Design of Lunar Structures New Jersey Governor’s School of Engineering and Technology

2015

Samantha Berek

samberek39@gmail.com Kevin Chaudhari kc2422@me.com

David Connelly connellypiano@gmail.com

Kunal Gangolli kulkan159@gmail.com

Amelia Miller Ameliamiller7@comcast.net

Abstract

Lunar Habitation 1 (LH-1) is a proposed permanent lunar base designed to facilitate astronomical research as well as study the feasibility of human colonization of the Moon. Specific emphasis is placed on the effectiveness of inflatable structures as permanent bases and the practicality of incorporating greenhouses in the base. A location on Malapert Mountain on the lunar south pole is selected as the optimal location for LH-1. A detailed design for the base is created, and stress analyses are conducted to validate the design. The analyses reveal that the structure is able to withstand the forces on it without failing. A preliminary discussion on packaging and transporting the base to the lunar surface is presented, and a coiling method is selected for the inflatable. The specific plants to be grown in the greenhouses are selected based on efforts to maximize nutritional value, and solar and nuclear energy use on the base is described. 1. Introduction 1.1 Goals

This study specifically focuses on

designing a habitat, Lunar Habitation-1 (LH-

1) that could lead to permanent colonization of the Moon. Its primary purpose is to develop, model, and test a structure that could withstand the environment of the Moon and conduct research regarding the lunar environment. In order to accomplish this goal, LH-1 was first modeled in Solidworks®, a 3-D computer aided design software. The habitat then underwent tests to simulate stresses present on the structures in ANSYS®, an engineering analysis program.

The secondary goal of the research is to ensure that LH-1 is fit for human habitation. Psychological and physical needs are considered throughout the research. Energy usage is also acknowledged, with solar panels and a nuclear reactor as the sources of power for LH-1. Throughout the entire study, the principle objective was to create a structure that can both withstand the lunar environment and provide a permanent habitat for humans. 1.2 Reasons for Building a Lunar Base

A major reason for the development of a lunar base is to more efficiently explore space and increase human involvement in said explorations. The Moon can be used as a platform for future space exploration endeavors, as its lack of atmosphere and low

gravity decrease the difficulty of deploying space shuttles and vehicles from Earth. Also, efforts toward lunar colonization can lead to the creation of new technologies, as space research has done in the past. For example, the alkaline fuel cell was created during the Apollo Missions in the mid-1960s.1 The Moon is also rich in many resources that can be utilized on Earth. Such resources found on the Moon include gold, iron, and helium-3, a gas that provides nuclear energy without creating radioactive waste.2 The development of a lunar base is the most pragmatic step in the study of space. 2. Background 2.1 Challenges with building on the Moon Important factors that must be accounted for in the development of a lunar habitat are the harsh environment, food and water supply, energy, and psychological needs of the residents. The Moon has no atmosphere, and thus no protection from the Sun’s ultraviolet rays. The Moon also rotates around its axis in such a way that it has two weeks of light and two weeks of dark. This leads to temperatures ranging from 102.4 K to 387.1 K. Micrometeorites could cause damage to the integrity of the structure if not accounted for. When building the lunar base, the low gravity must also be factored into the structure. Further challenges include the actual erection of the habitat on the Moon, as well as transporting all of the supplies.3 Other considerations include food and water supplies, the acquisition of energy, and the psychological needs of the crew.

2.2 Assumptions Creation of a permanent manned lunar base is a goal still decades away from realization. In some cases, LH-1 incorporates technology that is currently

undeveloped but feasible within tens of years. Examples include the ability to efficiently excavate lunar regolith and the technology for advanced batteries and energy storage. Furthermore, it is also assumed that the required financial resources for the deployment and continued operation of LH-1 are present and available. 3. Software

The computer aided design (CAD) software SketchUp was used for producing preliminary conceptual models of LH-1 and for producing some images of the base after its dimensions and layout were finalized. SketchUp was used for image production to allow for coloring of images and for showing only the aboveground portions of LH-1.

The CAD software AutoCAD was used to produce 2-D drawings of blueprints and cross-sectional views of LH-1, allowing for diagrams clearly defining the dimensions and layout of the lunar base.

