that at high temperatures outside the PSRs. Simulations of the selected craters are used to study the influence of polar day phenomena occurring at high-latitude craters during the summer and the effect of direct solar illumination at the floors of low-latitude craters on the temperature distribution of PSRs. The influence of crater shape is analyzed as well by investigating the temperature distributions within PSRs of flat-floored and bowl-shaped craters. With the analysis of the heat flux propagation distances, emission angles, and incident angles, this study quantitatively elucidates the spatial and temporal variations in PSR temperatures. To explain why the Diviner data are lower than the simulation results at the solar-illuminated crater walls, an undulating rough surface is generated. The locations of the Sun and the observer on opposite sides of the rough surface may decrease the observed infrared brightness temperature according to the simulations. The PSR peak temperatures simulated with the anisotropic emissivity and thermal conductivity for PSRs are used to search for low-temperature areas suitable for preserving water ice within de Gerlache and Shoemaker.

Analysis of Illumination Conditions in the Lunar South Polar Region Using Multi-Temporal High-Resolution Orbital Images

The illumination conditions of the lunar south pole region are complex due to the rugged terrain and very low solar elevation angles, posing significant challenges to the safety of lunar landing and rover explorations. High-spatial and temporal-resolution analyses of the illumination conditions in the south pole region are essential to support mission planning and surface operations. This paper proposes a method for illumination condition analysis in the lunar pole region using multi-temporal high-resolution orbital images with a pre-selected landing area of Chang’E-7 as the study area. Firstly, a database of historical multi-temporal high-resolution (0.69–1.97 m/pixel) orbital images, with associated image acquisition time, solar elevation angle, and azimuth angle, is established after preprocessing and registration. Secondly, images with the nearest solar elevation and azimuth at the planned time for mission operations are retrieved from the database for subsequent illumination condition analysis and exploration support. The differences in the actual solar positions at the mission moments from that of the nearest sun position image are calculated and their impact on illumination conditions is evaluated. Experimental results of the study area demonstrate that the constructed image database and the proposed illumination analysis method using multi-temporal images, with the assistance of DEM in a small number of cases, can effectively support the mission planning and operations for the Chang’E-7 mission in the near future.

Calibration of ShadowCam

ShadowCam is a high-sensitivity, high-resolution imager provided by NASA for the Danuri (KPLO) lunar mission. ShadowCam calibration shows that it is well suited for its purpose, to image permanently shadowed regions (PSRs) that occur near the lunar poles. It is 205 times as sensitive as the Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC). The signal to noise ratio (SNR) is greater than 100 over a large part of the dynamic range, and the top of the dynamic range is high enough to accommodate most brighter PSR pixels. The optical performance is good enough to take full advantage of the 1.7 meter/pixel image scale, and calibrated images have uniform response. We describe some instrument artifacts that are amenable to future corrections, making it possible to improve performance further. Stray light control is very challenging for this mission. In many cases, ShadowCam can image shadowed areas with directly illuminated terrain in or near the field of view (FOV). We include thorough qualitative descriptions of circumstances under which lunar brightness levels far higher than the top of the dynamic range cause detector or stray light artifacts and the size and extent of the artifact signal under those circumstances.

Constraints to Efficiently Find Interstellar Object Generated Craters on the Moon

Recent observations of interstellar objects (ISO) crossing the solar system suggest the possible existence of ISO-generated craters on the Moon. We explore how different crater properties such as age, size, melt, and position can be used to search for ISO-generated craters on the lunar surface. We find that selecting young, small craters with a high volume of melt located away from the lunar poles increases the likelihood of association with a high-speed ISO by 100 fold as compared to selecting randomly, assuming high-speed ISO impacts generate melt. We note that craters from other sources however still massively outnumber ISO-generated craters.

Analysis of the relation of hydrogen distribution and topographic roughness in the lunar south polar region

Appreciable amounts of hydrogen-bearing compounds have been detected within the lunar polar regions. Estimating the effect of the presence of water ice on surface topographic roughness is important for future exploration and activities in the vicinity of the lunar pole. To investigate this issue, we analyzed the correlations between water equivalent hydrogen in the top 1-m surface layer and topographic roughness of lunar south polar regions. The results show that water ice probably plays an important role in the surface roughness at the hectometer scale, and might has a suppressive effect on surface roughness. In the detailed analysis, most the surface roughness at the floor of Shoemaker, Faustini, Slater and Sverdrup shows a decreasing trend with increasing water equivalent hydrogen at different decreasing slopes; Haworth shows slightly increasing trend, contrary to the trend of other studied craters. These observations may be related to small-scale topographic features at the surface and/or subtle changes in surface and subsurface WEH, which in turn affect the roughness characteristics in detail.

Dynamic behavior and modeling of icy lunar regolith subjected to dynamic loading

The icy lunar regolith (ILR) in the permanently shadowed regions (PSRs) of the lunar poles is an important lunar water resource for humans, which can be efficiently explored in situ by using a high-speed kinetic penetrator. The dynamic mechanical properties of ILR need priority research since they are related to the ballistics and overload of the penetrator. Based on ILR occurrence form and microscopic composition analyses, four types of ILR simulant (ILRS) specimens with typical water contents are prepared in the present study according to the principle of similar mineral composition and physical state. The dynamic mechanical properties of the ILRS specimens are investigated by combining the results of split Hopkinson pressure bar (SHPB), quasi-static unconfined compression, and variable angle shear (VAS) tests. The results show that the loading strain rates alter the microcrack number and expansion rate of the specimens, which in turn significantly affects their damage mode, dynamic uniaxial compressive strength (DUCS) and toughness ratio. Finally, based on the relationship between stress and strain in the SHPB tests, the damage properties of the ILRS under dynamic loading are analyzed, and a segmental constitutive model is provided by combining it with the Drucker–Prager strength theory. The research results could form the basis for subsequent penetrator structure design and ballistic prediction.

Synergistic use of remote sensing data and in-situ investigations to characterize the lunar surface

This review article provides an overview of various aspects of lunar exploration, including missions to the Moon, collection and analysis of lunar sample data in laboratories, and the processing and analysis of remote sensing data, particularly using radar techniques. Both remote sensing and in-situ methods are critical for advancing our understanding of the lunar surface and its properties. This review article focuses on the identification and quantification of water–ice deposits located in areas such as Permanently shadowed areas (PSRs) and the lunar poles (section “Lunar Poles and PSRs: A Special Environment”). These volatile resources have the potential to serve as valuable sources of fuel for future missions, making it crucial for the lunar community to determine their abundance and distribution. After thoroughly examining lunar samples using high-precision laboratory techniques, many preconceptions were dispelled which is highlighted in the section “Laboratory Investigation of Lunar samples”. But as in-situ observations are difficult to acquire, especially terrestrial bodies samples, remote sensing techniques allow the global understanding of the surface. The article specifically highlights the importance of understanding the electrical characteristics of the lunar surface and how radar inversion can provide valuable information in this regard. The “Conclusion” section of this review article serves as a key takeaway for readers, underscoring the critical role that both in-situ and remote sensing techniques play in advancing our understanding of the Moon.