Some Comments on the Protection of Lunar Habitats against Damage from Meteoroid Impacts

The establishment of human habitats on the Moon and on Mars will require protecting them from the hazards of near-Earth and interplanetary space. In addition to solar radiation, another hazard to be faced by these habitats is the damage that can result from the high speed impact of a meteoroid on a critical structural component. Therefore, lunar habitats and their accompanying support facilities need to be designed with adequate levels of protection that will allow them to also withstand the damage that can result from a meteoroid impact. In this paper we discuss some approaches to shielding for lunar habitats, focusing on shielding that is intended primarily to provide protection against meteoroid impacts and on shielding approaches that use resources mined or extracted from the Moon. The Moon’s mineralogy is discussed and suggestions are presented for materials and material combinations that can be used to develop shielding for lunar habitats and which are comprised primarily or entirely of lunar materials. Several shielding mechanisms are also presented that could be effective against impacts by meteoroid particles having diameters on the order of that which are likely to strike a fairly large lunar habitat at least one or two times per year. The paper concludes with recommendations for continuing work in optimizing the design of meteoroid shielding for lunar habitats.     

Structural Design of a Lunar Habitat

A lunar base is an essential part of all the new space exploration programs because the Moon is the most logical first destination in space. Its hazardous environment will pose challenges for all engineering disciplines involved. A structural engineer’s approach is outlined in this paper, discussing possible materials and structural concepts for second-generation construction on the Moon. Several different concepts are evaluated and the most reasonable is chosen for a detailed design. During the design process, different solutions—for example, for the connections—were found. Although lunar construction is difficult, the proposed design offers a relatively simple structural frame for erection. A habitat on the Moon can be built with a reasonable factor of safety and existing technology. Even so, we recognize the very significant difficulties that await our return to the Moon.     

Construction of Pressurized, Self‐Supporting Membrane Structure on Moon

This paper draws attention to the importance of readiness time (i.e., the time it takes to develop the necessary supporting infrastructure on the Moon for the structure to be ready for use) of a lunar structure. It illustrates a rational process of determining readiness time using for an example the pressurized self‐supporting membrane structure (PSSMS), a concept proposed in 1989. To assess manpower requirement for construction, it is necessary to assess the productivity of a construction crew on the Moon, taking into consideration the hazardous conditions they confront, and the encumbrances due to the use of space suits and other protective systems. These handicaps can be compensated to some extent by making maximum use of mechanical and automatic equipment. The procedure adopted here is to determine the manpower requirement for a similar construction on Earth, then adjust it to the conditions on the Moon. Once the productivity factor relative to Earth is determined, the manpower requirement for lunar construction can be assessed.     

Considerations for Return to the Moon and Lunar Base Site Selection Workshops

The establishment of a lunar base with a permanent human presence is on the horizon. The scientific importance of the Moon and the potential use of local resources at a lunar base provide valuable concepts to consider. Importantly, there are significant ideas, concepts, and reports from the past, the products of a wealth of “mental calorie” inputs, which should be reconsidered; herein, many of these are placed within an historical perspective, in hopes that we may learn by our past experiences. The 1994 Clementine mission, its instrumentation and returned data, provides the first global coverage of the composition, structure, and topography of the Moon. The planned 1997 Lunar Prospector will add significantly to this database. These new global data are requisite for the selection of a lunar base. It is paramount to consider thoroughly the rationale for site selection, and much of the groundwork for this rationale has already been performed. The selection process should be led by a strategic purpose or vision that considers (1) scientific objectives, both on the Moon, as well as from the Moon (e.g., astronomy); (2) resource utilization; and (3) operational considerations, both orbital and surface. Many of the relationships between these factors were explored during workshops convened at Johnson Space Center by the National Aeronautics and Space Administration (NASA) in April and August 1990. However, these workshops have not resulted in official, catalogued NASA publications. The merits of numerous potential sites were analyzed in terms of lunar geoscience, geophysics, space physics, astronomy, and lunar resources, as well as operational constraints. The considerations and recommendations of the NASA Site Selection Committee should provide the basis for a realistic site selection for a human presence at an outpost on the lunar surface.     

Lunar Astronomical Observatories: Design Studies

The best location in the inner solar system for the grand observatories of the 21st century may be the Moon. A multidisciplinary team including university students and faculty in engineering, astronomy, physics, and geology, and engineers from industry is investigating the Moon as a site for astronomical observatories and is doing conceptual and preliminary designs for these future observatories. Studies encompass lunar facilities for radio astronomy and astronomy at optical, ultraviolet, and infrared wavelengths of the electromagnetic spectrum. Although there are significant engineering challenges in design and construction on the Moon, the rewards for astronomy can be great, such as detection and study of Earth‐like planets orbiting nearby stars, and the task for engineers promises to stimulate advances in analysis and design, materials and structures, automation and robotics, foundations, and controls. Fabricating structures in the reduced‐gravity environment of the Moon will be easier than in the zero‐gravity environment of Earth orbit, as Apollo and space‐shuttle missions have revealed. Construction of observatories on the Moon can be adapted from techniques developed on the Earth, with the advantage that the Moon's weaker gravitational pull makes it possible to build larger devices than are practical on Earth.     