The design of the 3-D model of LH-1 was made in a CAD program called SolidWorks®. Following the modeling of the main central hub in the shape of a cylinder with elliptical domes at its top and bottom, three greenhouses, one research module and the hallways were developed.

Once designs of each aspect of LH-1 were completed using SolidWorks®, the files were imported into ANSYS® Workbench, a finite element analysis software that runs specialized tests on structures. Upon input of the stresses on the structures and the properties of the building material, ANSYS® was used to produce stress and deformation diagrams for each of the structures. 4. Location

The location selected for this study is a peak on Malapert Mountain (86.00S,

2.9W), which has the distinct advantage of being illuminated for 74 percent of the year.4 The longer periods of daylight will result in a greater amount of solar power available for daily use. Since there are less severe temperature fluctuations on Malapert Mountain, it will be easier to regulate temperature inside the habitat.

The other area initially considered for this project was the rim of Shackleton Crater, as it is also one of many areas on the Moon with long periods of illumination - in this case 71 percent of the year. However, Malapert Mountain is almost always in a direct line of sight with Earth, allowing for direct communications between LH-1 and Earth. If the base were created on Shackleton Crater, then some form of intermediary satellite would be necessary for transmissions.5

Malapert Mountain has a relatively flat terrain when compared to other potential candidate sites, such as the rim of Shackleton Crater, because Malapert Mountain is much older and has had time to mature through constant bombardment with solar wind. Older sites tend to have thicker regolith than in newer sites, which is available at a smaller radius from the base and is much easier to excavate than thinner layers of regolith.5

Lunar ice is available in both sites, though the concentrations are slightly greater at Malapert. Lunar ice is important for the generation of fuel using hydrogen and oxygen. Malapert Mountain is also void of most radio interference from Earth, making it an ideal location for a lunar observatory.5

5. Structure 5.1 External Traditional pre-constructed space modules are heavy and therefore are restricted volumetrically. In order to create a

permanent settlement of habitable size, alternative solutions must be examined.

One proposed solution for this is the use of inflatable structures, which essentially functions like a balloon. Inflatable structures are flexible pressure vessels, which are initially empty but can be easily deployed to a much larger volume. The inflatable structure will have two layers made of Kevlar-29, a light material that is very strong for its weight. The thickness of the Kevlar itself would be insignificant when compared to the entire structure (in this case 5 millimeters).6 The structure would be hardened with rigidizing foam during deployment, and the interior will be filled with compressed gas which will be brought from Earth.

Due to a lack of any significant form of atmosphere on the Moon, temperature changes tend to be much more drastic than those observed on Earth. The lack of atmosphere also results in an increased amount of micrometeorite impacts on the Moon. Radiation is also a constant threat on the Moon due to a lack of a strong magnetic field in order to deflect solar wind and the absence of an ozone layer, which prevents humans from being exposed to dangerous levels of UV rays.

One solution to mitigate these dangers to LH-1 and its inhabitants is to cover the base with regolith, or lunar soil. Regolith is generally divided into two distinct layers: an upper “fluff” layer, which is about 2 centimeters deep, and an area of dense regolith which starts at 2 centimeters below ground and continues thereafter. The fluff layer is especially good at blocking heat from the sun due to its low thermal conductivity,3 which is on the magnitude of 10-5 W/(m x K). Most of the harmful radiation will be absorbed within the first 1-2 meters of regolith. Since LH-1 will be covered in 3 meters of regolith, radiation poisoning will not be a point of concern.

The same logic applies to micrometeorite impacts, where the foreign objects will have to penetrate a larger amount of material in order to reach the structure and create sizeable damage.7

In LH-1, at least 600 tons of regolith will be used in order to cover the building. Using lunar regolith saves extensive amounts of fuel because prefabricated radiation shields do not need to be brought from Earth.

A single inflatable membrane has many drawbacks. The internal pressurization is responsible for holding the shape and size of the structure. The combination of internal pressure and the downward directed gravitational force of the regolith could easily deform the structure, leaving it vulnerable to collapse. Therefore, a more structurally sound design was chosen.

