arXiv subjects

William M. Farrell

Publications and source records attributed to William M. Farrell.

5 recordsLinked to original sources

arXiv2026

The Radio-wave Observations at the Lunar Surface of the photoElectron Sheath (ROLSES) instrument onboard the Intuitive Machines-1 Mission to the Moon

The Radio wave Observations at the Lunar Surface of the photoElectron Sheath (ROLSES) instrument is a radio telescope system designed to characterize the radio and plasma wave environment of the nearside lunar surface at frequencies between 2 kHz and 30 MHz. The ROLSES sensor consists of a set of four 2.5 meter radio monopole antennas onboard the Intuitive Machines (IM 1) lander, Odysseus. The antennas were stowed during launch and deployed after landing on the lunar surface using a frangibolt mechanism. The frequency range is well suited to observing radio waves at frequencies below 15 MHz that cannot be observed from Earth due to the ionospheric cutoff. Radio waves from the Sun, the Milky Way galaxy, Jupiter, Earth's auroral region, and ground-based radio transmitters were expected to be present on the lunar surface. Radio data from each of the 4 antennas, after passing through an isolating pre-amp and signal conditioning analog electronics, were digitized to 14 bits at 120 mega samples per second and then digitally processed by a Field Programmable Gate Array (FPGA) that performs onboard spectral analysis via a Fast Fourier Transform (FFT). Time averaged spectral values are then stored and returned. Also telemetered to Earth are raw waveforms (unprocessed time sequence data) that are useful in studying dust impact on ROLSES antennas. ROLSES data are sent to the lander and subsequently downlinked for further processing. ROLSES is part of NASA's Commercial Lunar Payload Services (CLPS) program. Odysseus landed close to the south pole at Malapert A (80 S). This paper describes the design and operations of the ROLSES instrument and presents initial observations made during transit and surface operations despite the tilted landing of Odysseus. We also describe next version of this instrument (ROLSES 2) currently under development.

astro-ph.IM↗

arXiv2026

g4chargeit: Geant4-based kinetic Monte Carlo simulations of charging in dielectric materials

We present g4chargeit, a kinetic Monte Carlo framework built on Geant4 for self-consistent simulation of time-dependent electrostatic charging in dielectric materials. The model explicitly incorporates stochastic particle transport and scattering processes using validated Geant4 cross-sections, while self-consistently evolving the electric potential and field. As a representative application, we simulate the charging of regolith grains under average dayside conditions on the Moon. The surface of the Moon, in addition to other airless planetary bodies, are regularly exposed to solar ultraviolet photons and solar-wind plasma, creating a radiation environment in which electrostatic interactions among regolith grains become significant. Until now, simulations of regolith charging have often relied on analytical approximations that oversimplify grain geometry and interaction mechanisms. Our Geant4-based simulations reveal charge accumulation within intergrain micro-cavities, leading to repulsive electrostatic forces consistent with experimental observations. The framework establishes a multiscale approach that links microscopic scattering events to the continuity equation of surface charge density and to the formation of macroscopic surface charge patches in complex grain geometries. Although demonstrated here for planetary regolith, the method is general and applicable to a broad range of dielectric charging problems. The code is openly available at https://github.com/kgandhi63/g4chargeit.git.

physics.app-ph↗

arXiv2026

Venting and Outgassing Simulations of Pressurized Lunar Modules: Contamination of the Lunar Environment

One objective of Artemis science is to determine the impact human activities have on the lunar environment, which might compromise science objectives and measurements. We perform a preliminary analysis of the contamination associated with airlock venting and outgassing from a prototype lunar-module geometry intended to host astronauts on the lunar surface. The air flow generated by the depressurization of the airlock, expanding in the lunar exosphere, is studied using the Direct Simulation Monte Carlo (DSMC) method for two different venting configurations and the particle flux on the surface is computed as a function of the distance from the the module. Outgassing from the main body of the module -- assumed to be covered with a Multi-Layer Insulation (MLI) blanketing -- and from the solar panels is then analyzed using a view-factor method, employing outgassing rates from the literature.Our results give preliminary indications of the distance at which contamination levels fall below the values characteristic of native species in the lunar atmosphere. Scientific measurements targeting 40Ar should be carried farther than 30--100 meters from the module, while the detection of lower-abundance species such as polar-crater water might require to travel up to and beyond 3 km from the module.

physics.space-ph↗

arXiv2020

Lunar Volatiles and Solar System Science

Understanding the origin and evolution of the lunar volatile system is not only compelling lunar science, but also fundamental Solar System science. This white paper (submitted to the US National Academies' Decadal Survey in Planetary Science and Astrobiology 2023-2032) summarizes recent advances in our understanding of lunar volatiles, identifies outstanding questions for the next decade, and discusses key steps required to address these questions.

astro-ph.IM↗

arXiv2020

On the Effect of Magnetospheric Shielding on the Lunar Hydrogen Cycle

We examine how water is produced globally over the lunar surface as it orbits in/out of the magnetotail. Due to the interaction of the solar wind (SW) with Earth's magnetic field, upstream the magnetic field is compressed down to ~10 Earth radii. However, the diverted stream of SW around Earth's magnetic field results in an extended depleted region of SW protons (positively charged hydrogen) out to 1000's of Earth radii, referred to as the magnetotail. The Moon orbits at a distance of ~40 Earth radii; therefore, upstream it is within the SW, but downstream it is partially shielded while in the magnetotail during full Moon. SW protons penetrate lunar soil particles and some H atoms can chemical react with oxygen to form water-like molecules such as OH/H2O. Most of the H atoms bounce around within grains until finding another hydrogen atom, chemically combine, and then escape the grain as H2 into the thin atmosphere. We developed a model to calculate the global distribution of OH produced in the lunar surface and H2 released to the atmosphere as the Moon orbits in/out of Earth's magnetotail. The model results are in good agreement with available observations.

astro-ph.EP↗