Lunar Day Research Articles

Lunar Terrestrial Analog Experiment on the Spectral Interpretations of Rocks Observed by the Yutu-2 Rover

A visible and near-infrared imaging spectrometer (VNIS) loaded by the Chang’e-4 rover is the primary method for detecting the mineral composition of the lunar surface in the landing region. However, different data processing methods yield inconsistent mineral modes in measured lunar soil and rocks. To better constrain the mineral modes of the soil and rocks measured by Chang’e-4 VNIS, a noritic-gabbroic rock with a mineral composition similar to that of the lunar highland rocks is measured by scanning electron microscopy (SEM), the spare flight model of Chang’e-4 VNIS and TerraSpec-4 of ASD. Backscattered electron and energy dispersive spectrometry show that olivine, pyroxene, and plagioclase modal mineral abundances are 12.9, 35.0, and 52.2%, respectively. The estimated results of the spectrum by the Hapke radiative transfer model are 7.5, 39.3, and 53.2% for olivine, pyroxene, and plagioclase, respectively, which is consistent with to those of SEM mapping within error. In contrast, the estimated results of the modified Gaussian model are 29 and 71% for olivine and pyroxene, respectively, indicating the absence of plagioclase. Based on our implemented Hapke model, we decode the data of the two rocks detected by the rover on the 3rd and 26th lunar days of mission operations. The obtained results suggest that both rocks are norite or gabbro with noticeable differences. The first rock, with more olivine and pyroxene, may have been excavated from the Finsen crater. The second rock, with more plagioclase, may have been ejected from the southwestern edge of the Von Kármán crater, indicating the initial lunar crust.

Reassessing evidence of Moon–Earth dynamics from tidal bundles at 3.2 Ga (Moodies Group, Barberton Greenstone Belt, South Africa)

AbstractPast orbital parameters of the Moon are difficult to reconstruct from geological records because relevant data sets of tidal strata are scarce or incomplete. The sole Archean data point is from the Moodies Group (ca 3.22 Ga) of the Barberton Greenstone Belt, South Africa. From the time‐series analysis of tidal bundles from a well‐exposed subaqueous sand wave of this unit, Eriksson and Simpson (Geology, 28, 831) suggested that the Moon’s anomalistic month at 3.2 Ga was closer to 20 days than the present 27.5 days. This is in apparent accordance with models of orbital mechanics which place the Archean Moon in a closer orbit with a shorter period, resulting in stronger tidal action. Although this study’s detailed geological mapping and section measuring of the site confirmed that the sandstone bed in question is likely a migrating dune, the presence of angular mud clasts, channel‐margin slumps, laterally aggrading channel fills and bidirectional paleocurrents in overlying and underlying beds suggests that this bedform was likely located in a nearshore channel near lower‐intertidal flats and subtidal estuarine bars; it thus carries risk of incomplete preservation. Repeated measurements of foreset thicknesses along the published traverse, measured perpendicular to bedding, failed to show consistent spectral peaks. Larger data sets acquired along traverses measured parallel to bedding along the 20.5 m wide exposure are affected by minor faulting, uneven outcrop weathering, changing illumination, weather, observer bias and show a low reproducibility. The most robust measurements herein confirm the periodicity peak of approximately 14 in the original data of Eriksson and Simpson (Geology, 28, 831). Because laminae may have been eroded, the measurements may represent a lower bound of about 28 lunar days per synodic month. This estimate agrees well with Earth–Moon dynamic models which consider the conservation of angular momentum and place the Archaean Moon in a lower orbit around a faster‐spinning Earth.

Evaluation of the CBC-ORC energy system in lunar base: Working fluid combination selection, day and night operation performance

The lunar energy system must be able to provide continuous power supply on the day and night. However, the moon night is as long as 14 days, and the solar power generation system can’t work without solar radiation. The solution is that part of the heat in the daytime is used for storage, the other part is used for daytime power generation, and the heat stored in the daytime is used for power generation at night. Based on this, this paper proposes a closed Brayton cycle and organic Rankine cycle combined power generation system, and explores the operation performance of the composite power generation system in the whole lunar day process. The results show that the combination of He-Xe and toluene has the best performance among many working medium combinations. The thermal efficiency of the system can reach 33.82 %, and the heat exchange area of the radiator is 970.99 m2. Combined with supercritical CO2, the thermal efficiency is increased by 5.2 % and the heat exchange area is reduced by 8.5 %. In addition, in the case of night, the Brayton cycle system stops working at 7.75 earth days, which can maximize the power generation capacity of the coupling system, with a power generation capacity of 94.8 MJ.

