SelenAres Utah State University

Transcription

1 SelenAres Utah State University Team members: Ben Bodrero, Jessica Gregory, Aaron Jones, John Salmon, Erik Siggard, Juan Strömsdörfer Advisor: Dr. Todd J. Mosher Abstract - Many space exploration architectures exist to accomplish the goal of returning to the Moon but they fail to sufficiently consider Moon-Mars commonality as space exploration continues beyond the Earth-Moon system. By considering this commonality when making design choices, space exploration architectures can be more robust, flexible, and affordable for future planetary missions. In addition to optimal trajectory, launch vehicle and spacecraft selections, the SelenAres architecture presents the Modular Planetary Platform (MPP), which provides a large number of necessary uses for manned space exploration missions to the Moon and other locations in the solar system. The MPP is a versatile and flexible platform from which creative, robust and adaptable habitats, rovers and laboratories can easily be designed. The MPP subsystems include autonomous descent propulsion systems, connection system for initial lunar base establishment, mobility, communication, power, Environmental Control and Life Support (ECLSS), and interfacing capabilities with current and future launch vehicle and spacecraft designs. The MPP will also be sufficiently adaptable to accomplish other space experimentation such as green houses and science laboratories and achieve other mission requirements such as nuclear power modules and repair facilities. MPP modules can be combined in various ways to allow adaptable planetary bases appropriate to location, length, and type of exploratory mission. The adaptable MPP modules in connection with the other essential mission elements of SelenAres make this architecture an attractive and cost effective approach to return to the Moon and prepare for future missions beyond. 1. Introduction Since the release of President George W. Bush s Vision for Space Exploration, many individuals, small interest groups and large organizations have begun formulating and presenting various plans and mission architectures for realizing this vision and accomplishing the associated underlying goals. Some of these goals include completing the International Space Station (ISS), developing a new spacecraft for transporting humans, and returning to the Moon as the launching point for missions beyond [NASA 2004]. NASA has established plans for completing the ISS during the final missions of the Space Shuttle and a request for proposals to develop and build the Crew Exploration Vehicle (CEV) has been issued to contractors. The third main goal of returning to the Moon within the Vision for Space Exploration and its achievement has also been considered. However, a definitive plan or architecture remains to be developed by NASA. Creative and ingenious people both within and external to NASA have combined their ideas to offer the space community architectures, which could allow astronauts to eventually land and survive on the Moon, Mars and other planets. These architectures vary in complexity, cost and required levels of technology. Some include plans for short missions and temporary planetary bases on the Moon or Mars while others propose long-duration missions and potential permanent bases. Although a large variety of architectures for returning to the Moon are available for consideration, a few defining characteristics must surely be present for serious consideration and eventual approval. Perhaps the most important characteristic of a successful architecture will be affordability. Reducing cost for government sponsored programs is essential for the political and financial support of both the public and Congress. The new architecture must also have a reasonable schedule with appropriate financial deadlines and completion timelines for mission objectives. Lastly, the eventual selected architecture will need to be practical and flexible. It will not only need to be sufficiently robust to include modifications as technology improves but realizable with current technology in order to reduce cost and increase reliability. In an attempt to encourage affordable, robust and practical designs for space architectures and systems, NASA and the Lunar and Planetary Institute, have organized a forum for students from universities across the country. This Revolutionary Aerospace Systems Concept Academic Linkage (RASC-AL) Forum gives students the opportunity to propose and present innovative concepts and designs for human and robotic technology in regards to space exploration of the Moon and Mars. One of the main scenarios of the RASC-AL forum will be the application of mission or system elements and infrastructure in an innovative and unique manner in support of crewed exploration systems and that an example of this would be the application of technologies from one venue to another [RASC-AL 2005]. Therefore, an appropriately defined system level requirement is that the architecture proposed must demonstrate the required technologies, essential for a human mission to Mars, on a precursor mission to the Moon. The SelenAres space exploration architecture will meet these implied requirements in connection with RASC-AL forum theme for 2005.

