International Concrete Abstracts Portal

During the NASA 90-day study, in response to the President's statement on the space exploration initiative, the Jet Propulsion Laboratory conducted a study of potential astronomical observatories that could be situated on the lunar surface in conjunction with the lunar outpost. The scientific objectives were derived from the four NASA discipline management and operations working groups, several special workshops and symposia on lunar astrophysics, and the NASA Office of Space Science and Applications (OSSA). The overriding premise in selecting and defining the lunar observatories was that the moon must provide some unique advantage in performance, cost, or other significant parameter, such that the experiment could be executed better there than anywhere else. The unique properties of lunar siting include 1/6 gravity, a large stable platform, long continuous viewing times, and low nighttime temperatures. The four observatories were: a seven-element optical interferometer with a 1- to 2-km baseline; a seven-element submillimeter interferometer with coherent detectors and a 1-km baseline; a very low-frequency interferometer (ó 30 MHz) with 100 elements and a 200-km baseline on the lunar far side; and a gravitational wave detector with two 50-km arms, perhaps operating in conjunction with an earth-based gravitational detector. Advanced technology needs associated with the four observatories have been identified and include advances in optical delay lines and beam combiners, coherent heterodyne detectors, instrument cryogenic systems, and methods for construction on the moon, such as building foundations, trenching building roads, etc. In particular, the problems of construction and civil engineering commonplace on earth present a new class of problem for the lunar surface. The paper addresses some of these civil engineering needs and suggests precursor experiments that should be done to provide a firm basis for the construction of astronomical observatories on the moon.

Conventional structural engineering philosophy and experience can be inappropriate when it comes to designing structures for the moon. This paper illustrates the authors' adaptation of design philosophy for concrete, which involves changing the whole value system for this material. Far from being readily available, common, and plentiful, concrete will be an exotic and precious material on the moon. The use of concrete is proposed for such efficient structures as thin shell rather than the more common planar structures more suitable for earth. The structure containing one atmospheric pressure inside must be pressurized to resist such pressure, and a new value system must be derived.

The moon offers a stable platform with excellent visual conditions for astronomical observations. Some troublesome aspects of the lunar environment must be overcome to realize the full potential of the moon as an observatory site. Mitigation of negative effects of vacuum, thermal radiation, dust, and micrometeorite impact is feasible with careful engineering and operational planning. Shields against impact, dust, and solar radiation must be developed. Means of restoring degraded surfaces are probably essential for optical and thermal control surfaces deployed on long-lifetime lunar facilities. Precursor missions should be planned to validate and enhance the understanding of the lunar environment (e.g., dust behavior with and without human presence) and to determine environmental effects on surfaces and components. Precursor missions should generate data useful in establishing keepout zones around observatory facilities where rocket launches and landings, mining, and vehicular traffic could be detrimental to observatory operation. If lunar concrete becomes available, it could be a material of choice for observatory foundation construction. For concrete to be a viable choice, its production and use must be compatible with the observatories' needs for clean, precision optics, and for an environment free of dust, shock, vibration, and outgassing. It must also be economically competitive with alternative construction techniques.

The recently established Lunar/Mars Program Office at Johnson Space Center is studying options that include construction of lunar outposts in the early twenty-first century, and subsequent structures for industrial operations. Major industrialization on the moon cannot occur without access to lunar resources. Construction of such structures as large pressurized habitats, launching facilities, lunar surface transportation systems, and liquefied oxygen storage tanks requires enormous volumes of materials. Experiments sponsored by the National Aeoronautics and Space Administration (NASA) and carried out at construction technology laboratories show the following: cements can be made from lunar anorthite and basalt; concrete made with lunar soils as aggregate has strength exceeding 10,000 psi; and a dry mixture of cement and aggregate wetted by injected steam will simplify concreting procedures and minimize needs for water and heavy equipment. In addition, a preliminary analysis of a prestressed precast concrete structure measuring 120 ft in diameter and 72 ft high shows that a properly designed concrete structure can confine atmospheric internal pressure. This project further investigates the effect of lunar temperature extremes on the behavior of precast concrete panels during the construction period. The major work involves calculations of heat flow in concrete panels exposed to the sun on the lunar surface and thermal stresses in the panels caused by the transient heat flow. Computer programs were written for the computations and results are presented.

Effects of a vacuum environment on properties of hardened mortar made with cement-based materials are discussed. In this study, mortar specimens were exposed to a vacuum environment after various water curing periods. Several characteristics of the specimens, such as weight, strain, porosity, and strength, were measured before and after the vacuum exposure. A significant water loss and shrinkage strain were observed in tested specimens after specific vacuum exposure. Therefore, some measures are required to prevent shrinkage-induced cracks. In some cases, strengths for some vacuum-exposed mortar specimens were higher than water-cured companion specimens. Based on these experimental results, possible applications of concrete on the moon are recommended in this study.