04ICES-187 Systems Engineering Evaluation of a Mars Habitat Design
Klaus, D., Chluda, H., Ellis, T., Fehring, J., Howard, H., Jairala, J., Lloyd, T., Matthews, D., Morris, K., Rowley, K., Sauers, C. and Stephens, T. Aerospace Engineering Sciences Department, University of Colorado, Boulder, CO 80309 USA
Copyright © 2004 SAE International
ABSTRACT Key Assumptions - This design effort encompassed the surface habitat only, not transit or external equipment. The overall system architecture of a habitat intended for However, external interfaces were included. The habitat human occupancy on the surface of Mars was analyzed was designed to fully function only on the surface of as part of a graduate aerospace engineering design Mars, and will not be inhabited during transit. This class at the University of Colorado during the 2003 fall design therefore focuses only on the surface operations semester. The process was initiated by summarizing and of the habitat, although relevant aspects of launch, deriving the governing requirements and constraints transit, and Mars landing were considered. Also, it was based on NASA’s “Reference Mission for the Human assumed that the mission architecture delineated by the Exploration of Mars” (Hoffman and Kaplan, 1997; Drake, DRM would be present upon arrival of the habitat, 1998). With emphasis placed on requirement including a nuclear reactor providing 160 kW of power, identification and documentation, a baseline design was with 25 kW allocated to the habitat. The cabling to established that incorporated functional subsystem transfer the power is included with the reactor. The In definition and analysis of integration factors such as Situ Resource Utilization (ISRU) plant, along with 2 large structural layout, mass flows, power distribution, data pressurized rovers capable of moving the habitat, will be transmission, etc. In addition, a ‘human-in-the-loop’ located on the surface. Several small rovers will also be focus was stressed by designating a subsystem termed present. The planned launch vehicle will be capable of Crew Accommodations. To further support this function, lifting 80 metric tons (mt, or tonnes) to LEO. a Mission Operations team was established to ensure that relevant crew health and well being factors were Other assumptions are as follows. The crew would have included as integral components of the habitat design the capability to perform EVAs. There could be no and operational planning. Generic human spacecraft dependence on the Crew Transfer Vehicle (CTV). design requirements, detailed in the Man-Systems Communication satellites would be in orbit around Mars. Integration Standards (MSIS, NASA STD-3000 Rev. B, Up to a 40-minute communication delay would exist with 1995), were incorporated as applicable throughout the Earth. Physical profiles of all crewmembers would fall process. Results from the integration analysis were used between the 5th percentile Japanese female and the 95th in conjunction with detailed subsystem operational and percentile American male human profiles. Environmental volumetric requirements to assess compatibility of floor factors at the habitat site would be within the conditions plan options proposed in various existing architectural found by Viking and Pathfinder (Tillman 2003). habitat concepts. The resultant conceptual design, therefore, represents a unique merger of a traditional Engineering Requirements - The top-level requirements systems engineering approach with both architectural taken from the DRM are to support a crew of 6 for 600 interests and human factor considerations. days without re-supply while maintaining the health and safety of the crew, as well as minimizing the dependency BACKGROUND on Earth. Other key requirements include utilizing the 80 mt launch vehicle, deploying the habitat two years PROJECT DESCRIPTION before the first crew and providing capability for a 10- month standby between crews. Design Reference Mission (DRM) - This design exercise used the basic mission outlined in versions 1.0 (Hoffman Design Philosophy - As with all space missions, it was and Kaplan, 1997) and 3.0 (Drake, 1998) of the NASA essential to minimize mass, power and cost for this Mars DRM. This document outlines a large-scale project. However, mass proved a bigger driver than extended-stay human mission to Mars consisting of power because the launch capability was well defined, three separate crews over 10 years. while the power source has yet to be designed. The goal of this design was to focus on an overall systems engineering approach incorporating human factors and infrastructure interfaces. Hardware choices were limited The project was divided into 12 subsystems at the to technologies with TRLs of 7 or better, and subsystems beginning of the project termed ‘Mars or Bust’ (MOB), were designed to handle worst-case scenarios to including Program Management and Systems establish a baseline design. The design met the full Engineering and Integration. The remaining subsystems redundancy requirements of the DRM without analysis of and their functional descriptions follow. The ISRU reliability. Planetary environmental protection and interface subsystem is responsible for the interface mission justification factors were not considered, as they between the ISRU plant and the habitat’s consumables were deemed programmatic rather than engineering storage. The Structures subsystem provides a habitable decisions. The design was based heavily on the key volume and structural supports for the habitat and DRM requirements, as reevaluation of these top-level subsystem components. The Structures team is also requirements was not within the scope of this project. responsible for the overall layout of the habitat, taking into account mass distribution, radiation protection and Baseline Design Description - The habitat has a total thermal considerations. The Electrical Power pressurized (10.2 psi) volume of 616 m3, a usable Management and Allocation (EPMA) subsystem stores volume of 211 m3, an overall mass of ~68,000 kg, and a and distributes power from the nuclear reactor. The maximum power consumption of 43 kWe. The basic Environmental Control and Life Support system (ECLSS) geometry and structural layout is shown in Figure 1. is responsible for supplying necessary consumables and maintaining a ‘shirtsleeve’ environment. The Thermal Control subsystem is responsible for all thermal control and heat dissipation except the cabin air heat exchanger, which is the responsibility of ECLSS. The Crew Accommodations (CA) subsystem is responsible for incorporating human factors into the design (along with MO) and providing the day-to-day equipment required by the crew for hygiene, maintenance and medical needs. The Command, Control and Communication (C3) subsystem supports and manages the habitat’s data flows by providing data processing and communications equipment. The Robotics and Automation subsystem is responsible for interfacing with mission robotics and designing major structural mechanisms such as the radiator deployment device. The Extravehicular Activity Subsystem (EVAS) is responsible for designing the airlock and the interface between the habitat and the EVA suit and pressurized rover. The Mission Operations team is responsible for scheduling operations, delineating automated and crew- operated tasks, and addressing safety and efficiency Figure 1. Habitat structural layout. concerns.
