MoonDust Lunar Dust Simulation and Mitigation

Unlike the Earth, the Moon lacks is not protected from the atmosphere and global magnetic field, and will be directly exposed to complex radiation environments such as high-energy cosmic rays, solar wind, and the Earth’s magnetotail plasma. The surface of the Moon is covered with a thick layer of lunar soil, and the particles in the soil with a diameter between 30 nm–20 μm are called lunar dust. In the complex environments such as solar wind or magnetotail plasma, lunar dust carries an electric charge and becomes charged lunar dust. Charged lunar dust is prone to migration under the action of the electric field on the lunar surface. Charged migrated lunar dust is easy to adhere to the surface of instruments and equipment, resulting in visual impairment, astronauts’ movement disorders, equipment mechanical blockage, sealing failure, and material wear, which affects the lunar exploration mission. As an important lunar exploration landing site, the lunar south pole receives special solar radiation and produces a special dust plasma environment due to its special location. In order to provide an environmental reference for lunar south pole exploration, it is necessary to explore the characteristics of the dust plasma environment in the lunar south pole and its impact. In view of the lunar south pole environment, The Spacecraft Plasma Interactions Software (SPIS) software developed by the European Space Agency is used to carry out modelling and simulation in this work. Through the simulation, the logarithmic distribution of the lunar dust space density in a range of 0–200 m at the lunar south pole, the potential distribution near the lunar surface, and the spatial distribution characteristics of plasma electrons and ions are obtained. The obtained lunar dust space density and lunar surface potential are similar to the previous theoretical derivation and field detection data, so the simulation results have high reliability. The spatial potential distribution and the spatial density distribution of electrons and ions in the lunar environment with and without lunar dust are compared. Finally, the conclusions can be drawn as follows. The space potential increases with altitude increasing. The potential at 0–10 m near the lunar south pole is about –40 V, and the space potential at 100 m is about –20 V. The density of lunar dust in an altitude range below 10 m is 10<sup>7.22</sup> m<sup>–3</sup>–10<sup>4.66</sup> m<sup>–3</sup>. The electron density in the dust plasma near the lunar surface is 10<sup>5.47</sup> m<sup>–3</sup>, and the ion density is 10<sup>6.07</sup> m<sup>–3</sup>, and both increase with altitude increasing. Charged lunar dust affects the spatial distribution of lunar dust, mainly through affecting the distribution of the space electric field, which leads to difference in electron distribution, but has little effect on ions.

Sensing technologies for the challenging Lunar environment

Since the moon has an extremely rarefied atmosphere, the full spectrum of the electromagnetic radiation of the sun reaches the surface, charging the surface dust and affecting its current charge state. Lunar surface dust thus remains electrostatically charged at all times. Charged lunar dust will adversely affect the operations of most mechanical systems required by manned and unmanned exploration missions. Charged dust will also stubbornly adhere to solar panels and thermal radiators, thus reducing their efficiencies. Researches on the charged lunar dust can help to investigate lunar dusty environment as well as to solve those particle-induced problems by both simulation and experiment in laboratory. In this work, two different charging processes of charged lunar dust in the environment of electron beam and the radiation of ultraviolet source are considered. The computer numerical simulation method is used to analyze these two different charging processes of lunar dust, to explore the charging mechanisms of lunar dusts, and to choose an appropriate way of charging for the lunar environment simulation device in laboratory. On the basis of the classic dust charging equation, the charging equation of a dust in pure electron environment is given for the first time in this work. Meanwhile, the charging process under ultraviolet radiation is discussed and combined with the specific application of charging dusts. A solver of fourth-order Runge-Kutta algorithm is made to solve differential equations under two different irradiation sources. The main simulation results show that:1) in electron environment, the surface dust charge number increases as the particle size and the current intensity of electron guns increase, while the charge number increases as the beam spot radius of electron guns decreases; 2) under ultraviolet radiation, the dust charge number increases with the particle size and irradiance increasing, but charging efficiency is slow. A great dust charge number needs a long time radiation from sun (equivalent to 74 deuterium lamps), which means that more ultraviolet radiation sources are essential to speeding up the experiment in laboratory. Although the calculated efficiency of ultraviolet radiation is lower than electron irradiation, the secondary-electron emission, the scattering and the transmission process of electron irradiation are ignored, which can greatly reduce the efficiency of charging by energetic electron guns in the actual experiment. Therefore, comparing these two charging mechanisms and considering the actual design requirements for the space environment simulation device, charging by lots of ultraviolet radiation is an appropriate scheme for electrification of lunar dusts.

