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4 Technical Analysis and Affordability Assessment of Human Exploration Pathways 4.1 INTRODUCTION AND OVERVIEW Sending humans to destinations beyond low Earth orbit (LEO) is a technologically, programmatically, and politically complicated endeavor. As discussed elsewhere in this report, there are frequently cited but difficult-to-substantiate arguments that, despite the cost and risk to human life, such endeavors are justified by various national and more general societal benefits. In any resource-constrained environment, it is responsible to attempt to identify not just the potential benefits, but also to understand the level of proposed or required investments and the difficulty of the proposed tasks. Given the complexity of human space exploration (that is, human spaceflight [HSF] beyond LEO), as well as the fact that U.S. goals in HSF have changed on time scales much shorter than the time it takes to accomplish those goals, it makes sense to decompose an HSF program into smaller building blocks. This also has the advantage that those building blocks can be assembled in various configurations, allowing for the changes in goals that we experience as a nation to be addressed without analysis ab initio. A “capability-based” approach to space exploration focuses research and technology development resources on systems and capabilities that are expected to be of value in the future, with no particular mission or set of missions in mind. The process of selecting future missions then tends to favor those missions that can make use of the systems and capabilities that have been developed. The Asteroid Redirect Mission (ARM) is an example of this process in action. A “flexible-path” approach is a more sophisticated version of capability-based planning that takes into consideration what destinations might be desirable. By contrast, a pathway-based approach would commit the U.S. HSF program to a pathway with a specific sequence of missions normally of increasing difficulty and complexity that target specific exploration goals that are typically tied to various destinations that humans may explore. A pathway approach would facilitate continuity of development of required systems for increased capability and efficiency. NASA is currently developing systems that are modular and general-purpose in nature. Although NASA has characterized this approach as developing modular, capability-based, general-purpose systems, these systems may or may not be supportive of a pathway-based approach. Instead of pursuing a “capabilities-based”1 or “flexible path”2 approach where no specific sequence of destinations is specified, the committee’s prioritized recommendations (see Chapter 1), if adopted, would lead to NASA committing to design, maintain, and pursue the execution of an exploration pathway beyond LEO that leads toward a clear horizon goal. The committee is not recommending one pathway over another, but it does recommend (see Chapter 1) that NASA “maintain long-term focus on Mars as the ‘horizon goal’ for human space exploration.” PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-1

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The rest of this chapter contains three major sections:  Technical Requirements  Technology Programs  Key Results The Technical Requirements section begins by defining possible destinations for HSF. For the foreseeable future, limitations on human physiology and space exploration technology limit potential destinations to the Earth-Moon system, Earth-Sun Lagrange points, near-Earth asteroids, and Mars. Design reference missions (DRMs) to these destinations have been prepared by NASA, the International Space Exploration Coordination Group (ISECG), and others. This chapter assesses three specific, notional pathways as examples to illustrate the various trade- offs among schedule, development risk, affordability, and decommissioning date of the International Space Station (ISS). (Note that the analysis presented in this chapter was completed before the Administration announced its intention to extend the operation of the ISS to 2024; the bounding cases of 2020 and 2028 presented in this report nonetheless well illustrate the impact of ISS decommissioning date on HSF beyond LEO.) Although there are other possible pathways, the ones chosen for exposition sufficiently span the likely programmatic space to provide insight into affordability and technical difficulty. All three of the pathways terminate with a human mission to the most challenging, technically feasible destination: the Mars surface. Depending on practical factors, an actual HSF program might have to take an off-ramp to an intermediate destination before the final destination is reached. Each of the pathways to Mars includes 3 to 6 different DRMs, as follows:  ARM-to-Mars pathway  ARM  Martian Moons  Mars Surface  Moon-to-Mars pathway  Lunar Surface Sortie  Lunar Surface Outpost  Mars Surface  Enhanced Exploration pathway 1  Earth-Moon L2  Asteroid in Native Orbit  Lunar Surface Sortie  Lunar Surface Outpost  Martian Moons  Mars Surface Completing any of the above pathways would require a variety of mission elements. For example, a human mission to the Mars surface would require development of 11 primary mission elements, such as heavy lift launch vehicles, deep space habitats, and pressurized surface mobility systems. Eight additional mission elements would be necessary to complete all six of the other DRMs that appear in one or more of 1 As described later in the chapter, the Earth-Moon L2 point is a particular point in space defined by its relative position to the Earth and Moon. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-2

