Designing a Habitable Artificial Satellite for Private, Recreational

Designing a Habitable Artiﬁcial Satellite for Private, Recreational Use

Lia Formica Andrew Nazzari [email protected] [email protected]

Natalie Reptak Rohil Sheth Claire Yan [email protected] [email protected] [email protected]

New Jersey’s Governor’s School of Engineering and Technology July 27, 2018

*Corresponding Author

Abstract—As space is explored and researched more, space off of an ISS module. Then, when the ISS is planned to retire tourism will have the opportunity to grow as an industry. in 2024, the commercial space station would take complete This project aims to design and test a space station with the control over the ISS [2]. ultimate goal of housing civilians for private recreation. Examples of current and previous spacecrafts were researched for their With new innovations and designs making breakthroughs in design, purpose, and function. A new type of artificial satellite the space industry, the pressure to join commercial aerospace was then developed, keeping in mind the differences between all is increasing. This, combined with the upcoming retirement the other research-oriented spacecrafts and this commercial one. of the ISS, may be the final step in changing low earth orbit This paper is comprised of two main parts. The first part explores space stations from being known primarily in research to the logistics of life on the station and sending civilians into space. Meanwhile, the second part focuses on the processes by which commercial-based. Computer Aided Design (CAD) software and 3D modeling were used to create an external design of the space station. Stress II.BACKGROUND analysis tests were then performed to determine the design’s A. Space Stations viability. In order to create an external design of a space station, I.INTRODUCTION research was done on current and past stations and their components. The focus was placed on stations such as the Space is associated with scientific study because of existing International Space Station (ISS), Mir, Skylab, and Salyut. space stations, meteorological satellites, and optical telescopes, Some of the most crucial parts seen were the prefabricated all of which focus on discovery and exploration. This research- and inflatable modules, and nodes, among many other parts. oriented notion, however, has been challenged; although pre- Modules are the basic building blocks of a station that com- viously dominated by government agencies, the aerospace prise the living spaces, cargo storage, kitchen, and exercise industry has become more attractive to private companies. One facilities. There are two categories of modules: prefabricated of the reasons for this is that humans are likely to end up in and inflatable. Prefabricated modules (prefabs) require no space, whether it be out of necessity or desire. The extraction assembly aside from attachment to the rest of the station. of Earth’s natural resources has tripled in the last forty years Inflatable modules are a more recent development, having only [1]. It would be favorable for humans to find another source of one test with the ISS’s Bigelow Expandable Activity Module raw materials and space travel would make this search easier. (BEAM) [3]. BEAM did, however, have a successful test, and Space stations like the International Space Station (ISS), now is now serving as a cargo storage module on the ISS. As the serve as foundations for new commercial designs. name implies, inflatable modules are compressed when sent Currently, there are projects in development concerning to space, and require inflation upon arrival. Modules can be commercials space stations. Some of these designs are shown attached to one another, or attached through nodes. Nodes are to be located on the ISS while others are new. For instance, connectors on the station with no other specific function aside one commercial space station proposal intends to build directly from allowing spacecraft assembly. These modules and nodes

