AIAA Space Architecture Symposium AIAA 2002-6113 10-11 October 2002, Houston, Texas AN OVERVIEW of LUNAR BASE STRUCTURES: PAST and FUTURE * Haym Benaroya Rutgers University ABSTRACT being the placement of about 3 meters of regolith on top of the structure. This This paper aims to summarize the evolution of approach leads to challenging construction lunar base concepts over the past procedures, and also makes ingress and approximately half -century. We will discuss the egress difficult. Structure maintenance in various classes of concept s, the lunar the pre sence of an envelope of regolith environment as it pertains to structural design, remains to be addressed. construction, and human habitation. Topics introduced are: The Lunar Surface Human habitation requires ways to bring Environment; Lunar Base Concepts During the outside light and views into the structure, Apollo Era; More Recent Concepts for Lunar since long -term habitation in windowless Structures; Futuristic Concept s and spaces is viewed negatively. The internal Applications. pressurization turns out to be the controlling design load for a lunar surface structure, To understand the various classes of lunar even with 3 meters of regolith on the structures for habitation, it is important to outside. For inflatable structures, of explain the key environmental factors that particular concern is the loss of affect human survival on the Moon and pressurization. affect structural design and construction on the Moon. The key environmental factors Structural concepts for human habitation on are: the lunar surface inclu de the “tin can” (i) the surface is in a hard vacuum, and is structure, the inflatable structure, the truss- thus vulnerable to galactic and solar based structure, the fused -regolith structure, radiation and to micrometeorites, and hybrids. As expected, each class has (ii) a shirt -sleeve environment requires an its advantages and disadvantages. The “tin internally -pressurized structure, can” is comparatively easy to build on Earth (iii) suspended fines from the lunar orbit and transport and land on the Moon, surface can cause severe damage to with the disadvantage that it is not easily mechanisms and machines supporting expandable. A disadvantage of the structural operations. inflatable concept is the threat of deflation, but an important advantage is that large Lunar base structural concepts attempt to volumes can be enclosed by the inflatable, address the above issues in various ways. and it is easier to t ransport. The truss-based To reduce vulnerability to radiation and structure is most similar to Earth structures, micrometeorites, surface structures need to and most easily understood in terms of be s hielded, with the most popular approach current structural design and construction practice. However, strength requires heavy • Copyright 2002 by Haym Benaroya. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. 1 Copyright © 2002 by the author(s). Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. structural members, not likely to be “Moon First” and “Mars Direct” continues, manufactured on the M oon soon. although it is clear that without an extensive It is clear that the type of lunar and permanent human spaceflight civilization that can evolve depends on the infrastructure, the latter will do no more to infrastructure that we are capable of the expansion of civilization into the Solar building. System than did the Apollo program. It is also clear that we do not have the technology and experience to send people INTRODUCTION to Mars for an extended stay. Physiology and reliability issues are yet unresolved for Concepts for lunar base structures have a trip to Mars. The Moon is our best first been proposed since long before the dawn goal. Kraft Ehricke said in 1984: “If God of the space age. T his paper will abstract wanted man to go to Mars, he would have suggestions generated during the past given him a moon.” quarter century, as these are likely to form the pool from which eventual lunar base The emphasis here is on structures fo r designs will evolve. Significant studies were human habitation, a technically challenging made since the days of the Apollo program, fraction of the total number of structures when it appeared lik ely that the Moon would likely to comprise the lunar facility. The test become a second home to humans. for any proposed lunar base structure is how it meets certain basic as well as special For an early example of the gearing up of requirements. On the lunar surfa ce, R&D efforts, see the Army Corps of numerous constraints -- different from those Engineers study [Army 1963]. (Note the for terrestrial structures -- must be satisfied date of this report!) During the decade by all designs. A number of generic between the late eighties to mid -nineties, structural types are proposed for lunar base these studies intensified, both within NASA structures. These include concrete and outside the Government in industry and structures, metal frame structures, academe. The