Due to the preciousness of real lunar dust, the lunar dust simulant is usually employed to replace the real one in the large numbers of experimental investigations about its mechanical property and engineering property. Therefore, the investigation on mechanical property of lunar dust simulant is also extremely significant. This research has put forward several methods for measuring mechanical property, which are used to measure the parameters including particle size distribution, particle proportion, relative density, void ratio, cohesion, internal friction angle, etc. of lunar dust simulant. The lunar dust simulant is determined to be suitable for application in the moon exploration project experiment after comparing these parameters with relevant typical mechanical parameters of foreign lunar dust simulant.

The influence of lunar environment exposure on characteristics of nuclear energy He–Xe closed Brayton cycle

On the lunar surface there exists very localized and weak magnetic fields, leaving its surface essentially directly exposed to the impact of solar UV and X-rays as well as solar wind plasma and energetic particles. The lack of atmosphere results in a lunar environment charging positive in sunlight and negative in shadow regions resulting in potentials that can vary over orders of magnitude in response to changing solar illumination and plasma conditions. At the macro-scale, contaminant adhesion due to van der Waals' forces are very small and can be easily perturbed by other external forces. However, at the nano-scale, van der Waals forces can be significant. Lunar regolith or dust contamination is a serious problem for equipment and vehicles for space mission applications. Dust contamination gathers on photonic sensors inhibiting motion and data gathering. In addition, devices that require transparency to light for maximum efficiency such as solar photovoltaic power systems, video cameras and optical or infrared detectors will suffer from the dust accumulation. The electrostatic charging of the lunar surface is caused by its interaction with the local plasma environment and solar UV and X-rays induced photoemission of electrons. The lunar thermal environment poses unique challenges to vehicle and sensor surfaces since it is characterized by large temperature variations, long hot and cold soak times, and reduced heat rejection capability due to the presence of the lunar regolith. Fundamental forces (van der Waals) that allow certain contamination to adhere to critical surfaces and methods are being tailored to make these surfaces suitable for this harsh environment.

Under the dynamic influence of near-surface plasma, intricate dynamics of lunar dust have been observed during the Surveyors and Apollo missions in the form of Lunar horizontal glow. These dynamics are primarily driven by electrostatic forces generated by the continual bombardment of solar wind and highly energetic UV photons on the lunar surface and dust particles. This paper revisits the phenomenon of dust charging within the lunar photoelectron sheath and subsequent dynamics. The investigation has been carried out using a comprehensive model of the lunar photoelectron sheath characterized by observed solar spectra, latitude-dependent Fermionic photoelectrons, non-Maxwellian solar wind electrons, and cold ions. A test dust particle is introduced into the sheath, and equilibrium charge and static levitation conditions are derived. The result of dynamical evolution suggests the existence of a narrow parametric regime corresponding to the periodic hopping trajectory of the dust particle over the lunar surface. In other cases, the dust particles are found to re-impact the surface after a single ballistic hop. We further identify that the discrete charging of the dust could be crucial in determining the dust dynamics, particularly in the tenuous plasmas. The analysis of the discrete dust charging model reveals significant discrepancies with the continuous dust charging model and suggests a lower likelihood of static dust levitation in the lunar environment. The present study is important for unraveling the fundamental processes governing surface evolution on the Moon and other airless bodies throughout the Solar System.

