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Home , Lunar resources, Lunar soil

AIAA 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 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 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 , and is structure, the inflatable structure, the truss- thus vulnerable to galactic and solar based structure, the fused -regolith structure, radiation and to , 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 (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.

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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 “ 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 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 . 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, 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 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 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 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. It is not currently approach of lunar structural engineers.

3 All of NASA’s calculations have been Chua (1993). Chua et al. (1994) shows how done in kg-force rather than Newtons . structure -regolith simulations can be done Calculati ons are always without the using the finite element approach. gravity component; use kgf/cm2 as pressure, for example. • internal air pressurization : The lunar structure implicitly serves as a life - Analytical foundation design is primarily supporting closed environment. It based on the limit state condition. The will be a pressurized enclosed design is based on the limit of loading on a volume with an internal pressure of wall or footing to the point when a total nearly 15psi (103.42kPa) 1. The collapse occurs, that is, the plastic limit. enclosure structure must contain this Since many of the structures on the Moon pressure, and designed to be “fail - require accurate pointing capabilities for safe” against catas trophic astronomy, communication, etc., a decompression caused by settlement based design method would be accidental and natural impacts. more useful. Chua et al. (1990) propose a • shielding : A prime consideration in nonlinear h yperbolic stress strain model that the design is that the structure shield can be used for the lunar regolith in a finite against the types of hazards found element analysis. The paper also shows on the lunar surface: continuous how the finite element method can be used solar/cosmic radiation, to predict settlement of the railway under a impacts, and extreme variations in support -point of a large telescope. Chua et and radiation. In the al. (1992) show how a large deformation likely situation that a layer of regolith capable finite element program can predict is placed atop the structure for the load -displacement characteristics of a shielding, the added weight would circular spud -can footing, designed to partially balance (in the range of 10 - support a large lunar optical telescope. 20%) the forces on the structure caused by internal p ressurization Chua also warns against assuming that less mentioned above. Criswell et al. gravity me ans a footing can support more (1996) discuss this “balancing” for load: if can be assumed to be linearly inflatables. elastic, then the elastic modulus is not affected by gravity. However, the load Shielding against impacts is bearing capacity of a real soil depends on accomplished by providing dense and the confining stress around it. If the soil heavy materials, in this case compacted surrounding the point of interest were regolith, to absorb the kinetic energy . Lunar heavier because of a larger gravity, the rock would be more effective than regolith confining stress would be higher and the because it has fracture toughness but it may soil at the point of interest can support a be more difficult to obtain and much more higher load without collapsing. under difficult to place atop surface structures. reduced gravity may be less consolidated and have less cont ainment. Much effort in this country has determined the damage effects on human b eings and The area of (regolith) mechanics electronics resulting from nuclear weapon has been exhaustively explored in the detonation but little is known about long - 1970s. Much of the work was approached term sustained low -level radiation effects from interpretation based on classical soil such as those encountered on the Moon. mechanics. Newer work and development According to Silberberg et al. (1985), during of nonlinear stress-strain models to describe the times of low solar activity, the annual the mechanics of the lunar regolith appear in Johnson et al. (1995a), Johnson and 1 1 psi =6.89kPa

4 dose-equivalent on humans on the exposed Construction in a vacuum has several lunar surface may be about 30 rem (30 problems. One would be the possibility of centiSv) 2 and the dose-equivalent over an out -gassing of oil, vapors, and lubricants 11 -year solar cycle is about 1000 rem from pneumatic systems. Hydraulic (10Sv) with most of the solar systems using space-rated lubricants are, particles arriving in one or two gigantic however, in use today. The out -gassing is flares lasting one to two days. It appears detrimental to astronomical mirrors, solar that at least 2.5 m of regolith cover would be panels, and any other moving machine required to keep the annual dose of parts because they tend to cause dust radiation at 5 rem (5 centiSv), which is the particles to forms pods. See Chua and allowable level for radiation workers (0.5 Johnson (1991). Another problem is that rem for the general public). A shallower surface-to -surface contact becomes much cover may be inadequate to protect against more abrasive in the absence of an air the primary radiation and a thicker cover layer. The increase in dynamic friction may cause the secondary radiation (which would cause fusion at the interfaces, for consists of and other radiation as example, a drill bit fusing with the lunar a result of the primary radiation hitting rock. This is of course aggravated by the atoms along its path). fact that the vacuum is a bad conductor of heat. The increase in abrasiveness at In recent years, there i s a move away from interfaces also increases wear -and -tear on - and germanium -based electronic any moving parts, for example, railways and components towards the use of gallium wheels. arsenide. Lower current and voltage demand, and miniaturization of electronic Blasting in a vacuum is another serious components and machines would make problem to consider. Blasts create a gas, devices more radiation hardened. Four the pressure of which may exceed 10 0,000 basic ways to harden a device to radiation terrestrial atmospheres. It is difficult to are with: junction isolation, dielectric predict how this explosion and the resulting isolation, silicon -on -sapphire devices, and ejecta would affect the area around the silicon -on -insulator devices. All of these blast. Keeping in mind that a particle set in methods work on the principle of isolating motion from the firing of a lander rocket each device from surrounding components. could theoretically travel half way around This el iminates the possibility of latch up the Moon, the effects of surface blasting on and reduces the possibility of a single event the Moon must be considered in any upset because charged cannot travel construction scenario. Discussion of tests as far in the components. involving explosives performed on the Moon can be found in Watson (1988). Joachim Radiation transport codes can be used to (1988) discussed different candidate simulate cosmic radiation effects. One such explosives for extraterrestrial use. The Air code that has been found to be effective is Force Institute of Technology [Johnson et LAHET (Prael et al. 1990) developed at the al. 1969] studied cratering at various Los Alamos National Laboratory. gravities and/or in vacuum. Bernold (1991) presented experimental evidence from a • vacuum : A hard vacuum surrounds study of blasting to loosen regolith for the Moon. This vacuum precludes excav ation. the use of certain materials that may not be chemically or molecularly • dust: The lunar surface has a layer stable under such conditions. This is of fine particles that are disturbed an issue for research. and placed into suspension easily. These particles cling to all surfaces 2 1 Sievert (Sv) = 100 rem and pose serious challenges for the