KEY DESIGN DRIVERS AND CHALLENGES
SYSTEMS ENGINEERING – The responsibilities of the MARS ENVIRONMENT - The Mars Environment team’s Systems Engineering team were to ensure cohesiveness main objective was to collect all available environmental of the habitat design and fulfillment of all mission parameters for the surface of Mars and identify their requirements. Specific tasks include identifying and relevance to the surface habitat design. A Mars deriving requirements from the DRM, delegating those Environment Information Sheet was created and requirements to the subsystem teams, reviewing and distributed to all other subsystems to ensure consistent reconciling subsystem designs, and coordinating parameters were used throughout the design. Table 1 subsystem interfaces. This team also worked closely shows selected relevant parameters of the Martian with the Mission Operations (MO) group to ensure that Environment. consideration of human factors was addressed from the beginning of design. They teamed with project Gravity on Mars is ~1/3 of that on Earth and is basically management to oversee, organize and direct the constant over the planet. The atmospheric pressure subsystem teams, develop report and presentation varies from 4-10 millibars (mb) (Tillman, 2003). Surface templates, establish comprehensive project schedules, temperature is site-specific and was based on the Viking conduct meetings, and provide expertise to individual and Pathfinder missions for this exercise (Tillman, 2003). subsystems. Special attention was given to integration of Selection of the actual landing site will dictate the the habitat with the overall mission infrastructure, ultimate range. Radiation remains a major concern for a including rovers, cargo landers, and nuclear power Mars mission, although the expected annual dosage of plants. 21.2-24.7 cSv on the surface is less than the current low earth orbit (LEO) limits of 300 cSv for skin and 50 cSv not found, however. In addition, the launch vehicle for Blood Forming Organs (BFO) (Simonsen and Nealy, dimensions outlined in the DRM (Hoffman and Kaplan, 1993). The Earth-Mars transit period is of greater 1997; Drake, 1998) dictated a longer, narrower pressure concern in this regard, and considerable research is shell than that found in most Mars habitat designs. underway aboard the ISS to better understand the Therefore, it was decided that the MOB habitat would be issues. Surface wind speeds are relatively high horizontally oriented. Though habitat stability was the compared to Earth, but the actual dynamic pressure is primary driver for this decision, this orientation provided less due to the low atmospheric density (Withers, 2002). other benefits as well, including ease of exterior Wind, therefore, is not a major factor per se, although maintenance access, emergency ingress/egress from abrasion and dust accumulation can become a problem the second floor, and internal mobility (fewer stairs), as for external elements such as radiators and solar panels. well as a more open, psychologically pleasing floor plan.
Parameters Maximum Minimum Average There remain, however, some issues associated with this orientation that were not fully addressed in this Gravity (m/s2) 3.758 3.711 3.735 design iteration. For instance, the DRM indicates that the habitat will land on its end, in which case the habitat Atmosphere 10 4 8 would require a single-use mechanism to orient the Pressure (mb) habitat. This mechanism was not included within the scope of the MOB design, and may have a considerable Surface 27 -143 -63 mass penalty. Temperature (˚ C) Once the orientation was determined, volume Radiation (cSv) 24.7 21.2 allocations, use of curved wall space, ease of access, equipment noise isolation, systems proximity, center of Wind Speeds (kph) 36 0 mass, and radiation shielding were all considered in the layout of the habitat. However, these factors were not examined in detail and their influence on the orientation Wind Storm Speeds 127 of the habitat has yet to be fully determined. These issues must be studied in detail to determine, in a Table 1: Key Mars Environment Parameters subsequent design stage, whether they could be reasonably met, or if the horizontal orientation selection should be reevaluated.