2 In addition, this architecture considered the aforementioned requirements and attributes when developing the various subsystems and lower level mission elements to produce a practical and robust space exploration system. The project name itself SelenAres assists to keep in mind the key feature of practical Moon-Mars commonality, so that the proposed technologies can truly be applied from venue to another. As a result, SelenAres design choices reflect this quality and present technologies and plans, which can be used or easily modified for human space exploration missions on the Moon and beyond. One of these key design features, the Modular Planetary Platform (MPP), provides the required robustness and flexibility necessary for achieving this ideal. The MPP is an adaptable unit, which can be easily modified to meet a variety of human space exploratory functions such as habitats, laboratories, and power stations. The MPP design will be further discussed in the following report after a summary of the high-level mission elements and interfaces. 2. Mission Objectives, and Overview The SelenAres mission statement is To safely land humans on the surface of the Moon by 2015, have them return to the Earth and demonstrate the required technologies and necessary elements for a manned mission to Mars within the budgetary constraint of $15 billion. This will be accomplished by completing two additional mission objectives, namely to demonstrate an infrastructure to sustain a human mission to Mars and to establish common hardware between Moon and Mars missions. As mentioned in the introduction, the design of an architecture with the MPP as its characteristic feature is the major focus and design strategy for accomplishing the SelenAres mission. Missions to Mars are costly, lengthy and complex. However SelenAres presents and demonstrates hardware that could be used for a human mission to Mars through a precursor mission to the Moon. As much as possible, this precursor mission reflects the conditions, and constraints that exist for human mission to Mars. For example, the first human mission to Mars may have a minimum surface mission length of 30 days, due to launch opportunities and planet positions. Therefore, SelenAres has set a 30-day lunar surface mission requirement for the astronauts to survive in order to adequately demonstrate the technology for a future mission to Mars. Other characteristics of a human Mars mission have become requirements, which the SelenAres architecture and precursor mission to the Moon must satisfy as well. 3. Mission Architecture Element 3.1. Landing site Since specific science mission objectives are unpredictable for the first human missions to the Moon and Mars, and the landing sites and base locations depend on these science objectives, a particular surface location has not been defined within the SelenAres architecture. However, to further extend the Moon- Mars commonality characteristic of SelenAres mission elements, a mission scenario with potential landing sites was considered in order to specify environmental conditions to which MPP and other SelenAres elements have been designed. The lunar and Martian surfaces offer significantly different environmental conditions. Mars contains an atmosphere and a quicker rotational time relative to the Moon, resulting in shorter absolute days and nights. The Moon is much lighter and therefore has a smaller gravitational acceleration. Despite the differences of these two celestial spheres, some common environmental conditions at specific locations of the Moon and Mars exist, namely, temperature and landscape features. The Moon has dramatically variant temperatures at the equator while maintaining a near constant temperature of -96 C at either pole because of its orientation relative to the Sun. Mars, on the other hand, experiences temperature ranges comparable to that of Earth because its rotational velocity and axis tilt are fairly similar. The poles of Mars typically stay below -125 C while the equatorial regions stay between -89 C and -31 C as reported by the Viking 1 Lander [Levin 1997]. The main landscape features of interest on either body include maria and craters. Maria are relatively smooth terrain and advantageous for easy maneuverability and large landing areas. However, they also provide no shelter from some of the environmental hazards such as radiation, temperature, and meteoroids. Craters are of scientific interest because of the different material contained within in them due to comet and meteoroid impacts. They may also provide some shelter from low angled radiation or projectiles but are more difficult to maneuver through than maria. However, maria for a landing site were selected for the mission scenario because it safer and may provide terrain for exploration base expansion. After considering the environmental conditions of a number of possible surface locations for initial Moon and Mars missions, it was found that polar Moon and equatorial Mars locations will provide advantageous characteristics as well as high Moon- Mars commonality, such as cooler temperatures and the presence of maria. Some of the potential landing sites for the Moon and Mars are shown in Figure 1 and Figure 2 respectively.

3 Figure 1 Potential Polar Lunar Locations: Shoemaker (1), Amundsen (2), Ashbrook (3), Drygalski (4), Cabeus (5), and Idel son (6) Figure 2 Considered Martian locations: Chryse Planitia (1), Solis Planum (2), Amazonis Planitia (3), Elysium Planitia (4), and Isidius Planitia (5) 3.2. Crew Transport In order to interface with the rest of NASA s exploration plans, the SelenAres architecture will use NASA s Constellation program for transporting astronauts to the Moon and Mars. Since NASA has already begun preparations for a crewed vehicle to replace the Space Shuttle, the SelenAres architecture chose to interface with NASA s proposed CEV to fulfill the requirement for this spacecraft element. By assuming the development of the CEV, the SelenAres architecture has been able to focus in greater detail on the MPP design. Furthermore, for the purposes of this architecture it is assumed that interfacing features between the MPP and CEV (such as crew size and resources) are consistent and that the cost associated with CEV development falls outside the allocated budget for SelenAres. However, a short summary of CEV and its complementary components are given which are essential to the overall SelenAres mission concept and design. The CEV will provide the necessary crew habitation functions during ascent, in-orbit, and entry, including mission aborts [RFP-NNT05AA01J 2004, NNT05AA01J 2005]. It also provides the transportation functions to return from lunar orbit to the Earth surface. However, the CEV is only a part of a larger