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the roadmaps. Three of these additional mission elements are transitional in that they directly contribute to the development of one of the 11 primary missions elements. For example, the lunar orbital outpost is not needed for a Mars surface mission, but it would directly contribute to the development of the deep space habitats that would be needed. There are also five dead-end mission elements. Although necessary to complete one or more of the DRMs, the advanced capabilities of these mission elements are essentially not applicable to the Mars surface mission. Requirements for completing the pathways can also be framed as capabilities. A wide range of capabilities was assessed in terms of the technical challenges, capability gap, regulatory challenges, and cost and schedule challenges that would need to be overcome to complete their development. This assessment determined that current research and development programs would need to address the 10 capabilities below as a high priority, with a particular emphasis on the first three:  Mars Entry, Descent, and Landing (EDL)  Radiation Safety  In-Space Propulsion and Power2  Heavy Lift Launch Vehicles  Planetary Ascent Propulsion  Environmental Control and Life Support System (ECLSS)  Habitats  Extravehicular Activity (EVA) Suits  Crew Health  In-Situ Resource Utilization (ISRU) (using the Mars atmosphere as a raw material) For a pathway to be affordable, its cost profile must fit within the projected HSF budget profile. Given the uncertain nature of federal budget projections and to show the impact of budget profile on other pathway characteristics, the affordability of each pathway is assessed in terms of three scenarios.  Schedule-driven affordability scenario, in which the pace of progress is determined by the rate at which necessary development programs can be completed. This scenario would require a rapid growth in NASA’s HSF budget.  Budget-driven affordability scenario, in which the pace of progress is limited by an HSF budget that grows with inflation. This scenario results in an operational tempo (in terms of the overall launch rate and/or the frequency of crewed missions) that is far below historic norms.  Operationally viable affordability scenario, in which the pace of progress reflects a compromise in terms of the HSF budget and operational tempo. This scenario would require an HSF budget that increases faster than inflation, but not as much as the schedule-driven scenario. It would also result in an operational tempo that is below historic norms, but not nearly as much as the budget-driven scenario. Having examined mission elements, capabilities, and the affordability of the pathways, the Technical Requirements section concludes with an assessment of each pathway in terms of six desirable properties:  The horizon and intermediate destinations have profound scientific, cultural, economic, inspirational, and/or geopolitical benefits that justify public investment; 2 As development of NEP, NTP, SEP, and cryogenic propulsion technologies proceeds, a down-selection will be required. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-3

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 The sequence of missions and destinations permits stakeholders, including taxpayers, to see progress and develop confidence in NASA’s ability to execute the pathway;  The pathway is characterized by logical feed-forward of technical capabilities;  The pathway minimizes the use of dead-end mission elements that do not contribute to later destinations on the pathway;  The pathway is affordable without incurring unacceptable development risk; and  The pathway supports, in the context of available budget, an operational tempo that ensures retention of critical technical capability, proficiency of operators, and effective utilization of infrastructure. The Technology Programs section briefly summarizes HSF-related programs and plans of particular note that are underway by NASA, industry, the Department of Defense, and the international community. A subsequent discussion of robotic systems describes the importance of evolutionary improvements in robotic capabilities to the future of HSF and the possibility that rapid improvements in robotics over the coming decades may open new exploration pathways to Mars and beyond. The Key Results section contains seven statements that flow from the panel’s assessment of the following topics: 1. Feasible Destinations for Human Exploration. 2. Pace and Cost of Human Exploration. 3. Budget Projections. 4. Potential Cost Reductions. 5. Highest-Priority Capabilities. 6. Continuity of Goals. 7. Maintaining Forward Progress. The chapter finishes by emphasizing that without a strong national (and international) consensus about which exploration pathway to pursue along with the discipline to maintain course over many administrations and Congresses the horizons of human existence will not be expanded beyond LEO, at least not by the United States. 