Some possible alternatives to the MOB habitat design STRUCTURES - The Structures subsystem provides a might include designing the habitat to land in a horizontal habitable volume and structural supports for the habitat orientation or a shorter habitat with a larger diameter and subsystem components. The Structures team is also than that prescribed in the DRM (as is the case with responsible for the overall layout of the habitat, taking most previous designs). These alternatives would into account mass distribution, radiation protection and address many of the challenges described above. thermal considerations. Finding materials that will fulfill support requirements with a minimum mass was given a POWER - The primary responsibilities of the EPMA high priority. subsystem are to interface with the nuclear power source and other equipment external to the habitat, and The challenge for this design, structurally, was defining to condition power from the onsite nuclear reactor for an acceptable orientation and overall layout. The either distribution throughout the habitat or temporary baseline design described above is oriented on its side storage in mobile and stationary power storage units. rather than in an upright position, primarily for stability and ease of mobility. This orientation is contrary to the Mission Voltages – High voltage (≥120V AC) is desired majority of Martian habitat and analog designs that have to transfer power from the nuclear reactor to the habitat. been published to date. Mars Desert Research Station The MOB habitat voltage is designed to be 120V AC, a (The Mars Society, 2003a), Flashline Mars Arctic decision based primarily on the size of the habitat and Research Station (The Mars Society, 2003b), the the distance that power needed to be transferred within winning ESA Aurora student design (Fisackerly, et al., the habitat. However, as a significant amount of COTS 2003), and the Mars Direct design (Zubrin, 1996) are all technology is designed for 28V DC, a detailed trade oriented upright, but have a height half that of the MOB study to assess all operating voltages is advisable. habitat’s length and a larger diameter. One notable example of a habitat design with an orientation similar to Radiation/Electromagnetic Interference (EMI) Protection the MOB design was the NASA INTEGRITY mission – It will be vital to protect the EPMA subsystem from the (INTEGRITY, 2003), recently renamed Advanced potentially powerful solar events that may impact the Integration Matrix (AIM), which featured several habitat. Recent solar events have disrupted power grids horizontally oriented cylinders connected to each other on Earth, and the consequences of such storms on by a corridor. Published rationale for this orientation was Mars, where the atmospheric and magnetospheric protection is much less than that on Earth, may be water purification system is the best way to minimize the severe. For this reason it is recommended that the vital required water mass. However, the regenerative components be placed with communication equipment technologies reviewed in the trade study generally had inside a safe haven where radiation/EMI protection is TRLs of less than 6, which was deemed to low for this maximized. design. Extracting water from fecal matter would slightly reduce the required water mass. The launch mass of Survival Mode – It may be necessary to perform an EVA food for subsequent missions can be reduced once it is during a contingency ‘survival mode’ period in the demonstrated that crops can be successfully grown on habitat. Ensuring that power is available for this activity the surface of Mars. In addition, further optimization of requires that a relatively large amount of power be the ECLSS by increasing consumable recycling and stored. Hence, this mode may significantly drive the minimizing leakage could result in considerable mass design of the batteries and/or other backup systems. and volume savings.
Habitat Power During Setup – The habitat’s dependence Other issues remain unresolved. For example, the on power should be minimized or eliminated in standby location of waste storage has yet to be determined. In mode, since it may be separated from the nuclear the current design, all waste is stored outside of the reactor for an indeterminate amount of time after landing habitat, which requires crewmembers to carry it out. If on Mars. This will create challenges for all of the other EVAs are not scheduled approximately twice a week, a subsystems, particularly those that may require heat designated area for waste disposal inside the habitat will (batteries, consumables, etc.). Power storage may be necessary. There is also concern about planet alleviate this problem, but careful planning and a high surface contamination if waste is stored outside. degree of reliability in the Habitat/Nuclear Reactor Additionally, while advanced life support technologies connection process will likely be required for a robust are continually evolving, the design of this subsystem is solution. limited to technologies with current TRLs of 7 or more. Therefore, although the ECLSS successfully satisfies all Minimizing Heat Production – The size of the radiators the design requirements and assumptions laid out for was a major concern in this habitat’s design. In future this project, it is not optimized for future developments. iterations, the radiator design must improve dramatically or the heat load created by the habitat must be reduced. THERMAL - The thermal subsystem is responsible for Because a large amount of heat within the habitat is maintaining adequate operational temperatures for the generated through cabling and appliance inefficiency, habitat and all equipment under all mission improving overall system power efficiency, and thereby environmental extremes. This involves collecting heat minimizing heat generation, should be a major driver in from or providing heat to all the subsystems and the the design of this subsystem. crew. Any excess heat will be dissipated to the Mars environment. ENVIRONMENTAL CONTROL AND LIFE SUPPORT – ECLSS is comprised of four smaller subsystems: There are five main components of the thermal atmosphere, water, food, and waste management. The subsystem design: cold plates, fluid loops and piping, integration of these four subsystems is as follows: The pumps, heat exchangers, and radiators. Heat is Food Subsystem receives potable water from the Water collected from local sources by cold plates and Subsystem. This water is used for drinking and to re- transferred into an internal fluid loop. The fluid is hydrate food. Condensate is recovered from the pumped through a heat exchanger, which transfers heat Atmosphere Subsystem that, after undergoing treatment, into the external fluid loop. The fluid is then cycled qualifies as potable water. Urine is also recovered from through the radiators where the heat is rejected the Waste Subsystem for subsequent use. Water is passively into the Mars environment. provided to the Atmosphere Subsystem for oxygen production using Solid Polymer Water Electrolysis. The radiators in this design were far larger than Finally, unusable waste is passed from the Food expected. An estimate of the habitat’s heat load was Subsystem and Trace Contaminant Control to the Waste based on the total power coming into the habitat from Subsystem. This mass includes a combination of the power plant, human heat production and Martian packaging plastics and food waste generated during environmental factors. meal preparation and cleanup. Using this estimated heat load a worst-case radiator The current ECLSS design is primarily non-regenerative, area was determined, resulting in a radiator system of which results in a large consumable mass demand. It is over 3300 kg, representing over half of the total thermal therefore critical to conduct an accurate calculation of subsystem mass. This mass far exceeds the 550 kg consumables required for the mission. The required allocated for the thermal subsystem in the DRM. water mass should be determined by a detailed analysis of water use, loss, and recollection in a number of Another challenge with using radiators on the surface of habitat mission processes (i.e. drinking, hydrating food, Mars is dust accumulation and performance degradation oxygen production, cooling, showering, vapor leakage, over time. A more accurate analysis of radiator material and urine processing). Increasing the efficiency of the degradation in this environment is needed as well as an effective method for cleaning the panels after dust all must be designed to function effectively in the accumulation. reduced gravity environment.