Cable‐Based Lunar Transportation System

The establishment of an efficient transportation system is key to any human development on Earth or in space. Different technologies for transporting humans and goods have been developed, the diversity of which indicates that individual concepts have specific strengths and weaknesses. So far, transportation on the Moon has utilized a wheel‐based vehicle, the lunar rover. Present concepts for transporting goods and people in a lunar base of the future are generally based on using wheels and traction. While such systems have many advantages for a variety of applications, the hauling of heavy goods will require the preparation of stable and trafficable roadways, a challenging and potentially expensive undertaking. This paper presents an alternative based on using one of the fundamental means to move objects, namely ropes and cables. Because of their inherent characteristics, ropes have been used to lift and haul heavy loads for long distances with high levels of reliability. This mature and constantly perfected technology, not well known in this car‐oriented society, has been investigated for its use as a true alternative to the traditional wheel‐based transportation systems. As will be shown, innovative applications of cable‐based technologies may in effect provide many opportunities to leverage the differences between the Earth and the Moon for the purpose of creating efficient engineering products.     

Interlune-Intermars Business Initiative: Returning to Deep Space

The corporate vision of a proposed Interlune-Intermars Initiative encompasses commercial enterprises related to resources from space that support the preservation of the human species and our home planet. Within this vision, the major mission objectives of the Initiative are to provide investors with a competitive rate of return; protect the Earth's environment and expand the well-being of its inhabitants by using energy from space, particularly lunar 3He, as a major alternative to fossil and fission fuels; develop resources from space that will support future near-Earth and deep-space activities and human settlement; and develop reliable and robust capabilities to launch payloads from Earth to deep space at a cost of $1,000∕kg or less (1996 dollars). Attaining a level of sustaining operations for the core fusion power and lunar resource business of the Initiative requires about 15 years and 10–$15 billion of private investment capital as well as the successful marketing and profitable sales of a variety of applied fusion technologies.     

Engineering Issues for Early Lunar‐Based Telescopes

A telescope on the Moon is needed for astronomy and can be constructed in this decade or early in the next century. Design for this telescope will be fundamentally different from the design of free‐flying telescopes. Its design will be more like the new Keck telescope being completed on a mountaintop in Hawaii than the Hubble Space Telescope, in low Earth orbit. Success of the lunar‐based telescope will depend on an appropriately engineered structure, a suitable interface (foundation) in the lunar soil, and a carefully thought out construction process. Participation of engineers in identifying and resolving issues for this extraterrestrial engineering and construction project is a natural extension of the traditional engineering role, and will prepare the engineering and construction communities for the subsequent greater challenges associated with basing on the Moon. These communities need to document now the types of data and information that NASA should obtain in the next early lunar missions so that construction on the Moon will be facilitated.     

欧洲固体氧化物燃料电池（SOFC）产业化现状

固体氧化物燃料电池（SOFC）具有燃料适用范围广、能量转换效率高（发电效率40%～60%，综合能效≥80%）、全固态结构、模块化组装、零污染等优点，作为固定式或分布式发电可增强电网清洁供电的能力、安全性、可靠性和稳定性。SOFC具有多种不同的结构，其发电规模覆盖几十瓦至百兆瓦，可根据不同的应用场景选择不同的结构，应用场景主要包括固定式发电、分布式供电、热（冷）电联供、交通车辆辅助动力电源等领域。国内的SOFC技术发展较晚，目前已取得一定的研究进展，并且能够自主研发出十几千瓦的SOFC发电系统，但与国际领先水平还有很大的差距，主要体现在输出功率、生产成本及使用寿命等方面。欧洲的SOFC技术处于国际领先水平，具有一批成功实现产品化的公司，通过对其技术和产品的调研，可深入的了解欧洲SOFC技术现状和发展趋势，为国内SOFC技术的发展提供借鉴作用。      

Concept of Adaptability in Space Modules

The space program is aiming towards the permanent use of space; to build and establish an orbital space station, a Moon base and depart to Mars and beyond. We must look after the total independency from the Earth's natural resources and work in the design of a modular space base in which each module is capable of duplicating one natural process, and that all these modules in combination take us to conceive a space base capable of sustaining life. Every area of human knowledge must be involved. This modular concept will let us see other space goals as extentions of the primary project. The basic technology has to be defined, then relatively minor adjustments will let us reach new objectives such as a first approach for a lunar base and for a Mars manned mission. This concept aims towards an open technology in which standards and recommendations will be created to assemble huge space bases and spaceships from specific modules that perform certain functions, that in combination will let us reach the status of permanent use and exploration of space.     