Two layers of inflatable membrane are situated a half a meter apart, held in place by straps. The inside of the structure is then inflated, and once stable, the half a meter space in between the layers is filled with a rigidizing foam. The foam is given time to harden, and it becomes the primary support system for the stresses on the structure.

A foam suitable for this purpose needs to be strong and durable, not too brittle but not too flexible. Sawbones Solid Rigid Polyurethane Foam 30 pt Density8 was chosen because of its material properties, as shown in Table 1. It quickly

rigidizes to fill the exact shape that is necessary for the habitation, and hardens into a solid material capable of maintaining the integrity of the structure under the various stresses that are present in lunar environments.

Using the material6 Kevlar-29, LH-1 will have external and internal layers separated by the layer of rigidized foam. The external layer of the main central hub of LH-1 is 16.5 meters in diameter (Figure 1). There is a dome at the top of the central hub, making its height 6.25 meters above ground. The lower level and the storage floor in the bottom dome combine with a height of 5.75. These bottom floors will protrude into the ground, which will require digging into the surface of the Moon.

Extruding from the central hub of LH-1 are four corridors with hemispherical modules at each of their ends. The corridors are eight meters in length, three meters in width, and 4.5 meters in height. The four external modules will be ten meters in diameter and 5.5 in height on the outside. Figure 2 presents an aboveground view of LH-1. 5.2 Internal

Internal pressurization of LH-1 is a key component of both the erection and the prolonged operation of the base. The initial inflation expands the base from its packed form into its permanent shape. The outward force of the inflation pressure also counteracts the weight of the regolith shielding which will be added to the top of the base and thus assists the rigidizing foam in supporting the structure. The internal pressurization also functions as the air supply for its crew and for the greenhouses. Sufficient air to fully inflate the base and provide for its inhabitants must be brought from Earth upon the deployment of the base. As seen in Figure 1, the interior of the central hub module is defined by a

Poisson’s Ratio 0.30

Tensile Strength 12.0 MPa

Compressive Yield Strength 18.0 MPa

Density 0.480 g/cc

Tensile Modulus 0.592 GPa

Table 1. Rigidizing Foam Properties

titanium structure made up of two floors resting on four beams that run from the bottom to the top of the interior of the module. The beams are therefore curved at both ends in order to lie flush with the ellipsoid domes at the top and bottom of the hub, and are just under twelve meters long. The beams are placed along a circle of radius 3.3 meters from the center of the hub and are at 90 degree intervals along the circle so as to be equally spaced around the center of the module. Each beam spans five degrees of the circle. Furthermore, the layout of the beams is designed to be 45 degrees offset from the positions of the four entrances to corridors in the central hub, to prevent the beams from inhibiting movement around the base.

The two floors rest on the beams and divide LH-1 into three levels. Each floor is half a meter thick. The lowest floor is placed such that the floor level lies two meters above the lowest point of the interior of the ellipsoid dome at the bottom of the module. The other floor is placed such that its floor level lies 4.25 meters above that of the

bottom floor. Therefore, the top level is as high as the interior of the structure goes, the middle level is 3.75 meters high, and the bottommost level consists of the remainder of the space between the bottom floor and the bottom of the structure. Movement from the basement to the ground floor is enabled by two ladders along the edge of the interior of the module.

Titanium is forty percent lighter than steel; therefore it was chosen for the support structure because of its combination of strength and relatively low weight.6 Titanium is often considered challenging to manufacture and is more expensive than other metals. However, since in the case of LH-1 titanium is used not for the primary shell of the base but instead only for the support structure, the amount required would be significantly less than in a traditional structure, thereby alleviating most of the concerns regarding titanium.

The topmost level of LH-1, hereafter referred to as the ground floor, has a floor level of half a meter above the external ground level and serves as the primary living space for the astronauts in the base. The ground floor includes facilities for some scientific research. However, the primary function of the ground floor is to provide a control center for managing the infrastructure of LH-1 while also serving as a living space for the astronauts manning the base. As such, all sensors and control interfaces relevant to the running of the base

Figure 1. A dimensioned cross-sectional view of LH-1

Figure 2. Aboveground view of LH-1

- oxygen levels, airlock controls, climate monitors for the greenhouses - are accessible from the ground floor of the central module. Basic amenities are present on the ground floor as well, including a lavatory system. The interior of the ground floor includes the additional space provided by the dome on the top of the structure and contains significant volume, thereby decreasing the chances of claustrophobia among the astronauts and increasing their overall psychological well being. While physical windows in the walls of the module provide another potential measure to promote mental health, they are impractical due to both the general stress windows impose on physical structures and the specific difficulty of installing a window in an inflatable bilayer. To compensate, the interior walls of the central module feature television screens capable of displaying views of both the external lunar surface and views of landscapes on Earth, providing another method of preventing claustrophobia on the base.