The Martian environment is a major design driver. Crew psychological health is dependent on the layout Because environmental factors vary widely depending and use of habitable volume. Human factors studies on the habitat’s location, the thermal system cannot be suggest that Mars crews will benefit greatly from a large fully optimized until a specific landing site is selected. gathering area where meals, meetings, and celebrations can be shared. In addition, it is suggested that crews There are many ways to reject heat to the environment. will benefit from personal quarters, ideally including Radiators can quickly become massive depending on sleep provisions, personal storage and a desk. the environment in which they are designed to operate and lifetime degradation factors. Alternative heat The transmission delay between Mars and Earth of rejection methods, including use of convection, approximately 20 minutes will drive the selection of conduction to the ground, and phase change materials, communications equipment, as crewmembers must may provide a more mass-efficient cooling system. utilize methods other than real-time voice loops to stay in touch with friends and family on Earth. As a result, Convective cooling could be incorporated into the outer ample personal video, audio, and e-mail transfer to and skin structure of the habitat and heat could be conducted from Earth must be supported. to the Martian soil. The day / night cycle of Mars may allow the use of a heat sink inside the structure that Crew selection will drive the design of many CA could store heat produced during the day and then provisions. Size and gender of crewmembers will affect release it at night when the radiator panels would be aspects such as food quantity needs, exercise much more efficient. Phase change materials could melt equipment design, clothing requirements, privacy issues, by absorbing heat during the day and refreeze by medical equipment, and toilet designs. This project rejecting heat during the night. assumed human body size to fall within the MSIS human profile definition of 5th percentile Japanese female to 95th CREW ACCOMMODATIONS – The success of the percentile American male (NASA-STD-3000 rev. B, mission is clearly dependent on the ability of the crew to 1995). If crewmembers were selected from the low end execute their assigned tasks. Therefore, maintaining of this range, food and clothing mass alone could be crew mental and physical health is a high priority. The considerably reduced. The reduction, however, may not Crew Accommodations (CA) subsystem is responsible be worth excluding qualified astronauts who fall in the for providing the everyday necessities, not provided by higher end of the range. ECLSS, which are needed to support the crew physically and psychologically during all stages of the mission. CA Crew well-being will be greatly enhanced through support falls into six main categories: hygiene, habitat workstation designs that consider human reach profiles, maintenance and cleanliness, psychological support, encourage comfortable body posture, and provide routine and emergency medical supplies, exercise adequate lighting for the crew members (Larson and equipment, and habitat ergonomics. Most of these Pranke, 2000). Human factors engineers must work with categories utilize hardware that will require crew habitat architects early in the design to ensure these operations; therefore, CA must work closely with Mission needs are met in the Martian environment. Operations to develop the associated operational plans and to select hardware with human factors in mind. In Current designs and reliability numbers suggest that addition, CA and Mission Ops must develop activities sufficient risks are posed such as to rule out EVA and schedules that promote crew health. intended solely for recreational purposes. If this level of risk decreases, the use of EVA as a primary tool for Design Drivers – The level of autonomy of the CA recreation could reduce the need for internal exercise equipment is an important design driver, as there is a equipment, consequently reducing mass, design and critical trade-off between mass and crew time demands. fabrication time, as well as dedicated volume required In this case, a mass balance trade study determined that for equipment use and stowage. a Mars mission of 600 days should utilize appliances such as dishwashers and clothes washing machines, Challenges – Human factors and CA will be more crucial even though these units require their own mass and in a Mars mission than for any space mission to date, power (Larson and Pranke, 2000). The use of such due to the mission’s duration and distance from Earth. equipment optimizes water need and allows for reusable Therefore, CA must work with the other Habitat items such as kitchenware and clothes rather than subsystems early in the design process to ensure that disposables (Lynn, 2003). the integrated system will be capable of supporting the crew physically and psychologically. The Mars gravity of approximately 1/3 g is a significant design driver for CA, since the subsystem requires a Although our project focused on Mars surface phase of variety of active hardware that is affected by gravity. the mission, the transfer to and from Earth entails many Hardware such as medical equipment, dishwasher, psychological concerns for humans. With current washing machine, clothes dryer, and exercise equipment propulsion technologies, the crew will endure long- duration exposure to weightlessness and harmful The C3 subsystem throughput capacity resulted almost radiation, along with significant acceleration profiles exclusively from human factors related communication during launch and landing activities. needs. Communication needs were determined by polling each of the other subsystems. Based on Careful consideration needs to be given to the selection subsystem input, a time-averaged data rate of roughly of a variety of mission equipment. An area that needs 11.6 kbps is necessary to meet the habitat’s additional attention is the selection of medical equipment communication needs. Human factors communications and consumables. Due to mass constraints, medical requirements account for 11.1 kbps of the time averaged provisions will be limited. Not all medical emergencies data rate. Despite the uncertainty in these estimates it is can be foreseen, so developing a limited suite of obvious that human factors will account for the majority equipment that can meet all medical needs is difficult. of the communication load. These communications Thorough analyses need to be performed to determine include personal and mission related transmission what exercise equipment and routines will be most directed toward or generated by the crew. These effective in the Mars gravity environment. Attention also messages consist of large, high data rate voice, video needs to be given to the selection of recreational and TCP/IP packets. This communication driver equipment needed to address associated topics such as represents a major difference between human and news, entertainment, religion, sports, and family. robotic missions, and must therefore be considered early in the C3 design process. Although considerable work remains to be done to ensure a physically and psychologically safe mission for Challenges – A human mission to Mars creates C3 the crew, the current CA subsystem conceptual design related challenges that must be resolved to help ensure to date did not identify any ‘show-stoppers’. mission success. Three key challenges were identified during the design process. COMMAND, CONTROL AND COMMUNICATIONS - The C3 subsystem supports and manages the habitat’s Flight ready C3 