1 have to be attached as well; this is done through Common 2) Water Filtration and Waste Management: Another com- Berthing Mechanisms (CBMs). The CBMs dock modules and ponent of the LSS is the Water Recovery System (WRS). Both nodes to one another. The last external features considered sweat and urine from the passengers would be transported to include solar panels and radiators. Solar panels are the primary the WRS and pumped into a Distillation Assembly, a keg- energy source for many space vehicles and radiators, for the sized drum that spins to create an artificial gravity that pulls thermal systems, regulate the temperature of spacecraft. the liquid waste to its walls. With the solutes of the urine and In terms of configuration, space stations follow similar con- sweat stationary relative to the walls, the drum is heated so struction patterns. For instance, the first module sent to space that the water evaporates from the waste and then condenses in should have the primary and secondary systems that enable the outer chamber of the Distillation Assembly as distillate [9]. it to be self-sufficient. It should also have the capabilities of The distillate goes through multiple filters that extract odorous providing power to the later modules. The next component gas, dissolved contaminants, organics, and microorganisms. should be nodes and adapters that would allow modules to be Iodine is added for microbial control. The water then moves attached to the first. By that point, humans could be sent up to to a final checkpoint where it will either be stored for the the station and assist with the rest of the assembly [4]. After inhabitant’s use or sent back through the filtration process [8]. the crew is sent up, any following pieces and their locations As supplies are utilized, waste is produced. On the station, are entirely up to the needs of the station. the crew hand-compacts waste material in a bag, duct tapes it shut, and stores it safely until the next supply vehicle arrives. The bagged waste is then loaded into an empty supply vehicle B. Software that is sent back to Earth, burning up upon reentry. The process The computer aided design software SolidWorks© Educa- for managing fecal matter is similar. Waste is sealed tightly tion Edition 2016-2017 was used to create three dimensional in a bag and stored in a rigid container to prevent cross drawings of each module of the space station. These parts were contamination between waste, crew, and space station [10]. then combined into an assembly of the entire station to ensure The garbage in the space station is stored in the inflatable proper connections. Each three-dimensional drawing was also module until a supply vehicle is available. used to make a two-dimensional drawing in the SolidWorks© 3) Thermal Systems: A space station in a low earth orbit software. similar to the International Space Station experiences sixteen SolidWorks© Education Edition 2016-2017 was also uti- sunrises and sunsets during one twenty-four hour period [11]. lized to perform stress analyses on each module. Using Sunlight has a significant effect on closed systems because SolidWorks© simulation software, the modules were tested the light can heat the satellite. The result is a sinusoidal for deformation and the von Mises stress experienced while relationship between temperature and time, where temperature under pressure. will rise when the satellite is exposed to sunlight and drop when on the dark side of Earth. This temperature range becomes a problem when thinking about passengers and cargo III.LOGISTICALCONSIDERATIONS on the satellite. Due to the nature of the satellite, the comfort A. Life Support System of passengers is a priority. The majority of space tourists are accustomed to air conditioning and other temperature control 1) Air Filtration: The main internal requirement for this systems, and expect similar treatment on the station. However, space station to sustain life is the Life Support System (LSS). thermal control systems are not solely for comfort as they are This system involves air filtration, water renewability and necessary for the station to function. The space station was filtration, and waste management. To begin and ensure proper designed to carry electronics and propellant, both sensitive air filtration, silica gel dehumidifies the cabin air [5]. Then, the to temperature change. Batteries are the most sensitive piece air passes through several filters, such as the lithium-hydroxide of equipment, and in order to work properly they need to bed, catalytic oxidizer, and activated charcoal bed [6]. This be stored in temperatures between, -5◦C to 20◦C [13]. This removes trace contaminants, such as methyl alcohol, acetone, is a significant problem as the station’s temperature without carbon monoxide, and other byproducts of human metabolism, thermal control would range goes from a high of 93◦C to leaving carbon dioxide as the end product. about -130◦C [12]. This means the spacecraft needs to take a To obtain oxygen, water electrolysis is frequently utilized 223◦C temperature range and shrink it to only 25◦C so that it and pressurized oxygen containers are considered as backups. can continue routine function. Electrolysis involves the decomposition of water into oxygen The space station utilizes both passive and active thermal and hydrogen gas. The oxygen vents back into the cabin while control systems. Passive systems include features like insu- the hydrogen byproduct vents out into space or is used with lation, special surface coatings, and heat pipes [12]. Satel- carbon dioxide in a Sabatier reactor. The end products of this lites in low earth orbit have experienced massive variation reaction are water and methane [6]. Water produced is used by in temperature, which results in the need for variable heat the crew while the methane vents into space or is expelled as systems, known as active thermal control systems. Active a way to provide additional thrust for maintaining the station's thermal control systems include radiators and heaters and are orbit [7]. only used when they are needed [14]. The radiators on this