5 utility of construction equipment, air tools, especially those performed with locks, and all exposed surf aces computers, can accurately predict events. It [Slane 1994]. is also a misconception that astronauts would have to work around the structure Lunar dust consists of pulverized regolith rather than designing the structure in such a and appears to be charged. The charge way as to make construction easy for the may come from the fractured crystalline astronauts. Cohen and Kennedy (1997) structure of the material or it may be of a provide a comprehensive discussion of surficial nature, for example, charged these issues, with a vision of automated particles from the solar a ttaching delivery and emplacement of habitats and themselves to the dust particles. Criswell surface facilities. reported [1972] that dust particles are levitated at the lunar (line • use of local materials : This is to be between and lunar night) and this viewed as extremely important in the may be due to a change in polarity of the long -term view of extrat errestrial surficial materials. Johnson et al. (1995b) habitation. But feasibility will have to discussed the issue of lunar dust and its wait until a minimal presence has effects on operations on the Moon. Haljian been established on the Moon. Initial et al. (1964) and Seiheimer and Johnson lunar structures will be transported (1969) studied the adhesive characteristics for the most part in components from of regolith dust. the Earth. See Figure 1.

• ease of construction : The remoteness of the lunar site, in conjunction with the high costs associated with launches from Earth, suggests that lunar structures be designed for ease of construction so that the extra -vehicular activity of the astronaut construction team is minimized. Construction components must be practical and, in a sense, modular, in order to minimize local fabrication for initial structural outposts.

Chua et al. (1993) discuss guidelines and the developmental process for lunar -based structures. They presented the governing Figure 1: Lunar Exploration Systems for Apollo, from criteria and also gen eral misconceptions in Lowman. Lunar Bases: A Post -Apollo Evaluation , Lunar st designing space structures. For example, a Bases and Space Activities of the 21 Century, Proceedings of the Lunar and Planetary Institute, Houston Reproduced by device that is simple, conventional looking, permission of the publisher. and has no moving part is preferred over one which involves multiple degrees of The use of local resources, normally freedom in an exotic configuration involving referred to as ISRU (in -situ resource a yet -to -be develop ed artificial intelligence utilization) is a topic that has been studied, control if the former meets the functional more intensely now than ever, because of requirements. Another misconception is the possibility of actually establishing that constructing on the Moon is simply a human presence on the Moon, on Near - scaling of the effects of similar operations Earth -Orbit [NEO] and Mars. Some of the on Earth and that theoretical predictive earl ier work is found in Johnson and Chua

6 (1992). Cohen (2002) states that the In a light flexible structural system in low - predicted water at the lunar poles is less gravity, light structural members (e.g., dense and lower grade than the residual composite cylind ers that have wall - water in concrete. If concrete existed thickness of only a few 1/1000 ths of an inch) naturally on the Moon, ISRU proponents may be designed to limit their load carrying would be pushing for the mining of that capacity by designing for buckling when that concrete to recover the water. limit is met. In turn, the load is re -distributed to other less loaded structural members. Outline of Other Important Considerations Such an a pproach offers possibilities for inflatable and other lunar surface structures The problem of designing a structure for where it would be simpler and less costly to construction on the lunar surface is a include limit -state and sacrificial structural difficult one. Some important topics not elements. Some of these discussions have discussed in detail in this paper ar e outline started [Benaroya and Ettouney 1992], in next: par ticular regarding the design process for • the relationships between severe lunar an extraterrestrial structure. temperature cycles and structural and material fatigue, a problem for exposed Another crucial aspect of a lunar structural structures, seals and hatches design involves an evaluation of the total life • structural sensitivity to temperature cycle, that is, taking a system from differentials between different sections conception through retirement and of the same component disposition, or the recycling of the system • very low -temperature effects and the and its components. Many factors affecting possibility of brittle fractures system life cannot be predicted due to the • out -gassing for exposed and nature of the lunar environment and the other effects of high vacuum on , inability to realistically assess the system alloys, and advanced materials before it is built and utilized. • factors of safety, originally developed to account for uncertainties in the Earth Finally, it appears t hat concurrent design and construction process, engineering will be a byword for lunar undoubtedly need adjustment for the structural analysis, design, and erection. lunar environment, either up or down Concurrent engineering simultaneously depending on one's perspective and considers system design, manufacturing, tolerance for risk and construction, moving major items in the • reliability (and risk) must be major cycle to as early a stage as possible in components for lunar structures as they order to anticipate potential problems. Here, are for significant Earth structures another dimension is added to this [Benaroya 1994] definition: Given the extreme nature of the • dead loads/live loads under lunar gravity environment contemplated for the structure, concurrency must imply flexibility of design • buckling, stiffening, bracing and construction. Parallelism in the d esign requirements for lunar structures, which space helps to ensure that at each juncture will be internally pressurized alternate solutions exist that will permit the • consideration of new failure modes such continuation of the construction, even in the as those due to high -veloc ity face of completely unanticipated difficulties. micrometeorite impacts, and This factor needs to be further addressed, • nontechnical but crucial issues such as and its implications clearly explored. A financing the return to the Moon, and discussion of lunar design codes has understanding human physiology in already started [Benaroya and Ettouney space. 1992], and there is a need to study how lunar and Earth codes diverge.