technological options are currently very data flows. It provides the data processing and limited. The C3 subsystem design utilized only flight- communications equipment required to monitor and qualified technologies currently in use on the control the habitat’s environment and subsystems, International Space Station and Shuttle. The primary monitor crew health and safety, communicate with Earth, benefit of these technologies is their ability to support rovers and EVA crewmembers, and support data proven operational needs outside Earth’s environment. processing related to the mission objectives. The C3 Flight-qualified technologies are more mass intensive subsystem is comprised of two major functional than their contemporary counterparts and have limited components. The first component is the habitat’s processing capabilities by today’s standards. The result Internal Computing Network (ICN). The ICN manages of using flight ready technologies was a complex, dated the data flows required to monitor and control the C3 subsystem that exceeded our mass budget. Newer habitat’s automated systems and provides a computing technologies would likely resolve these issues, but interface for the crew. The External Communications research and testing will be necessary to establish TRL’s (EC) subsystem handles data flows outside the habitat, greater than 7 and ensure they can meet the demands including communication with Earth, rovers and EVA of a human mission to Mars. crewmembers. The Earth-based communications infrastructure is Design Drivers –The C3 subsystem design was driven by currently inadequate to support a human mission to two key requirements. DRM requirements for real-time Mars based on needs identified in our analysis. The communication with rovers and Earth drove the EC Deep Space Network (DSN) is the primary means of system architecture, and communication requirements communicating with spacecraft outside Earth’s related to human factors drove the C3 subsystem immediate vicinity. The DSN is currently overtaxed transmission and data processing capacity. supporting unmanned missions. It is unlikely that the existing DSN will be able to handle the high The DRM requires the habitat to support (near) real-time communication volume required to support a human communication with Earth. This was assumed to refer to mission to Mars, so the existing infrastructure will likely continuous link availability because the light delay for need to be upgraded prior to sending humans to Mars. radio propagation is unavoidable. An additional requirement for direct communication between the Key operational issues also need to be addressed in habitat and robotic rovers working beyond the habitat’s order to design an appropriate C3 architecture. To date, direct line of sight was derived from the DRM. To meet crewed space missions have relied on near-continuous these requirements, the EC design assumed an aero- contact with Earth. This level of communication will be stationary satellite to be in place above the habitat site impossible for a manned Mars mission. A Mars based providing direct communications coverage over crew will need to function autonomously due to the approximately 50% of the Martian surface and roughly roughly 20 minute round-trip communications delay and 50% Earth-Mars link availability. EC architecture, power limited Earth-Mars link availability. The operational requirements and throughput estimates are tied to the strategy selected will affect the C3 requirements, so Mars orbiting communication satellite capabilities. extensive coordination with the mission operations team the ISRU and power plant. With all of these tasks is required during the design process. being performed without the assistance of EVA crews, the LPR must be able to be fully automated, but will also ROBOTICS AND AUTOMATION – Due to the harsh have telerobotic capabilities. The LPR interfaces will conditions on the Martian surface and the many time- include a physical hatch for EVAs as well as interfaces consuming and monotonous tasks required, robotics and supporting the transfer of data, including telemetry, automation will play a vital role in habitat operations. The audio, and video. robotics and automation subsystem is responsible for designing the automated systems that are outside of the EVAS AND PLANETARY SURFACE VEHICLE scope of other subsystems, as well as the interfaces INTERFACES - EVAS is primarily responsible for between all robotics systems and the habitat. The providing the equipment and supplies (except the EVA automated processes required to develop the surface suit) required for individual crewmembers to move infrastructure include site analysis, habitat assembly, around and conduct useful tasks outside the pressurized instrument deployment and scientific investigation. The habitat. major robotics that will be required for habitat operations are three types of rovers: the small scientific rover, the Four major components are integrated by EVAS: a local unpressurized rover, and the large pressurized space suit designed to be used on the surface of Mars rover (Hoffman and Kaplan, 1997). and be compatible with other EVA equipment, tools, and transport aids; an umbilical system to provide The following list gives examples of tasks that may be connections from the habitat to the airlock and rover automated in the habitat. Various commercial off-the- systems; a large pressurized rover that allows the crew shelf (COTS) technologies were evaluated in this design to safely explore distant sites; and an airlock providing to accomplish these tasks. suited crewmembers with the ability to safely transition from the habitat pressure to the Martian surface. Sealing the habitat in case of depressurization Deployment of communications hardware Several key drivers were identified in the design Monitoring habitat exterior process. During the 600 days spent on Mars, the crew Deployment of radiator panels will be performing up to 2 EVAs per week (Hoffman and Leveling of habitat Kaplan, 1997). Because of the frequency of planned Compaction of waste EVAs, the typical lengthy pre-breathe time for the Deployment of airlock astronauts was a concern. If the habitat was maintained Connection of power plant to habitat and ISRU at an internal total pressure of 14.7 psi (1 atm, 21% O 2), Connection of ISRU to habitat and the EVA suit has an internal pressure of 4.3 psi Inspection and maintenance of habitat and ISRU (100% O2), as does the current shuttle/ISS space suit, an oxygen pre-breathe time of several hours would be needed. In an effort to minimize this pre-breathe time, Two small scientific rovers will be used primarily for the internal pressure of the habitat was reduced to 10.2 exploration. These rovers will be autonomous a majority psi, resulting in a 40 minute pre-breathe for a 4.3 psi of the time, but will have the capability to perform suit. Because this time is brloe the minimum of 50 telerobotic operations, with the controller stationed in the minutes required for depress and egress, the astronauts habitat. This type of rover will be required to deploy are able to begin EVAs immediately after completing scientific instruments, collect and return samples from depress and egress procedures. This decision added the Martian surface, determine safe routes for crew over 700 available person-hours to the 600-day stay, travel, and act as a communications relay in contingency and represented a primary design driver for the overall situations. The interface between these rovers and the habitat. A timeline of the EVA process is illustrated in habitat will be minimal. Data consisting of telemetry, Figure 2. audio, video will be transferred to and from the habitat.