2 spacecraft extend into space and are used to carry heat from Another prominent issue that affects people when they go inside to the vacuum of space. The system on this station to space is muscular atrophy. Muscular atrophy is a result closely parallels that of the ISS because radiator technology of the weightlessness that comes with staying in space [19]. has not made many advances since its introduction on the ISS. Though often thought otherwise, even people going on short- The system pumps ammonia, which was chosen for its heat term vacations, which would be the initial target audience of transfer properties and comparative safety, through tubing in the station, can be significantly harmed by muscular atrophy. order to carry the heat into space [12]. Since ammonia was This is a detriment that can be prevented, or at least mitigated, already determined to be the best choice for the heat transfer, through exercise routines and closely-watched diets [20]. The this space station also implements this system. ISS offers exercise equipment such as treadmills, resistance Two common radiator designs are extending systems and machines, and stationary bikes. While exercise routines are radiators on the side of the craft; however, expendable designs highly dependent on the person, astronauts did five hours are superior due to their ability to save space and dissipate of moderate aerobic exercise weekly, and resistance exercise heat on both sides of the radiator [13]. As a result, this three to six days per week [21]. satellite features two extending radiators on the sides of the Radiation also poses a large issue to humans when they Utility Module (UM). This mounting point was chosen due leave Earth's atmosphere. On Earth, humans are significantly to its proximity to electrical systems and optimal location for shielded from radiation because of the protective magnetic ammonia pumps. Additionally, the UM allows the radiators to field. Further in space, however, there is less protection. be placed in the direction of motion of the craft, which in turn Radiation mutates genetic material, kills cells, and can lead limits atmospheric drag. The radiators have to be large enough to cancer in high enough amounts [15]. A typical astronaut to dissipate all heat necessary; the size depended on all the is exposed to fifty to two thousand Millisieverts (mSv) of energy within the system, like the electricity used in different ionizing radiation, or the equivalent of one hundred fifty to electronics, and the energy from the environment [13]. The six thousand X-rays [22]. The station would thus need to space craft utilizes two radiator loops each that have eight compensate for the differences in atmospheric protection. panels, of comparable size to the ISS, that extend out into Microgravity also has the potential to cause pharmacologic space. The resulting system sends excess heat into surrounding and pharmacokinetic issues. Pharmacology investigates drug space to keep a consistent and comfortable temperature on the uses and effectiveness while pharmacokinetics pertains to the inside. rate of drug absorption and movement through the body [23]. In microgravity conditions, cardiovascular systems function B. Mental and Physical Health differently since blood pressure gravity-driven gradients are no longer present. This causes fluids, including blood, to There are many aspects of space that differ from the shift from lower extremities and limbs to the upper parts of atmosphere, climate, and environment that exist on Earth. the body, leading to an overall blood volume level decrease. Humans have evolved over time to live comfortably on Earth, Therefore, drug-receptor interaction and the absorption of but once sent into space, human bodies are put into disarray. drugs are altered. In addition to this, drug stability decreases in They are affected by radiation, muscle atrophy, and changes microgravity, with many medications changing physically and in sleeping patterns, among many other disruptions that would failing to meet dissolution requirements [24]. To ensure the interfere in guests’ daily lives on the satellite. Because all of effectiveness of pharmaceuticals, further research and testing these are conditions that would affect the guests and crew will have to be conducted. members, they need to be accounted for. Some other factors are the mental and psychological effects One of the most significant disturbances for passengers on of being in space. Although physical deterioration is important, the spacecraft is the sleep schedule. There are constant noise it cannot be forgotten that it is not just the body that is disturbances on the station from elements such as fans, pumps, going to respond to the extreme changes experienced in space. and motors that are in place to regulate the environment in the All the drastic environmental differences can make a short- station [15]. In addition, the station would be in a similar orbit term stay uncomfortable or unpleasant for a guest because to the ISS, which has sixteen sunsets and sunrises per Earth of the way cognitive functions and mood may be affected. day [16]. All of this means that guests would inevitably have These psychological factors are only significant during the their sleep disturbed. There are, however, ways to minimize the first few weeks in space, and the first few weeks back on sleep disturbances. After reviewing the lighting, temperature, Earth after returning [25]. Since the assumed stay time will airflow, humidity, comfort, noise, privacy, and security, it has not be extremely long, however, effects on cognitive functions been determined that the best sleep environment is cool, will have an impact on the guests'stay. dark, and quiet. To guests, this is a habitat perceived as Considering that visitors will need to adapt to an entirely safe and private [17]. In addition, when humans lack sleep, new environment in space and that there is no easy escape their immune systems suffer. This is an effect that could be route, it is evident that there will need to be extensive prevented by two two-hour naps [18]. To counter the multiple background checks and prerequisites for people to stay on sunrises and sunsets, artificial light and darkness would be the artificial satellite. A person's medical history, background, provided. drug usage, criminal record, blood tests, and psychological