The level below the ground floor, the basement, houses the bulk of the residential facilities in LH-1. All sleeping quarters are located in the basement as are a kitchen and a lavatory. The square footage of the basement exceeds 2000 square feet - as does that of the ground floor - and so the hub provides ample space for all ten inhabitants to live and work comfortably.

The bottommost floor is of an elliptical shape and thus has limited functionality for any kind of base operations. Therefore, this level is designated as a storage level and will house equipment and materials not needed immediately on the base.

Each external module is connected to the central hub by a corridor with a semi-elliptical cross section. Each corridor contains a floor of half a meter thickness that lies at the same level as the floor level

of the ground floor. The maximum height of the interior of the corridor is therefore three meters to ensure ample walking room in the low gravity of the lunar environment.

The interiors of the external modules themselves are hemispherical in shape except where the corridor intersects the module. The floors in the external modules are again half a meter thick and flush with the floors in the corridors. The interiors of the external modules therefore have a maximum height of four meters.

One module houses the bulk of the scientific equipment contained in LH-1. This module serves as the site of the vast majority of the research the crew will perform. Equipment present includes both that necessary for traditional lunar science disciplines such as soil and atmospheric analysis as well as astronomical equipment capable of taking advantage of the unique perspective offered by a lunar base.

The remaining three external modules are designed to serve as greenhouses for the base. As such, some special considerations are made in the facilities available in the greenhouses. Climate control is a necessary capability in the greenhouses, as the conditions inside must be optimized to the plants they produce. The greenhouse modules are also equipped with artificial sunlight lamps. Attempting to use real sunlight for lunar agriculture is impractical due to the irregularity of solar illumination and the difficulty of installing light-admitting windows in the inflatable bilayer. The ability to control air temperature and humidity of each greenhouse independent of the others and of the central hub and the capability to consistently provide artificial sunlight are crucial to successful agriculture on LH-1.

6. Stress Analyses 6.1 Forces Exerted by Regolith:

Before a stress analysis can be performed on the structure, it is necessary to know the forces that are acting upon the building. The inside of the structure is set at a fixed air pressure of 101.3 kPa, equivalent to atmospheric pressure, which exerts a force on the interior of the building.

The structure that has been produced for this project is unique in that it shows characteristics of both thick- and thin-walled pressure vessels. A thin walled pressure vessel is defined as having a radius which is at least 10 times greater than the depth of the foam, and anything less would be thick-walled. The elliptical dome of the central hub has a semi-major radius of 7.75 meters, which is 15.5 times greater than the 0.5 meter thickness of the wall. The semi-minor radius, however, is only two meters, which is a mere four times greater than the thickness. These issues were factored in when simulating the stress test. This does not apply for the hallways and the greenhouse, which both function as thick-walled pressure vessels for the entire perimeter of the structure.

The outside of the structure will be covered in regolith three meters thick which, in addition to protecting the structure from heat, radiation, and meteorites, exerts a force which will be able to counteract the force of the pressure acting on the vessel. The total force on the central hub was first calculated by finding the volume of regolith required to cover the central hub, then multiplying by the density of the fluff layer, which is 1.3 g/cm3. The resulting mass was multiplied by the gravitational acceleration on the Moon, which is 1.622 m/s2, in order to find the total force acting upon the structure. A similar method was used for the hallways and the greenhouses.

6.2 Conducting Stress Analyses With all the necessary information about the various stresses and pressures that the habitation will be exposed to, stress analyses were conducted using ANSYS®. Although the structure is inflatable, the rigidizing foam is responsible for enduring the stresses and pressures on the base. The membranes become a secondary support system, and the internal system of beams is redundant, present only for emergencies. Therefore, the properties of the foam were used in all tests conducted, to ensure that all other support systems are purely in case of failure. Each component of LH-1 (main hub, hallway, and greenhouse) was analyzed separately.

