The United States Air Force Academy's Engineering 410 class, Spring 1989, tested the feasibility of using concrete as a lunar construction material. This was a continuation of two previous semesters' effort. Concrete specimens were tested by combining different cement types, mixing environments, and additives to determine their effects on strengths and other engineering properties of the specimens. Using 5 different variables, a total of 80 possible combinations existed. The group used a D-optimal design with 18 possible combinations to build a prediction equation to optimize the concrete design mixture. Confirmation tests were conducted on the optimal design and compared with the mathematical algorithm prediction. The results demonstrate the power of this approach in experimentation for concrete applications.

Early in the next century, humans will return to the surface of the moon for stays of increasingly longer duration. Many civil engineering challenges must be addressed so that these twenty-first century pioneers will have the shelter and life-support systems needed to survive and thrive in a largely benign but, in some ways, hostile environment. Depending on the stage of the lunar presence, different structures and processes will be feasible. Reliance on lunar resources, including manufactured forms such as lunar concrete, will become more important as the base size and maturity grows. It is the task of the universities in these endeavors to provide the basic knowledge to help meet these challenges and to produce enthusiastic and well-prepared graduates who can best continue to develop the solutions needed to support the expansion of humans into space. Educational programs in space civil engineering now undergoing development at Colorado State University under a NASA space grant college program are described. An undergraduate option that supplements the existing civil engineering program through a cluster of classes that can be taken within the existing elective structure is being developed. Concepts for an MS graduate program are also outlined.

In the lunar environment, the use of solar thermal energy has obvious advantages over any combustion or electrical furnace for driving high-temperature processes. However, extremely high temperatures, in the range of 1700 to 2000 C, will be necessary to produce cement from lunar minerals and will, in turn, require very high levels of solar flux concentration. Such levels can only be achieved in practice with some form of ideal or near-ideal nonimaging concentrator that can approach the maximum concentration permitted by physical conservation laws. In particular, very substantial gains in efficiency can be generated through the incorporation of a properly designed ideal or near-ideal nonimaging secondary concentrator in a two-stage configuration with a long focal ratio primary concentrator. A preliminary design configuration for such a high-flux nonimaging solar concentrating furnace for lunar applications is presented. It employs a tracking heliostat and a fixed, off-axis, two-stage concentrator with a long focal length utilizing a nonimaging trumpet or CPC-type secondary deployed in the focal zone of the primary. An analysis of the benefits associated with this configuration employed as a solar furnace in the lunar environment shows that the thermal conversion efficiency can be about 3 to 5 times that of the corresponding conventional design at 2000 C. Furthermore, this configuration allows the primary collecting aperture to remain unshaded by the furnace or any associated support structure.

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.

An important aspect of lunar concrete production will be the production of lime (CaO) from lunar rocks. Chemical and thermodynamic data show that lime could most easily be distracted from abundant lunar anorthite (CaAl2Si2O8) the major mineral in the anorthositic lunar highlands. If fluorine gas, produced on site by electrolysis of molten NaF, is used as the extracting agent, oxygen, silicon, and aluminum can be recovered at the same time. Of these, oxygen is likely to be the most valuable product. Lime is recovered from fluorite, CaF2, by reaction with soda, Na2O; the resulting NaF is recycled into fluorine production immediately before use. No fluorine gas is transported or stored in this process; it is used up as soon as it is made.