3 history will all have to be analyzed before they are sent to by the carbon dioxide removal system. To reduce the noise, space. This will maintain safety not only for that one person, several additional acoustic blankets are placed near the micro- but also for the other guests staying in the station [26]. compressor. Also, the air conditioning system has fluid line Finally, food selection needs to be considered closely wrappings, acoustic covers on each air conditioning unit, and because of how diet affects conditions such as muscular covers on the compressors and centrifugal fan. Generally, the atrophy. Currently, existent stations all have similar modes type of fan used throughout the space station is a flight quiet of selecting food; it is a process that mainly takes place on fan developed by NASA. When compared to current ISS fans, Earth. Astronauts select foods they prefer from a selection this fan increases flow rate while reducing isolated noise levels of a few hundred that can be taken and prepared in space; from around 61-64 dBA to 48 dBA [30]. Therefore, through based on those choices, foods are selected that will properly these implementations, the possibility of significant health fulfill necessary nutritional requirements. With this system, it damages from acoustic disturbances is lowered drastically. would be possible for guests to have satisfactory meals while staying at the station. The food itself depends on the systems E. Energy Systems and Power Usage the station would have available. Because this station will The most plausible options for energy sources in space are not be using fuel cells, foods would be thermostabilized as solar and nuclear energy. Nuclear energy has not been permit- opposed to rehydratable. The reason behind this is that fuel ted for near earth human space travel as per a United Nations cells generate excess water that could be used to rehydrate resolution, so solar power is the safest option for commercial foods; however, this idea would be less plausible and efficient station purposes [31]. The satellite uses a derivative of NASA’s if implemented with solar cells. Food would be packed into Roll Out Solar Array (ROSA), with four separate panels that single-use containers to facilitate any meal exchanges in each provide 25 kilowatts (kW) of power, totaling 100 kW space and prevent food transfers with reusable containers in [32]. This provides sufficient power needed for all essential microgravity [27]. and entertainment systems. To store the energy produced by the solar panels, the C. Hygiene station utilizes 25 Lithium-Ion batteries. The ISS currently Hygiene in space is drastically different from hygiene uses 27 Lithium-Ion batteries, replacing two Ni-H batteries on Earth, and is thus something that should be addressed each in a lighter, more efficient format. The Li-Ion batteries separately, as it will affect the lives of guests and crew. To have been tested in space and are better suited to serve the start, while showers are possible in space, they are difficult station’s purposes than Nickel-Hydrogen batteries. They are to manage and extremely time-consuming, not to mention stored internally in the UM to minimize temperature deviation a waste of water. Skylab was the first station to include a and maintain a safe, stable environment. shower, and Mir was the last. In microgravity, because water Along with understanding the structure and function of the clings to the skin as opposed to sliding off, there is a long solar arrays, the power the station generates and the number of drying process that actually ends up dehydrating the skin of panels needed was studied. The ISS has eight solar arrays that the astronauts. Due to the complications, astronauts prefer provide 120 kW of power, but the ISS runs numerous energy- using wipes. Routines such as shaving, brushing teeth, and consuming research projects [34]. Since the artificial satellite washing hair were adapted to save water. Astronauts use edible is smaller and does not include labs, fewer solar arrays are toothpaste and no-rinse shampoos. For any kind of self-care needed. The number of arrays was calculated based on the involving hair (eg. washing hair, shaving, etc.), astronauts need ISS’s power consumption. For instance, the Functional Cargo to make sure that no hair is left floating in the air as it poses Block uses three kilowatts of power, the Columbus External a safety hazard. This means that usually astronauts will get Payload Facility Resources uses 2.5 kW of power, and the haircuts before going to space, and any additional haircuts are research accommodations payload racks use 3 kW, 6 kW, or 12 done through a vacuum. It also means that for shaving of any kW of power [35]. In total, the estimated energy consumption sort, electric razors are preferred, as they automatically collect of the ISS is 90-100 kW. For this satellite, energy usage is hair. Lastly, skincare is also important because skin dries out lower, at 85-95 kW. This addresses the essential systems and twice as fast in space as on Earth. Therefore, astronauts would recreational power needed for the initial modules. require lotion frequently [28]. F. Navigation Systems D. Noise Control The station requires regular reboosts and corrections to To ensure proper health, the Noise Criterion (NC), which maintain its orbit and avoid micrometeoroids and orbital debris ensures comfortable and safe acoustic levels, is adhered to (MMOD). Micrometeroids are small, microscopic particles [29]. One of the main contributing factors to acoustic dis- that can cause significant damage while traveling at high turbances is the space station ventilation system. This issue is velocities in space. As a result of atmospheric drag changing addressed by mounting the fans using vibration isolators rather the orbit of the station, a berthed capsule pushes the station to than a hard mount. In addition, acoustic linings are installed on the required orbit. For slight attitude control adjustments and fan control structures and fan speeds are limited. Another noise rotations, the satellite uses a combination of Control Moment disturbance is caused by an always-running micro-compressor Gyroscopes (CMGs) and thrusters distributed throughout the