<italic>In situ</italic> temperature measurement of shallow lunar soil on the far side of the Moon based on Chang’e-4 Mission

<p indent="0mm">The Chang’e-4 lander has completed the first full cycle measurement of lunar soil temperature in the South Pole-Aitken basin on the far side of the Moon. This paper introduces the theory and implementation of measuring the temperature of lunar soil in the shallow layer of the Chang’e-4 lander, as well as the results of three lunar days in orbit and preliminary analysis. The Chang’e-4 lander is outfitted with temperature measuring points that can be buried in the shallow lunar soil at the end of the transfer mechanism. The Chang’e-4 lander surface also has temperature measuring points with a good view of the lunar surface. Furthermore, a comparison was made between the measured low temperature data of lunar soil during the lunar night phase and the calculated results based on NASA’s Apollo 17 data. The measured results enrich the measured data about shallow lunar soil temperature on the surface of the Moon and provide an important basis for the inversion of the lunar thermal characteristics model and future study of lunar soil and lunar interior thermal characteristics.

Yutu-2 Radar Sounding Evidence of a Buried Crater at Chang’E-4 Landing Site

Buried craters within tens of meters of lunar regolith are rarely studied but are significant for understanding the evolution of surface processes on the Moon. Here, we first report the evidence of an intact buried crater within the layered strata at Chang’E-4 (CE-4) landing site revealed by the lunar penetrating radar (LPR). The time–frequency comparative analysis method based on the variational mode decomposition (VMD) and the rock quantitative analysis method based on the local unit correlation (LUC) are proposed and applied to the processing and analysis of LPR data within 15 lunar days. The results presented by the two methods provide evidence of a buried crater at the CE-4 landing site and simultaneously reveal the rock-concentrated structure within the buried crater. According to the results, it is considered that the filling materials within the buried crater have survived the impaction and gardening during the formation of the overlying fine-grained regolith. Recent works have proposed that the near-surface material at the CE-4 landing site is mainly the lunar mantle materials excavated from the nearby Finsen crater. Therefore, the buried crater probably preserves the initial lunar mantle materials.

Temporal variability of internal solitary waves in the northern South China Sea revealed by long-term mooring observations

The temporal variability of internal solitary waves (ISWs) in the northern South China Sea (SCS) is examined from hourly to interannual timescales based on nearly four-year-long measurements from the SCS Mooring Array between August 2010 and June 2014. On an hourly timescale, large ISWs tend to occur at the moorings around certain hours due to the concentrated occurrence of strong ebbing tidal beats in the Luzon Strait at approximately 0300 h and 1500 h (local time, UTC + 8 h) modulated by the S2 tide and the sum of the K1 and P1 tides. Intraseasonally, the mean ISW amplitudes on the 4th and 19th lunar days are twice as large as those on the 11th and 26th lunar days, corresponding to the spring-neap tidal cycles; the ISW intensity varies by as much as a factor of two in two months ascribed to the occurrence and movement of mesoscale eddies. Seasonally, ISWs are 37% weaker on average in winter than in summer over the continental shelf slope but are only 14% weaker in winter than in summer in the eastern deep basin near the Luzon Strait. The common occurrence of energetic eddies in winter significantly reduces the monthly mean ISW intensity, playing an important role in the seasonal variations of ISWs. Interannually, the monthly mean ISW intensity varies by up to 171%, which is likely associated with the year-to-year variations in mesoscale processes and tides. The observational results presented here reveal that the ISWs in the northern SCS vary significantly over multiple timescales following the trends that are shaped by tides and mesoscale processes.