following references are pneumat ic construction, and hybrid representative: Benaroya and Ettouney structures. In addition, options may exist for 1989, Benaroya and Ettouney 1990, subsurface architectures and the use of Benaroya 1993a, Benaroya 1995, Benaroya natural features such as lava tubes. Each of et al. 2002, Duke and Benaroya 1993, these approaches can, in principle, satisfy Ettouney and Benaroya 1992, Galloway and the various and numerous constraints, but Lokaj 1994 and 1998, Johnson and Wetzel differentl y. 1988, 1990a,c and Johnson 1996, Mendell 1985, Sadeh et al. 1992. A recent review is Lowman [1985] made a post-Apollo by Benaroya, Chua and Bernold (2002). evaluation of the need for a lunar base with Numerous other references discuss science the following reasons for such a base: on the Moon, the economics of lunar • lunar science and astronomy development, and human physiology in • as a stimulus to space technology and space and on planetary bodies. An equally as a test bed for the technologies large literature exists about related policy required to place humans on Ma rs and issues. beyond • the utilization of lunar resources Unfortunately, by the mid -seventies, and • establishment of a U.S. presence again in the mid -nineties, the politi cal • stimulate interest in young Americans in climate turned against a return to the Moon science and engineering, and to stay, and began to look at Mars as the “appropriate” destination, essentially skipping the Moon. The debate between 2 • as the beginning of a long -range possible, for example, to experimentally program to ensure the survival of the assess the effects of suspended (due to species. one -sixth g ) lunar regolith fines on lunar These are all still primary reasons for a machinery. Apollo experience may be return to the Moon. extrapolated, but only to a point beyond which new information is necessary. The potential for an astronomical observatory on the Moon is very great and it Our focus in this paper is to explore the could be serviced periodically in a lunar environment and how this affects reasonable fashion from a lunar base. possible type s of structures considered for Several bold proposals for astronomy from the Moon. Other important topics for study, the Moon have be en made [Burns et al. beyond the scope of this paper, are outlined 1990]. Nearly all of these proposals involve afterwards. use of advanced materials and structural concepts to erect large long -life astronomy Loading, environment, and regolith facilities on the Moon. These facilities will mechanics challenge structural designers, constructors, and logistic s planners in the 21 st Century Any lunar structure will be designed and [Johnson 1989, Johnson and Wetzel built with the following prime con siderations 1990b]. One example is a 16 -meter in mind: diameter reflector with its supporting • safety and reliability : Human safety and structure and foundation investigated by the minimization of risk to “acceptable” NASA and several consortia. levels should always top the list of considerations for any engineering Selection of the proper site for a lunar project. Minimization of risk implies in astron omical facility, however, involves particular structural robustness, many difficult decisions. Scientific redun dancy, and when all else fails, advantages of a polar location for a lunar easy escape for the inhabitants. The key base [Burke 1985] are that half the sky be word is “acceptable.” It is a subjective continuously visible for astronomy from consideration, deeply rooted in each pole and that cryogenic instruments economic considerations. What is an can readily be op erated there since there acceptable level of safety and reliability are shaded regions in perpetual darkness. for a lunar site, one that must be Disadvantages arise also from the fact that considered highly hazardous? Such the sun will essentially trace the horizon, questions go beyond engineering leaving the outside workspace in extreme considerations and must include policy contrast, and will pose practical problems considerations: Can we afford to fail? Or regarding solar p ower and communications better yet, What kind of failure can we with Earth; relays will be required. Recently, afford or allow? See Cohen [1996] for a van Susante [2002] studied the possibility of related discussion. using the South Pole for an infrared • 1/6 -g gravity : A given structure will have, telescope. in gross terms, six times the weight bearing capacity on the Moon as on the The Environment Earth. Or, to support a certain loading condition, one -sixth the load bearing Important components in a design process strength is required on the Moon as on are the creation of a detailed de sign and the Earth. In order to m aximize the utility prototyping process. For a structure in the of concepts developed for lunar lunar environment, such building and structural design, mass-based rather realistic testing cannot be performed on the than weight -based criteria will drive the Earth or even in orbit.