Lunar Orbit Research Articles

Spectral Imaging for Lunar Orbit Exploration: Research Status and Technical Challenges

Spectral Imaging for Lunar Orbit Exploration: Research Status and Technical Challenges

Analysis of the KPLO magnetic cleanliness for the KMAG instrument

• Analysis of magnetic cleanliness of instruments on space missions using a Python program. • Analysis conducted on the soon-to-be-launched Korea Pathfinder Lunar Orbiter (KPLO). • Magnetic interference from the spacecraft field is within the accepted mission requirements. In space exploration, instruments measuring magnetic fields require magnetic cleanliness because it helps to distinguish the magnetic field generated by the spacecraft from the ambient field. A spacecraft has its own DC and AC magnetic fields generated by the current flow and residual moments of the spacecraft instruments. Therefore, analysis and testing are required in the development phase. The Korea Pathfinder Lunar Orbiter (KPLO) carries the KPLO Magnetometer (KMAG) instrument to observe magnetic fields on the lunar surface and the space environment around the Moon. To verify the magnetic cleanliness of the KPLO, we analyzed the magnetic field generated by it. We used the positional information and the magnetic dipole moments of twenty-five instruments, with which the KPLO is equipped. The analysis method was a Python program using magpylib. Finally, the worst-case analysis results showed that the spacecraft field around the magnetometer is less than 700 nT, which is the KMAG magnetic cleanliness requirement.

Imaging sensitivity of a linear interferometer array on lunar orbit

ABSTRACT Ground-based observation at frequencies below 30 MHz is hindered by the ionosphere of the Earth and radio frequency interference. To map the sky at these low frequencies, we have proposed the Discovering the Sky at the Longest wavelength mission (DSL, also known as the ‘Hongmeng’ mission, which means ‘Primordial Universe’ in Chinese) concept, which employs a linear array of micro-satellites orbiting the Moon. Such an array can make interferometric observations achieving good angular resolutions despite the small size of the antennas. However, it differs from the conventional ground-based interferometer array or even the previous orbital interferometers in many aspects, new data-processing methods need to be developed. In this work, we make a series of simulations to assess the imaging quality and sensitivity of such an array. We start with an input sky model and a simple orbit model, generate mock interferometric visibilities, and then reconstruct the sky map. We consider various observational effects and practical issues, such as the system noise, antenna response, and Moon blockage. Based on the quality of the recovered image, we quantify the imaging capability of the array for different satellite numbers and array configurations. For the first time, we make practical estimates of the point source sensitivity for such a lunar orbit array, and predict the expected number of detectable sources for the mission. Depending on the radio source number distribution which is still very uncertain at these frequencies, the proposed mission can detect 102–104 sources during its operation.

Long-Term Earth-Moon Evolution With High-Level Orbit and Ocean Tide Models.

Tides and Earth‐Moon system evolution are coupled over geological time. Tidal energy dissipation on Earth slows Earth′s rotation rate, increases obliquity, lunar orbit semi‐major axis and eccentricity, and decreases lunar inclination. Tidal and core‐mantle boundary dissipation within the Moon decrease inclination, eccentricity and semi‐major axis. Here we integrate the Earth‐Moon system backwards for 4.5 Ga with orbital dynamics and explicit ocean tide models that are “high‐level” (i.e., not idealized). To account for uncertain plate tectonic histories, we employ Monte Carlo simulations, with tidal energy dissipation rates (normalized relative to astronomical forcing parameters) randomly selected from ocean tide simulations with modern ocean basin geometry and with 55, 116, and 252 Ma reconstructed basin paleogeometries. The normalized dissipation rates depend upon basin geometry and Earth′s rotation rate. Faster Earth rotation generally yields lower normalized dissipation rates. The Monte Carlo results provide a spread of possible early values for the Earth‐Moon system parameters. Of consequence for ocean circulation and climate, absolute (un‐normalized) ocean tidal energy dissipation rates on the early Earth may have exceeded today′s rate due to a closer Moon. Prior to ∼3Ga, evolution of inclination and eccentricity is dominated by tidal and core‐mantle boundary dissipation within the Moon, which yield high lunar orbit inclinations in the early Earth‐Moon system. A drawback for our results is that the semi‐major axis does not collapse to near‐zero values at 4.5 Ga, as indicated by most lunar formation models. Additional processes, missing from our current efforts, are discussed as topics for future investigation.