system called the Crew Transportation System (CTS), which is part of the Constellation Program within NASA. This transportation system includes all elements needed for human space flight. The Crew Exploration Vehicle - Launch Vehicle (CEVLV) will safely transport the crew from the surface of the Earth to LEO. Another element of the CTS is the Cargo Delivery System (CDS), which delivers un-crewed elements to LEO. The CDS consists of an Earth Departure Stage (EDS) and a Cargo Launch Vehicle for un-crewed elements, (assumed to be the Shuttle-Z within the SelenAres program). The EDS will provide the propulsive acceleration needed to transfer the CEV from LEO to lunar orbit and provide the deceleration for lunar orbit insertion. The Lunar Surface Access Module (LSAM), a detachable unit from the CEV, provides the crew transportation functions from lunar orbit, to the lunar surface, and the return back to rendezvous with the CEV in lunar orbit. In addition, the LSAM provides the capability for the crew to conduct limited science experiments and perform Extra Vehicular Activities (EVA) on the surface of the Moon. The LSAM itself will have enough supplies for astronauts to survive for only a short duration and ideally only until the initial MPP habitats have been deployed and made ready for habitation. Although the above elements have not been developed, the SelenAres architecture assumes they will be developed and operational before the required mission dates listed later in this report Launch Vehicles Since all mission hardware specified in the SelenAres architecture should allow for Moon-Mars commonality, the launch vehicle selected for lifting payloads to LEO for the lunar missions should also accomplish the same task for a mission to Mars with minimum modifications. The trade studies performed indicate that the Shuttle-Z (similar to the currently existing STS but modified to only carry cargo) will best suit the needs of the SelenAres architecture. Although the Shuttle-Z has not been fully developed and the exact specifications have yet to be determined, SelenAres assumes that this launch vehicle will be available and operational to use for the manned mission to the Moon in 2015 with a maximum deliverable payload mass to LEO (350km) of 140 metric tons. Although the SelenAres architecture assumes the future development of the Shuttle-Z, the design of the MPP has been constrained so that other launch vehicles, such as the Delta IV, can deliver MPP components to LEO (See Section 5.1) Therefore,

4 although the Shuttle-Z is the preferred launch vehicle to accomplish the mission, back-up plans exist to accomplish most mission objectives in the case where the Shuttle-Z Project is scratched, loses funding, or falls behind schedule Orbital Mechanics For human space missions, the most important design constraint of the orbital mechanics is the safety of the occupants on the spacecraft. Several trajectories have been explored and compared in various trade studies to establish the basic trajectory to be employed by the SelenAres architecture. These studies reveal that in order to ensure Moon-Mars commonality and the safety of the human astronauts, both mentally and physically, a Hohmann transfer will be used for human missions to the Moon and Mars. The substantial shorter time of flight, low duration in radiation fields, high commonality, and low complexity with only a moderate V requirement provides a cost effective transfer trajectory. Proposed Mission Mission description Date 2008* Investigate polar regions for initial lunar base with remote sensing satellites 2011 Test Shuttle-Z functionality by delivering large payloads (to LEO) Table 1 SelenAres Missions Schedule Comments In addition to the Hohmann trajectory proposed for the crew to maintain commonality for both Moon and Mars missions, the MPP modules will also use a Hohmann transfer for similar reasons to the above discussion. More specific V requirements for the MPP can be found in Section Mission Schedule Although, the SelenAres cannot predict exactly which missions and in what order they will be performed, the following proposed mission scenarios have assisted in developing a conceptual idea of when and what major system elements will be tested on different missions. The following table summarizes in greater detail the mission schedule for the SelenAres architecture. Some of the missions are impending missions (marked with an asterisk) since they will only be performed if funding and mission progression permit. This potential mission has been proposed in the event that additional information is required in regards to the selected lunar site for the lunar base. However, a lot of information is already available from such missions as SMART-1 and therefore this mission may be unnecessary. Testing of Shuttle-Z performed within Project Constellation Project Payloads may be additional modules for the ISS or other large satellites and equipment for LEO. Early 2012 First CEV flight (without LSAM) Testing of basic maneuverability, life support systems and EVA capabilities. Late 2012 CEV testing with LSAM in LEO Testing of detaching maneuvers and rendezvous between LSAM and CEV. Testing of LSAM life support and propulsion systems Early 2013 MPP testing in LEO Testing of MPP maneuverability and propulsion system for lunar surface descent. Most testing will be autonomous, since MPP descent to lunar surface will be autonomous Late 2013* Integration between CEV and MPP systems 2014 CEV to lunar orbit with MPP descent and landing on surface of the Moon 2014* Two MPP units deployed to the surface of the Moon - LSAM landing on lunar surface with two astronauts EVA with initial MPP base construction day manned mission on the Moon Deployment of additional two MPP units to lunar surface Testing of interfacing between MPP and CEV system (including EDS). May be combined with mission above. Autonomous landing of two MPP on lunar surface at lunar base site location. CEV via EDS will travel to lunar orbit and test MPP deployment processes for future lunar missions. This mission would mark the first manned mission to the lunar surface but would not complete all program objectives, in that all the technology for a mission to Mars would not yet be demonstrated. However, astronauts will test the MPP construction and connection capabilities of the two MPP units with the other MPP sent earlier in MPP life support systems will be tested. Mission length will not exceed one week on the surface of the Moon. MPP units will be deployed and sent to the surface of the Moon. LSAM with 4 astronauts will then land on the lunar surface. Astronauts will live on the lunar surface for 30 days demonstrating all remaining technology including the addition and connection of the two newest MPP.