7 Inflatables POSSIBLE STRUCTURAL CONCEPTS Vanderbilt et al. (1988) proposed a pillow - In order to assess the overall efficiency of shaped structure as a possible concept for a individual lu nar structural concepts, decision permanent lunar base. The proposed base science and operations research tools are consists of quilted inflatable pre ssurized proposed, used [Benaroya and Ettouney tensile structures using fiber composites. An 1989] and demonstrated [Benaroya and overburden of regolith provides shielding, Ettouney 1990]. Along these lines, Richter with accommodation for sunlight ingress. and Drake (1990) compared concepts for an Nowak et al. (1990) considered the extraterrestrial bui lding system, including foundation problem and additional reliability pneumatic, framed/rigid foam, prefabricated, concerns and analysis [Nowak et al. 1992]. and hybrid (inflatable/rigid) concepts. This concept marks a significant departure from numerous other inflatable concepts in In a very early lunar structural design study, that it shows an alternative to spheroidal Johnson (1964) presented available inflatables and optimizes volume for information with the goal of furthering the habitation. Broad (1989) proposed inflatable development of cri teria for the design of structural concepts for a lunar base as a permanent lunar structures. Johnson details means to simplify and speed up the process the lunar environment, discusses lunar soil while lessening the costs. The inflatable from the perspective of foundation design, structure can be used as a generic test bed and reviews excavation concepts. A review structure for a variety of lunar applications of the evolution of concepts for lunar bases [Sadeh and Criswell 1994]. Design criteria up through the mid -1980s is available are also put forward [Criswell et al. 1996]. [Johnson and Leonard 1985] as is a review See Figure 2. of more recent work on lunar bases [Johnson and Wetzel 1990c]. Chow and Lin (1988, 1989) proposed a pressurized membrane structure a Hypes and Wright (1990) surveyed surface permanent lunar base. See Figure 3. It is and subsurface concepts for lunar bases constructed of a double -skin membrane with a recommendation that preliminary filled with structural foam. A pressurized desig ns focus on specific applications. torus -shaped substructure provides e dge America's future on the Moon is outlined as support. Shielding is provided by an supporting scientific research, exploiting overburden of regolith. Briefly, the lunar resources for use in building a space construction procedure requires shaping the infrastructure, and attaining of self - ground and spreading the uninflated sufficiency in the lunar environment as a structure upon it, after which the torus - first step in planetary settlement. The shaped substructure is pressurized. complexities and costs of building such a Structur al foam is then injected into the base will depend on the mission or missions inflatable component, and the internal for which such a base is to be built. compartment is pressurized. The bottoms of both inflated structures are filled with Hoffman and Niehoff (1985) used criteria compacted soil to provide stability and a flat such as scientific objectives and transport interior floor surface. In a similar vein, requirements i n a preliminary design of a Eichold ( 2000) presented the concept of a permanently manned lunar surface research lunar base in a crater. base.

8 include tetrahedral, hexahedral, and octahedral.

A concept is proposed [King et al. 1989] for using the liquid tank portions of the space shuttle external tank assembly for a basic lunar habitat. The modifications of the tank, to tak e place in low Earth orbit, will include separation from the main external tank structure, the installation of living quarters, instrumentation, air locks, life support systems, and environmental control systems. The habitat is then transported to the Moon for a soft landing.

Figure 2: An inflatable structure concept from Vanderbilt et al. Engineering, Construction, and Operations in Space, Proceedings of the ASCE, New York, 1988. Reprinted by permission of the pu blisher, ASCE.

Kennedy (1992) proposed a detailed architectural master plan for a horizontal inflatable habitat .