Autonomous orbit determination and timekeeping in lunar distant retrograde orbits by observing X‐ray pulsars

<h3>Abstract</h3> A server satellite that is parked in a stable distant retrograde orbit (DRO) in the vicinity of the Moon can provide navigation service for satellites in the Earth– Moon system. In this study, X-ray pulsar navigation (XPNAV) is investigated to determine the server’s orbital position and velocity, and maintain its onboard timing autonomously to ensure the autonomy of the server. First, the feasibility and potential advantages of XPNAV in DRO are analyzed qualitatively based on the unique properties of DRO: long-term orbital stability and short-term, nearly uniform-velocity rectilinear motion. Second, high-fidelity X-ray photon timestamps are simulated to serve as the original measurements for XPNAV. A classical extended Kalman filter is used to estimate the orbital states (i.e., position and velocity) and the clock timing of the satellite in DRO, wherein the pulse phase and Doppler frequency are estimated as intermediate measurements. Finally, Monte Carlo simulations are conducted to assess the variation in the XPNAV performance with the DRO orbital period, clock noise, and detector effective area. The simulation results show that XPNAV in DRO can achieve considerably improved position accuracy than that in low Earth orbit using the same hardware while maintaining the long-term stability of the satellite onboard clock, thus demonstrating the capability of XPNAV to be used in an operational spaceflight mission around or beyond the Moon.

Modelling the penetration of subsonic rigid projectile probes into granular materials using the cavity expansion theory

Typical subsurface investigation tools used on Earth are not applicable for subsurface exploration of the Moon and other extraterrestrial bodies due to payload limitations in space missions. Instead, light and compact subsonic projectile probes can be considered as an alternative subsurface investigation tool in such exploratory missions to overcome a host of challenges. Such probes can be launched from a lunar orbiter or lander to the surface of the Moon to provide the initial effective penetration from the impact. Here, we develop a model based on the spherical cavity expansion theory to predict the deceleration rate and final penetration depth of a rigid projectile probe into geological targets under the perpendicular subsonic impact. Two stress fields are assumed to propagate in the medium, plastic (near field) and elastic (far field), upon the impact. The stresses at the cavity wall are obtained by combining the Mohr–Coulomb failure criterion for the target failure (plastic region) considering two different assumptions for plastic wave propagation. Two field experiments are used to compare and assess the robustness of the proposed solutions in the subsonic range. Base on the simulation results and the experiments, it is concluded that the cavity expansion model considering the locked hydrostat assumption, with the modification here introduced for the volumetric strain, can provide us with a reasonable prediction of the projectile penetration, final penetration depth and the stresses on the probe. Thus, our proposed solution can be used as a benchmark for sophisticated and computationally-expensive numerical calculations.

Lowering the barriers to lunar sourced propellant via competitive parity pricing

Recent remote sensing results and the current Artemis lunar exploration program have heightened interest in the potential for producing propellant on the lunar surface to contribute to the sustainability of ongoing activity in cislunar space. In this paper, we examine the case of lunar propellant competing against Earth-sourced propellant both on the lunar surface and in low lunar orbit. We restrict ourselves to providing lunar propellant for the purpose of landing cargo from low lunar orbit onto the lunar surface. In our analysis, we derive the revenue recoverable from, or value delivered by, lunar propellant by matching the cost of landing cargo using Earth-sourced propellant, rather than the cost of transporting propellant from Earth. We present the arguments in commercial and non-commercial contexts. We find that there are opportunities on the lunar surface for extracting value above the competing propellant transportation cost from Earth. When competing against Earth-sourced propellants in low lunar orbit, there are opportunities to extract more value than one could by supplying commodity propellants. The opportunities arise from expanding the factors contributing to competing costs, using combined cargo and propellant concepts of operations that deliver higher propellant efficiency, and from consolidating transportation assets with propellant supply to achieve higher capital efficiency. By using this analytical approach to transportation and transportation support services we were able to lower the barriers to the production and use of lunar sourced propellant.

NASA 워크숍 및 해외 착륙임무에 기반한 달 착륙 후보 지역과 임무에 대한 고찰

Korea plans to send a pathfinder lunar orbiter to the Moon for the first time in August 2022. And according to the 3rd Basic Plan for Space Development Promotion, the plan is to send a lunar lander to the Moon before 2030. The selection of the lunar landing area can be varied depending on the lunar lander

Influences of accreting primordial black holes on the global 21 cm signal in the dark ages