Preparation of geopolymer based on lunar regolith simulant at in-situ lunar temperature and its durability under lunar high and cryogenic temperature

Lunar base construction is of great importance for deep space exploration, and the establishment of lunar pavements for the movement of machinery and transportation of materials is essential to improve construction efficiency. Lunar regolith as an in-situ resource has been demonstrated to be used as raw materials to prepare geopolymers for lunar pavements. In this paper, geopolymers based on lunar regolith simulant with different concentrations of alkali activator were synthesized using the natural high-temperature of the lunar surface. Then, the durability of the resulting geopolymer under lunar high and cryogenic temperature was investigated. The flexural and compressive strength was tested, and the microstructure was characterized using Scanning Electron Microscope coupled with Energy Dispersive Spectroscopy (SEM-EDS), 29Si Magic Angle Spinning-Nuclear Magnetic Resonance (29Si MAS-NMR), and Mercury Intrusion Porosimetry (MIP). The results of the curing section showed that the geopolymer with 8 mol/L sodium hydroxide (NaOH) generated high strength and dense structure, and the period of 420 h–492 h of a lunar day corresponding to a temperature variation from 84.5 °C to 33.5 °C in 72 h was suitable for preparation, with 5.7 MPa and 31.2 MPa 72-h flexural and compressive strength. Three test points were selected on the lunar 30° latitude temperature curve, corresponding to before and after the cryogenic attack, and after high temperature again to investigate the durability of the geopolymer, and the degradation was found noticeable. The flexural strength decreased about 49% and 70%, and the compressive strength decreased about 15% and 18% after the cryogenic temperature and high temperature again, respectively. Microscopic observations revealed that the geopolymer structure was significantly granulated with obvious cracks and increased porosity. In addition, the formation of the zeolitic phase was unexpectedly found, leading to interfacial cracks and mechanical strength reduction of the geopolymer. This paper will be beneficial to explore the evolution of properties of lunar pavement construction materials in the lunar environment.

Energetic Neutral Atom Distribution on the Lunar Surface and Its Relationship with Solar Wind Conditions

Abstract The Advanced Small Analyzer for Neutrals (ASAN) on board the Chang’E-4 Yutu-2 rover first detected energetic neutral atoms (ENAs) originating from the lunar surface at various lunar local times on the lunar farside. In this work, we examine the ENA energy spectra, obtained in the first 23 lunar days from 2019 January 11 to 2020 October 12, and find a higher ENA differential flux on the lunar dawnside than on the duskside. Combined with Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun (ARTEMIS) data, we analyze the correlation between the ENA differential flux and solar wind parameters, such as flux, density, dynamic pressure, and velocity, for each ASAN energy channel on the dawnside and duskside. The results show that ENA differential flux is positively correlated with solar wind flux, density, and dynamic pressure and relatively lower on the duskside than on the dawnside. To determine the relationship between solar wind energy and ENA energy, we analyze the correlation between solar wind energy and ENA cutoff energy and temperature on the dawnside and duskside. The results show that the ENA cutoff energy and temperature are lower on the duskside than on the dawnside at the same solar wind energy. The difference between the ENA–solar wind observation on the dawnside and duskside is possibly caused by solar wind deflection and deceleration on the duskside, which can be attributed to the interaction between solar wind and the lunar magnetic anomalies located nearby in the northwestern direction of the Chang’E-4 landing site.

Mixed‐diurnal tidal record from a Palaeoproterozoic embayment in the Par Formation, Gwalior Group, Central India

The Palaeoproterozoic Par Formation, Gwalior Group, central India contains a mixed, predominantly diurnal, tidal record in an embayment‐like estuarine setting where flood energy exceeded the ebb energy. From two order differences in set thickness between flood‐ and ebb‐generated bedforms an asymmetry in peak tidal current velocity of flood and ebb is inferred with domination of flood current. From the presence of crossover in successive neap records and 27.75 neap‐spring cycles per year, an unambiguous clue for tidal forcing by lunar declination rather than lunar phase is inferred. Harmonic analysis of foreset‐lamina thickness from tidal sand waves suggests that a tropical month of minimum 26 lunar days was in effect at the Gwalior Sea during the late Palaeoproterozoic (2,000–1,791 Ma).