Finite element simulations of inflatable structures are needed because it is impossible to reproduce a hard vacuum and low gravity conditio n on Earth. The finite element modeling would be large - deformation capable, have membrane element (which are essentially beam elements without bending) stiffness and axial tensile stiffness but not the axial compression stiffness, since the membrane cann ot resist compression. The program should also ideally be able to model regolith -structure interaction. GEOT2D Figure 3: An inflatable structure concept from Chow and Lin. (Chua et al. 1994) is a program that has the Engineering, Construction, and Operations in Space, Proceedings of the ASCE, New York, 1988. Reprinted by capabilities needed to simulate inflatable permission of the publisher, ASCE. structure -regolith interaction. Erectables A semi -quantitative approa ch to lunar base structures is provided [Kelso et al. 1988]. Mangan (1 988) proposes an expandable Some attention is given to economic platform structural concept consisting of considerations and the structural concepts various geometrically configured three - included could be developed in the future. dimensional trussed octet or space frame elements utilized both as building blocks Schroeder et al. (1994a) propose a and as a platform for expansion of the modular approach to lunar base des ign and structure. Examples of th e shapes used construction as a flexible approach to

9 developing a variety of structures for the Site Planning lunar surface. In a related vein, Schroeder et al. (1994b) propose a membrane Site pla ns [Sherwood 1990] and surface structure for an open structure that may be system architectures [Pieniazek and Toups utilized for assembly on the lunar surface. A 1990] are forcefully presented as being tensile -integrity structure was suggested as fundamental to any development of a possible concept for larger surface structural concepts. structures [Benaroya 1993b]. SPACE TOURISM Concrete and lunar materials To get a sense of where we might be in 50 - Lin et al. (1989) provide a structural analysis 100 years, we look to the con cepts of the and preliminary design of a precast, Inston Design Team’s concepts for a Lunar prestressed concrete lun ar base. A floating Hilton. These concepts were developed foundation is proposed to maintain under contract with Hilton International, and structural integrity, and thus air tightness, are reproduced here with permission of when differential settlement occurs. All Inston. There have been studies of space materials for such a lunar concrete tourism as the driving force behind a structure, except possibly for the permanent return to the Moon. Collins making of water, may be derivable from (2002) is a good place to start. lunar resources, however, at very high cost.

Utilizing unprocessed or minimally processed lunar materials for base structures, as well as for shielding, may be possible [Khalili 1989] by adopting and extending terrestrial techniques developed in ant iquity for harsh environments. Khalili discusses a variety of materials and techniques that are candidates for unpressurized applications.

Happel (1992a, 1992b) bases his design of a tied -arch structure on indigenous materials. The study is extensive and detailed, and includes an exposition on lunar materials. Construction using layered embankments of regolith and filmy materials (geotextiles) is an option using robotic construction [Okumura et al. 1994], as are fabric -confined soil structures [Harrison 1992].

In order to avoid the difficulties of mixing Figure 4: Hilton International concept for lunar hotel and commercial properties. Inston Design Team, with concrete on the lunar surface due to lack of permission. water, it has been suggested that a sulfur concrete be examined [Gracia and Construction in a New Environment Casanova 1998]. Sulfur is readily available on the Moon. One of the challenges to the extraterrestrial structures community is that of construction. Lunar construction techniques have

10 differences from those on Earth, for structures considering human safety and example, the construction team will likely operations needs. Using harsh Earth operate in pressure suits, motion is enviro nments such as the Antarctic as test dominated by one -sixth g, solar a nd cosmic beds for extraterrestrial operations is radiation not shielded by an Earth -type advocated [Bell and Neubek 1988]. atmosphere, and the existence of suspended dust in the construction site. An The performance of materials and assessment is provided [Toups 1990] of equipment used on lunar construction various construction techniques for the needs to be examined in terms of the many classes of structures and their respective constraints discussed so far. Structures that materia ls. These fall into three categories: are unsuitable for Earth construction may 1. methods that require Earth support prove adequate for the reduced -gravity 2. methods that use natural surface lunar environment [Chow and Lin 1989]. and subsurface features, and Several research efforts were directed to 3. techniques that primarily use lunar produce construction materials, such as resources. cement, concrete, and sulfur -based mat erials, from the elements available on Structural and architectural designs, along the Moon [Agosto 1988, Leonard 1988, Lin with manufacturing plants, an d construction 1987, Namba et al. 1988b, Yong and Berger methods are discussed [Namba et al. 1988, Strenski et al. 1990]. 1988a] for a habitable structure on the The Appendix to this paper provides a long Moon using concrete modules. The module list of structures that require not only a study can be disassembled into frame and panels. of the materi als that could be used for The framed and interconnected modular construction, but also the necessary tools construction permits internal pressurization . and equipment, methods of operation and control, and most importantly how to A qualitative study [Drake and Richter 1990] construct structures with and within the is made of the design and construction of a lunar environment (i.e., regolith, vacuum, lunar outpost assembly facility. Such a 1/6 g). Because most of the construction facility would be used to construct structures methods that have been developed since too large for transport to the Moon in one the beginning of mankind are adapted to fit piece. The assembly facility woul d support and take advantage of the terrestrial operation and maintenance operations environments (i.e., soil characteristics, during the functional life of the lunar atmosphere with oxygen, 1 g gravity), outpost. technologies that are common on Earth will either not work on the Moon, are too costly, Construction of a lunar base will at least or too inefficient. partially rest on the capabilities of the Army Corps of Engineers. Preparations are Creating the Base Infrastructure outlined [Simmerer 1988] and c hallenges discussed [Sargent and Hampson 1996]. The availability of an adequate infrastructure and resources are key to the All the above are contingent on the survival and growth of any society. Basic “practical” aspects of building structures on necessities such as shelter, wat er, waste the Moon. These aspects include the sort of disposal, and transportation are the machinery needed to move equipment and foundation of any viable society. Also, and astronauts about the surface; the methods especially for the lunar base, we have to needed to construct in one -sixth g with an add communication and power as part of extremely fine regolith dust working its way the physical infrastructure. All of these into every interface and opening; and the constructed facilities have one issue in determination of the appropriate layout of common, namely the interaction with lunar