ABSTRACT Baryonic matter can be accreted on to primordial back holes (PBHs) formed in the early Universe. The radiation from accreting PBHs is capable of altering the evolution of the intergalactic medium (IGM), leaving marks on the global 21 cm signal in the dark ages. For accreting PBHs with mass MPBH = 103(104) M⊙ and mass fraction fPBH = 10−1(10−3), the brightness temperature deviation ΔδTb reaches $\sim 18~(26)~\rm mK$ at redshift z ∼ 90 ($\nu \sim 16~\rm MHz$), and the gradient of the brightness temperature dδTb/dν reaches $\sim 0.8~(0.5)~\rm mK~MHz^{-1}$ at frequency $\nu \sim 28~\rm MHz$ (z ∼ 50). For larger PBHs with higher mass fraction, the brightness temperature deviation is larger in the redshift range z ∼ 30–300 ($\nu \sim 5\!-\!46~\rm MHz$), and the gradient is lower at the frequency range $\nu \sim 20\!-\!60~\rm MHz$ (z ∼ 23–70). It is impossible to detect these low-frequency radio signals from the Earth due to the influence of the Earth’s ionosphere. However, after taking care of the essential factors properly, e.g. the foreground and interference, a future radio telescope in lunar orbit or on the farside surface of the Moon has a chance of detecting the global 21 cm signals impacted by accreting PBHs and distinguishing them from the standard model.

Hyperspectral polarimetry of eight Apollo soils

The reflected light from the lunar surface is polarized and contains perpendicular (I⊥) and parallel (I∥) branches. To provide supporting data for the first polarimetric camera (PolCam) on board the Korean Pathfinder lunar orbiter, in this work, we built a polarimeter and measured the polarized spectra for eight Apollo soils that span a wide range in composition and maturity. We found a linear correlation between reflectance R and the difference of perpendicular and parallel branches: R+a′⋅(I⊥−I∥)=b′, and b’ might be sensitive to the grain size of lunar soils. The regression coefficient b’ can be derived from both positive and negative polarization spectra and has little dependence on wavelength, thus it has great potential in estimating grain size for lunar soils. We also used radiative transfer equations to calculate the real index of optical constants and to reproduce the perpendicular and parallel polarized spectra for the lunar soils. We correlated polarimetry indexes including polarization degree (P=(I⊥−I∥)/(I⊥+I∥)) and the difference of the perpendicular and parallel branches (I⊥−I∥) with the abundances of FeO and TiO2 and soil maturity, and our result indicates that these two polarimetry indexes show dependence on both the compositions and soil maturity.

The Creation of Moon: Comparative Analysis between Modern Sciences and Religious Studies

Curiosity is among the pre-eminent traits of human beings that differentiates them from other species. The majority of human beings believe in a religion that provides them with standards to be followed in this world and knowledge about the hereafter. Holy scriptures as a source of guidance also provide profound knowledge about the universe, its beginning and end, its solar and lunar systems, orbits and functions and other aspects. Modern science and its discoveries sometimes contradict the premises mentioned in religious theology, which need a rational outlook acceptable to the people with a scientific approach along with a theological perspective. In Islamic cosmological perspective, it is believed that Allah Almighty made two stars in the early days for the planet earth. The moon was also a shining star emitting light from the day first. It was a source of light by itself, not merely reflecting the light of the sun. In parallel to these divine theories, various scientific theories also explain the creation of the moon. Prominent among these are the Giant Impactor, Co-Accretion, and the Capture theory. The present research fills the knowledge gap and provides concrete and rationalized information regarding the creation of the moon in religion and modern science.

Перспективы применения околоземной ГНСС в качестве инфраструктуры для навигационного обеспечения лунных миссий

An increasing number of space agencies consider Moon exploration as a part of national and international space programs. Exploration plans include a distributed network of facilities on and around the Moon; opportunities for “driving force” projects based on the International Space Station program experience; and, on the whole, formation of the “Earth – low lunar orbit – Moon surface” payload traffic flow. The payload needs analysis shows that the cutting-edge Moon exploration program requires high quality navigation services (precise estimation of coordinates and velocity in near-real time). The subject of this paper is the issues of creating a navigation service based on the experience of the Russian segment of ISS and using the existing near-Earth GNSS systems as a navigation infrastructure.

Shape-Based Approach for Low-Thrust Earth–Moon Trajectories Initial Design

A robust finite Fourier series (R-FFS) approach is developed for fast generation of Earth–moon trajectories using continuous low thrust. Each component of the position vector is approximated using a finite Fourier series as a function of time; these approximations are then used to design a trajectory that satisfies the equations of motion and the constraints, at discrete points, as well as the problem boundary conditions. The R-FFS method leverages the three-body problem characteristics to achieve all the required plane change without the use of propulsion. The trajectory is divided into phases: escape, intermediate, and capture. The escape phase is further divided into segments. The phase of the trajectory near the L1 Lagrange point is designed first and is always a thrust-free phase. This thrust-free phase is optimized to achieve the required plane change, enabling planar trajectories in the other phases. The initial guess needed by the solver, in the escape and capture phases, is generated using an analytic approximation developed in this paper. The numerical results show that the R-FFS can generate three-dimensional transfers to high lunar orbits, low lunar orbits, and halo orbits, while meeting constraints on the maximum thrust level of the engine.

