scholarly journals Detection of the Lunar Surface Soil Permittivity with Megahertz Electromagnetic Wave

Sensors ◽  
2021 ◽  
Vol 21 (7) ◽  
pp. 2466
Author(s):  
Qingwen Rao ◽  
Guanjun Xu ◽  
Wangchen Mao
Keyword(s):  
Lunar Surface ◽  
Scattering Theory ◽  
Surface Soil ◽  
Low Frequency ◽  
Stable Phase ◽  
Em Scattering ◽  
Lunar Dust ◽  
Lunar Ionosphere ◽  
Spaceborne Radar ◽  
Reflection Characteristics

In this paper, the detection of the lunar surface soil permittivity with megahertz electromagnetic (EM) waves by spaceborne radar is studied based on the EM scattering theory, the Boltzmann–Shukla equations, and the improved scattering matrix method (ISMM). The reflection characteristics of the lunar surface soil subject to megahertz waves are analyzed through the EM scattering theory and expressed by the lunar surface soil permittivity. Then, the lunar ionosphere is assumed to be composed of dusty plasma, and its EM characteristics are described with the Boltzmann–Shukla equations. Finally, the transmission and reflection characteristics of the propagation of EM waves in the lunar ionosphere are numerically calculated with ISMM. Thus, the complex permittivity of lunar surface soil is obtained. In addition, the effects of detection environment situations, such as the lunar illumination intensity, characteristics of the lunar dust and dust charging process in the lunar ionosphere, on the amplitude and phase of EM waves are also investigated in this study. The simulation results show that an EM wave at a high frequency induces a strong effective wave with a stable phase shift and a significantly small interferential wave. Moreover, the lunar illumination is more effective under EM waves in low frequency bands; the characteristics of the lunar dust have a notable influence on the transmission and absorption coefficients of the effective waves. These conclusions help in real applications involving the detection of the lunar surface soil permittivity by spaceborne radar in various lunar environments.

Future lunar missions and investigation of dusty plasma processes on the Moon

2013 ◽  
Vol 79 (4) ◽  
pp. 405-411 ◽  
Author(s):  
SERGEY I. POPEL ◽  
LEV M. ZELENYI
Keyword(s):  
Dusty Plasma ◽  
Lunar Surface ◽  
Dust Particles ◽  
Maximum Height ◽  
Charged Dust ◽  
The Moon ◽  
Plasma System ◽  
Lunar Dust ◽  
The Impact ◽  
Dusty Plasma System

AbstractFrom the Apollo era of exploration, it was discovered that sunlight was scattered at the terminators giving rise to “horizon glow” and “streamers” above the lunar surface. Subsequent investigations have shown that the sunlight was most likely scattered by electrostatically charged dust grains originating from the surface. A renaissance is being observed currently in investigations of the Moon. The Luna-Glob and Luna-Resource missions (the latter jointly with India) are being prepared in Russia. Some of these missions will include investigations of lunar dust. Here we discuss the future experimental investigations of lunar dust within the missions of Luna-Glob and Luna-Resource. We consider the dusty plasma system over the lunar surface and determine the maximum height of dust rise. We describe mechanisms of formation of the dusty plasma system over the Moon and its main properties, determine distributions of electrons and dust over the lunar surface, and show a possibility of rising dust particles over the surface of the illuminated part of the Moon in the entire range of lunar latitudes. Finally, we discuss the effect of condensation of micrometeoriod substance during the expansion of the impact plume and show that this effect is important from the viewpoint of explanation of dust particle rise to high altitudes in addition to the dusty plasma effects.

The importance of lunar dust mitigation during future human led lunar missions

2021 ◽  
Author(s):  
Donald Hendrix
Keyword(s):  
Lunar Surface ◽  
Health And Safety ◽  
Dust Exposure ◽  
Space Suit ◽  
Lunar Dust ◽  
Silica Dust ◽  
Pass Through ◽  
High Level ◽  
Vacuum Systems ◽  
Lunar Missions

<p>With the Artemis mission set to launch in 2024, returning humans to the lunar surface for the first time in over half a century, it is imperative to ensure human health and safety on a variety of fronts. Lunar dust exposure is one of many areas of concern regarding astronaut health and safety. During the Apollo missions it was reported that lunar dust was a nuisance and induced allergic-like symptoms upon exposure. In addition, it was also reported that instruments became coated with dust that was difficult to remove, and that the dust adhered to everything and tore through space suit fabric. Numerous inhalation studies have determined that lunar dust is more toxic than analogous terrestrial materials but less so than silica dust. Apollo dust mitigation systems were successful on some missions but failed on others. As humans are to stay on the lunar surface for extended periods relative to the Apollo missions, it is vital to fabricate instruments that would address the lunar dust problem with greater reliability. There must be multiple steps to remove all lunar dust, including the ultra-fine <10 µm fraction which was the most difficult dust size to remove. There must be multiple steps regarding lunar dust removal including a chamber to remove dust and de-suit, and a vacuum with high level HEPA filtration to remove dust. The first chamber would be to filter out any dust that comes into the module from the outside. Once all the air is clear, then the next step would be to remove any remaining dust on the suits using a hand-held vacuum with a HEPA H14 filter which only allows up to a maximum 0.005% of particles 100 nm in size to pass through the filter. Then, it would be safe to de-suit. It would be wise to have a second chamber between the first chamber and the command center of the lunar module that would vacuum any remaining dust before opening to the main command chamber. Ultra-high quality HEPA filters of both the chamber and hand-held vacuum systems should be replaced frequently to maintain optimal dust mitigation. Investing time and resources into lunar dust mitigation should be a top priority for the upcoming Artemis mission to avoid the issues encountered on the Apollo missions.</p>

