Electrostatic Dust Mitigation and Manipulation Techniques for Planetary Dust

By Nima Gharib, Javad Farrokhi Derakhshandeh and Peter Radziszewski

Electrostatic Dust Mitigation and Manipulation Techniques for Planetary Dust explains how to control and remove dust in space due to the presence of a vacuum, abrasiveness of dust particles and electrostatic charge on particles. The book introduces innovative technologies that use electrostatic and di-electrophoretic forces to remove and transport small particles away from surfaces. In addition, it discusses how to resolve thermal control problems and reduce lung inhalation and eye irritation problems. The book includes two abrasive wear test devices that were designed to study the rate of volume wear for di?erent materials when subjected to lunar dust simulant of di?erent size ranges.

This will be an ideal resource for space system engineers, space exploration researchers, and advanced students and professionals in space engineering.

• Provides a comprehensive background on lunar and Martian dust properties and challenges and compares currently available mitigation strategies
• Highlights the problems from dust on various space systems and crew
• Features discrete element models which were created and calibrated based on experimental results to study the capacity of the proposed technique for removing and cleaning dust in a planetary environment

• Language: English
• Publisher: Elsevier Science
• Release date: Aug 18, 2022
• ISBN: 9780128232552

Nima Gharib

Nima Gharib is a former Assistant Professor and McGill graduate. He has been a space enthusiast and studied dust mitigation techniques experimentally and numerically for years. He received an award from the Canadian Space Agency for his article on dust mitigation. He is now consulting on combining different numerical methods (CFD, FEM and DEM) to model and optimise multidisciplinary problems.

Book preview

Chapter 1: Introduction

Abstract

In this chapter, the lunar and Martian environments will be discussed. The dust levitation mechanism on both Mars and the Moon is different, but nevertheless, it creates electrostatically charged dust particles suspended above the surface. These suspended particles have exposed challenges to previous missions to the moon and Mars and will endanger future longer term missions and stays on these planetary bodies. This lofting dust has also been observed by other planetary objects and asteroids and challenged the missions' objectives. To overcome these issues, it is important to understand the environment and the mechanism that levitates the dust and suspends it above the surface.

Keywords

Charged dust; Dust devil; Horizon glow; Lunar environment; Martian dust; Space dust

The Apollo missions were the start of lunar exploration and a giant leap for mankind. Planetary missions and sending robots and humans are defined in the future roadmaps of space agencies as shown in Fig. 1.1. Each Apollo landing location was different and the astronauts had a loss in visibility owing to dust clouds, with the severity of the problem changing. This shows that the thickness of the dust layer on the lunar surface varies depending on the location of the lunar surface. An instrument’s thermal control system may fail if a substantial amount of dust accumulates on it. This might lead to inaccurate results. The Apollo missions were the start of lunar exploration and a giant leap for mankind. The lack of adhesion is also a problem, although it’s not as significant as the loss of mobility. Nevertheless, Neil Armstrong noted that, at the end of the excursions, the dust that had accumulated beneath his boots made it more difficult to ascend the staircase of the lunar module. However, the buildup of dust within exploration equipment might lead to mission failure. The Sun visors on astronaut helmets and zippers, for example, get clogged with lunar dust on a regular basis. As it turned out, this dust may cause severe abrasion when it accumulates. The problem with dust exists in other planetary environments such as Mars and on asteroids as well. These challenges have to be addressed before planning a mission. Planetary missions and sending robots and humans are defined in the future roadmaps of space agencies as shown in Fig. 1.1. International Space Station (ISS) development and low earth orbit satellites, understanding the surface of the Moon and Mars are considered for upcoming missions. Fig. 1.2 shows the near-future common international strategy for global space exploration which emphasizes maximizing the use of the ISS, expanding the synergy between human and robotic missions, and launching exploration missions in the vicinity of the Moon that enable discoveries on the Moon and near-Earth asteroids and pave the way for enhancing the technologies for Marian mission.