Trans-Earth insertion method based on the reversedEarth-to-Moon transformation

<p indent=0mm>The Moon-to-Earth transformation is the reversed procession of the Earth-to-Moon transformation. Thus, the trans-Earth insertion method based on reversing the Earth-to-Moon transformation is proposed. The trans-Earth insertion is obtained by using the intersection of the low lunar orbit and Moon-to-Earth transformation orbit and adjusting the scale for the height of the low lunar orbit’s perigee. The optimal inclination of the trans-Earth insertion orbit is analytically obtained by minimizing the velocity increment and is proven by numerical searching. Based on the pulse results, the finite-force control parameter is also proposed for determining the optimal pitch angle. Finally, the trans-Earth insertion parameter is calculated by using a low lunar orbit, and the minimized velocity increment is found to not always be present for instances when the yaw angle is zero.

Analysis of the process of deployment of a lunar tether system taking into account the Earth's gravity

The development of space transport systems for the delivery of payloads and the study of the lunar surface is an important scientific and technical challenge. The article considers a near-lunar space tether system consisting of a station and a microsatellite. The station is considered as a rigid body having a cylindrical shape, and the microsatellite is considered as a spherical rigid body. The tether is considered as a weightless inextensible rod of variable length. The station moves in a near-lunar orbit, which is influenced by the Earth's gravity. The process of deployment of a radially directed near-lunar tether system is considered. The equations of motion of the space tether system are obtained using Newton's second law and the theorem on the change in the angular momentum. To release the tether and bring the orbital tether system to a working state, the article proposes to use the control program of tethers tension force, which ensures the deployment of the tether system to a position close to the vertical. A comparison of the motion of the tether system along the unperturbed lunar orbit and along the perturbed one, taking into account the gravitational influence of the Earth, is made. To substantiate the theoretical results, a numerical simulation was carried out, based on the results of which a conclusion was made about the influence of the Earth's gravity on the amplitude of oscillations of the microsatellite relative to the local vertical.

Petrology and geochemistry of lunar feldspathic meteorite Northwest Africa 11111: Insights into the lithology of the lunar farside highlands

AbstractWe performed a petrological, mineralogical, and geochemical study of the lunar feldspathic meteorite Northwest Africa (NWA) 11111. This meteorite contains several types of lithic clasts, including feldspathic clasts, mafic‐rich clasts, granulites, impact melt breccias, minor basaltic clasts, and highly evolved clasts cemented in a recrystallized fine grain matrix. Both mineral chemistry and geochemical characteristics indicate a lunar origin for NWA 11111. The bulk analysis suggests that NWA 11111 is a typical feldspathic lunar meteorite, which is consistent with its large population of anorthositic clasts and plagioclase fragments. A comparison of geochemical data made by lunar orbiter missions indicates that this meteorite was likely launched from the Feldspathic Highland Terrane on the lunar farside. The chemical zoning, coupled with extensive exsolution lamellae (up to 20 μm in width) occurring in pyroxene across three sections of NWA 11111, demonstrates that this meteorite contains components derived from the surface to about 10 km of lunar crust. Magnesian anorthosite clasts are commonly present in the meteorite, indicating that magnesian anorthosite probably represents an important lithology in the lunar farside crust. Basaltic clasts in NWA 11111 range from a very low‐Ti to a low‐Ti mare basalt, possibly representing cryptomare on the lunar farside. Although a KREEPy signature for NWA 11111 is not evident, highly evolved clasts containing various silica polymorphs and/or K‐feldspar are present. They may originate from late‐stage residual liquids. Lithic clasts and mineral fragments within NWA 11111 provide new insights into the diversity of lunar crust lithology and magmatic processes on the lunar farside. This meteorite also offers rocky materials from a wide vertical section of lunar crust.