5 4. MPP Overview and Variants A major feature of the SelenAres architecture as mentioned in previous sections is the MPP. The MPP allows human missions to the Moon or Mars to be flexible, re-configurable and robust by providing similar units that can be modified quickly to meet unpredictable needs or requirements. The principle of building blocks to create space systems was described by one author as a construction system, a set of standard modules and interfaces that can be moved, added, and replaced as needs change. [Dornheim, 1992] The MPP within the SelenAres architecture is one of these basic building units that can be easily modified to serve various purposes. Since planet exploration missions cannot be entirely predicted, these missions may require adaptable modules to accomplish tasks and meet objectives. For example, if it was essential that the entire lunar base or at least a habitat be relocated, motors and wheels could easily be attached to the MPP and these building units could be relocated individually and reconstructed in another area. Furthermore, the MPP unit completely allows for additions or changes to planetary bases. More MPP units could be sent to the surface to allow greater living space or resources for a greater number of astronauts. These units could be placed in various configurations, fulfilling various roles to build up a lunar base from very few initial MPP modules. In general, the MPP offers a versatile and flexible platform, from which creative, robust, and adaptable habitats, laboratories and other functional units, which can easily be modified to meet unpredictable requirements on the surface of a planet. Table 2, on the following page, illustrates some of the available roles or functions of an MPP. The MPP modules are easily adaptable even after they are on the lunar or Martian surface. For example, an MPP- Supply/Node module, once emptied, could serve as a central node, command module or laboratory. Another example is an MPP-Habitat, once its resources have been expended, serving as parts for a future MPP-Green House. With these various options, the MPP unit makes the SelenAres architecture very robust and adaptable. As a lunar base increases in size or number of inhabitants, more MPP units can be sent with different attributes to meet the needs of the evolving lunar base. Thus, the MPP provides countless combinations for lunar and planetary exploration bases. Using this quasi-standardized construction system and a common platform on which future parts will be based, the unit price for each part decreases, making the low cost MPP an attractive aspect of the SelenAres architecture. 5. MPP Subsystems 5.1. Structure The MPP s structure needs to endure any ground transportation, lift off, orbit, and lunar descent accelerations. Various shapes and geometries were considered for the MPP however, hexagons proved to be the best choice after evaluating criteria like area/perimeter ratio, manufacturability, and stability. The MPP s are placed on their hexagonal faces so that the vertical sides match up for interfacing between modules. The size of the MPP was restricted primarily by the shroud size of the Delta IV. As mentioned earlier, the Delta IV serves as a back-up launch vehicle in the event that the Shuttle-Z is not developed. Using the Delta IV as a design driver contributes to the redundancy and risk mitigation strategies characteristic of the SelenAres architecture. Furthermore, the potential to use a Delta IV launch vehicle is an application of current technology, which reduces the overall cost of the space architecture. Therefore, using the payload fairing dimension of the existing Delta IV as 4.57m in diameter [MDC 00H ], the length of one side of the hexagonal face of the MPP is 2.25m, giving a 4.5m separation distance of opposing corners. To provide sufficient volume for subsystem requirements, such as sufficient ECLSS resources, the height was set to 4m, which provides an internal volume of 52.6m 3. High strength composite carbon is used for the design of the MPP s structure. Composite carbon has a high-strength-to-weight ratio and low coefficient of thermal expansion. Geometries that allow pultrusion are ideal for manufacturing carbon composites. The structure is composed of a vertical stringer for each vertex, horizontal stringers for the lateral connections. Buckling calculations and finite element analysis allow the design to be iteratively improved to a safety factor of 1.25 [Larson 1999, Zubrin 2005]. Figure 3 MPP Structural Design (With and without cross-braces)

6 Table 2 Summary of MPP Module Variants MPP Habitat Contains sufficient food, air and water for two astronauts for 30 days (with additional reserves) Contains other equipment for extended lunar stay (i.e. two beds, bathroom, cooking galley, etc.) Independent communication and some power storage to provide power until MPP-Power is integrated MPP Power Nuclear power reactor containment module May be buried below surface or located a long distance from habitat modules for radiation protection MPP Lab Lab module is dedicated for scientific and space experiments. Contains equipment for astronomical observation, computation, biology and chemistry experiments, etc. MPP Mobility MPP Propulsion MPP Green House MPP Supply/ Node All MPP will be equipped with attachments for motors and wheels so that any MPP can be moved short distances (approximately 500m) Used to transport various MPP modules sufficiently close for connection with base structure May also be used for pressurized rover if some MPP components are removed All MPP require attachments for a propulsion system for autonomous descent. Propulsion system is removable in order to modify MPP further to attach wheels and make other modifications. Contains a jack type mechanism to lower or raise the MPP structure. This mechanism may be combined as part of the landing gear and pads. MPP skeletal structure used for support Windows are doubly paned and air tight to maintain pressure Window may be plastics or another light material (to reduce weight) through which sunlight is permeable MPP Green House will not be constructed on earliest missions Contains re-supply of consumables, necessary survival stores, and/or science equipment and can be used to connect adjacent MPP modules. One MPP-Supply/Node can potential connect to six other MPP in a spoke wheel type configuration. Note: All MPP have the ability to connect to other MPP via connection system which can both share power, air and other supplies Thermal The Thermal Control Subsystem (TCS) considers both the interplanetary and surface mission phases. Inherent in the analysis is the effects of radiation, conduction, and convection. During transport, no MPP systems are powered and there are no humans onboard. Therefore, the main requirement during the transport phase is deflection of solar radiation while maintaining the instrument survival temperatures. Once the MPP modules are on the surface, connected to power, and the subsystems are operational, the TCS will be required to maintain human touch temperatures between 40 C and 4 C for bare skin within the MPP [NASA-STD-3000].