Figure 1.1  Roadmap1.Space exploration pathway proposed in the Global Exploration Roadmap. From Laurini, K.C., Gerstenmaier, W.H., 2014. The Global Exploration Roadmap and its significance for NASA. Space Policy 30 (3, Part B), 149–155. https://doi.org/10.1016/j.spacepol.2014.08.004.

Figure 1.2  Roadmap2.Near-term highlights from the Global Exploration Roadmap. From Laurini, K.C., Gerstenmaier, W.H., 2014. The Global Exploration Roadmap and its significance for NASA. Space Policy, 30 (3, Part B), 149–155. https://doi.org/10.1016/j.spacepol.2014.08.004.

The exploration of the Moon and Mars might serve as a platform to create and test new technologies, experience life on an extraterrestrial surface, and gain insights into the genesis of the cosmos. A fresh space habitat, on the other hand, is not easily constructed. This severe environment, which includes high levels of solar radiation, a wide range of temperature variations, and an almost nonexistent atmosphere, will provide a challenge to future human and robotic expeditions. Due to dust’s electrical charge and tendency to stick to everything it comes into contact with, one of the most significant obstacles to furthering human space travel is its existence. Dust movement across areas without winds or flowing water has also been reported. Apollo astronauts' reported horizon glow above the surface of the Moon (Mccoy and Criswell, 1974). Radial spokes were observed by Voyagers around Saturn (Smith et al., 1981, 1982) and fine dust ponds recorded by the Rendezvous-Shoemaker mission on Eros (Robinson et al., 2001). The dust is fine and could be highly abrasive. In addition to that, the dust grains could acquire electrical charge from solar radiation or local weathering processes. These electrically charged glass-like particles with sharp edges that float above the surface of the planetary system could potentially expose hazards to the future manned or unmanned missions. They can infiltrate into mechanical devices, cover optical instruments, and impose health risks to the astronauts. Problems exposed by the dust on the Moon have been characterized by Apollo missions. The Martian dust storm has been captured by different rovers on the surface of Mars and on different asteroid missions, dust particles exposed sampling difficulties and seal failures.

In this book, the following points will be discussed: the harsh environment of the planetary systems such as the Moon, Mars, and asteroids and their environment where the robotic systems and astronauts will be facing. We summarize the problems that previous missions had encountered and propose a potential solution to avoid them in future. We study the potential of using electrostatic and dielectrophoretic forces to remove and transport small particles away from surfaces by using a traveling electric field generated by a series of parallel electrodes connected to single or multiple AC power source(s). The traveling electric field created then serves as an invisible brush to clean surfaces and prevent dust from entering joints in space applications (e.g., bearing, solar panels, camera). Along the same route, we will discuss astronaut suit cleaning with magnetic device and dust sampling and classification. Then, we will look into numerical modeling and simulation of the electric field by finite element method and then we introduce dynamics equations for the bulk particle movement using discrete element models to examine the capacity of using the electric curtain for removing and cleaning dust from the apparatuses' surfaces in the planetary environments.

1. Lunar environment

There are several theories regarding the origin of the Moon which can be summarized into three categories:

1.1. Fission from the earth

This idea dates back to George Darwin’s 1878 theory that the Moon and Earth were separated by tidal forces. In the first edition of The Earth (1929), Jefferies (Jeffries, 1929) argued that the tides would not rise high enough. Despite this, the hypothesis remained popular because it gave a convenient explanation for the Moon's density that could be matched to the uncompressed density of the upper mantle. Fig. 1.3 shows the mathematical simulation of the possibility of the formation of the Moon by an oblique impact of a Mars-sized object. However, it is clear from this comparison of the lunar basalts' chemistry to that of their terrestrial counterparts that the lunar interior is unique from that of the Earth's mantle. A powerful and perhaps critical challenge to the fission hypothesis is posed by this argument (Levinson and Taylor, 2015).

1.2. Captured by the earth

This is a common theory; however, it takes the Moon's origin from the solar system to a distant location. It was formerly considered that the Moon's low density indicated that it was a primitive object, since the Sun's iron richness was supposed to be lower. In comparison to terrestrial basalts, the significant deficits of siderophile and volatile elements, as well as the enrichment of refractory elements, suggest that the interior of the Moon is farther away from primordial compositions than the interior of the Earth (Levinson and Taylor, 2015).