11 surface materials: rocks, regolith, and moisture content in the regolith at the breccias. Regolith differs from soil on Earth bottom of the crater might be between 0.3% in several respects that are significant for and 1%. construction. While the soil that establishes the top layers (10 -20 cm) is loose and USING GEOSYNTHETICS in the powdery, easily observable in Apollo EXTRATERRESTRIAL ENVIRONMENT movies, the regolith reaches the relative density of 90 -100 percent below 30 cm. Some recent papers suggested using The grain size distribution of a common geosynthetics as soil reinforcement to regolith, as well as its high density below construct earth structures such as berms, the top layers, is rare in the terrestrial walls, slopes, etc. Chua [in Benaroya et al. enviro nment. This condition creates unique 2002] points to several problems that have problems for excavating, trenching, to be considered in order for this to be a backfilling, and compacting the soil reality: (Goodings et al., 1992). These operations, • Plastic materials are susceptible to however, are needed to create: 1) building degradation when subjected to foundations, 2) roadbeds, 3) launch-pads, radiation. 4) buried utiliti es (power, communication), • The transition temperature of 5) shelters and covers, 6) open -pit mining, many if not all of the geosynthetics 7) and underground storage facilities. used on Earth is well above the cold that are encountered on candidate sites including those THE ISSUE of WATER on the MOON on the Moon. This would make the plastics brittle thus rendering them In a recent development, it appears that useless as reinforcing elements. there may be water -ice in some craters near • There is little experience on how the poles of the Moon. It was suggested geosynthetics fare in a hard vacuum that water/water -laden and and respond to the relatively more may have deposited the water. If abrasive regolith. water does exist in those craters, it was conjectured by Chua and Johnson (1998) CONCLUDING SUMMARY that the moisture distribution may consist of water -ice mixing with the regolith t o We have presented a summary of current saturation or near saturation, and reducing thinking regarding some of the issues outwards according to the matric suction surrounding the engineering and pressure (which is influenced by the particle construction of structures for long -term lunar size distribution and is defined as the pore human habitation. The key lunar air pressure minus the pore water environmental facts have been summarized. pressure). Since the gravitation potential is Key structural types have been studied. relatively small compared to the matric suction potential, the water would have ACKNOWLEDGEMENTS been drawn laterally or even upwards over some distance. [Note: Since the regolith This paper is dedicated to the vision, and has no clays, unlike Earth, there would not those who are willing to make it happen. I be an osmotic suction component to also acknowledge my colleagues Koon - influence moisture migration]. The extent of Meng Chua for our discussions and Marc this unsaturated zone is primarily influenced Cohen for inviting me to prepare this by how fast the water vapor condensed at presentation and for his numerous useful the bottom of the crater, which have suggestions. temperatures as low as -230 oC. The Lunar Mission team indicated that the