The cargo carrier will also be bringing one Local Unpressurized Rover (LUR). This rover will be required to provide local transport within ~100 km from the habitat for EVA crews and will have two interfaces with the habitat for exchanging power and data. Data transferred will include audio and telemetry.
The third type of rover required for habitat operation is the Large Pressurized Rover (LPR). Two LPRs will be brought to the surface on the first cargo carrier. The LPRs will have critical responsibilities that must be carried out before the first crew arrives, including site preparation, moving, deploying, and inspecting the habitat’s infrastructure, and connection and inspection of Figure 2: Timeline for Airlock Don/Doff Cycle specified by the DRM (Hoffman and Kaplan, 1997). For the surface habitat designed in this document, all necessary consumable mass is being launched with the habitat. The ISPP plant will demonstrate that these consumables can be produced in a timely, efficient Spacesuit – The EVA suit was assumed to have an manner. This demonstration will be monitored and will internal pressure of 4.3 psi (based on the current NASA be used primarily to save mass for future missions to design). If pre-breathe time was increased, the internal Mars. The first crew may use this consumables reserve pressure of the suit could be lowered even further to if it is needed. increase the mobility and dexterity of the suit. One of the driving requirements is that the suit make use of a Key Design Challenges - Four design challenges were regenerable, non-venting heat sink. If sublimated water identified for the ISRU subsystem. The first was was used to cool the suit, the required mass of water transferring consumables (e.g. oxygen, nitrogen and by- transported from Earth would more than double in this products such as water) safely from the low pressure design. A robust, durable suit is also needed to Martian environment through the pressure shell of the minimize spare parts. The mass can be further habitat. Another challenge was insulating the pipes to decreased if parts are designed to be modular and easily protect them from the diurnal temperature variations. interchangeable (especially those that experience the Redundant safety valves must also be implemented in to most wear) to the maximum extent possible. keep the habitat pressurized in case of pipe failure.
This design provides the crew with a total of thirteen A third challenge was to choose the most efficient ISPP, suits including seven backup suits. Based on two, two- understand the inputs and outputs of the plant, and then crew EVAs per week, each of the six primary suits must design the interfaces. The final design challenge was to be able to withstand over 430 hours of cumulative use. determine the optimal location of the habitat relative to the ISPP. The distance between the two elements Airlock – The DRM requires the airlock to be an largely drives the solution selected for transferring independent element capable of being relocated or consumables to the habitat. Possible methods ‘plugged’ (Hoffman and Kaplan, 1997). The airlock will considered were continuously pumping the consumables be a solid shell as opposed to the inflatable airlocks that directly to the habitat or transferring them via the rover’s have been proposed in other designs. This decision was storage tanks. based on durability issues and ease of relocation during the mission. In case of fire or rapid depress, the entire Martian soil can be used as a very efficient material for crew must be able to exit the habitat quickly and safely. radiation shielding and insulation (Larson and Pranke, Therefore, the MOB habitat has a total of three airlocks, 2000). Soil could either be poured into bags or combined two operational airlocks on the bottom floor and one with water and heated in a kiln to form bricks. emergency/back-up on the second floor. The third Subsequent Mars missions might take advantage of the airlock ensures that astronauts on the second floor abundant iron, silicon, and other metals in the soil as (living quarters) can easily escape the habitat. For added well. redundancy, each airlock is equipped with three EVA suits, two operational and one emergency/backup suit. Using the ISPP to provide consumables to the crew will The emergency suit will be sized to fit any of the six save on overall mass of the long-term mission and thus crewmembers. The dimensions of the airlock are 4 m decrease the cost of future missions. Ultimate mass and long, 3.5 m wide, and 2.5 m high, with a total volume of cost savings are dependent on the ISPP design and 35 m3. This design provides sufficient room for donning, method of consumables transfer. doffing, storing, and servicing the EVA suits. MISSION OPERATIONS AND HUMAN FACTORS - The airlock is the main door to the surface of Mars. It will Mission Operations is an element often left out of provide the astronauts with the ability to access the academic design classes, where the focus tends to be surface at a high cost: the possible introduction of toxic placed on designing ’hardware’ subsystems. Because of particulate contaminants through the airlock and into the the length of this mission, however, it was deemed astronaut living area (Shidemantle et. al., 2003). If not imperative to include the human factors considerations controlled, this permeation may cause health problems typically encompassed by the MO and Crew (such as cancer which may be induced by breathing the Accommodations subsystems. By including these as hexavelant chromium within the dust) as well as ’subsystems’ at the beginning of the design process, the equipment failure. For this reason, a particulate cleaning habitat design can be further optimized with respect to system must be designed with the airlock. crew time, safety, and comfort.