Next, the forces of 1,360,000 N, 224,000 N, and 412,000 N for the main hub, hallway, and greenhouse respectively, were added to the top domes of the structures to model the downward force of the three meters of regolith. The internal air pressure of 101.3 kPa was applied normal to the walls, since it presses against all walls of the structure with the same amount of force. The underground components of the structure are held in place by the lunar soil and were therefore treated as fixed supports. After all forces were entered, the analyses were ready to be run. Three types of analyses were selected- total stress, total deformation, and directional deformation. The total deformation tests display the net deformation, and the directional deformation tests show deformation only in the vertical direction. These tests were chosen because they give a comprehensive overview of the performance of LH-1 as a lunar base and outline the chance of failure. 6.3 Results The stress analysis on the main hub showed a large, but not problematic, amount of stress. As shown in Figure 3, the

underground section of the hub displayed minimal stress, since the hub is being held in place by the lunar rock surrounding it. On the outer part of the structure, the most stress was present at the top of the dome, due to the combination of the force of the regolith and the internal pressure. On the inside walls of the hub, most of the stress was concentrated around the rim of the dome, because of the change in geometry present in this area of the structure. Unlike on the outer surface, there was minimal

stress on the inside of the topmost part of the dome. The highest levels of stress on the dome reached a magnitude of approximately 5.534 x 106 Pa. This was well within the strength parameters of the rigidizing foam. The stress on the material was approximately 30.74 percent of its yield strength of 18 x 106 Pascals, which was within a safe range. A material is not considered unsafe until it has reached between 50 and 60 percent of its maximum

Figure 4. Deformation diagram of central hub

Figure 3. Stress analysis of central hub (a) External view of hub (b) Internal view of hub

(a) (b)

yield strength, which was nearly double the stress that the LH-1 hub experiences.9 The most deformation of the central hub occurred on the dome in the vertical direction, as demonstrated in Figure 4. The top of the dome balanced two stresses working in opposite directions and deformed upwards slightly, showing that the internal pressurization of the hub was a larger force than the external gravitational force of the regolith shielding. The maximum deformation, present at the vertex of the dome, was about 6.4 x 10-4 meters, which was not significant compared to the half-meter thick walls of the structure.

The hallways, as depicted in Figure 5, experienced the least amount of stress on the bottom of the structure, since it was grounded to the lunar surface and there was no gravitational force from regolith present. The part of the structure that underwent the most stress is the section of the wall directly above the bottom floor, where the part of the base attached to the lunar surface met the part of the base not attached to the surface. The connection caused added stress on the foam, which reached a maximum value of 3.95 x 106 Pascals. Even the bottom edge of the structure with the most stress only reached about 22 percent of the maximum

Figure 5. Stress analysis of hallway

Figure 6. Total deformation of hallway

yield strength of the foam, making the design structurally sound.

It should be noted that the aforementioned stress analyses have not considered the complete design of LH-1. Where the hallways connect to the central hub and hemispheres, extra weight from the regolith surrounding the upper cylindrical wall of the hub and hemispheres contributes to the downward stress on the hallways. Since this extra regolith is inconsistently distributed and does not have a large value, it was not considered for the tests conducted. In the stress tests that were run, the hallways experienced much less than half of their yield strength, so it is unlikely that the additional stress that was not considered is problematic.

The most total deformation was around the middle of the vertical walls, which deformed outward, as displayed in Figure 6, with a maximum on the front and back ends of 3.04 x 10-5 meters. This value was not large enough to be of concern.