Restoring light transmission of dusty glass surfaces on the Moon

Abstract The Lunar Laser Ranging Retro-reflectors (LRR) allow for the precise measurement of the travel time of laser pulses from the Earth to the lunar surface and back. Dust accumulation on the LRRs scatters the reflected light used for laser interferometry measurements leading to a reduction in the return signal amplitude by a factor of ≃ 10. We report on a series of experiments utilizing a method of an iterative application and removal of an acrylic adhesive kapton tape to remove lunar dust simulant from a glass substrate. The effectiveness of adhesive tape was determined by measuring the transmission of an expanded laser beam through a glass substrate with a dusted surface. Calibration data was obtained before the glass was exposed to any dust, and light transmission was measured after each iteration of adhesive removal using a power meter. The procedure was repeated using heavy gloves while keeping the glass substrate at 120 ° C to simulate the temperature conditions of a lunar day on the surface. A third test was conducted at room temperature in high-vacuum to ensure functionality in the lunar environment. These experiments show that glass substrates can be restored to 98 ± 2 % of their original transmission using the adhesive tape method. Therefore the light that travels into and out of the quartz surface of the LLRs can be restored up to 96 ± 4 % of their initial transmission.

Non‐palimpsested crowded Skolithos ichnofabrics in a Carboniferous tidal rhythmite: Disentangling ecological signatures from the spatio‐temporal bias of outcrop

AbstractA heterolithic tidalite succession yielding spring–neap bundles is newly reported from a mid‐Carboniferous (Serpukhovian) section of the Alston Formation of Northumberland, England. The rhythmite records deposition over an interval that can be confidently calibrated to at least 84 lunar days, and attests to a non‐negligible tidal range in parts of the Northwest European Seaway in the late Mississippian. The tidalite is notable for the presence of a striking crowded Skolithos ichnofabric on both bedding planes and in vertical section. Bedding plane expressions of the ichnofabric reveal true substrates of sand piles excavated during burrow construction, in addition to an apparently remarkable equal spacing between individual burrows that is shown to be genuine through pair correlation function analysis. These characteristics show that the burrowed horizons were registered by contemporaneous ichnocoenoses, with no palimpsesting of burrows. The irregular vertical distribution of burrow horizons, despite a near‐continuous semi‐diurnal record of sedimentation, is suggested to be an artefact of spatial patchiness of burrowing communities in the depositional environment; imperfectly registered in a vertical profile with high‐temporal, low‐spatial resolution. The succession proves that burrow palimpsesting is not an inevitable ichnological conclusion of sedimentary stasis, and attests to intermittent palaeoecological fidelity of the stratigraphic record at the small spatio‐temporal scales recorded at outcrop.

A Novel Approach for Permittivity Estimation of Lunar Regolith Using the Lunar Penetrating Radar Onboard Chang’E-4 Rover

Accurate relative permittivity is essential to the further analysis of lunar regolith. The traditional hyperbola fitting method for the relative permittivity estimation using the lunar penetrating radar generally ignored the effect of the position and geometry of antennas. This paper proposed a new approach considering the antenna mounting height and spacing in more detail. The proposed method is verified by numerical simulations of the regolith models. Hence the relative permittivity of the lunar regolith is calculated using the latest high-frequency radar image obtained by the Yutu-2 rover within the first 24 lunar days. The simulation results show that the relative permittivity is underestimated when derived by the traditional method, especially at the shallow depth. The proposed method has improved the accuracy of the estimated lunar regolith relative permittivity at a depth of 0–3 m, 3–6 m, and 6–10 m by 35%, 14%, and 9%, respectively. The thickness of the lunar regolith at the Chang’E 4 landing site is reappraised to be 11.1 m, which improved by ~8% compared with previous studies.

Preparation and evaluation of geopolymer based on BH-2 lunar regolith simulant under lunar surface temperature and vacuum condition

The construction of a lunar base and habitation on the moon has always been of great significance to utilizing lunar resources and deep space exploration. In this paper, a new type of lunar regolith simulant denoted as BH-2 of similar compositions and particle size distribution with real one was developed and used for geopolymer synthesis under simulated lunar surface temperature and vacuum conditions. The geopolymer products were characterized by compressive strength test, Mercury Intrusion Porosimetry (MIP), Scanning Electron Microscope coupled, and 29Si magic angle spinning-nuclear magnetic resonance (29Si MAS-NMR). The results showed that BH-2 lunar regolith simulant could be used to synthesize geopolymer. And the 72-h compressive strength of the geopolymer cured at the temperature of group C, corresponding to the 324–384 h of one lunar day, could reach 38.2 MPa, which was advantageous in the early stages of lunar construction because no additional curing equipment is required. The pores originated from lunar regolith simulant and caused by incomplete geopolymerization resulted in decreased compressive strength of the resulting geopolymer. Vacuum conditions on the moon favored the preparation of lunar geopolymers due to the lack of carbon dioxide weakening the efflorescence effect. This study benefits to lunar base construction with in-situ resource.