scholarly journals 2.2.5 Electrostatic Disruption of Lunar Dust Particles

1976 ◽  
Vol 31 ◽  
pp. 238-240 ◽  
Author(s):  
John W. Rhee
Keyword(s):  
Surface Potential ◽  
Lunar Surface ◽  
Dust Particles ◽  
Dark Side ◽  
Lunar Dust ◽  
Electrostatic Charging

An investigation has been made to study a possibility that dust particles might catastrophically explode on the lunar surface due to electrostatic charging. It is shown that for the dark side along the terminator zone, dust balls and compact stony particles of micron and submicron sizes will be blown up if their surface potential is as low as a kilovolt negative. This mechanism will not operate on the sunlit side because the potential is only 3.5 ~ 20 volts positive. Some of these fragments may possibly levitate in the vicinity of the terminator.

Low-frequency technology for a lunar interferometer

2020 ◽  
Vol 379 (2188) ◽  
pp. 20190575 ◽  
Author(s):  
Kristian Zarb Adami ◽  
I. O. Farhat
Keyword(s):  
Radio Frequency ◽  
Signal Detection ◽  
Radio Astronomy ◽  
Lunar Surface ◽  
Low Frequency ◽  
Radio Interferometer ◽  
Radio Frequency Interference ◽  
The Moon ◽  
Single Antenna ◽  
Global Signal

This work sketches a possible design architecture of a low-frequency radio interferometer located on the lunar surface. The design has evolved from single antenna experiments aimed at the global signal detection of the epoch of reionization (EoR) to the square kilometre array (SKA) which, when complete, will be capable of imaging the highly red-shifted H 1 -signal from the cosmic dawn through to the EoR. However, due to the opacity of the ionosphere below 10 MHz and the anthropogenic radio-frequency interference, these terrestrial facilities are incapable of detecting pre-ionization signals and the moon becomes an attractive location to build a low-frequency radio interferometer capable of detecting such cosmological signals. Even though there are enormous engineering challenges to overcome, having this scientific facility on the lunar surface also opens up several new exciting possibilities for low-frequency radio astronomy. This article is part of a discussion meeting issue ‘Astronomy from the Moon: the next decades’.

Self-synchronization theory of tri-motor excitation with double-frequency in far resonance system

2020 ◽  
Vol 234 (16) ◽  
pp. 3166-3184 ◽  
Author(s):  
Min Zou ◽  
Pan Fang ◽  
Yongjun Hou ◽  
Guodong Chai ◽  
Jinsong Chen
Keyword(s):  
Drilling Fluid ◽  
Structural Parameters ◽  
Rapid Development ◽  
Low Frequency ◽  
Single Frequency ◽  
Stable Phase ◽  
Resonance System ◽  
Double Frequency ◽  
Differential Motion ◽  
Motor Excitation

With the rapid development of petroleum exploitation industry, vibrating screen actuated with a single frequency is unsuitable to separate cuttings from drilling fluid, since it usually results in screen blocking. Hence, for solving the above-mentioned problem, tri-motor excitation with double-frequency in far resonance system is introduced. This paper aims to explore the self-synchronization mechanism of the proposed system. First, dynamic equation is established according to physical model of the system. Then, displacement response of the system in steady state is obtained with dynamic formulas. Subsequently, synchronous condition among the three exciters is determined by small parameters method, and criterion of synchronous stability among the three exciters is derived by Poincare-Lyapunov method. Finally, in light of the differential motion equation, Runge-Kutta principle is assigned to validate the reliability of self-synchronous theory and the stability of the double-frequency system. The results indicate that electromagnetic torques of low-frequency motors are dynamically antisymmetric in synchronous operation, and synchronous ability of the system is determined by the mass ratio among the rotors. In addition, stable phase difference among the rotors is significantly influenced by the structural parameters of the system. And this study will be helpful for the improvement of separation technology.

scholarly journals The Role of Pacific Climate on Low-Frequency Hydroclimatic Variability and Predictability in Southern Alberta, Canada

2009 ◽  
Vol 10 (6) ◽  
pp. 1465-1478 ◽  
Author(s):  
Adam K. Gobena ◽  
Thian Y. Gan
Keyword(s):  
Phase Difference ◽  
Southern Oscillation ◽  
Spatial Coherence ◽  
Low Frequency ◽  
Rank Correlation ◽  
Stable Phase ◽  
Climate Indices ◽  
Southern Alberta ◽  
The 1950S ◽  
Hydroclimatic Variability