7 The MPP TCS design will see modifications between Moon and Mars missions since rotational periods (and therefore temperatures cycles) vary. Also, the atmosphere on Mars has the capability of producing significant convection. The MPP modules will make use of both passive and active thermal control equipment to maintain appropriate equipment and life support temperatures. The SelenAres architecture proposes utilizing louvers, for switching between hot and cold time periods, heat pipes, which will effectively transport heat without the use of pumped fluids, and heat sinks to maintain proper operating temperatures of MPP subsystems Power Based upon the power requirements from other MPP subsystems, the power required for the initial mission in 2015 is shown in Table 3. Table 3 MPP Modules Power Requirements for Initial Lunar Mission Module MPP- MPP- MPP- Total Habitat Power Lab Quantity Lighting (W) Communication (W) ECLSS (W) Thermal (W) Instruments (W) Module Total (W) In order to provide this power and demonstrate a technology that can be used for missions to Mars, the SelenAres architecture proposes the use of a SAFE-400 nuclear reactor. The SAFE (Safe Affordable Fission Engine) -400 space fission reactor is a 400 kwt HPS producing 100 kwe to power the mission s MPP modules The reactor uses heat pipe modules made of molybdenum, or niobium with 1% zirconium. The mass for the power system is 584 kg. Although, radiation is a concern, the SAFE-400 uses a Lithium isotope in a stainless steel frame for neutron shielding, and Tungsten for gamma shielding. The MPP- Power module will be located approximately 500km away from the main base and eventually buried or covered with radiation shield. While the nuclear reactor is being connected to other MPP modules, the power required operating the food, air, and water systems will be provided temporarily by fuel cell power plants. The fuel cells provide 12kWe, covering the 850W needed to run the ECLSS system at a minimum. Each fuel cell is a selfcontained unit 0.90 x 0.97 x 2.90 m, weighing 118 kg. The power plants are fueled by hydrogen and oxygen from cryogenic tanks located underneath the MPP- Habitat. In addition, the water produced by the electrochemical reaction of the fuel cells can be used for spacecraft cooling Communication For both lunar and Martian missions, it is possible to transmit directly to Earth with radio communication. SelenAres will use a direct Moon to Earth radio communication system when the lunar base is in direct line of sight with the Earth and will utilize relay satellites during the times when the lunar bases faces away from the earth. In addition, SelenAres will test the CEV as a relay communication station. This will demonstrate a back-up plan and introduce communication system redundancy required for missions to Mars. For the SelenAres mission architecture the operating frequency has been selected as 10 GHz. This frequency will reduce the antenna size on a mission to Mars, where the signal propagation distance is so large. SelenAres communication systems will also be compatible with the Ka-Band (operating frequency range is GHz) for testing and possible future upgrades but to reduce cost by using current technology SelenAres will rely on the 10 GHz operating frequency. The communication system is located on the MPP-Habitat modules. As our initial mission has two MPP-Habitat modules, the communications systems are independent, to reduce risk through redundancy. The power required for the communications system for one MPP is estimated at 1200 W, and the required communication mass is 1800 kg spread over two MPP modules. For local communications (between the different MPP modules and during EVAs) an additional 20 W are available ECLSS The fundamental ECLSS system is able to support two crewmembers for 30 days and is contained within the MPP-Habitat. Missions requiring additional crewmembers or longer durations can be supported with added MPP and will be discussed. The basic MPP-Habitat contains: 1. Galley and Food supply - permits the preparation, consumption, clean up, and storage of a thirty-day supply of food. The Galley includes a freezer, an oven, a dishwasher, a sink/faucet, and other cooking/eating supplies. Based on the ISS requirements for food, each crewmember is allotted 2.3 kg/person/day of food requiring m 3 /person/day of volume [Bourland 1993, Lane 1996]. 2. Waste Collection system collects biologically decomposable, reclaimable, and non-recoverable

8 waste products that are in liquid, solid, or mixed form. Initially, the system is only able to recycle wastewater into potable water with the rest of the material being compacted for disposal. However, as the program develops with greater number of missions more of the waste materials will be decomposed, reclaimed, and recycled. 3. Personal Hygiene supplies - includes a shower, sink/faucet, and personal hygiene kit. 4. Clothing provides 15 changes of clothing and one EVA suit for each crewmember amounting to a mass of 64.5 kg/person and a volume of 0.42 m 3 /person. 5. Recreation equipment - includes supplies for communication with family, reading books, watching movies or TV, listening to music, playing board/card/computer games, etc. 6. Housekeeping supplies - provides a vacuum, wipes and cloths, and a trash disposal system to maintain a safe and habitable working environment that is free of disease and contamination. 7. Operations equipment - includes office supply and other miscellaneous items. 8. Maintenance equipment - provides the tools necessary to make essential repairs to the major systems on the MPP. 9. Water system provides the required 1.9 kg of potable water per day for drinking and food rehydration and 28.1 kg of hygienic water per day for showering, hand washing, laundry, dishwashing, and urinal flushing [Beasley 2004]. 10. Air equipment and source - continuously monitors and controls the partial and total cabin pressure, temperature, humidity, and contaminants, detects smoke and supplies oxygen, nitrogen, and other trace gases. 11. Sleep Compartments - similar to those on Earth with typical mattresses and bedding. 