Again, the bottom of the structure did not deform, since it was attached to the lunar surface. On the outside surface, the structure deformed downward slightly in the lower section of the wall, but upward to a maximum of 8.34 x 10-6 meters on the upper

wall. The top dome of the hallway deformed downward as well, to a minimum of 9.63 x 10-6 meters inward at the top of the curved ceiling. On the inside of the walls, the maximum upward deformation was lower on the walls than on the outside. The greenhouses and science dome underwent very little stress, as shown in Figure 7. The hemispherical domes had no sharp edges or other weak points, and this design made them very structurally sound. The most stress was present around the middle of the dome, where the air pressure had the most effect on the structure. The stress on the inside surface of the foam had a similar pattern to the stress on the outside surface of the foam. The largest amount of stress that the hemisphere had to withstand was 6.23 x 106 Pascals, which was only approximately 35 percent of its yield strength, well under the stress limit. The modules deformed slightly outward due to the larger magnitude of the internal pressurization, as demonstrated in Figure 8. However, the maximum deformation was approximately 9.87 x 10-6 meters, which is insignificant in the scope of the design. On the inner surface of the dome, deformation was relatively constant throughout the entire top portion of the

Figure 7. Stress analysis of external modules.

dome, reaching a maximum of about the same as on the outside surface. The area of maximum deformation was smaller in the vertical direction than it was totally. On the outside of the structure, the most amount of vertical deformation was not in a central ring as it was in the total. Instead, maximum deformation took place in a circular area at the topmost section of the hemisphere. The vertical deformation was similar on the outside and inside surface of the dome. All deformation was more prevalent on the inner surface of the hemisphere than on the outer surface. 7. Packing and Deployment of the Inflatable Structure One of the most attractive qualities of an inflatable lunar base is its ability to be compressed to a small fraction of its full volume for transportation to the Moon. An ideal packing solution distorts the inflatable as little as possible while reducing the volume to a great degree. Mark Schenk describes two simple packing configurations for various inflatables, coiling and z-folding.10 Both methods were considered for LH-1 and the results were analyzed.

7.1 Coiling

Coiling involves rolling the uninflated structure into a cylinder, in some cases wrapping it around a hub.10 The radius of the coil depends on the width of the hub if one is present, and it follows that the volume of the packed structure varies depending on the hub’s size. While a tighter coil and a smaller hub allows for a reduction in volume, reducing the radius of the coil requires the structure to be rolled around the center more times and thus risks a larger distortion in the structure.10 Therefore, the goals of minimizing number of revolutions and minimizing volume must be considered against each other in determining an optimal coiled packing configuration.

For the purpose of approximation, the coiled configuration was modeled as a series of concentric circles around an inner hub, each circle representing a layer of the inflatable rolled around the center. Each layer is five millimeters thick.6 However, because LH-1 employs an inflatable bilayer and because in flattening the structure prior to coiling it the top and bottom layers are pressed against each other, each layer in the model has an effective thickness of four times that value, or 20 millimeters.

Figure 8. Net deformation of external modules

Furthermore, in the case of the central module, the model proposes that the structure be folded in half along its vertical axis prior to folding as a volume-reducing measure, therefore making each layer in the model 40 millimeters for the central module. After modeling the configuration as a group of concentric circles, the structure was described by a mathematical series. Polynomials were found to approximate the partial sums of these series and these polynomials were solved to determine the number of revolutions each module would need to make around a hub of a given size. This information was then used to determine the diameter of the overall structure and therefore the volume.

Table 2 shows the volumes of various packing configurations for both the main module and the combined greenhouse-corridor modules based on various hub diameters, as well as displaying the number of necessary revolutions, the volume of the packed structure, and the percentage of the fully deployed volume each configuration occupies.

7.2 Z-Folding Z-folding is a simple packing configuration in which the uninflated structure is repeatedly folded in half back and forth upon itself until it is of manageable size.10 Calculations were performed to determine the dimensions of z-folded packing configurations for the components of LH-1. It was determined that z-folding is volumetrically more efficient than coiling or wrapping. However, z-folding creates more severe deformation in the structure as the packing configuration requires that definite creases be made in the membrane, which have been shown to hinder airflow upon the deployment of the base.10

7.3 Packing LH-1 After analysis of the aforementioned packaging options, coiling was selected as the configuration for LH-1, since it produces volumes comparable with those of the z-folded configurations with less risk of a problematic deployment due to deformation to the structure. Furthermore, the hub in a coiled configuration need not be solid, and

Central Hub Module Dfgfdfg

Hub diameter (m) Revolutions Volume (m3) Volume Percentage (%)

1 3.5 10.62 0.55

1.25 2.9 14.29 0.74

1.5 2.5 18.76 0.97

Greenhouse/Corridor Module

Hub diameter (m) Revolutions Volume (m3) Volume Percentage (%)

1 5.1 11.42 2.62

1.25 4.3 15.85 3.63

1.5 3.6 21.25 4.87

Table 2. Dimensions for coiled configurations

so the interior of the hub can be hollow and used for additional storage of other necessities, thereby nearly making up for the slightly larger volume.