Practical Algorithms on Lunar Reference Frame Transformations for Korea Pathfinder Lunar Orbiter Flight Operation

This technical paper deals the practical transformation algorithms between several lunar reference frames which will be used for Korea pathfinder lunar orbiter (KPLO) flight operation. Despite of various lunar reference frame definitions already exist, use of a common transformation algorithm while establishing lunar reference frame is very important for all members related to KPLO mission. This is because use of slight different parameters during frame transformation may result significant misleading while reprocessing data based on KPLO flight dynamics. Therefore, details of practical transformation algorithms for the KPLO mission specific lunar reference frames is presented with step by step implementation procedures. Examples of transformation results are also presented to support KPLO flight dynamics data user community which is expected to give practical guidelines while post processing the data as their needs. With this technical paper, common understandings of reference frames that will be used throughout not only the KPLO flight operation but also science data reprocessing can be established. It is expected to eliminate, or at least minimize, unnecessary confusion among all of the KPLO mission members including: Korea Aerospace Research Institute (KARI), National Aeronautics and Space Administration (NASA) as well as other organizations participating in KPLO payload development and operation, or further lunar science community world-wide who are interested in KPLO science data post processing.

Science Missions of the Korean Lunar Exploration Program

The Korea Pathfinder Lunar Orbiter (KPLO), which is the Korean first lunar and space exploration spacecraft, will be launched in August 2022 and arrive in a lunar orbit in December 2022. The KPLO will carry out nominal missions while in a lunar polar orbit an ~100-km altitude for one year. The KPLO has five lunar science mission payloads and one technology demonstration payload in order to achieve their own science and technology goals. The science payloads consist of four Korean domestic instruments and one internationally collaborated science instrument for scientific investigations on the lunar surface and in a space environment. The Korean dometstic science instruments are the gamma-ray spectrometer named KGRS, the wide-angle polarimetric camera named PolCam, the fluxgate magnetometer named KMAG, and the high resolution camera named LUTI. The name of the internationally collaborated science instrument is ShandowCam, which was developed by Arizona State University, U.S., and funded and managed by NASA. The science data acquired by the science payloads will be released to the public in order to enhance scientific and educational achievements. The science data acquired by each science instrument will be archived and released through the web sites of the KPDS (KARI Planetary Data System) for the Korean science instruments and the NASA PDS (Planetary Data System) for the internationally collaborated science instrument.

Trajectory optimization for the Horyu-VI international lunar mission

The Horyu-VI nano-satellite is an international lunar mission with the purpose of studying the lunar horizon glow (LHG)—a still unclear phenomenon caused by electrostatically charged lunar dust particles. This study analyzes the mission trajectory with the hypothesis that it is launched as a secondary payload of the NASA ARTEMIS-II mission. In particular, the effect of the solar gravity gradient is studied; in fact, depending on the starting relative position of the Moon, the Earth, and the Sun, the solar gradient acts differently on the trajectory—changing it significantly. Therefore, the transfer and lunar capture problem is solved in several cases with the initial Sun–Earth–Moon angle as the key parameter. Furthermore, the inclination with respect to the Moon at capture is constrained to be equatorial. Finally, the problem of stabilization and circularization of the lunar orbit is addressed in a specific case, providing an estimate of the total propellant cost to reach the final orbit around the Moon.

Application of a high-precision calibration technology for lunar liftoff and verification using Chang&amp;rsquo;E-5 mission

<p indent=0mm>Chang’E-5 explorer landed on the lunar surface on December 1, 2020, Beijing time, completed China’s first lunar surface sampling, lunar surface liftoff, and lunar orbital rendezvous and docking, and then returned to the Earth successfully. Accurate positioning of the lander and ascending vehicle assembly are the key to the success of lunar liftoff and as well as lunar orbital rendezvous and docking. Aiming at fulfilling the requirement of high-precision calibration of lunar liftoff of the lander and ascending vehicle assembly of Chang’E-5 mission, the method of using a “three-way ranging and Doppler system + VLBI interferometry system” to realize high precision of a landing position is proposed herein. Then, a high-precision determination algorithm for the lunar liftoff datum mark is provided. Using 20-min observables of Chang’E-5 mission after landing, the landing location of the lander and ascending vehicle assembly could be calculated rapidly, which was 43.0595°N and −51.9214°E, having a −2446-m elevation. Results showed that the difference between the positioning results obtained using the tracking data only <sc>20 min</sc> after landing and the lunar reconnaissance orbiter (LRO) image data provided by NASA was <sc>180 m.</sc> When only longitude and latitude were calculated and elevation was obtained from the lunar digital elevation model, the difference between the positioning result and LRO image data was<sc>97 m,</sc> which could be effectively used as the lunar surface liftoff datum mark. Using <sc>48-h</sc> observables after landing, the landing location of the lander and ascending vehicle assembly was 43.0594°N and −51.9167°E, having a −2550-m elevation, with a difference of only <sc>60 m</sc> compared with the results of LRO.