IN SITU RESOURCE UTILIZATION - The responsibility The purpose of the MO team is to oversee all activities of the ISRU team was to design the interfaces between during the mission. These activities may be manual, the In Situ propellant production (ISPP) plant and the automated, or Earth-controlled, and will include a wide habitat. The ISPP will provide an additional 4.5 mt of range of functions, such as maintenance of crew oxygen, 3.9 mt of nitrogen and 23.2 mt of water, as psychological and physiological health, science investigations, habitat maintenance and operations, the mission. Each operation was then designated as public relations, and communications and data transfer either automated, Earth-controlled, requiring crew, or with Earth. some combination of the three. In addition to the tasks required by each subsystem, there were a number of The primary task of the MO support team is to identify activities required by the overall mission that were not and coordinate operations within each of these included under any specific subsystem. These activities, functions, and schedule activities so that stated mission which include obvious elements such as sleeping, goals are achieved. The MO team works closely with the eating, and cleaning, as well as less obvious tasks such design engineers to establish clear hardware operational as collecting medical data from crewmembers and requirements incorporating human factors and writing e-mails to family, were gathered into a separate scheduling considerations and to revise these ops list. MOB compiled a list of 153 maintenance and requirements as needed. Before and during the mission, day-to-day type tasks that need to be scheduled the MO team is responsible for creating and modifying throughout the mission. the operations schedule (in concert with the engineering and science teams), developing procedures for all Once all of these mission operations were catalogued, operations and failure scenarios, identifying and they were consolidated into representative mission delivering relevant system status data to the crew, and timelines. These timelines were a useful tool that working with crew during the mission to identify and provided a reality check of the expectations put upon the respond to any off-nominal situations that may arise. crew to perform maintenance, science, and all other Ultimately, the MO team will help to engineer a habitat mission tasks. In a habitat that required too much crew that meets all physiological and psychological needs of time for maintenance, the creation of a representative the crew, in addition to developing and implementing a timeline could expose design shortcomings that may comprehensive mission activity schedule that leads to otherwise be missed. It became apparent that mission the successful achievement of the mission goals. scheduling in this manner needed to be concurrently iterated as the design evolved. For this four-month class exercise, the scope of the MO team was limited to developing operations within the Crew Day/Night Schedules – Additional trade studies habitat (as it was being designed), but excluded crew need to be conducted to optimize the crew’s day/night operations during transit or training. Consideration was schedules. MOB chose a crew schedule that is given, however, to automated operations that may occur synchronized with the Mars day/night cycle. In each within the habitat during transit and to functions of the daily schedule, the six crew members are divided into ground operations crew. three groups, and each group follows separate schedules, which are similar but shifted in starting and As a result of this project, some important points were ending times (wake and sleep times) by a period of 15 brought to light that should be included as key minutes. This division of schedules allows time for the considerations in future design efforts. There were two Mission Commander (MC) and Second-in-Command key drivers for the MO team. The first was to integrate (SIC) to engage in mission planning and other activities human factors considerations from the beginning of the special to the crew commanders, while the slight shifts in design, rather than “forcing” them in at the end. This the schedules helps to avoid potential “traffic jams” in philosophy allows the crew’s time, comfort, and safety, areas such as the bathroom and laundry room. It was and therefore the overall mission’s success, to be thought that the “all-awake, all-asleep” (or four-A) optimized by design. The second design driver was the schedule would be easiest on the crew psychologically, time delay for communication between Earth and Mars in addition to minimizing sleep interference from “awake” and resupply opportunities. Because real-time crew members showering, doing laundry, etc. This type communication and control are not possible, and flights of schedule should be carefully weighed against a bringing cargo or crew from Earth are separated by schedule that rotates the crew through 8-hour sleep years, the crew and habitat must attain an shifts so that someone is always awake in the habitat, unprecedented level of independence. which does provide an element of safety that may outweigh the benefits of a “four-A” schedule. Thus, a Operations Scheduling – A vital component enabling careful trade study should be done before opting for the MO’s integration with all subsystems was the operations specific type of schedule. Circadian rhythm (ops) list. This list defined scheduling of activities, which desynchronization may pose long-term adaptation in turn allowed the MO team to ensure that all activities issues, since the Martian day differs from Earth’s. could be accomplished within a specified period (day, week, month, mission). The ops list helped to determine Ground Support / Crew Command Architecture – At this which operations should be automated, Earth-controlled, early stage of development, it is difficult to clearly plan or performed by the crew, by elucidating factors such as the separation of duties between the ground (Earth- ease, frequency and duration of the task, as well as any based) segment and Mars-based segment of the related safety concerns. operations team. However, it is important to begin to delineate tasks between these two segments. Each of the subsystems provided MO with a list of operational activities that they expected to require during It is expected that the ground operations shifts will be set life support system, the crew’s psychological up in a similar hierarchical structure to the