In determining approximations for optimal packaging dimensions, the dimensions of the cargo bay of the now-retired space shuttle, roughly 18 meters long and five meters wide were used as a benchmark.11 However, due to the futuristic nature of the design of LH-1, it is likely that larger payloads will be feasible by the time lunar bases are under construction.

It is proposed that the four greenhouse-corridor modules and the central hub modules each by coiled around a hub approximately 1.25 meters in diameter. Dimensions around this number allow for both a minimal size and a minimal number of rotations. These coils can be arranged to fall within the cargo bay dimensions used for comparison, further validating the choice of an inflatable structure to maximize deployed volume while minimizing packed volume. 7.4 Inflating LH-1 Wrapped inflatables can be deployed using air released at the center of the hub, pushing the outer layers to unroll.10 At a minimum, enough inflation gas must be brought to fill the entirety of the internal volume at atmospheric pressure. The internal volume of LH-1 was calculated and it was determined that 3000 cubic meters of air would provide sufficient inflation air while leaving a small reservoir of extra gas in the event that the base unexpectedly experiences air leakage. NASA currently has developed tanks of breathable gas pressurized at 6000 pounds per square inch to supply the International Space Station.12 By using Boyle’s Law, it was determined that at this pressure the necessary inflation air for LH-1 would occupy only just over 7 cubic meters. The relatively minimal volume

required for the inflatable bilayers and inflation gas of LH-1 makes the base easier and more cost effective to deploy while allowing for transport spacecraft to carry additional payload necessary for the base, including internal structure and infrastructure and technology necessary for operating the base. 8. Greenhouses/Plants 8.1 Reasons for Lunar Greenhouses

In designing a lunar structure, food, air supply, and the psychological condition of the crew are important considerations. As a partial solution, greenhouses are included in the structure of LH-1. The greenhouses are used primarily to grow food for the inhabitants of the base, but are also used to study how plants grow in space.13 Plant respiration also reduces the need for oxygen replenishments from Earth and makes the air inside LH-1 more breathable for its crew. 8.2 Logistics of Greenhouses

The primary consideration in selecting plants to grow in LH-1 was nutritional value. All humans need the six basic macronutrients - water, carbohydrates, proteins, fats, vitamins, and minerals. The goal of the plant selection for the base is to obtain as many of these nutrients as possible in a space-efficient manner. Based on this criteria, kale, spinach, carrots, white potatoes, sweet potatoes, black beans, and lentils are grown in the greenhouses.14 15 16 17 18

Temperature, humidity, and light are controlled in each greenhouse based on the plants growing in them in order to increase the growth rate of the plants and provide a safe environment for the vegetation. The climate in the enclosures attempts to mimic the environment that the plants grow in on

Earth. The greenhouses also use artificial sunlight because it allows better regulation of light and is a more viable option that using natural light on the Moon. The plants were then organized into different greenhouses, with kale and spinach in one, carrots and white potatoes growing in another, and sweet potatoes, black beans, and lentils in the final greenhouse.17 19 20 21 22

The vegetables will be grown through hydroponics - an emerging method of growing plants in nutrient rich water, without dirt of any form.23 This method has been found to be successful on the International Space Station.24

9. Energy 9.1 Solar Energy

In order to run the functions and processes of the lunar base, LH-1 must have energy sources. Solar energy is the primary source of energy for LH-1, while nuclear energy is used as an alternative energy source when solar energy is unattainable. For the 74 percent of the time that the peak receives full sunlight, solar panels obtain the energy necessary for LH-1 to provide enough power to control the base’s functions.4 These panels are placed on the highest peak of Malapert Mountain to obtain optimal sunlight. In order to maximize the amount of energy produced from the solar panels, they are placed on a rotating motor and can then be angled into positions that receive the most amount of sunlight at different times of the day.

