Lunar Dust on Heat Rejection System Surfaces: Problems and Prospects

<div class="htmlview paragraph">The increasing need for higher electrical power levels for military and scientific space purposes has spurred development of energy conversion systems with higher efficiencies than the traditional solar array. Numerous nuclear options are currently under development. These fuels eliminate the need for large deployable solar arrays or concentrators, allow unrestricted pointing and maneuvering, and are inherently less susceptible to natural and threat environments; they are the only viable energy source for outer planetary exploration. Fission reactors are the most desirable nuclear source for electric power levels above 10 kW. Radioisotope sources have been used in conjunction with thermoelectrics up to 1 kWe for planetary exploration. However, for radioisotope systems in the 1 to 10 kWe range, a much higher conversion efficiency is required. For over 15 years, NASA and the Department of Energy (DOE) have been developing closed cycle turbo-alternator (dynamic) power conversion systems for space use. The Air Force and DOE are jointly developing such a system under the Dynamic Isotope Power System (DIPS) program.</div> <div class="htmlview paragraph">Two closed dynamic cycles are being evaluated for use as part of the DIPS system. They are the Closed Brayton Cycle (CBC) which uses an inert (single phase) gas as the working fluid. The other system is the Organic Rankine Cycle (ORC) which utilizes the phase change properties of the working fluid. Each has a significantly different effect on the design of a radiative heat rejection system, primarily because of the temperature variation of the CBC single phase heat rejection versus the nearly constant temperature two-phase (condensing) ORC heat rejection. The heat rejection system plays an important role, since the power conversion efficiency is strongly dependent on the heat rejection temperature. The lower the rejection temperature, the higher the efficiency. However, the radiator area requirement increases as the rejection temperature is reduced. On a weight optimization basis both systems are comparable, however, the ORC system requires more radiator area for the same cycle efficiency. With the design requirement that the radiator be mounted around the circumference of the vehicle, available area is limited. Therefore, the heat rejection system design may not be a clear-cut weight optimization but rather a matter of area reduction at minimum penalty to efficiency and weight.</div> <div class="htmlview paragraph">The paper presents the results of an optimization study performed on the heat rejection system for a space based ORC power system using an isotope heat source. The radiator sizing depends on the heat rejection temperature, radiator configuration, and radiator properties such as the fin effectiveness, emissivity, and absorptivity. The optimization analysis to evaluate the effect of each of these parameters on the system weight and area is presented.</div>

Heat rejection with mechanical pumped cooling loop for lunar surface nuclear reactor power system

This paper describes potential heat rejection design concepts for lunar surface Brayton power conversion systems. Brayton conversion systems are currently under study by NASA for surface power applications. Surface reactors may be used for the moon to power human outposts enabling extended stays and closed loop life support. The Brayton Heat Rejection System (HRS) must dissipate waste heat generated by the power conversion system due to inefficiencies in the thermal-to-electric conversion process. Space Brayton conversion system designs tend to optimize at efficiencies of about 20 to 25 percent with radiator temperatures in the 400 K to 600 K range. A notional HRS was developed for a 100 kWe-class Brayton power system that uses a pumped water heat transport loop coupled to a water heat pipe radiator. The radiator panels employ a tube and fin construction consisting of regularly-spaced circular heat pipes contained within two composite facesheets. The water heat pipes interface to the coolant through curved sections partially contained within the cooling loop. The paper evaluates various design parameters including radiator panel orientation, coolant flow path, and facesheet thickness. Parameters were varied to compare design options on the basis of H2O pump pressure rise and required power, heat pipe unit power and radial flux, radiator area, radiator panel areal mass, and overall HRS mass.

Modelling and optimization of a forced convection heat exchanger for Mars waste heat rejection for power cycle and cryocooling applications

Heat rejection design for zero liquid discharge Shand coal-fired power station integrated with CO2 capture and storage

The primary objective of the Mars Exploration Rover (MER) 2003 Project focused on the search for evidence of water on Mars. The launch of two identical flight systems occurred in June and July of 2003. The roving science vehicles are expected to land on the Martian surface in early and late January of 2004, respectively. The flight system design inherited many successfully features and approaches from the Mars Pathfinder Mission. This included the use of a mechanically‐pumped fluid loop, known as the Heat Rejection System (HRS), to transport heat from the Rover to radiators on the Cruise Stage during the quiescent trek to Mars. While the heritage of the HRS was evident, application of this system for MER presented unique and difficult challenges with respect to hardware implementation. We will discuss these hardware challenges in each HRS hardware element: the integrated pump assembly, cruise stage HRS, lander HRS, and Rover HRS. These challenges span the entire development cycle including fabrication, as...