Electrostatic particle collection in vacuum

<div class="htmlview paragraph">ORBITEC is currently developing simulant materials that mimic many of the unique properties of lunar dust. First, a proprietary process creates simulated agglutinates and glass spherules that contain metallic iron globules (including nanophase Fe<sup>0</sup>). The processed material is then ground down to create the lunar dust simulant. This paper will discuss the characteristics of lunar dust, provide an overview of the process used to create several prototype lunar dust simulants, and summarize the NASA characterization of the prototype lunar dust simulants.</div>

Dust is the Number 1 environmental hazard on the Moon, yet its movements and adhesive properties are little understood. Matchbox‐sized, 270‐gram Dust Detector Experiments (DDEs) measured contrasting effects triggered by rocket exhausts of Lunar Modules (LM) after deployment 17 m and 130 m from Apollo 11 and 12 LMs. Apollo 11 Lunar Seismometer was contaminated, overheated and terminated after 21 days operation. Apollo 12 hardware was splashed with collateral lunar dust during deployment. DDE horizontal solar cell was cleansed of nominally 0.3 mg cm−2 dust by 80% promptly at LM ascent and totally within 7 minutes. A vertical cell facing East was half‐cleaned promptly then totally over hundreds of hours. Each cell cooled slightly. For the first time lunar electrostatic adhesive forces on smooth silicon were directly measured by comparison with lunar gravity. Analyses imply this adhesive force weakens as solar angle of incidence decreases. If valid, future lunar astronauts may have greater problems with dust adhesion in the middle half of the day than faced by Apollo missions in early morning. A sunproof shed may provide dust‐free working environments on the Moon. Low‐cost laboratory tests with DDEs and simulated lunar dust can use DDE benchmark lunar data quickly, optimising theoretical modelling and planning of future lunar expeditions, human and robotic.

Three-dimensional Discrete Element Method simulation system of the interaction between irregular structure wheel and lunar soil simulant

Upper limits for a lunar dust exosphere from far-ultraviolet spectroscopy by LRO/LAMP

This paper presents a detailed thermal simulation analysis of the drilling process for icy soil in the lunar polar region. The aim is to investigate the temperature changes that occur in the debris removal area during the drilling process. We developed a multi-level particle size simulation model that includes a thermal sieve based on geometric constraints to evaluate the influence of specific heat capacity and thermal conductivity on particle temperature. Using the central composite design method, we carried out the simulation test design and analyzed the average temperature difference of particles within and outside the range of the thermal sieve. The parameters of the discrete element model were determined by comparing the temperature of the debris removal zone in the lunar environment with the temperature simulated by the discrete element method. The results show that the thermal conductivity of the sieve ranges from 100 to 400 W/m, and the average temperature inside the thermal sieve is negatively related to the specific heat capacity. The temperature deviation of the chip removal area is ±10 °C, which is consistent with the temperature deviation observed in the lunar environment and the lunar icy regolith drilling test. Furthermore, the addition of the thermal sieve to the multi-stage particle size simulation modeling significantly reduces the calculation time by 86%. This reduction in computational time may potentially increase the efficiency of drilling operations in the future. Our study provides insights into the thermal behavior of lunar icy regolith during drilling, and proposes a numerical model of heat transfer with a thermal sieve that can effectively reduce computational time while ensuring accurate temperature calculations.

In this study, we present a new quantification method for surface concentrations of lunar dust and lunar simulant. This technique demonstrates the use of portable X-ray fluorescence spectroscopy (pXRF) to quantify surface lunar dust loading on surfaces using an adaption of existing pXRF techniques and is the first demonstration of a high accuracy and precision tool designed to quantify lunar dust loading in-situ on large surfaces within seconds. This study shows the background in current methodologies for quantification of lunar dust in tests as well as current and potential future techniques for lunar surface missions, as well as current applications of commercial off-the-shelf (COTS) pXRF technology. The methodology for adapting current pXRF techniques is presented, followed by a demonstration of this new method on a variety of materials and test campaigns related to spaceflight or lunar surface missions. This technique shows high fidelity for immediate utilization as well as a demonstration of high potential for future surface missions. Potential current uses can include development and qualification testing, as well as requirement verification and validation. Included future work outlines calibration adjustments to make this technique more adaptable and hardware developments for eventually using this tool during lunar missions.

WHEN Duke et al.1 measured the size of lunar soil returned by Apollo 11, they found a size distribution similar to that of glacial till and other terrestrial soil, except that the lunar soil is noticeably deficient in material finer than 15 µm. They feel that a partial explanation for this deficiency is that it is caused by melting and consequent consolidation into clumps of finer particles on the Moon. We wish to suggest another partial explanation, derived from wear theory—it is that the finer particles are missing in lunar soil because materials in a lunar environment have a higher surface energy.