1.3. Double planet hypotheses

Because the Moon's density is so low compared to the Earth, the theory of Moon accretion or condensation as a sister planet to the Earth has been less popular than other concepts. If we assume they were formed from the same nebula at the same time then we can not explain that one body is 1.6 times denser than the other one. Because lunar silicates are different from those found on Earth, extra selective fractionation of silicates is required in order to account for these changes in chemical composition (Levinson and Taylor, 2015).

Figure 1.3  IT.Mathematical model of examining the impact theory of origin of the Moon. From Hiesinger, H., Jaumann, R., Spohn, T., Breuer, D., Johnson, T.V., 2014. Chapter 23 – The Moon. Elsevier, pp. 493–538. https://doi.org/10.1016/B978-0-12-415845-0.00023-2.

Analysis of lunar soil samples from the Apollo missions shows that lunar soil consists of basaltic and anorthositic materials. Consistent soil distribution on the surface of the Moon is mainly attributed to meteorite impacts through fragmentation, melting, and glass formation.

Thermal energy resulted from direct impact or hypervelocity or indirect influence of seismic motion of the rock acts contrary to the comminution effect. This thermal energy can be sufficiently intensive to melt the material or to weld the particles together. Melting can form glass as the result of a rapid chilling, or it can crystalize the melts. The product of crystallization is called breccias, which can be very solid or very friable rocks. Micrometeorites impact products are normally exceptional cases. Stronger energy impacts lead to either more breaking of particles or welding them together. This process may cut larger particles such as rocks from the surface, transform mineral grains into glass, or weld smaller particles into agglutinates. There was no significant geological process to renew the surface of the Moon for a billion years. As shown in artistic concept in Fig. 1.4, continuous meteor bombardment of the lunar surface has transformed it into a wide range of fragment-sized particles into large rock blocks. This mixture is believed to cover the lunar surface several meters deep (Rickman and Street, 2008).

Figure 1.4  Bombardment.Moon surface bombardment by meteorite. From Khan-Mayberry, N., 2008. The lunar environment: Determining the health effects of exposure to Moon dusts. From Dream to Reality: Living, Working and Creating for Humans in Space–A Selection of Papers Presented at the 16th IAA Humans in Space Symposium, Beijing, China, 2007. Acta Astronaut. 63(7), 1006–1014. https://doi.org/10.1016/j.actaastro.2008.03.015.

The surface of the Moon is covered with dusty soil from highland to maria (Fig. 1.5), over 95% of which is finer that 1mm, about 50% is finer than 60μm, i.e., equivalent to the thickness of a human hair, and 10%–20% is finer than 20microns. As a result, the lunar surface involves a wide and well-graded range of particle distribution. Analysis of samples taken from different landing sites of Apollo missions and JSC-1A lunar simulant is presented in Fig. 1.6. Volcanic activity occurred in a vacuum during the early formation of the lunar crust and surface meteorite impacts occurred for millions of years. These events caused various lunar dust particle shapes, from spherical to very complex. In general, lunar dust particles are considered to be elongate. This elongation causes particles to form an interlocking pattern on the surface and increases the cohesiveness of lunar soil.

The most significant characteristic of lunar dust is its irregular shape, with sharp edges as shown in Fig. 1.7 (Carrier, 2005). Moreover, the specific surface area is high, about 0.5m²/g, due to the irregular and reentrant shape of particles. Generally, the surface area of lunar soil particles is about 8 times the surface area of an assemblage of spheres with a similar size distribution. These peculiarities prevent lunar soil particles effectively packing together like uniform spheres (Taylor et al., 2005).

Figure 1.5  Full Moon.A composite full-Moon image showcasing the strong difference between the dark, smooth maria plains, and the extensively cratered highlands. From Taylor, S.R., McFadden, L.-A., Weissman, P.R., Johnson, T.V., 2007. Chapter 12–The Moon. Academic Press, pp. 227–250. https://doi.org/10.1016/B978-012088589-3/50016-5.