ISS discomfort from eating or drinking recycled waste is operations team, with the notable exception that the a very real concern. Conversely, waste storage or chain of command from the operations team to the Mars- disposal is equally an issue yet to be fully resolved. based astronauts will be hampered by the up to 25- C3’s data flows were driven by MO’s need for high- minute one-way time delay. Because of this delay, real- bandwidth communication, such as audio and video; time conversations between the ground segment and the if MO were not integrated into the design from the astronauts will not be possible. Any ground control/crew beginning this driver might have been missed. architecture will need to take into account the up to 25- minute one-way time delay, as well as the usage of the Numerous hardware choices will be affected by MO Deep Space Network (DSN) for communication with considerations. For example, radiator performance is Mars. The different duration of days also poses a unique expected to degrade when covered in dust after a problem in keeping both crews in synch. Martian storm, and they will therefore need cleaning. Cleaning can be automated or manual, which will be Due to the time delay, as well as the bandwidth a factor in the radiator trade study. limitations, the ground team will not be monitoring all data at all times. Rather, they will monitor key telemetry items from each subsystem in near real time, and SUMMARY analyze long-term trends using more complete data downlinked at regular intervals. Telemetry, including The design process undertaken in this semester long sensors and data types, should be designed with this in effort highlighted several significant aspects of how mind. closely the engineering requirements for a planetary base depend upon exact mission parameters (number of Automated vs. Crewed Processes – Consideration crew, duration, mission and scientific objectives, etc.). needs to be given for determining an appropriate Optimization of the life support system, trades between balance between automated and crewed processes recycling and single use elements (as diverse as from throughout the entire end-to-end mission. Ideally, a oxygen, food and water to clothing and packaging maximum number of processes would be automated so material), selection of the habitat and space suit that the crew’s time could be utilized for ‘value-added’ operating pressures, enabling communication needs and activities, yet these automated processes should still be thermal control, are among the many variables that able to be overridden and controlled by the crew to cannot begin to be adequately addressed without ensure safety and reliability. Optimization of this balance specific mission objectives having been identified. is key to mission success, and may differ from previous Going to the moon or Mars will likely drive ultimate space missions in terms of the unique demands designs in very different directions, although the associated with the Earth-Mars orbital transit period fundamental goals are virtually identical – to keep versus those specific to surface operations. humans alive and healthy, both physiologically and psychologically, in a hostile, alien environment far from Specific Design Influences – In addition to the general Earth. Giving due consideration to systems engineering considerations noted above, integration of MO from the analyses, architectural guidelines and human factor beginning of the project influenced a number of specific concerns concurrently from the initial mission planning elements of the habitat design in ways that may have stages through actual operations will allow the future been overlooked and are relevant to future endeavors. human exploration of space to proceed as safely and efficiently as possible. Consideration of EVA operational aspects drove the decision to set the habitat internal pressure at 10.2 ACKNOWLEDGMENTS psi, as it significantly reduced pre-breathe time. The habitat will be deployed horizontally. This The authors would like to acknowledge the efforts of orientation was chosen for a number of structural their classmates S. Baker, E. Dekruif, B. Duenas, K. Hill, and MO reasons. As a result of the horizontal N. Kungsakawin, E. Schleicher, M. Silbaugh, J. Uchida orientation, the crew will have fewer stairs to deal and T. White; and also thank the following individuals for with, and in the event of an emergency they can their assistance in technical matters and design reviews: potentially egress from a second story airlock, which D. Anderson (Mars Society), M. Benoit (CU), B. Clark may not be an option in a vertical configuration. This (Lockheed Martin), J. Clawson (CU), C. Craig (Lockheed layout was also considered to allow a more open, Martin), T. Gasparrini (Lockheed Martin), A. Hoehn (CU), ‘psychologically pleasing’ floor plan than would a K. Mankoff (Honeybee Robotics), R. McCall (CU and vertical configuration. It is important to remember NexTerra), T. Muscatello (Mars Society and Pioneer that in a mission of this magnitude, psychological Astronautics), S. Price (Lockheed Martin), J. Russell, health of the crew will be a significant factor for (CU), K. Stroud (CU) and R. Zubrin (Mars Society and success. Pioneer Astronautics). ECLSS waste disposal will not recycle feces. Though recycling feces would create a more closed REFERENCES DEFINITIONS, ACRONYMS, ABBREVIATIONS
1. Drake, BG, ed. Reference Mission Version 3.0: AIM: Advanced Integration Matrix Addendum to the Human Exploration of Mars: The Reference Mission of the NASA Mars Exploration BFO: Blood-Forming Organ Study Team. Lyndon B. Johnson Space Center, Houston, TX: June 1998. C3: Command, Control, and Communication subsystem 2. Fisackerly, et al. Cranfield Aurora: Mars Excursion Module. Cranfield University; 1st Aurora Student CA: Crew Accommodations Design Contest, Barcelona: 2003. 3. Hoffman, SJ and Kaplan, DL. Human Exploration of COTS: Commercial Off-The-Shelf Mars: The Reference Mission of the NASA Mars Exploration Study Team. Lyndon B. Johnson Space CTV: Crew Transfer Vehicle Center, Houston, TX: July 1997. 4. “INTEGRITY Team Kickoff Meeting.” PowerPoint CU: University of Colorado (Boulder) Presentation. NASA JSC INTEGRITY: 26 Feb. 2003. DRM: Design Reference Mission 5. Larson, WJ. and Pranke, LK. Human Spaceflight Mission Analysis and Design. The Mc-Graw-Hill DSN: Deep Space Network Companies, Inc., New York: 2000. 6. Lynn, V. Peace in Space. theGuardians.com, 6 EC: External Communications Dec. 2003 ECLSS: Environmental Control and Life Support