4 different modules. The preferred method of attitude control J. Fire Control is the use of CMGs, which are 98 kilogram steel wheels In case of a fire, the satellite is equipped with several smoke that spin at 660 rotations per minute [4]. The CMGs have detectors installed in ventilation systems that link back to a a high rotation velocity coupled with a large mass that allows main control system panel. The control panel is observed by a considerable amount of angular momentum to be stored and the crew [41] and sounds alarms, also stating the location of used to reposition the station as needed. They are located in the fire. Based off of the ISS’s current fire control, if there is the UM, and use electrical power generated by the solar arrays. a fire, fans and electrical systems to its location shut down to For small adjustments, a series of attitude control thrusters will stifle the fire [42]. If this process does not succeed, the crew be used, which are scattered throughout the spacecraft. These inserts a fire-extinguisher nozzle filled with either water-based thrusters will have small openings to thrust in any direction. foam or carbon dioxide into fire ports [41]. For the purposes of this space station, there are both water-based foam and carbon G. Orbital Inclination and Altitude dioxide fire extinguishers onboard as each serve differently for The satellite orbits at an altitude of 390-440 km. This different types of fires. If the extinguishers do not function specific orbital altitude was chosen to minimize atmospheric against the fire, the module where the fire is taking place is drag while still keeping the satellite out of the highly irradiated depressurized [42]. Van Allen Belts which are filled with highly charged particles. The inner Van Allen belt is present at altitudes of 600˜ km to K. Ammonia Leak Control 1500˜ km, so the satellite must stay out of the belt in order to reduce harmful radiation exposure to the crew members and To address toxic ammonia leaks, a system control software passengers aboard [36]. Furthermore, the satellite must remain detects leaks and triggers the caution and warning (C&W) as high as possible to reduce the effects of atmospheric drag. toxic alarm. Along with this, the intermodule ventilation shuts The drag would cause the satellite to use fuel inefficiently down while leak isolation occurs. To ensure the safety of all when maintaining its orbit. Polar orbits do not provide the aboard, the passengers wear oxygen masks and move to the same amount of magnetic field protection against radiation, emergency evacuation capsules, which do not utilize ammonia. and are not easily accessed from launch locations such as Cape Removing the ammonia involves using trace contaminant Canaveral [37]. Therefore, the station will orbit in the same control equipment, harmful contaminants filters, and humidity rotation of Earth. This would allow the spacecraft to travel control equipment. If there is a large saturation of ammonia over multiple land masses and provide an optimal view for in the trace contaminant control equipment and the harmful the commercial passengers. contaminants filters, then the humidity control equipment is the primary method of ammonia removal. It collects condensate and then uses absorption techniques to remove ammonia H. Launch Vehicle from this condensate [43]. Once the space station modules To launch the elements of the station, a launch vehicle must have acceptable ammonia levels, the crew and passengers are comfortably fit the structures. After consideration, SpaceX’s allowed back into the main modules. Falcon 9 will launch the nodes and the inflatable module into orbit. The Falcon 9’s payload fairing has a diameter of 181.2 L. Radiation Protection inches and a utilizable length of 264 inches, which accommo- dates the nodes and the compressed inflatable module [38]. To Radiation is one main source of harm to people when in fit the larger modules, specifically the prefabricated modules, space. On the space station, guests and crew will be exposed the United Launch Alliance Atlas V rocket will be used to to two types of radiation. The first type is radiation from the launch the structures in orbit. The Atlas V long payload fairing sun; this radiation mainly consists of protons. While there has a diameter of 180 inches and a utilizable length of 480 are a large quantity of protons, they are all low energy. This inches, which is able to handle all large modules [39]. This makes it so that this radiation is mainly harmless as the combination of launch vehicles provides the most efficient way spacecraft itself shields those inside from the protons. The to launch the necessary modules. second type of radiation is the more harmful one, coming from galactic cosmic rays (GCRs). GCRs are also mainly protons, but they are made of heavier elements that can scatter I. Evacuation Procedures atoms in materials that they encounter. As a solution to this In the event of a catastrophic emergency, such as unexpected form of radiation, it is possible to either use more mass of depressurization or an uncontrollable fire, emergency evacua- traditional materials, or use materials that are more efficient tions take place. To facilitate this, several capsules can separate at shielding. With more materials, it adds mass to launch and from the main station and descend to Earth. This is similar also money to the cost, whereas with finding more effective to the ISS’s current evacuation procedure which involves the materials, mass and costs are cut but research is required. Soyuz TMA spacecraft capsules [40]. By incorporating this Some research has already been done, however, that shows same and tested procedure, this allows for a reliable and safe that hydrogenated boron nitride nanotubes form one of the passenger evacuation. best shielding materials against both types of radiation [44].