Abstract Wavelet and rank correlation analysis were used to identify the links between primary Pacific climate variability modes and low-frequency hydroclimatic variability in the South Saskatchewan River basin (SSRB) of southern Alberta. The April–September average streamflow shows strong interdecadal oscillations with dominant scales of 19–22, 41–42, and 62 yr whereas statistically significant wavelet power in the interannual scale was organized on a background scale of approximately 20–25 yr. At interannual scales, strong coherency is observed between streamflow and the Niño-3 index prior to the 1940s, and in the 1950s, 1970s, and 1980s. However, a change in the phase difference from near 0° in the 1950s to near 180° in the 1980s indicates that the relationship between streamflow and the El Niño–Southern Oscillation (ENSO) is not consistent. Streamflow–Pacific–North America pattern (PNA) and streamflow–Pacific decadal oscillation (PDO) relationships at interannual scales also exhibit similar inconsistencies in phase difference. At interdecadal scales, PDO and streamflow exhibited consistently strong coherence with a stable phase difference of 180° for scales >20 yr. From the period of 1913–2001, the median partial correlation between streamflow and PDO|Niño-3 (read as PDO given Niño-3) was −0.36, whereas it was zero between streamflow and Niño-3|PDO, suggesting that PDO is the primary mode of importance in streamflow variability and predictability in the SSRB. Precipitation variability was also dominated by interdecadal oscillations; however, there is less spatial coherence for dominant scales. Correlations between the basin’s winter precipitation and climate indices are also weaker than with streamflow.

scholarly journals Finding Rare Quasars: VLA Snapshot Continuum Survey of FRI Quasar Candidates Selected from the LOFAR Two-Metre Sky Survey (LoTSS)

Galaxies ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 2
Author(s):  
Gülay Gürkan ◽  
Judith Croston ◽  
Martin J. Hardcastle ◽  
Vijay Mahatma ◽  
Beatriz Mingo ◽  
...  
Keyword(s):  
Low Frequency ◽  
Stable Phase ◽  
Galactic Centre ◽  
Very Large Array ◽  
Sky Survey ◽  
Two Factors ◽  
Radiative Power ◽  
Galaxy Environment ◽  
Systematic Selection ◽  
Jet Power

The radiative and jet power in active galactic nuclei is generated by accretion of material on to supermassive galactic-centre black holes. For quasars, where the radiative power is by definition very high, objects with high radio luminosities form ∼10 per cent of the population, although it is not clear whether this is a stable phase. Traditionally, quasars with high radio luminosities have been thought to present jets with edge-brightened morphology (Fanaroff-Riley II−FR II) due to the limitations of previous radio surveys (i.e., FRIs were not observed as part of the quasar population). The LOw Frequency ARray (LOFAR) Two-metre Sky Survey (LoTSS) with its unprecedented sensitivity and resolution covering wide sky areas has enabled the first systematic selection and investigation of quasars with core-brightened morphology (Fanaroff-Riley I−FR). We carried out a Very Large Array (VLA) snapshot survey to reveal inner structures of jets in selected quasar candidates; 15 (25 per cent) out of 60 sources show clear inner jet structures that are diagnostic of FRI jets and 13 quasars (∼22 per cent) show extended structures similar to those of FRI jets. Black hole masses and Eddington ratios do not show a clear difference between FRI and FRII quasars. FRII quasars tend to have higher jet powers than FRI quasars. Our results show that the occurrence of FRI jets in powerful radiatively efficient systems is not common, probably mainly due to two factors: galaxy environment and jet power.

scholarly journals Low-frequency magnetic variations at the high-<i>β</i> Earth bow shock

2019 ◽  
Vol 37 (5) ◽  
pp. 877-889
Author(s):  
Anatoli A. Petrukovich ◽  
Olga M. Chugunova ◽  
Pavel I. Shustov
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Spatial Scales ◽  
Low Frequency ◽  
Background Field ◽  
Bow Shock ◽  
Stable Phase ◽  
Main Magnetic Field ◽  
Astrophysical Plasmas ◽  
Earth’S Bow Shock

Abstract. Observations of Earth's bow shock during high-β (ratio of thermal to magnetic pressure) solar wind streams are rare. However, such shocks are ubiquitous in astrophysical plasmas. Typical solar wind parameters related to high β (here β>10) are as follows: low speed, high density, and a very low interplanetary magnetic field of 1–2 nT. These conditions are usually quite transient and need to be verified immediately upstream of the observed shock crossings. In this report, three characteristic crossings by the Cluster project (from the 22 found) are studied using multipoint analysis, allowing us to determine spatial scales. The main magnetic field and density spatial scale of about a couple of hundred of kilometers generally corresponds to the increased proton convective gyroradius. Observed magnetic variations are different from those for supercritical shocks, with β∼1. Dominant magnetic variations in the shock transition have amplitudes much larger than the background field and have a frequency of ∼ 0.3–0.5 Hz (in some events – 1–2 Hz). The wave polarization has no stable phase and is closer to linear, which complicates the determination of the wave propagation direction. Spatial scales (wavelengths) of variations are within several tens to a couple of hundred of kilometers.

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