Implications of surface roughness in models of water desorption on the Moon

ABSTRACT The observed presence of water molecules in the dayside lunar regolith was an unexpected discovery and remains poorly understood. Standard thermophysical models predict temperatures that are too high for adsorbed water to be stable. We propose that this problem can be caused by the assumption of locally flat surfaces that is common in such models. Here, we apply a model that explicitly considers surface roughness, and accounts for solar illumination, shadows cast by topography, self-heating, thermal reradiation, and heat conduction. We couple the thermophysical model to a model of first-order desorption of lunar surface water and demonstrate that surface roughness substantially increases the capability of the Moon to retain water on its sunlit hemisphere at any latitude, and within 45○ of the poles, at any time of the lunar day. Hence, we show that lunar surface roughness has a strong influence on lunar water adsorption and desorption. Therefore, it is of critical importance to take account of surface roughness to get an accurate picture of the amount of water on the Moon’s surface and in its exosphere.

Mineralogical and chemical properties inversed from 21-lunar-day VNIS observations taken during the Chang\u2019E-4 mission

We report on the mineralogical and chemical properties of materials investigated by the lunar rover Yutu-2, which landed on the Von Kármán crater in the pre-Nectarian South Pole–Aitken (SPA) basin. Yutu-2 carried several scientific payloads, including the Visible and Near-infrared Imaging Spectrometer (VNIS), which is used for mineral identification, offering insights into lunar evolution. We used 86 valid VNIS data for 21 lunar days, with mineral abundance obtained using the Hapke radiative transfer model and sparse unmixing algorithm and chemical compositions empirically estimated. The mineralogical properties of the materials at the Chang’E-4 (CE-4) site referred to as norite/gabbro, based on findings of mineral abundance, indicate that they may be SPA impact melt components excavated by a surrounding impact crater. We find that CE-4 materials are dominated by plagioclase and pyroxene and feature little olivine, with 50 of 86 observations showing higher LCP than HCP in pyroxene. In view of the effects of space weathering, olivine content may be underestimated, with FeO and TiO2 content estimated using the maturity-corrected method. Estimates of chemical content are 7.42–18.82 wt% FeO and 1.48–2.1 wt% TiO2, with a low-medium Mg number (Mg # ~ 55). Olivine-rich materials are not present at the CE-4 landing site, based on the low-medium Mg #. Multi-origin materials at the CE-4 landing site were analyzed with regard to concentrations of FeO and TiO2 content, supporting our conclusion that the materials at CE-4 do not have a single source but rather are likely a mixture of SPA impact melt components excavated by surrounding impact crater and volcanic product ejecta.