5 M. Shielding The artificial satellite will be traveling in Earth’s lower orbit, which means it would be in danger of the space debris and micrometeroids that fly around Earth. Space debris is classified into three categories: small particles, which have a diameter of less than one centimeter, medium sized particles, which have a diameter between one to ten centimeters, and large particles which are over ten centimeters. The average speed of the debris is 22,000 miles per hour [45]. The current forms of shielding NASA uses for its satellites and spacecrafts are Whipple shielding, avoidance maneuvers, and multi shock shielding [46], [45]. Whipple shielding involves a thin aluminum wall that is mounted from the module's rear wall. This acts as a bumper designed to break up the projectiles and distribute Fig. 2. Exploded view of assembly the impact momentum of the object over the wall of the spacecraft. The biggest flaw with this method is that once the shield is punctured, its structural integrity decreases and continues to do so until it can be replaced. Space debris that are greater than ten centimeters in diameters are tracked by the USSPACECOM radar. When the radar detects that these objects are a few kilometers away from the station, it alerts the satellites so they can perform their own manual maneuvers to avoid the projectile. The final form of shielding is multi shock shielding. This utilizes layers of lightweight ceramic fabric to act as bumpers, shocking objects to such high levels that they melt or evaporate before they can break into the spacecraft’s walls [45]. This project’s spacecraft will implement a mix of all three shielding methods to minimize the chance of space Fig. 3. The prefabricated module debris collision and maximize the crew's safety. IV. STRUCTURE impact from micrometeoroids. Additionally, the modules were designed with modern launch vehicles in mind. The prefab was made to fit in the largest launch structure available. The sizing and transport vehicle are discussed in a later section; however, it is important to mention the large scale of these modules. The prefabricated design is about ten meters long and has a diameter of just over 4.5 meters.

B. Observation Deck

Fig. 1. The full assembly

A. Prefabricated Module Prefabricated modules (Figure 3) are versatile tools in the design of the commercial satellite, as seen above in Figure 1. These modules are utilized in four different locations on the design, better displayed in Figure 2, with various degrees of modiﬁcation; for example, one of the prefabricated modules was modiﬁed with an observation area. The cylindrical shape was chosen for its strength and lack of failing points. The Fig. 4. A prefabricated module with two observation decks installed prefabricated modules are designed to be rigid. Multiple layers of aluminum and other protective materials allow the craft The Observation Deck (OD) is an essential part of the to hold up to internal air pressure as well as withstand station’s entertainment. This feature entertains guests with a

6 view of the cosmos. There would be two ODs on a modified prefabricated module, one on the bottom and one on the top to see Earth and space, respectively (Figure 4). When designing the ODs for the space station, the Cupola, or the ISS’s observation deck, was used as a model. The ODs are structured in a similar manner to the Cupola, with six windows on a hexagonal slant. Because the glass windows are more susceptible to MMODs, there will be shutters on all windows to protect from collisions. The rest of the ODs will be made of space-grade aluminum. One of the prefabricated modules was modified to allow for the incorporation of these two domes. The prefabricated module utilizes two ports, each of two-meter diameter, to incorporate these observation decks. Fig. 6. Isometric view of the inflatable module. C. Berthing Module fibers and other materials. Vectran has property retention over a wide range of temperatures, low moisture absorption and no measurable creep when loaded up to 50% of the breaking load [50]. Vectran is also twice as strong as Kevlar, a popular material used in aerospace applications [51] [3]. The design of the inflatable module (Figure 6) was based off of an ellipsoid shape, with an opening for a CBM at the curved end for connection to the station.

E. Utility Module

Fig. 5. Berthing module

The berthing module serves as a combination of an airlock and docking port, similar to the structure of the Pirs module [49]. The docking port uses the CBM standard throughout the rest of the station to connect to visiting spacecraft that are stationed as a reboost and emergency escape vehicle. As for the airlock component, there is a 48-inch diameter opening that juts out to serve as an isolated room for pressurization and Fig. 7. An isometric view of the utility module depressurization. The airlock is used for possible maintenance extravehicular activities (EVAs) or passenger excursions. The The design of the UM was based on the Zarya module, frame of the module is made of space-grade aluminum. The technically known as the Functional Cargo Block. Zarya was main body of the docking/airlock combination is a cylindrical the first step toward the ISS and fully autonomous [52]. shell. For the docking port, a conical shape was created that Similarly, the UM was designed to be the first module sent sloped inward. This design is seen above in Figure 5. into orbit and to bring up the batteries for electronic usage, radiators for thermal control, and the life support system. The D. Inflatable Module UM is a specialized block that is meant to be a self-sustaining The inflatable module is modeled off of BEAM. This tool to help start and grow the station. The structure, in Figure module serves as a storage compartment, as there is still some 7, was designed to fit all necessary equipment, and specific risk in using an inflatable structure as a fully habitable module. dimensions can be found in Figure 11. In addition to the This is due to increased vulnerability to MMODs compared to hidden interior systems, the UM also houses the equipment prefabricated aluminum structures. It mainly contains racks for for propulsion and repositioning. Inside of the block are the storage as well as a possible recreation center. The inflatable CMGs, which are used to rotate the spacecraft. Additionally, structure is composed of an aluminum skeleton and layers on the outside of the craft, there are attitude control thrusters of fabric. The fabric is Vectran, a proprietary material man- - which are too small to see on the module - that are used to ufactured by Kuraray, a Japanese manufacturer of chemicals, make smaller adjustments.