This paper addresses heat rejection concepts intended to reject 100 W (or more) from the CPU of a desktop computer or server. A high-performance, air-cooled thermo-syphon heat rejection system is described that meets the goal. This concept is believed to represent the highest performance that has been reported for an air-cooled heat rejection system. A working fluid is boiled in a small chamber mounted on the CPU, and the vapor is condensed in the tubes of the remotely located air-cooled condenser. The air-cooled heat exchanger provides much higher performance than is obtainable with conventional round-tube technology. The boiling design is compared with other systems that have been proposed, e.g., liquid or two-phase cooling in micro-channels, and is shown to provide better performance. The heat exchange technology may also be applied to refrigerated cooling.

Titanium-water thermosyphons are being considered for use in heat rejection systems for fission power systems. Their proximity to the nuclear reactor will result in some gamma irradiation. Noncondensable gas formation from radiation-induced breakdown of water over time may render portions of the thermosyphon condenser inoperable. A series of developmental thermosyphons were operated at nominal operating temperature under accelerated gamma irradiation, with exposures on the same order of magnitude as that expected in 8 years of heat rejection system operation. Temperature data were obtained during exposure at three locations on each thermosyphon: evaporator, condenser, and condenser end cap. Some noncondensable gas was evident; however, thermosyphon performance was not affected because the noncondensable gas was compressed into the fill tube region at the top of the thermosyphon, away from the heat rejecting fin. The trend appeared to be an increasing amount of noncondensable gas formation with increasing gamma irradiation dose. Hydrogen is thought to be the most likely candidate for the noncondensable gas and hydrogen is known to diffuse through grain boundaries. Post-exposure evaluation of one thermosyphon in a vacuum chamber and at temperature revealed that the noncondensable gas diffused out of the thermosyphon over a relatively short period of time. Further research shows a number of experimental and theoretical examples of radiolysis occurring through gamma radiation alone in pure water.

This paper provides an overview of the Lunar Laser Ranging (LLR) experiments. The measurement principle is explained and its theory is derived. Both contributions, the direct reflected light from retroreflectors as well as the scattered light from the lunar surface are considered. The measurement results from the Sixties until 2007 are then compared between different LLR stations and with the theoretical forecast. The very first experiment was in 1962: a laser beam was directed to the Moon and the scattered light from the lunar surface was detected. The number of received photons was in line with the theory. Then from 1969 the laser beams were directed to retroreflectors placed by Apollo astronauts and Luna space crafts. Retroreflectors are on the one hand reference points for long term measurements; on the other hand they deliver a much stronger return signal compared to the scattered return. But none of the stations could measure the expected amplification of the retroreflectors. The number of received photons remained in line with measurements to the bare surface of the Moon. Therefore either all retroreflectors have degraded such that their return signals fit to the scattered return from the lunar soil or the measurements were indeed taken to the lunar surface only.

<div class="htmlview paragraph">Future space stations and platforms will require a centralized thermal utility to provide temperature control of various heat sinks or sources. Its purpose is to transport large amounts of energy over long distances towards a heat rejection system, with very small temperature differences.</div> <div class="htmlview paragraph">The present paper deals with the heat rejection system. A concept of a multi-tubes condenser has been selected and designed, using ammonia as the working fluid. In order to support and confirm the modelization software, an experiment is set up with a one-tube condenser uniformly cooled, involving limited heat power, but representative of thermo-hydraulic conditions.</div> <div class="htmlview paragraph">This paper presents the test programme. Objectives are first to confirm the selected technology, and to assess internal operation from the measurements of the external temperature along the tube, and differential pressure drop. The experiment which is thought out from an industrial viewpoint also has for purpose to enable simplifications in the modelization, without going into the condensation phenomenon. A description of the test apparatus is also given.</div> <div class="htmlview paragraph">A second condenser tube with asymmetrical cooling, more representative of the space concept (Og), will be tested to quantify the influence of the cooling device on the condensation of the fluid, and adapt the modelization to the space case.</div>

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.

Current Lunar dust mitigation techniques and future directions

Lunar soil simulants play a crucial role in scientific research, payload tests and in-situ resource utilization (ISRU) experiments. However, the currently available lunar soil simulants are either low in TiO2 content (≤3 wt%) or high in TiO2 content (≥6.7 wt%), despite orbital observations indicating lunar soils with moderate TiO2 content being widely distributed on the lunar surface. In December 2020, China's Chang'e−5 (CE-5) mission successfully returned a new mare soil sample characterized by high FeO content (22.5 wt%) and moderate TiO2 content (5.5 wt%), providing an opportunity to develop moderate-TiO2 lunar soil simulants. This study presents a newly developed simulant of the CE-5 lunar soil named IGG-01, which closely replicates the major physical and chemical properties of the CE-5 lunar soil. The median particle size of IGG-01 is 68.69 ± 4.44 μm, and its estimated specific surface area is 0.34 m2/g. It contains 17.6 wt% FeO and 4.8 wt% TiO2. It consists of pyroxene (49.3 wt%), plagioclase (40.9 wt%), ilmenite (6.1 wt%), and olivine (3.7 wt%), with specific gravity and bulk density are 3.33 g/cm³ and 1.86 g/cm³, respectively. The friction angle is 41.8°, and the cohesion is 19.2 kPa. It exhibits strong and weak reflectance absorption features in the 1 and 2 μm band centers. The physical properties of IGG-01 are also comparable to those of Apollo samples and typical lunar mare soil simulants. The unique chemical composition of IGG-01 makes it suitable for various scientific and engineering experiments, including but not limited to the study of dusty plasma migration, water formation via solar wind injection, oxygen preparation via hydrogen reduction, and tests involving the movement of rovers and excavation equipment.