The solar panels also must be protected from micrometeorites and other space debris that can possibly cause damage. Two thick layers of fused silica glass, which is widely used for the windows of space shuttles, are used to protect the solar panels.25 The outer aluminum silicate glass layer acts as the sacrificial layer, meaning that it takes the damage that space debris

would otherwise cause to the solar panels. Solar energy is the most promising prospect for energy on the Moon, especially on Malapert Mountain, which is exposed to a great amount of sunlight. 9.2 Nuclear Energy

Even though the location of LH-1 receives sunlight over 74 percent of the time, the remaining 26 percent of time in darkness poses a problem for the acquisition of energy from solar cells.4 Therefore, nuclear energy is used during times of darkness, when solar energy is unattainable. This source of energy is the most pragmatic alternate source of energy for a lunar base as there is abundance of helium-3 on the Moon. The use of helium-3 in the production of nuclear energy removes the risk of radiation.2

10. Conclusions and Future Research 10.1 Conclusion LH-1 was chosen to be located at Malapert Mountain, primarily due to its near-constant illumination and ease of communication with Earth. The design consists of a cylindrical building with an elliptical dome as the central hub, with four hemispheres branching out, three of which are greenhouses and one a scientific laboratory.

An inflatable structure was designed and is packed in a coiled configuration. The structure is supported with rigidizing foam and is covered with regolith in order to protect the crew from the harmful conditions of the Moon’s environment. The stability of the structure was verified through stress tests conducted in ANSYS®.

The design of LH-1 reiterated the feasibility of inflatable structures as a mode of lunar design. The stress analyses

conducted on the structure found that stresses from regolith and internal pressurization fell well below unacceptable percentages of the rigidizing foam’s yield strength and thereby verified the potential of structurally sound inflatables employing foam.

The practicality of a polar location for lunar bases was also reaffirmed. Malapert Mountain proved an effective site for erection of LH-1. The research also demonstrated that choice of location can effectively mitigate challenges faced in lunar construction, the most notable example being the choice of a polar location to avoid the intensity of temperature and sunlight fluctuations resulting from the Moon’s diurnal cycle.

Overall, the design of LH-1 serves as a testament to the attainability of lunar colonization. The realization of a permanent base is at least decades away, but the significant amount of research and design work currently being conducted demonstrates that the path to lunar colonization is one that humanity has already started down.

10.2 Future Research There are a number of further topics that require additional study for the successful implementation of a lunar base. Airlocks are a necessity and would impact the structural integrity of LH-1 or a similar project. Similarly, the effects of the lunar environment on plant growth must be explored further, expanding upon research into the topic already conducted on Earth.26 One of the most compelling reasons for the erection of a lunar base is the potential for use in future space endeavors. The distinctive conditions of the Moon make it an excellent site for the location of an astronomical observatory,27 as well as a

staging site for missions to other bodies in the solar system and beyond.28

11. Acknowledgments All of the research and work done for this paper would not have been possible without an extensive list of people and institutions, and the authors would like to express their gratitude to all of them for their support. They would first like to thank their invaluable mentors, Professor Haym Benaroya, and Nitika Yadlapalli, for the extensive amount of time and effort that they put into the research. Additionally, the authors would like to express their appreciation to the director of the Governor’s School of Engineering and Technology, Dr. Ilene Rosen, as well as the assistant director, Dean Jean Patrick Antoine, without whom this study could not have been pursued.

They would also like to thank all of the Governor School of Engineering and Technology staff for the hard work and planning that they put into the program and for making it the experience that it was. The authors thank Hack R Space for providing a 3-D model of LH-1. Finally, they would like to thank the many sponsors who have graciously donated to the program and allowed them to pursue their interests in science, technology, engineering, and, mathematics throughout this research project: Rutgers, the State University of New Jersey, Rutgers School of Engineering, the State of New Jersey, SilverLine Windows and Doors, Lockheed Martin, South Jersey Industries, Inc., Novo Nordisk Pharmaceuticals, Inc., and NJ Resources. 12. References

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