Ultra-safe nuclear thermal rockets using lunar-derived fuel

Rocket launch failure rate is slightly higher than five percent. Concerned citizens are likely to protest against private-sector launches involving fission reactors. Yet, fission reactors can power long-duration lunar operations for science, observation, and in situ resource utilization. Furthermore, fission reactors are needed for rapid transport around the solar system, especially considering natural radiation doses for crews visiting Mars or an asteroid. A novel approach is to create nuclear fuel on the Moon. In this way, a rocket launched from the earth with no radioactive material can be fueled in outer space, avoiding the risks of spreading uranium across Earth's biosphere. A solution is to harvest fertile thorium on the lunar surface, then transmute it into fissile uranium using the gamma ray fog which pervades the deep sky. It is only at lunar orbit, at the very edge of cislunar space, that the Earth-launched machine becomes a nuclear thermal rocket (NTR). Thorium is not abundant, but can be concentrated by mechanical methods because of its very high specific density relative to the bulk of lunar regolith. Thorium dioxide (ThO2) has an extremely high melting point, such that skull crucible heating can be used to separate it from supernatant magma. When filled into a graphite-lined beryllium container (brought from Earth) and set out on the lunar surface, high-energy gamma rays will liberate neutrons from the Be. After moderation by the graphite, these thermal neutrons are captured by the thorium nucleus, which is transmuted into protactinium (Pa91). This element can be extracted using the THOREX process, and will then decay naturally into U-233 within two or three lunar days. The uranium is oxidized and packed into fuel pellets, ready to be inserted into a non-radioactive machine, which now becomes an NTR. Additionally, hydrogen can be extracted from deposits in permanently-shadowed regions on the Moon, providing reaction mass for the NTR. A novel method of solid-state hydrogen storage, which can be entirely fabricated using in situ resources, can deliver said hydrogen to the fission reactor to provide high and efficient propulsive thrust. These combined operations lead to an ultra-safe (for the Earth) means for private sector, commercial transport and power generation throughout the Solar System. With the hydrogen storage material used as radiation shielding for crewed spacecraft, and greatly-reduced transit times relative to chemical rocketry, this innovative approach could fundamentally transform how humans work, play, and explore in outer space.

High Pressure Water Electrolyser Development for Space Exploration Surface Missions

Onsite production of oxygen and hydrogen is an essential contribution to any manned mission to the Moon or to Mars. In both environments there are elements consisting of bound oxygen, such as water ice-bearing consolidated regolith on the moon and carbon dioxide on Mars. These resources can be used to generate oxygen gas through electrolysis, together with energy carriers, namely hydrogen and CO, as by-products. Solid Oxide Electrolysis (SOE) technology possesses the highest potential for this application, due to the high operation temperature ranging from, 650°C to 900°C. Therefore, it can split each or both H2O and CO2, into H2, CO and O2 without compromising the integrity of the electrodes by poisoning, while the process can be further integrated with other thermal processes, such as the reduction of mineral oxide to provide overall very high system efficiencies. The solid oxide cell (SOC) technology is also fully reversible (i.e., the cell works both as electrolyser and as fuel cell) and can be used for unitised reversible fuel cell systems (URFCS) for energy storage and generation. This paper describes the developments under a European Space Agency (ESA) activity for the development of a high-pressure steam electrolyser system for exploration surface missions. The base case scenario considered is a hydrogen and oxygen production unit for lunar missions, where water for the electrolyser is generated from ice-bearing consolidated regolith.The development of the electrolyte supported cells was based in an all-ceramic approach. Specifically, electrolyte (8YSZ, 3YSZ, 6Sc1CeSZ and 10Sc1CeSZ) supported cells were fabricated comprising substituted lanthanum chromite La0.75Sr0.25Cr0.9Fe0.1O3 (LSCrF), as fuel electrode, and (La0.80Sr0.20)0.95MnO3-x (LSM) or (La0.60Sr0.40)0.95Co0.20Fe0.80O3-x (LSCoF), as oxygen electrodes. The electrochemical characterization and performance assessment in button cells (with an electrode footprint of ~0.8 cm2) was conducted for (i) steam electrolysis and (ii) reversible cell operation (fuel cell and electrolysis modes). All cells exhibited stable performance within the whole range of potentials, thus revealing the fact that Solid Oxide technology is in principle reversible and versatile in functionalities. Regarding steam electrolysis, the effect of hydrogen co-fed was investigated. The lack of reducing agent (H2) in the fuel side results in a non-trivial evolution of the current-potential curve, as the Nernst potential is not fixed and the production of a substantial concentration of hydrogen is required for the IV curve to follow the typical linear relation. However, within the linear IV region the performance of the cells is similar in presence or in absence of hydrogen, exhibiting ~2 A/cm2 at 1.5 V.Following these key developments, a high-pressure short stack is designed and constructed, comprising five (5) cells with an active area of 42 cm2. The stack is enclosed in a hot box consisting of the mechanical and thermal environment for the stack. To operate at pressure up to 10 bars, the hot box is placed inside a stainless-steel chamber made of standard piping elements. The hot box is complemented with all necessary balance of plant (steam generator, water system, gas storage) to realise a complete a steam electrolysis system which will be validated in operation against a load profile representing energy storage in Lunar environment for 3 lunar days (~2,126 h). Figure 1