12. Crew Health Care - provides for the maintenance of optimal health (i.e. exercise equipment), allows for the diagnoses and treatment of sick crewmembers, and monitors and warns the astronauts of unsafe radiation levels or other chemicals in the air or water. Table 4 reports the mass, volume, and power requirements for the ECLSS subsystems within the MPP-Habitat [Larson 1999]. Figure 4 and Figure 5 and shows an isometric view of the MPP-Habitat and a potential MPP-Habitat layout, respectively. Other MPP modules contain emergency supplies of water, air, and food and can also house additional operations, maintenance and exercise equipment depending on individual mission requirements [Conners 1995, Allen 2003, JSC-38571C 2003]. Table 4 MPP Mass, Volume and Power Budget ECLSS Subsystem for ECLSS system Mass Subtotal (kg) Volume Subtotal (m3) Power Subtotal (kw) Galley and Food Waste Collection Personal Hygiene Clothing Recreation Housekeeping Operations Maintenance Water Air Sleep compartments Crew Health Care Total Figure 4 MPP-Habitat Isometric View Figure 5 Potential MPP-Habitat Layout

9 5.6. Propulsion The MPP propulsion system uses bi-propellant liquid hydrogen and liquid oxygen to transport the MPP modules from LEO to lunar orbit and eventually to the surface of the Moon. Analysis of the staging of the propulsion system revealed that three stages would be the optimal balance between propellant mass savings and complexity. Table 5 summarizes the propellant mass, volume, and burn times of the three separates stages of the MPP-Propulsion system [Bate 1971, Chobotov 2002]. Table 5 Propellant Characteristics of MPP-Propulsion System Stages prepare for lunar descent. Table 6 summarizes the V requirements for both a Mars and Moon trajectory and the MPP propulsion system staging for the various mission phases. The lunar descent stage inert mass must be removed from the MPP before attaching the mobility system as discussed in the next section. The propulsion system will be connected to the MPP by a standard interface that can also be used for the connection of the mobility system to the MPP. This connection interface will consist of a powered rod that can extend and then retract to clamp the various interfaces to the frame. The extension/retraction mechanism is controlled by a worm gear that will be mounted in the MPP at each corner. Figure 6 shows the MPP Propulsion system. Stage Number Total Propellant Mass 42,580 kg 6570 kg 5400 kg Total Propellant Volume 131 m m m 3 Burn Time 437 s 130 s variable Thrust 370 kn 190 kn 37 kn Total V 4158 m/s 1618 m/s 2250 m/s Each MPP will have its own propulsion system and will be autonomously landed on the lunar or Martian surface. Once the Shuttle-Z has delivered the MPP modules to LEO, the MPP modules will be individually transferred from LEO to lunar orbit and Figure 6 MPP Propulsion System Table 6 Moon and Mars V Approximations and MPP Propulsion Staging Mission Phase Trans-Planetary Injection (TPI) Planetary-Orbit Insertion (POI) Circularize Planetary Orbit Descent Transfer Orbit Powered Descent/Landing Total V to Surface Moon Manned/Cargo Trajectory Hohmann Transfer V RV = 25 m/s V TPI = 3083 m/s V PC = 1050 m/s V MCC = 80 m/s Mars Manned/Cargo Trajectory Hohmann Transfer V RV = 25 m/s V TPI = 4244 m/s V MCC = 80 m/s MPP Propulsion Stage (for Moon Only) Stage 1 V = 914 m/s V = 183 m/s Stage 2 V = 621 m/s V = 1297 m/s Stage 2 V = 20 m/s V = 246 m/s Stage 3 V = 2050 m/s V = 1000 m/s Stage 3 V =7843 m/s V =7075 m/s Comments Rendezvous and departure from 350x350 km, transfer plane 28.5 o, 20.7 o (Moon 2012) arrival plane, 83.4 hour (Moon) RV=Rendezvous, TPI=Trans-Planetary Injection, PC=Plane Change, MCC=Mid-Course Corrections Initiate 100 km (Moon) 200 km (Mars) for Planetary Orbit Insertion (POI), (Moon) initiate plane change to 90 o inclination for polar orbit, 11.5 hour (Moon) transit, 10.6 hour (Mars) transit Establish 100x100 km (Moon) 200x200 km (Mars) circular orbit Separate from transfer stage, and obtain elliptical approach ellipse 100x14 km (Moon) 200x50 km (Mars), Transit time 3473 s (Moon) 3290 s (Mars) (Moon) Staged Descent: braking phase, pitch up-down throttle phase, landing phase, transit time ~730 s (Mars) Staged Descent: braking phase, parachute deployment, assisted landing phase, transit time ~1.5 hours

10 5.7. MPP Mobility The MPP Mobility System (MPP-MS) allows the transport of MPP modules from the landing site to the base location. Since, the precise terrain on both the Moon and Mars is unpredictable, the MPP-MS must be sufficiently robust to transport MPP modules over varying surface inclines and over or around varying sizes of rocks and craters. Furthermore, it will provide a minimum transportation distance of 500m for MPP modules. (In designing the various MPP subsystems, SelenAres has assumed the landing site for MPP modules will be at a minimum 500m from the specific base location). Once the MPP module has landed, the MPP-MS is attached to the module s outer structure followed by the removal of the propulsion system and lowering of the MPP module. The MPP-MS is stored under the MPP near the propulsion tanks in the compartments on the edges of the MPP, which are covered to protect the wheels and other MPP-MS components during flight (See Figure 7). The MPP-MS components are stored within the MPP mobility compartments with the defined dimensions of 1.05 x 1.05 x 0.75m.The MPP-MS features a removable wheel structure with an electric motor in each of the wheel hubs. The MPP-MS has a basic wheel design with a wire mesh over a solid surface ( Figure 8) The wheels are approximately 1m in diameter and 0.25m wide at the widest point, with a center hub to house the electric motor of 0.20m diameter, and 0.10m wide. This design was chosen because of the modularity, ease of integration, and interface. Four wheels (with one wheel as a spare), with individual electric motors, contribute to the redundancy of the MPP-MS system, since up to two wheel-motor systems can fail before the MPP s mobility ceases entirely. The remaining two functioning wheel-motor systems can still transport the MPP over some terrain