Space Solar Power: A Major New Energy Option?

Large space solar-power systems have intermittently been a topic for consideration during the past 30 years. However, the last major studies in the United States on these concepts were conducted in the late 1970s. After two decades of relative inactivity, large-scale space solar power (SSP), including the generation of solar power in space for transmission to terrestrial markets, has recently reemerged as a potential energy option. This occurrence is timely because global energy demand continues to grow dramatically while environmental concerns increase. Demand for power in space is also likely to increase during the same time frame. A wide range of technology advances would be needed to enable such systems. In addition to very low cost space transportation and highly efficient and high voltage solar arrays, significant developments must also take place in technologies such as wireless power transmission, large space structures, robotic assembly and maintenance, and others. However, recent NASA studies and focused research and development progress in a number of key areas suggest that such systems are technically feasible. This paper presents an overview of the subject of space solar power, including results of recent NASA activities.     

Technical Issues for Lunar Base Structures

The establishment of a permanent human presence on other planets will require establishing permanent infrastructure in new environments. Civil engineers select, define, and implement solutions to infrastructure design problems in unique environmental contexts. Wind and seismic loading are two examples of constraints long familiar to terrestrial civil engineering. Designing structures for lunar exploration, development and eventual settlement will make use of the same design processes already practiced by the civil engineering profession. However, the extensive experience base resulting from centuries of terrestrial work does not adequately prepare civil engineers for the unprecedented constraints and environmental conditions that are encountered in space. The limited knowledge we already have about the Moon (mostly from the Apollo program) is a place to start. By assimilating and working with this knowledge, those pursuing the design of lunar base structures can begin to produce realistic and valid design solutions. The paper presents technical, operations, and programmatic issues that the writers consider fundamental to understanding the facts of life in this promising new design arena.     

Behavior of Compacted Lunar Simulants Using New Vacuum Triaxial Device

Development and study of mechanical properties of engineering materials from locally available materials in space is a vital endeavor toward establishment of bases on the Moon and other planets. The objectives of this study are to create a lunar simulant locally from a basaltic rock, and to design and develop a new vacuum triaxial test device that can permit testing of compacted lunar simulant under cyclic loading with different levels of initial vacuum. Then, triaxial testing is performed in the device itself without removing the compacted specimen; this is achieved by a special mechanism installed within the device. Preliminary constrained compression and triaxial shear tests are performed to identify effects of initial confinements and vacuums. The results are used to define deformation and strength parameters. At this time, vacuum levels up to 10?4 are possible; subsequent research should involve higher vacuum levels, e.g., 10?14?torr as they occur on the Moon. The research can have significant potential toward development of methodology so as to develop compacted materials for various construction applications, and also toward stress‐strain‐strength testing of lunar simulants with different vacuum levels.     

Preparing to Bridge the Lunar Gap

The United States is committed to the exploration of and the expansion into space. A manned earth‐orbiting space station is planned for the next decade and studies continue looking at manned lunar bases. Appropriate planning should be initiated for such a mission now as a high national priority. Many systems must be examined and technologies developed as soon as possible. Some of these include types of power sources, life support systems, construction equipment and techniques, construction methods, lunar mapping, and logistical constraints.     

Global Rural Electrification: A Different Race Initiative

“Perhaps the single greatest contribution that could be made to environmental conservation would be the invention of a satisfactory fuel‐wood substitute” for developing nations. Providing electric power from orbit under a program of energy as foreign aid to developing nations will benefit the local and global environment and people living on the margins of existence, and it will provide technically challenging jobs to the engineers and scientists of all the nations that undertake such a massive project. Civil engineers can, if they and their professional societies so choose, play a significant, if not integral, role in using the resources of Earth and its surroundings for the benefit of mankind under a program of energy from space. This paper extends the concepts from a previous work by the writer to global rural electrification based on electric power from power stations, built in geosynchronous orbit out of lunar materials, distributed to individual villages and rural electric cooperatives via microwaves for a cost of between 6 cents and 45 cents per kilowatt‐hour. Power would be available in modular increments of 25–100 kilowatts with an average capital cost as low as $5,000 per kilowatt. The goals of the program for global rural electrification are twofold: to provide electric power from space at competitive costs, relative to current costs, to rural and agricultural areas, and to divert resources from weapons development to infrastructure development. The potential for involvement by civil engineers is limited only by their own lack of vision and daring.     