Effect of Lunar Complex Illumination on In Situ Measurements Obtained Using Visible and Near-Infrared Imaging Spectrometer of Chang’E-4

In-situ measurements of the spectral information on the lunar surface are of significance to study the geological evolution of the Moon. China’s Chang’E-4 (CE-4) Yutu-2 rover has conducted several in-situ spectral explorations on the Moon. The visible and near-infrared imaging spectrometer (VNIS) onboard the rover has acquired a series of in-situ spectra of the regolith at the landing site. In general, the mineralogical research of the lunar surface relies on the accuracy of the in-situ data. However, the spectral measurements of the Yutu-2 rover may be affected by shadows and stray illumination. In this study, we analyzed 106 CE-4 VNIS spectra acquired in the first 24 lunar days of the mission and noted that six of these spectra were affected by the shadows of the rover. Therefore, a method was established to correct the effects of the rover shadow on the spectral measurements. After shadow correction, the FeO content in the affected area is corrected to 14.46 wt.%, which was similar to the result calculated in the normal regolith. Furthermore, according to the visible images, certain areas of the explored sites were noted to be unusually bright. Considering the reflectance, geometric information, and shining patterns of the multi-layer insulation (MLI), we examined the influence of the specular reflection of the MLI on the bright spot regionsd, and found that the five sets of data were likely not affected by the specular reflection of the MLI. The results indicated that the complex illumination considerably influences the in situ spectral data. This study can provide a basis to analyze the VNIS scientific data and help enhance the accuracy of interpretation of the composition at CE-4 landing sites.

Properties of Lunar Regolith on the Moon's Farside Unveiled by Chang'E‐4 Lunar Penetrating Radar

AbstractThe complex thermal history of the Moon leads to an unequal distribution of volcanic products between the lunar nearside and the farside. So far, no lunar materials have been sampled from the Moon's farside and no detailed properties of lunar regolith on the farside have been detected before. On January 3, 2019, Chang'E‐4 (CE‐4) touched down onto the Von Kármán crater on the Moon's farside. CE‐4 Lunar Penetrating Radar (LPR) onboard the Yutu‐2 rover is the first surface radar on the Moon's farside. Here we show the subsurface structure and properties of regolith materials at the landing region with LPR data during the first five lunar days. The thickness of lunar regolith is constrained as ∼12 m, much thicker than that at Chang'E‐3 (CE‐3) landing site, which is expected since CE‐3 landed on lunar maria. The relative permittivity of lunar surface (&lt;30 cm) at CE‐4 landing region is identified to be 2.35 0.20. The loss tangent and TiO2 + FeO content of the regolith materials layer (0–∼12 m) are constrained to be and wt.%, respectively, much lower than those at CE‐3 landing site. It indicates that local surface materials possess less attenuation for radiowave, in accordance with the greater penetrating depth of CE‐4 LPR than that of CE‐3 LPR. Furthermore, the results also prove that the growth rate of lunar weathered regolith successively declines over time and the growth rate of lunar regolith on the Moon's farside may well be higher than that on the nearside due to the more frequent meteorite impacts.

Energy storage selection and operation for night-time survival of small lunar surface systems

In the coming decade, a multitude of small, carry-on payloads in the form of miniature rovers, scientific instruments and surface deployed stand-alone systems will provide many new and exciting possibilities for lunar exploration. For these system, the survival of and operation in the extreme cold of the lunar night will be the biggest challenge, as most will be purely battery driven and unable to rely on radioisotope heaters. Maximizing battery lifetime in these conditions requires a trade-off between energy density, low-temperature performance and insulation, but comparable temperature and current dependent discharge capacities of batteries and other energy storage devices are often not reported in datasheets or literature. For this reason, a selection of energy storage devices was chosen and tested to determine their low-temperature performance in a representative environment. Based on this data, the theoretical lifetime per battery weight and optimal operational temperature for varying degrees of insulation was determined. It was shown that the selection of the optimal energy storage device and operational temperature depends on the insulation, emphasizing the need for multi-disciplinary design optimization.