12 CONTACT INFORMATION Benaroya, H., Ettouney, M. (1992a). Design Codes for Lunar Structures , SPACE 92, H. Benaroya, Assoc. Fellow, AIAA Engineering, Construction, and Professor, Department of Mechani cal and Ope rations in Space, ASCE, New York, 1 - Aerospace Engineering 12. Rutgers University Benaroya, H., Ettouney, M. (1992b). Design and Piscataway, New Jersey 08854 Construction Considerations for Lunar [email protected] Outpost, J. Aerospace Engineering, Vol.5, No.3, 261 -273. REFERENCES Bernold, L.E. (1991). Experimental Studies on Mechanics of Lunar Excavatio n, ASCE, Journal of Aerospace Engineering, Vol.4, Agosto, W.N., Wickman, J.H., and James, E. No.1, January. (1988). Lunar Cement/Concrete for Orbital Broad, W.J., (1989). Lab Offers to Develop an Struct ures , Proceedings SPACE 88, Inflatable Space Base , The New York Engineering, Construction, and Times, 14 November. Operations in Space ASCE, New York, Brooks, R. A. (1986). “A Robust Layered Control 157 -168. System for a Mobile Robot,” IEEE Journal Army, Department of the (1963). Special Study of Robotics and Automation RA -2, 14 -23. of the Research and Development Effort Brooks, R.A. (1990). “Elephants Don’t Play Required to Provide a US Lunar Chess,” in P. Mae, ed., ‘Designing Construction Capability , Office of t he Chief Autonomous Agents: Theory and Practice of Engineers. from Biology to Engineering and Back’, Bell, L., Neubek, D.J. (1988) Antarctic Testbed MIT Press, Cambridge, Massachusetts, for Extraterrestrial Operations , SPACE 88, pp. 3 -15. Engineering, Construction, and Burke, J.D. ( 1985). Merits of a Lunar Polar Base Operations in Space, ASCE, New York. Location , Lunar Bases and Space Benaroya, H., Editor (1993a). Applied Activities of the 21 st Century, Proceedings Mechanics of a Lunar Base , Applied of the Lunar and Planetary Institute, Mechanics Reviews, Vol.46, No.6, 265 - Houston, 77 -84. 358. Burns, J.O., Duric, N., Taylor, G.J., and Benaroya, H. (1993b). Tensile -Integrity Johnson, S.W. (1990). Astronomy on the Structures for the Moon , Applied Moon , Sci entific American. Mechanics of a Lunar Base, Applied Casanova, I. and Aulesa, V. (2000). Mechanics Reviews, Vol.46, No.6, 326 - “Construction Materials from In -Situ 335. Resources on the Moon and Mars.” Proc. Benaroya, H. (1994). Reliability of Structures for of Seventh Int. Conference and Exposition the Moon , Stru ctural Safety, 15, 67 -84. on Engineering, Construction, Operations Benaroya, H., Editor (1995). Lunar Structures , J and Business in Space, ASCE, British Interplanetary Society, Vol.48, Albuquerque, N .M., Feb. 27 -March 2, pp. No.1. 638 -644. Benaroya, H., Bernold, L., Chua, K -M., (2002) CETEC: Hart, P.A., Howe, S.D., Johnson, S.W., Engineering, Design and Construction of Leigh, G.G., and Leonard, R.S. (1990). A Lunar Bases, J Aerospace Engineering, Center for Extraterrestrial Engineering and Vol. 15, No . 2, 33 -45. Construction (CETEC), SPACE 90 Benaroya, H., Ettouney, M. (1989). Framework Engineering, Construction, and for the Evaluation of Lunar Base Structural th Operations in Space, Proceed ings of the Concepts, 9 Biennial SSI/Princeton ASCE, New York, 1198 -1205. Conference on Space Manufacturing, Chow, P.Y., Lin, T.Y. (1988). Structures for the Princeton, 297 -302. Moon , SPACE 88 Engineering, Benaroya, H., Ettouney, M. (1990). A Construction, and Operations in Space, Preliminary Framework for the Proceedings of the ASCE, New York, 362 - Comparison of Two Lunar Base Structural 374. Concepts, SPACE 90, Engineering, Chow, P.Y., Lin T.Y. (1989). Structural Construction, and Operations in Space, Engineer’s Concep t of Lunar Structures , J ASCE, New York, 490 -499.

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15 Johnson, S.W., Wetz el, J.P. Editors (1990a). Lin, T.D., Senseney, J.A., Arp, L.D., and Engineering, Construction, and Lindbergh, C. (1989). Concrete Lunar Operations in Space, Proceedings of the Base Investigation , J Aero space ASCE, New York. Engineering ASCE, Vol.2, No.1, January. Johnson, S.W., Wetzel, J.P. (1990b). Lunar Lowman, P.D. (1985). Lunar Bases: A Post - Astronomical Observatories: Design Apollo Evaluation , Lunar Bases and Studies , J Aerospace Engineering ASCE, Space Activities of the 21 st Century, Vol.3, No.4, October. Proceedings of the Lunar and Planetary John son, S.W., Wetzel, J.P. (1990c). Science Institute, Houston, 35 -46. and Engineering for Space: Technologies Mangan, J.J. (1988). The Expan dable Platform from SPACE 88 , Engineering, as a Structure on the Moon , SPACE 88 Construction, and Operations in Space, Engineering, Construction, and Proceedings of the ASCE, New York. Operations in Space, Proceedings of the Kelso, H.M., Hopkins, J., Morris, R., and ASCE, New York, 375 -388. Thomas, M. (1988). Design of a Second Mendell, W., Editor (1985). Lunar Bases and Generation Lunar Base , SPACE 88 Space Activities of the 21 st Century , Engineering, Construction, and Proceedings of the Lunar a nd Planetary Operations in Space, Proceedings of the Institute, Houston. ASCE, New York, 389 -399. Namba, H., Yoshida, T., Matsumoto, S., Kemurdjian, A. and Khakhanov, U.A. (2000) Sugihara, K., and Kai, Y. (1988a). Development of Simulation Means for Concrete Habitable Structure on the Gravity Forces , Proc. of Fourth Int. Moon , SPACE 88 Engineering, Confe rence and Exposition on Robotics Construction, and Operations in Space, for Challenging Environments, ASCE, Proceedings of the ASCE, New York, 178 - Albuquerque, N.M., Feb. 27 -March 2, pp. 189. 220 -225 Na mba, H., Ishikawa, N., Kanamori, H., and Kennedy, K.J. (1992). A Horizontal Inflatable Okada, T. (1988b). Concrete Production Habitat for SEI , SPACE 92 Engineering, Method for Construction of Lunar Bases , Construction, and Operations in Space, SPACE 88 Engineering, Construction, and Proceedings of the ASCE , New York, 135 - Operations in Space, Proceedings of the 146. ASCE, New York, 169 -177. Khalili, E.N. (1989). Lunar Structures Generated Nelson, T.J., Olson, M.R., and Wood, H.C. and Shielded with On -Site Materials , J (1998) Long Delay Telecontrol of Lunar Aerospace Engineering, Vol.2, No.3, July. Equipment , Proc. of Sixth Int. Conference King, C.B., Butterfield, A.J., Hyper, W.D., and and Exposition on Engineering, Nealy, J.E. (1989). A Concept for Using Construction, and Operations in Space, the Exter nal Tank from a NSTS for a ASCE, Albuquerque, N.M., April 26 -30, Lunar Habitat , Proceedings, 9 th Biennial pp. 477 -484 SSI/Princeton Conference on Space Nowak, P.S., Criswell, M.E., and Sadeh, W.Z. Manufacturing, May, Princeton, 47 -56. (1990). Inflatable Structures for a Lunar Leonard, R.S., Johnson, S.W. (1988). Sulfur - Base , SPACE 90 Engineering, Based Construction Materials for Lunar Construction, and Operations in Space, Construction , SPACE 88 Engineerin g, Proceedings of the ASCE, New York, 510 - Construction, and Operations in Space, 519. Proceedings of the ASCE, New York, Nowak, P.S., Sadeh, W.Z., and Criswell, M.E. 1295 -1307. (1992). An Analysis of an Inflatable Lin, Ch.P., Goodings, D.J., Bernold, L.E., Dick, Module for Planetary Surfaces , SPACE 92 R.D., and Fourney, W.L. (1994) Model Engineering, Construction, and Studies of Effects on Lunar Soil of Operations in Space, Proceedings of the Chemical Explosions , ASCE, J ASCE, New York, 78 -87. Geotechnical En gineering, Vol. 120, No. Okumura, M., Ohashi, Y., Ueno, T., Motoyui, S., 10, October, pp. 1684 -1703 and Murakawa, K. (1994). Lunar Base Lin, T.D. (1987). Concrete for Lunar Base Construction Using the Reinforced Earth Construction , Concrete International (ACI), Method with Geotex tiles , SPACE 94 Vol.9, No.7. Engineering, Construction, and