Following the renewed interest in the volatile inventory of the Moon witnessed in the last decade, from both sample studies and data from orbital missions, it is timely to reassess the distribution and likely source(s) of light element volatiles (C, N, He, Ne, and Ar) in a diverse suite of lunar mare basalts and soils, providing new insights about volatiles indigenous to the lunar interior, volatiles produced <i>in situ</i> at the lunar surface, and volatiles delivered to and implanted into the lunar surface. Simultaneous static-mode mass spectrometric measurements of these key volatiles, extracted from the same aliquot of sample by high-resolution stepped combustion, enable a more detailed identification of the different volatile components present by comparing their varying release patterns across a range of temperature steps. Taken in context with other studies of different volatile elements, this new data contributes towards a greater understanding of the Earth-Moon system, with additional implications for future <i>in situ</i> resource utilisation at the lunar surface. <br><br> With an average δ¹⁵N value of +0.93 ± 9.39 ‰, the indigenous N component measured in mare basalts is most compatible with a CO carbonaceous chondrite source for nitrogen in the lunar interior, although some caveats exist. Variations in abundance and isotopic composition of indigenous nitrogen imply a heterogeneous lunar mantle. Assuming up to ~50 % loss of solar wind ³⁶Ar from lunar soils, nitrogen trapped in soils can be reconciled with up to 87 % being contributed from a non-solar source with an isotopic composition of between +87 ‰ and +160 ‰. <br><br> Noble gases in soils are dominated by solar wind components, with only minor amounts of cosmogenic neon being released at the highest temperature steps. In mare basalts, noble gases are a mixture of trapped, radiogenic, and cosmogenic components (from which cosmogenic production rates can be calculated and exposure ages for previously undated samples suggested

NASA's Artemis campaign is making heavy use of simulation to help return humans to the lunar surface by the end of the decade. There are several aspects of the lunar surface and its environment which must be accurately modeled before these simulations can be relied upon to influence decisions being made under these programs. Digital Lunar Exploration Sites, a paper submitted to the 2022 IEEE Aerospace Conference, outlined the process used to generate the lunar surface in a digital environment. This paper will expand upon this topic and delve into the steps being taken by the NASA Exploration Systems Simulations (NExSyS) team at NASA's Johnson Space Center (JSC) to properly verify and validate these simulations, with a focus on the visual aspects of the environment. Natural lighting validation relies in part on the wealth of data generated during the Apollo program. Many images taken by Apollo astronauts on the lunar surface have been replicated in the simulated environments to gain confidence in the accuracy of terrain and lighting models. However, because the environment the Artemis astronauts will experience at the Lunar South Pole (LSP) is dissimilar from the near-equatorial Apollo sites, other validation techniques must be applied. At the LSP, the sun crests only about 1.5 degrees above the horizon and when combined with the lack of a lunar atmosphere, lighting in this region is often very different than what a human would experience on Earth. Solar illumination, earthshine, human eye response, solar blooming, lunar regolith optical properties, and shadows cast by rocks and crater walls will play a significant role in an astronaut's ability to safely conduct an Extra-Vehicular Activity (EVA) or perform a traverse with a lunar rover. Approaches for validation of these aspects of the rendered LSP environment are considered in this paper. In addition to natural lighting, approaches for the validation of artificial lighting models at the LSP are discussed. The JSC Lighting Lab has been studying the illumination profile of the Exploration Informatics Subsystem (xINFO) lighting on the Exploration EVA Mobility Unit (xEMU). How these lights interact with the solar illumination and the shadows being cast on the lunar surface is of particular interest, so the validity of models representing these lights in a human-in-the-loop virtual reality environment becomes very important. This paper also touches on some of the simulation performance considerations when a Human in the Loop (HITL) is present, which drives the need for realtime rendering of the environment. Natural and artificial lighting will play a crucial role to decisions being made when planning and executing missions at the Lunar South Pole (LSP) and it is vitally important to understand the LSP environment before we return.