albeit more slowly. While the MPP is transported to the specified base position, an astronaut, walking nearby, controls the MPP-MS using a hand held wireless controller. The MPP is maneuvered and directed by driving the wheels on one side faster than the other. For more precise maneuvers the wheels can reverse on one side resulting in very small turning radii for the MPP module. The motor in the wheel hubs will transport the MPP at a maximum 5 km/hr, which results to a power requirement of approximately 8kW. The MPP-MS is designed to use the same power connection as the MPP descent stage in order to simplify integration below the MPP and potentially share resources between subsystems. The MPP-MS controller is designed to allow the astronaut using an EVA suit to be able to control the MPP. The controller is designed with large buttons and control sticks for ease of operation with defined dimensions of 0.25 x 0.25 x 0.025m. Figure 7 MPP-MS compartments Figure 8 Wheel for MPP-MS 5.8. MPP Connection System The MPP Connection System (MPP-CS) is the link between the various MPP modules of the Moon or Mars base architecture and must maintain an airlock to the surface and the ambient atmosphere of the MPP modules. The MPP-CS is a dual layer hybrid structure, which is a combination of an inflatable structure and a semi-rigid, fixed, or panel structure. This selection offers the advantages of low mass, volume compressibility and strength of inflatable and rigid connection options respectively.. The outer rigid structure supplies the necessary safety shell from radiation, debris and meteorites. The inner inflatable structure provides the interfacing and sharing for life support system resources, such as power, water and air and a physical access passageway between the modules if both connected MPP hatches are open. The inflatable structure of the MPP-CS is made of a multi-ply Kevlar and matrix material. The rigid skin is 6061-T6 aluminum paneling to protect from the outside environment. Rigid, reinforced aluminum planks are used for the MPP-CS floor and are stored under the MPP during transfer. The inner shell forms an airtight seal with MPP hatches through the MPP-CS attachment point and attachment brackets inside the Kevlar mesh. The attachment brackets have

11 long teeth that extend and secure the Kevlar matrix material into the hull of the MPP (See Figure 9). One or two astronauts in less than three hours can perform the construction and integration between the MPP-CS and MPP modules MPP Mass Summary Figure 9 MPP-CS Attachment The MPP-CS is comprised of two components, the MPP-CS corridor and the MPP-CS surface access portal. The interior dimensions of the MPP-CS corridor are 2.25m in height by 1.5m in width. It can connect MPP modules up to a distance of 3m apart and at maximum misalignment of 5 o. The MPP-CS surface access portal provides an airlock for compression and decompression, a don/doff station and a suit-stowage locker. It is approximately 4 meters in length and maintains the same cross-sectional area as the corridor (2.25x1.5m). The standardized cross-sectional area and the ability to construct the MPP-CS in various configurations contribute to the modularity of the MPP system. It also allows the astronauts to adjust the lunar base system to a variety of interconnections and orientations as the lunar base increases in size (See section 6). Some of the basic MPP-CS configurations are shown below in Figure 10. Table 7 summarizes the mass budget for a characteristic MPP-Habitat. Other MPP module variants are expected to have a smaller total mass since they will not include the entire ECLSS system capabilities. However, their mass budgets may vary according to their respective functions, components and requirements. Table 7 MPP Mass Summary MPP subsystem Mass (kg) Communication (per MPP-Habitat) 900 Power (Not MPP Power module) 118 Thermal 400 Structure 600 Propulsion System Propellant Mass Engine, tanks, insulation, etc ECLSS 2984 Mobility System 152 Connection System (per MPP) 700 Total mass (without propellant) 7354 Total mass (with propellant) MPP Base Development Since the MPP in connection with the MPP- CS allows for a variety of base configurations, an initial base architecture from the specified SelenAres mission scenario has been established. According to the schedule and mission descriptions, (See Table 1) four MPP modules will be used to demonstrating necessary technologies and mission elements for a human mission to Mars with a precursor mission on the surface of the Moon. One MPP-Power, one MPP-Lab and two MPP- Habitat modules and their successful integration for 30 days on the surface of the Moon will sufficiently demonstrate the essential mission elements to complete the SelenAres mission objectives. Figure 11 illustrates the initial proposed configuration of the four MPP modules on the first mission in Figure 10 Potential MPP-CS Configurations

12 Figure 11 Initial Base Configuration 2015 Mission Although, the SelenAres mission objectives are completed with the above lunar base, the MPP modules and the complementary modular features allow for any degree of expansion. From this above lunar base nucleus, more complex base structures can be developed. Attaching more MPP variants and building onto this basic structure, human exploratory missions can be comprised of short, long or permanent surface durations. Furthermore, the crew size can slowly increase in number as more MPP-Habitats are attached and integrated. Figures 12 and 13 illustrate two possibilities of using the MPP modules in various configurations for lunar bases with more astronauts and longer mission durations. A later mission configuration (Figure 12) shows a lunar base with four MPP-Habitats providing enough resources for eight astronauts. An MPP- Supply/Node is also shown, with three adjacent MPP connections, which would be filled with more food, water and air for the astronauts once the 30-day provisions of each MPP-Habitat are exhausted. Also, more living space would be provided in these additional MPP-Habitats since some equipment, such as bathroom facilities or kitchen