16 Operations in Space, Proceedings of the Metal Alloys in Ultrahigh Vacuum , Journal ASCE, New York, 1106 -1115. of Geophysical Research, vol.74, no.22, Pieniazek, L.A., Toups, L. (1990). A Lunar pp.5321 -533 0, October. Outpost Surface Systems Architecture , Sherwood, B. (1990). Site Constraints for a SPACE 90 Engineering, Construction, and Lunar Base , SPACE 90 Engineering, Operations in Space, Proceedings of the Construction, and Operations in Space, ASCE, New York, 480 -489. Proceedings of the ASCE, New York, 984 - Prael, R.E., Strottman, D.D., Strniste G.F., and 993. Feldman W.C. (1990). Radiation Exposure Silberberg, R., Tsao, C.H., Adams, Jr., J.H. and and Protection for Moon and Mars J.R. Letaw (1985). Radiation Tran sport of Missions, Report LA -UR -90 -1297, Los Cosmic Ray Nuclei in Lunar Material and Alamos National Laboratory, Los Alamos, Radiation Doses , Lunar Bases and Space New Mexico, Ap ril. Activities of the 21st Century, Ed. W.W. Richter, P.J., Drake, R.M. (1990). A Preliminary Mendell, Lunar and Planetary Institute. Evaluation of Extraterrestrial Building Simmerer, S.J. (1988). Preparing to Bridge the Systems , SPACE 90 Engineering, Lunar Gap , J Aerospace Engineering Construction, and Operations in Space, ASCE, Vol.1, No.2, April. Proceedings of the ASCE, New York, 409 - Slane, F.A. (1994). Engineering Implications of 418. Levitating Lunar Dust , SPACE 94 Richter, T., Lorenc, S.J., and Bernold, L.E. Engineering, Construction, and (19 98) Cable Based Robotic Work Operations in Space, Proceedings of the Platform for Construction , 15 th ASCE, New York, 1097 -1105. International Symposium on Automation Strenski, D., Yankee, S., Holasek, R., Pletka, B., and Robotics in Construction, Munich, Hellaw ell, A. (1990). Brick Design for the Germany, Mar. 31 -Apr. 1, pp. 137 -144 Lunar Surface , SPACE 90 Engineering, Sadeh, W.Z., Sture, S., and Miller, R.J., Editors Construction, and Operations in Space, (1992). Engineering, Constructio n, and Proceedings of the ASCE, New York, 458 - Operations in Space, Proceedings of the 467. ASCE, New York. Toups, L. (1990) A Survey of Lunar Construction Sadeh, W.Z., Criswell, M.E. (1994). A Generic Techniques, SPACE 90, Engineering, Inflatable Structure for a lunar/Martian Construction, an d Operations in Space, Base , SPACE 94 Engineering, ASCE, New York. Construction, and Operations in Space, Van Susante, P., (2002) Scenario Description of Proceedings of the ASCE, New York, the Construction of a 1146 -1156. Infrared Telescope, SPACE 02, Sargent, R., Hampson, K. (1996). Challenges in Engineering, Construction, and the Construction of a Lunar Base, SPACE Operations in Space, ASCE, New York. 96, Engineering, Construction, and Vanderbilt, M.D., Criswell, M.E. , and Sadeh, Operations in Space, Proceedings of the W.Z. (1988). Structures for a Lunar Base , ASCE, New York, 881 -888. SPACE 88 Engineering, Construction, and Schroeder, M.E., Richter, P.J., and Day, J. Operations in Space, Proceedings of the (1994a). Design Te chniques for ASCE, New York, 352 -361. Rectangular Lunar Modules , SPACE 94 Watson, P.M. (1988). Explosives Research for Engineering, Construction, and Lunar Applications: A Review , Operations in Space, Proceedings of the Engineering, Construc tion and Operations ASCE, New York, 176 -185. in Space, S.W. Johnson & J.P. Wetzel, Schroeder, M.E., Richter, P.J. (1994b). A Eds, American Society of Civil Engineers, Membrane Structure for a Lunar Assembly Albuquerque, N.Y., pp. 322 -331. Building , SPACE 94 Engineerin g, Yong, J.F., and Berger, R.L. (1988) Cement - Construction, and Operations in Space, Based Materials for Planetary Materials, Proceedings of the ASCE, New York, 186 - SPACE 88, Engineering, Construction, 195. and Operations in Space, ASCE, New Seiheimer, H.E., Johnson, S.W. (1969). York. Adhesion of Comminuted Rock to