7 F. Common Berthing Mechanism

Fig. 8. Isometric view of the passive CBM. Fig. 10. Isometric view of the solar panels.

of a ROSA design with increased dimensions of 8.25m by 16.5m. This concept, depicted in Figure 10, should be able to produce between 23kW to 25kW of power. With four solar areas, it should produce between 92kW to 100kW of energy to power the station. This would be plenty to support the guests, with some extra energy production for battery storage and in case of solar panel degradation. Although radiation is not high in low earth orbit, it is still present and known to degrade solar Fig. 9. Isometric view of the active CBM. panel arrays. This long-term effect was factored into the design of the craft [56]. The commercial satellite was designed to follow common practices in order to integrate well with current and new technology. As a result, the station’s design includes the CBM to link the modules and to use as a berthing port. The CBM is the mechanism NASA uses on the ISS to link any two pressurized systems [53]. The CBM has become a standard model for berthing in space. As a result, most other pressurized systems should have no issues integrating into the station. It further allows for easy expansion later in the lifetime of the station. The CBM has two parts, an active and a passive piece, used in conjunction to create a connection. The active system, Figure 9, is usually the first put into orbit, then utilized to capture the module with the passive system [53]. To incorporate this idea, the node was designed with six active CBM each in a different direction. Although the node is the second piece to be launched, after connecting the UM the node was designed to be the central point of the station, and would Fig. 11. All the sizes associated with each module allow for five other modules to rendezvous with it. Each of those modules is equipped with a passive CBM, Figure 8, so V. STRESS ANALYSIS it could be captured by the station and quickly integrated. A. Analysis Set Up G. Solar Panels Testing each module was a crucial part of our research as The spacecraft was designed with Roll Out Solar Arrays it showed the capability of the designs. When setting up the (ROSA). ROSA is a new development from NASA, recently experiment, the goal was to create a simulation with values tested aboard the ISS, measuring 6.5m by 13.1m and produc- equivalent to what a space station would experience on a ing 18.2kW of power [54]. As discussed earlier, the energy daily basis. In order for passengers to breath comfortably, needs of the space station would be roughly 85 kW. To surpass the station was pressurized to 1.01 × 105 N/m2, or the air that energy necessity, the design would need five or more pressure of Earth at sea level [57]. This pressure was then used ROSAs. The ROSA design is an expandable format, shown to for the simulation tests. Due to the space around the station produce more energy when the number of panels is increased. being a near-vacuum the simulation only took into account For example, if the panels were increased by a factor of 26%, the atmosphere on the inside of the space station. This means the blanket would produce about five more kilowatts of power the modules were all tested by putting a constant pressure [55]. Due to the proved concept, the satellite takes advantage of 1.01 × 105 N/m2 on the interior and running a simulation

8 to see the materials’ responses. The simulation returned data about 9 × 105 N/m2. This means the module has the ability about the stress on different components and the deformation to handle over 1000 times the stress that is placed on it under experienced (displayed in Figure 18), which was sufﬁcient data standard pressure. Although the simulations seem promising, to draw conclusions about general structural concerns. the inﬂatable structure is only one piece of the larger satellite structure; the next step was to analyze all the different modules B. Stress Analysis Results to ensure passenger safety.

2.81 × 104 Fig. 12. Stress analysis test on the inﬂatable module. Scale ranges from Fig. 13. Stress test on the berthing module. Scale ranges from 2.818 × 106 2 4.91 × 101 to 1.029 × 106 N/m2 to N/m