appliances would already be available in previous MPP modules. Figure 13 shows a lunar base for 12 astronauts. Although, only five MPP- Habitats are shown, the fifth habitat will have sleeping accommodations for 4 astronauts. As mentioned in the previous paragraph, equipment (i.e. cooking appliances, exercise equipment) for these four additional crewmembers will be available in earlier MPP-Habitat modules. Also, in Figure 13 a variation of the MPP-CS is shown. One of the MPP-Lab modules is connect via two MPP-CS corridors to the main base. This illustrates modularity within the MPP and MPP-CS systems as the pattern becomes slightly distorted in this direction. Connection options, such as the one pointed out, allow for even greater possible arrangements, which may be necessary to avoid large obstacles such as rocks or craters as the base increases in size. Figure 12 Post-2015 Base Configuration-8 astronauts Figure 13 Post-2015 Base Configuration-12 astronauts 7. Conclusion 7.1. Budget The funds allocated for various mission elements within the SelenAres architecture are shown below in Table 8. Although this table was based on analogous space programs and projects, this budget has been beneficial in identifying a constraint on the development of the MPP, which is the main focus and scope of the SelenAres Mission. As indicated in Table 8 the design and construction of the MPP has been granted a budget of $8.5 billion US. It is expected that after the initial design process, the unit cost of MPP modules will decrease as similar components and manufacturing techniques are used to build MPP modules during, and after, the SelenAres Program.

13 Table 8 SelenAres Mission Architecture Budget Summary Budget Allocated SelenAres Mission Element ($Millions US) (FY2005) Shuttle-Z* (~4 launches) 2000 Other Launches (i.e. Delta IV) (~3) 1000 CEV* (~5 launches + ground control) 2000 MPP (~6 units) 8500 Programmatics 500 Margin 1000 TOTAL *SelenAres assumes Shuttle-Z and CEV are developed in a separate NASA program The above mission or program budget was based on a top-down approach in order to allocate a preset maximum amount of funds ($15 billion) that would potentially be accepted by Congress for a precursor human mission to the Moon. For an estimate of the actual cost of the various subsystems of the MPP a bottom-up approach is taken. This cost estimating method used the Advanced Missions Cost Model developed by NASA. This parametric model was created using the analysis of mission costs of many past missions and programs. This model uses subsystem mass budgets for the various subsystems to calculate the overall MPP development and fabrication costs for all 6 MPP (two test MPP modules and four flight MPP modules) required in the SelenAres architecture. Table 9 MPP Cost Summary MPP subsystem Communication Power (including MPP-Power) Thermal Structure Propulsion ECLSS MPP-Habitat MPP-Lab Cost ($ millions US) Mobility Connection System Total (for 6 MPP modules) Based on the parametric model, the estimated 6 MPP units required for the SelenAres architecture will be designed and manufactured at a cost estimated at just over $8 billion US. This cost falls within the budgetary constraint specified by the SelenAres mission statement, with around $500 million as a margin for the MPP design and an allotted $1billion as margin for the remaining SelenAres mission elements SelenAres Architecture Summary The SelenAres Architecture incorporates innovative ideas to allow hardware development that can be used for missions to the Moon as well as to Mars. A key component to this Moon-Mars commonality is the MPP, which is a highly modular and adaptable platform unit that can be easily modified and combined in different configurations to provide for a variety of space exploration needs. The small, nodelike MPPs can be arranged and used in various ways to accommodate different crew sizes and mission lengths. The versatility of this platform will allow astronauts to live, perform scientific experiments, and serve as a hub for travel and exploration of the lunar and Martian surface. It will be characterized by a smaller volume and weight than most other popular architecture habitats, to allow facilitated transport and the ability to connect with other MPP type nodes. The MPP is to be sufficiently modular that various attachments will enhance or modify its functions to perform roles such as a habitat, laboratory, green house structures, or power system containment. This architecture offers complete flexibility for future missions, since these adaptable MPP units can be used for both short and long missions and can be built up into larger and more complex networks if permanent bases on planetary surfaces are required. Furthermore, the SelenAres architecture is less expensive than other architectures since it uses smaller units to build the infrastructure, which reduces the cost of manufacturing components and development time since the platform and structure are reused in different orientations and configurations. Since more than one MPP will be produced and used on space exploratory missions, the overall unit price of one MPP will be significantly lower than a system with various platforms and designs Future Studies Further analysis of radiation shielding options for the MPP-Habitat will be performed as well as possibilities of using the propulsion system remaining fuel in fuel cells to power the MPP-CS and other MPP subsystems. Further modular variants of the MPP will be considered such as an independent pressurized MPP- Rover for extended science missions at locations large distances from the base Lessons Learned Designing an architecture, which is adaptable for unpredictable factors, and which achieves high commonality for both Mars and Moon missions is very challenging. Design choices that work for one of the locations are sometimes difficult to apply completely to the other and vice versa. The presence of astronauts and meeting human requirements significantly complicates designs with increased mass payloads, biological hazards, life support limitations and higher hardware reliability expectations.