Model for Granular Materials with Surface Energy Forces

In light of environmental differences (such as gravitational fields, surface temperatures, atmospheric pressures, etc.), the mechanical behavior of the subsurface soil on the Moon is expected to be different from that on the Earth. Before any construction on the Moon can be envisaged, a proper understanding of soil properties and its mechanical behavior in these different environmental conditions is essential. This paper investigates the possible effect of surface-energy forces on the shear strength of lunar soil. All materials, with or without a net surface charge, exhibit surface-energy forces, which act at a very short range. Although, these forces are negligible for usual sand or silty sand on Earth, they may be important for surface activated particles under extremely low lunar atmospheric pressure. This paper describes a constitutive modeling method for granular material considering particle level interactions. Comparisons of numerical simulations and experimental results on Hostun sand show that the model can accurately reproduce the overall mechanical behavior of soils under terrestrial conditions. The model is then extended to include surface-energy forces between particles in order to describe the possible behavior of lunar soil under extremely low atmospheric pressure conditions. Under these conditions, the model shows that soil has an increase of shear strength due to the effect of surface-energy forces. The magnitude of increased shear strength is in reasonable agreement with the observations of lunar soil made on the Moon’s surface.     

Space Solar Power: An Assessment of Challenges and Progress

The capability to generate power in space for transmission to terrestrial markets is a long-term visionary goal that embodies a wide range of technical challenges. Space solar-power (SSP) systems will be very large, but they must be affordable if they are to be developed some day. Addressing the technologies required to construct gigawatt-class, commercial “solar-power satellites” in the distant future can open many other applications opportunities in space and on Earth in the near future. Technical hurdles have been explored and characterized by NASA's recent SSP Exploratory Research and Technology Program. The strategic technology areas examined include solar power generation; wireless power transmission; onboard power management and distribution; structural concepts, materials, and controls; and others. Important progress has been achieved since major space power system studies were conducted in the 1970s. However, significant and highly challenging research and technology development must be conducted successfully across a wide range of areas so that affordable and abundant SSP can be realized.     

Atmospheric Pressure within Lunar Structure

Design and construction of a structure on the Moon requires addressing a host of issues not encountered on Earth. Since there is no atmosphere on the Moon, a lunar structure must contain an artificial atmosphere. One critical design issue is the magnitude of the pressure of this atmosphere. Much of the current literature on the design of lunar structures assumes a pressure of 101.3 kPa (14.7 psi), corresponding to that at sea level on Earth, which is an order of magnitude larger than any other loading on the structure. An assessment of the outcome of lowering the internal pressure for a lunar structure is presented that accounts for human physiology, plant growth, mechanical equipment for gas circulation, structural aspects, leak rate, decompression, flammability, combustion, and economic issues. Options for the magnitude and content of an internal atmosphere for a lunar structure are given. Results clearly show that there is a great savings if the pressure is lowered by an amount that does not greatly affect the inhabitants' physiology or safety.     

Indigenous Resource Utilization in Design of Advanced Lunar Facility

The most important consideration in the establishment and support of a permanently manned lunar base will be resource utilization. Seven potential lunar construction materials were analyzed with respect to their physical properties, processes, energy requirements, and resource efficiency. Reviewing the advantages and disadvantages of each material led to the selection of basalt as the primary construction material for initial use on a lunar base. The team conceptualized a construction system that combines lunar regolith sintering and casting to make pressurized structures. The design uses a machine that simultaneously excavates and sinters the lunar regolith to create a cylindrical hole. The hole is then enclosed with cast basalt slabs, allowing the volume to be pressurized for use as a living or work environment. Cylinder depths up to 4–6 m in the lunar mare and 10–12 m in the lunar highlands can be achieved. Advantages identified in the construction system include maximum resource utilization, relatively large habitable volumes, interior flexibility, and minimal construction equipment needs. The conclusions of this study indicate that there is significant potential for the use of basalt as a low‐cost alternative to Earth‐based materials. It remains to be determined, during lunar base phasing, whether this construction method should be implemented.     

Lunar Dust Levitation

Observations of a lunar “horizon glow” by several Surveyor spacecraft on the lunar surface in the 1960s and detections of dust particle impacts by the Apollo 17 Lunar Ejecta and Meteoroid Experiment have been explained as the result of micron-sized charged particles lifting off the surface. The surface of the Moon is exposed to the solar wind and solar UV radiation causing photoemission, so it develops a surface charge and an electric field near the surface. Dust particles injected into this plasma from the lunar regolith, whether from human and mechanical activity or from meteoroid impacts or electrostatic forces, may be stably levitated above the surface and may undergo preferential deposition onto areas of the lunar surface (or equipment) with different electrical properties. This can lead to a net transport as well as contamination of sensitive equipment. This paper reports on new experimental measurements and numerical simulations of the plasma environment above the lunar surface and the related behavior of charged dust.