Figure 1.6  Size.Lunar soil particle size distribution from different Apollo mission samples and Lunar simulant JSC-1A. On average, 95% by weight of the soil is finer than 1.37mm; and 5% is finer than 0.0033mm. The average or median particle size, D50 (where 50 refers to 50% passing) is approximately 0.072mm. This size is very close to the boundary between sand and silt (0.074mm), and the lunar soil is usually described as either silty sand or sandy silt" (Carrier, 2005). From Isachenkov, M., Chugunov, S., Akhatov, I., Shishkovsky, I., 2021. Regolith-based additive manufacturing for sustainable development of lunar infrastructure–An overview. Acta Astronaut. 180, 650–678. https://doi.org/10.1016/j.actaastro.2021.01.005.

Figure 1.7  Flake.Lunar dust agglutinate particle (courtesy of D. McKay, NASA/JSC). From D. McKay, NASA/JSC.

The lunar surface is essentially nonconductive due to lack of liquid water as well as insulating characteristics of minerals constituting regolith in the lunar environment. This implies an equilibration between charges produced on the surface and the external environment, contrary to the terrestrial environment where conduction to an interior ground potential may occur.

1.4. Electrostatic environment

The electrostatic activity on the surfaces of Mars, Moon, and asteroids originated from different sources, creating challenges for exploratory missions conducted by humans or robots. A layer of dust covers the surface of Mars and global dust storms redistribute this dust layer all over the planet. This dust layer is expected to have electrostatic charge which is resulting from grain collisions in the dusty atmosphere. However, the electrostatic charge of the dust layer on the Moon seems to be the result of different factors including solar wind, cosmic rays, and solar radiation created by the photoelectric effect. Dust layers with electrostatic charge potentially tend to stick to surfaces. NASA explorations on Mars indicate that the efficiency of its exploration rovers can be influenced by the dust falling on their solar panels. So, it can interfere with their operation, making them unusable. Moreover, Apollo missions to the Moon indicate that the sticking of lunar dust on the surface could interrupt future manned or unmanned missions (Calle, 2011).

Ambient plasma conditions and photoemission of electrons on the dayside of the Moon resulted from solar UV and X-ray radiation can control the potential of lunar surface (Fig. 1.8). The key elements in controlling this potential are the collection of electrons and ions from the surrounding plasma, photoemission of electrons, and electrons emitted from the lunar surface.

The lunar electrostatic environment is created by plasma and photon fluxes to the Moon. Photoelectric charge created by solar UV photons dominates the dayside. A positive charge of a potential is developed as the result of photoelectrons' emission. However, plasma electrons are dominated on the dark side, negatively charging the surface to a negative potential (Manka, 1973). However, plasma electrons are dominated on the dark side, negatively charging the surface to a negative potential, −50 to 100V (Halekas et al., 2002).

Figure 1.8  Photoionization.Electric field at night and the dayside of the Moon. From Zakharov, A., Horanyi, M., Lee, P., Witasse, O., Cipriani, F., 2014. Dust at the Martian Moons and in the circummartian space. Phobos, 102, 171–175. https://doi.org/10.1016/j.pss.2013.12.011.

Plasma develops the Moon into a charged body and accordingly creates a screen-like effect with significant distance or Debye of length. The layer of plasma is developed around the Moon as Debye or electrostatic sheath with a length of about a meter on the dayside or several kilometers on the dark side. The Debye sheath on dayside is dominated by photoelectrons and normally is known as photoelectron sheath (Calle, 2011).

Escaping UV-released photoelectrons into space occurs when the terminator passes and faces the sunrise. This phenomenon charges the surface of the Moon positively. However, before being absorbed and releasing photoelectrons, the produced UV photons penetrate surface particles to less than a micron depth. This leads to ionization of UV on the sunlit part of particles on the lunar surface. However, some of the UV-released electrons cannot escape into space, as they are slowed by lunar gravity and the electrical field resulting from the surface charge. Then, the lunar surface is covered by a low-density electron plasma over the height of ∼1m. These electrons impact the surface, neutralizing some positive surface charges on the particles. As a result, an equilibrium is established between photoelectrons leaving the surface and returning plasma electrons (Walton, 2007).