After the completion of the modeling of our space station, each component was analyzed using SolidWorks© Simulation Software to ensure they would stand up to the pressure forces the system could experience. The first module that was completed was the inflatable structure. This design was the newest and most experimental, so it was important to design it such that the materials were strong enough to hold in the pressure and retain shape. BEAM on the ISS utilizes a material similar to Vectran, a Kevlar-like cloth with high strength, for the structure of the module [58]. Since this technology has been proven, the inflatable module was designed to utilize Vectran as well. Additionally, the stress Fig. 14. Isometric depiction of the stress analysis test done on the node. Scale analysis was done on a simplified version of the structure with ranges from 6.306 × 105 to 2.475 × 106 N/m2 only one layer of material in place of the final design that would feature a multi-layer system with materials that have varying degrees of structural capabilities. The stress test for the inflatable module can be seen in Figure 12. The bright orange coloration indicates that the stress is focused on the center of the inflatable module; however, it was determined to be of minor significance when the deformation of the module was analyzed. The resulting deformation on the inflatable module was only 1.29 × 10−4 meters. This means that when the inflatable module is pressurized, the Kevlar-like material that holds the module’s structure would expand. However, it would be by an amount so minimal that it would be barely even visible. Additionally, when comparing the stress experienced Fig. 15. Isometric depiction of the stress analysis test done on the Prefabri- by the module to strength capabilities, the inflatable module cated Module without the Observation Deck. Scale ranges from 2.975 × 104 is strong enough to hold the pressure. The yield strength of to 2.161 × 106 N/m2 Vectran is not disclosed to the public, but due to its close relation to Kevlar, the simulation was set to utilize the yield The next modules tested were the UM, nodes, prefabricated strength of Kevlar. To determine the strength, Von Mises stress modules, and the berthing port, each of which passed its distribution was utilized to compare the yield strength of stress and deformation test. All of these modules were made Kevlar, 1.24×109 N/m2, to the stress the structure experienced of the same material: aluminum 7075-T6, an alloy primarily [59]. The Kevlar-like material was found to be significantly used in the aerospace industry. This aluminum alloy has stronger than the maximum stress experienced which was a yield strength of 5.05 × 108 N/m2 [60]. As depicted in

9 Fig. 16. Isometric depiction of the stress analysis test done on the utility module. Scale ranges from 1.911 × 105 to 1.692 × 107 N/m2

Fig. 18. This table shows all the data associated with each module and their respective stress tests.

including prefabricated modules, inflatable modules, nodes, solar panels, radiators, a utility module, docking ports, and airlocks. With a stress analysis test conducted in SolidWorks© Fig. 17. Isometric depiction of the stress analysis test done on the prefabri- Simulation, the integrity and safety of the structures were cated module with the observation deck. Scale ranges from 0 to 5.813 × 106 proved, showing no significant points of failure or areas that N/m2 needed further reinforcement. This signified the practicality of using such structures made out of certain materials including their corresponding pictures, the modules easily passed the aluminum and Vectran in a harsh, unforgiving environment stress analyses and held up the pressure experienced on the such as space. On the non-technical side, numerous con- satellite. The stress analysis on the berthing module, nodes, siderations were researched to provide a holistic view of prefabricated module, and the observation deck can be seen the station. Through exploring essential systems such as life in Figure 13, Figure 14, Figure 15, and Figure 17, respectively. support, propulsion, and energy as well as life on board The greatest stress experienced by any of the four modules was and the safety and health of the passengers considered, spe- in the UM, which experienced about 1.82×107 N/m2 of stress. cific commercially-based applications were developed. With The stress analysis of the UM can be viewed in Figure 16. This a complete, comprehensive design for a space habitat from was not an issue that raised concern due to the fact that the scratch, this project serves as initial leap into the future of the aluminum yield strength was still 27 times stronger than the industry of space tourism and a blueprint for organizations and standard pressure of the module. Additionally, the deformation companies in the aerospace sector to begin developing such of each module was also monitored during the simulations. stations. The results were the aluminum structures barely deformed B. Further Research in the pressure. For example, the UM, which experiences the greatest stress of all the modules was shown to deform There are a few additional points of future research that by only 1.18 × 10−3 meters which helped to show that the need to be considered to develop a more thorough plan for modules were very sturdy structures. This helps to prove a space habitat. A more detailed modeling and design of the that the modules are more than capable of withstanding the station could be completed to include parts of structures that constant pressure that they could experience in space. Figure were simplified in this version of the station. Furthermore, an 18 includes more statistics from each respective stress test. interior structure and plan could be developed to take a look at how passengers can navigate through different modules and VI.CONCLUSIONS additional features that may need to be added internally. A. Conclusion This project successfully served as a thorough exploration ACKNOWLEDGMENTS into the practicality and design of commercial space structures The authors of this paper gratefully acknowledge the fol- meant for recreational purposes. Through intensive research lowing: mentor Michael Higgins for his invaluable assistance and CAD modeling of modules and features of the station, and aerospace expertise; Dean Ilene Rosen, the Director of a fully functional, aesthetic structure was produced that can GSET and Dean Jean Patrick Antoine, the Associate Director serve as a template for future organizations to develop com- of GSET for their management and guidance; research coordi- mercial stations. Detailed, realistic components were modeled, nator Brian Lai and head counselor Nicholas Ferraro for their

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