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.     

Lunar Habitat Micrometeoroid and Radiation Shielding: Options, Applications, and Assessments

Various shielding approaches to protect lunar habitats from micrometeoroid and radiation hazards present major trade-off considerations. Popular scenarios that envision covering modules with in situ regolith will necessitate means to excavate and move large amounts of material; will complicate evolutionary outpost growth; and may require long tunnels between connecting pressurized elements. Strategies that incorporate shielding materials into module structures or internal shelters add very substantial launch mass penalties. Utilization of water bladders can make efficient use of consumable/recyclable supplies, but may impose excess capacity deliveries at early development stages. This paper addresses these different shielding approaches from a top-level application perspective, highlighting pros and cons of each. Examples draw upon research and design investigations undertaken by the Sasakawa International Center for Space Architecture in support of separate National Aeronautics and Space Administration (NASA) contracts awarded to teams headed by Boeing and ILC-Dover for a “Minimum Functionality Habitation Systems Concept Study.” Comprehensive team study results were presented to NASA in February 2009, and have been released as public information.     

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.     

Hypervelocity Impact Penetration Phenomena in Aluminum Space Structures

All long‐duration spacecraft are susceptible to high‐speed impacts by meteoroids and pieces of orbiting space debris. Damage to critical spacecraft systems caused by such impacts can lead to spacecraft failure and loss of life. In order to develop adequate protection against penetration for crew compartments and other critical spacecraft systems, an aerospace design engineer must possess a full understanding of the penetration mechanics involved in the hypervelocity impact loading of a variety of structural components. This paper describes the results of an experimental investigation of the penetration phenomena associated with oblique hypervelocity projectile impact of aluminum dual‐wall structures. Equations that quantitatively describe these phenomena are obtained through a regression of hypervelocity impact test data. These equations characterize observed penetration phenomena as functions of the geometric and material properties of the impacted structure and the diameter, obliquity, and velocity of the impacting projectile. A review of the test data shows that oblique hypervelocity impact penetration phenomena are strongly dependent on impact obliquity and therefore can differ significantly from those associated with normal high‐speed impacts. It is concluded that the possibility of non‐normal impacts and their effects on structural integrity must be considered in the design of any structure that is to be exposed to the hazardous meteoroid and space debris environment.     

Silicon PV Cell Production on the Moon

A concept has been developed for the production of photovoltaic energy collection systems on the Moon by vacuum deposition directly onto the lunar surface. Using this technique it would be possible to quickly install quite large capacities of power on the Moon at relatively low cost. Most of the material required for photovoltaic devices is readily available on the Moon, and taking production machinery to the Moon can further lower the cost of power if the machinery can be operated for long periods of time. Low-cost energy on the Moon could enable a wide range of activities including support of robust human outposts, production of propellants for use on the Moon or for export, production of a wide range of other materials for use in space, and beaming of energy from the Moon to space and to Earth. A proposed strategy by which lunar power can be developed in the near future is closely connected to the establishment of a human outpost on the Moon.     

Analysis of Lunar-Habitat Structure Using Waterless Concrete and Tension Glass Fibers

The studies reported in this paper were undertaken to evaluate the maximum use of lunar in situ resources for surface construction, such as a habitat structure for a permanent manned lunar base. This type of activity is well into the future, but there are possible near-term applications that could utilize in situ resources for protection from radiation of surface power reactors, solar flares, and micrometeorite damage. “Waterless” concrete made of sulfur, a by-product material of oxygen and carbon extractions, is a viable alternative to hydraulic cement. Sulfur–lunar regolith concrete is an ideal material for building structures on the moon. Its availability, high strength, and durability properties make it a very attractive candidate for the development of the first lunar-construction activities. Regolith-derived glass rebar and fiber can also be used with “concrete” made with in situ regolith. Development of such habitats pose tremendous challenges that can be met by the combination of innovative design with cutting-edge technologies that are appropriate for planetary surface habitats with multiple applications for Earth and beyond.     

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.     

Projectile Shape and Material Effects in Hypervelocity Impact Response of Dual‐Wall Structures

All large spacecraft are susceptible to impacts by meteoroids and pieces of orbiting space debris. These impacts occur at extremely high speeds and can damage flight‐critical systems, which can in turn lead to catastrophic failure of the spacecraft. A long‐duration spacecraft developed for a mission into this environment must include adequate protection against perforation of pressurized components by such impacts. This paper presents the results of an investigation into the effects of projectile shape and material on the perforation of aluminum dual‐wall structural systems. Impact damage is characterized according to the extent of perforation, crater, and spall damage in the structural systems as a result of hypervelocity projectile impact loadings. Analysis of the damage data shows that there are distinct differences in impact damage from cylindrical and sherical projectiles. Projectile density is also found to affect the type and extent of damage sustained by dual‐wall structural systems.     

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.     

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.