The first observations of plasma wake on the Moon were provided by the Explorer 35 spacecraft and the Apollo 15 and 16 subsatellites (Schubert and Lichtenstein, 1974). Explorer 35 provided a survey of the wake from 1000 to 10,000km above the lunar surface, whereas Apollo subsatellites could only provide limited observations of 100–160km above the surface of the Moon. Recent data from Wind spacecraft on particles and magnetic fields indicated that there is an indication of a wake at ∼11,000km downstream from the lunar surface (Bosqued et al., 1996, 1996, 1996).

Research indicates that ambient plasma conditions and photoemission of electrons on the dayside of the Moon resulted from solar UV and X-ray radiation can control the potential of the lunar surface. The key elements in controlling this potential are the collection of electrons and ions from the surrounding plasma, photoemission of electrons, and electrons emitted from the lunar surface. Current data indicates high variability of lunar surface potential, the value of which not only depends on ambient plasma conditions but also on the location of the lunar surface such as the subsolar point, night side, and the terminator region. Lunar surface potentials estimated during the Apollo mission under solar wind indicates that on the dayside of the lunar surface, it is about +10V, and near the terminator and on night side regions, it is about −100V (Orger et al., 2018). Manka (1973) and Freeman and Ibrahim (1975) estimated this potential under average solar wind by the current balance calculation as +10V on the dayside and −38V on the lunar terminator. Stubbs et al. (2005) estimated the lunar surface potential for slow stream of solar wind as +2.85V on the subsolar point and −47.47V on the lunar terminator, and for fast stream of solar wind, it was estimated as+4.22V on the subsolar point and −44.9V on the lunar terminator.

The changes in the solar wind and cosmic rays greatly determine the potential of the lunar surface, affecting the plasma environment. Negative potentials of the surface can be in order of several kV, as the Moon crossing the Earth's plasma. Up to −5kV surface potential is recorded by Lunar Prospector during intense solar activity (Halekas et al., 2005).

1.5. Dynamic environment

Dust on the surface of the Moon seems to be static but influenced by an electrostatic environment. Five decades ago, images taken by the Surveyor 5, 6, and 7 television cameras from the Moon provided the first space observation of horizon glow resulting from dust motion above the dust horizon. It was suggested that this horizon glow with high intensity and long duration resulted from the scattering of a cloud of dust particles with ∼10μm diameter which was raised within 1m above the surface of the Moon (Criswell, 1973). Fig. 1.9 shows Surveyor 6 observations of light scattering by levitated dust clouds for less than 3h duration above the terminator region. It is suggested by Rennilson and Criswell (1974) that electrically charged particles eject 10⁷ more particles per unit time compared to micro-meteorite bombardment of the surface.

Apollo astronauts reported a horizon glow (Fig. 1.10) which seems to be evidence of dust cloud movement up to several kilometers above the lunar surface. The presence of dust clouds is evidenced by observations by the Lunar Surveyor spacecraft and the Lunar Ejecta and Meteorites Experiment (LEAM) on Apollo 17. There are various models to explain this phenomenon through theoretical definitions. However, it is proposed that movement and transport of dust particles can be created by charged particles from the solar wind and UV radiation which result in electronic charging of the lunar surface.

For example, the dynamic fountain model suggested by Stubbs et al. (2005) explains the existence of submicron particles at high altitudes above the Moon's surface (≈100km) which is shown in Fig. 1.11. In this model, electrostatic forces and gravitational forces on the dust grains are equal and acting in different directions. This makes particles suspended in the environment. The assumption is that, since the dust particles are so small, the main force acting on them could be regarded as an electrostatic force making them accelerate and detach from the surface and follow a parabolic trajectory returning to the surface once they exchange their charge. In this case, the dominant force becomes