17 Appendix: BUILDING SYSTEMS

TYPES of APPLICATIONS Habitats • people (living & working) • agriculture • airlocks: ingress/egress • temporary storm shelters for emergencies and radiation • open volumes

Storage Facilities/Shelt ers • cryogenic (fuels & science) • hazardous materials • general supplies • surface equipment storage • servicing and maintenance • temporary protective structures

Supporting Infrastructure • foundations/roadbeds/launchpads • communication towers and antennas • waste mana gement/life support • power generation, conditioning and distribution • mobile systems • industrial processing facilities • conduits/pipes

APPLICATION REQUIREMENTS Habitats • pressure containment • atmosphere composition/control • thermal control (active / passive) • ac oustic control • • protection • integrated/natural lighting • local waste management/recycling • airlocks with scrub areas • emergency systems • psychological/social factors

Storage Facilities/Shelters • refrigeration/insulation/cryogenic s ystems • pressurization/atmospheric control • thermal control (active / passive) • radiation protection • meteoroid protection • hazardous material containment • maintenance equipment/tools

Supporting Infrastructure • all of the above • regenerative life support (physica l / chemical and biological) • industrial waste management

18 TYPES of STRUCTURES Habitats • landed self -contained structures • rigid modules (prefabricated / in situ) • inflatable modules/membranes (prefabricated / in situ) • tunneling/coring • exploited caverns

Storage Facilities/Shelters • open tensile (tents / awning) • "tinker toy" • modules (rigid / inflatable) • trenches/underground • /masonry (arches / tubes) • mobile • shells

Supporting Infrastructure • slabs (melts / compaction / additives) • trusses/frames • all of the above

MATERIAL CONSIDERATIONS Habitats • shelf life/life cycle • resistance to space environment (uv / thermal / radiation / abrasion / vacuum) • resistance to fatigue (acoustic and machine vibration / pressurization / thermal) • resistance to acute stresses (la unch loads / pressurization / impact) • resistance to penetration ( / mechanical impacts) • biological/chemical inertness • reparability (process / materials)

Operational Suitability/Economy • availability (Lunar / planetary sources) • ease of production and use (labor / equipment / power / automation & robotics) • versatility (materials and related processes / equipment) • radiation/thermal shielding characteristics • meteoroid/debris shielding characteristics • acoustic properties • launch weight/compactability (Earth sources) • transmission of visible light • pressurization leak resistance (permeability / bonding) • thermal and electrical properties (conductivity / specific heat)

Safety • process operations (chemical / heat) • flammability/smoke/explosive potential • outgass ing • toxicity

19 STRUCTURES TECHNOLOGY DRIVERS

Mission/Application Influences • mission objectives and size • specific site --related conditions (resources / terrain features) • site preparation requirements (excavation / infrastructure) • available equipment/ tools (construction / maintenance) • surface transportation/infrastructure • crew size/specialization • available power • priority given to use of lunar material & material processing • evolutionary growth/reconfiguration requirements • resupply versus reuse strategie s

General Planning/Design Considerations • automation & robotics • EVA time for assembly • ease and safety of assembly (handling / connections) • optimization of teleoperated/automated systems • influences of reduced gravity (anchorage / excavation / traction) • qual ity control and validation • reliability/risk analysis • optimization of in situ materials utilization • maintenance procedures/requirements • cost/availability of materials • flexibility for reconfiguration/expansion • utility interfaces (lines / structures) • emergenc y procedures/equipment • logistics (delivery of equipment / materials) • evolutionary system upgrades/changeouts • tribology

REQUIREMENT DEFINITION/EVALUATION

Requirement/Option Studies • identify site implications (Lunar soil / geologic models) • identify missi on -driven requirements (function & purpose / staging of structures) • identify conceptual options (site preparation / construction) • identify evaluation criteria (costs / equipment / labor) • identify architectural program (human environmental needs) • Evaluatio n Studies • technology development requirements • cost/benefit models (early / long -term) • system design optimization/analysis

20