4.2 TECHNICAL REQUIREMENTS 4.2.1 Possible Destinations in the Context of Foreseeable Technology NASA’s vision includes “expanding human presence“ in the solar system. This concept was first made part of U.S. national space policy by President Ronald Reagan in the classified Presidential Directive on National Space Policy.3 Succeeding administrations (except one) articulated similar goals, and various committees and commissions outlined proposed pathways, and projected budgets for achieving those goals.4,5,6,7,8 President Obama commissioned the Review of United States Human Space 3 Presidential Directive on National Space Policy, February 11, 1988, available in NASA Historical Reference Collection, History Office, NASA, Washington, D.C., http://www.hq.nasa.gov/office/pao/History/policy88.html. 4 NASA, Report of the 90-Day Study on Human Exploration of the Moon and Mars, November 1989, available in NASA Historical Reference Collection, History Office, NASA, Washington, D.C., http://history.nasa.gov/90_day_study.pdf. 5 Advisory Committee on the Future of the U.S. Space Program, Report of the Advisory Committee on the Future of the U.S. Space Program, U.S. Government Printing Office, Washington, D.C., December 1990. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-4

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Flight Plans Committee9 (also known as the Augustine Committee), which concluded in 2009 that “the ultimate goal of human exploration is to chart a path for human expansion into the solar system,” but noted the need for both physical and economic sustainability. The report of the Augustine Committee detailed various options, such as “Mars first,” “Moon first,” and “Flexible Path,” potentially involving missions to lunar orbit, Lagrange points, near-Earth objects, the moons of Mars, the surface of the Moon, and the surface of Mars. Ultimately, President Barack Obama declared10 that the near-term goal for U.S. HSF beyond the Earth-Moon system would be a near-Earth asteroid, leading to human orbital missions to Mars, with a Mars landing following thereafter. By contrast, the Clinton administration’s space policy11 committed the United States only to establish a permanent human presence in Earth orbit, where “the International Space Station (ISS) will support future decisions on the feasibility and desirability of conducting further human exploration activities.” Thus, since 1988, except for the Clinton administration, presidential space policy has advocated expanding human presence in some form throughout the solar system; however, since President Reagan, the United States for practical purposes has executed the Clinton administration space policy. Congressional guidance for NASA has, in general, been less expansive than the executive branch’s HSF vision. The appetite for Apollo-style, ambitious goals beyond LEO, and the attendant budgets, has been notably lacking. Even so, the 2010 NASA Authorization Act,12 which mandated this report, called explicitly for the development of a heavy-lift launch vehicle capable of supporting human spaceflight beyond the ISS and LEO, focusing specifically on cislunar space in the near term. Indeed, this Congressional direction constitutes a significant boundary condition for the report’s analysis, which is based on the assumption that the SLS would be the primary launcher enabling exploration beyond LEO. It is critically important for stakeholders of U.S. HSF to understand, however, that currently understood physiological limitations of human beings to endure the space radiation and zero-gravity of space, the limited effectiveness of foreseeable technological and medical countermeasures in addressing many of those limitations, and the performance of future in-space propulsion systems, severely limit the destinations in the solar system to which humans may travel. For example, using traditional standards for lifetime cancer risk, the NASA Human Research Program has established that the risk of cancer induced by galactic cosmic rays (GCR)13 exceeds current guidelines14 for missions with durations longer than 615 days. This is the most optimistic case, for 55-year-old males, without previous radiation exposure, who have never smoked, assuming complete engineered protection (such as shielding crew quarters with water) from solar particle events (SPE). For female astronauts, for astronauts younger than 55, for astronauts with previous radiation exposure, and for missions not taking place during solar maximum 6 Executive Office of the President, “President Bush Announces New Vision for Space Exploration Program: Remarks by the President on U.S. Space Policy, NASA Headquarters,” Washington, D.C., January 14, 2004, http://history.nasa.gov/Bush%20SEP.htm. 7 NASA, The Vision for Space Exploration, NASA, Washington, D.C., February 2004, http://history.nasa.gov/Vision_For_Space_Exploration.pdf. 8 Executive Office of the President, “U.S. National Space Policy,” August 31, 2006, available at http://history.nasa.gov/ostp_space_policy06.pdf. 9 Review of U.S. Human Space Flight Plans Committee, Seeking a Human Spaceflight Program Worthy of a Great Nation, October 2009, http://www.nasa.gov/pdf/396093main_HSF_Cmte_FinalReport.pdf. 10 Remarks by the President on Space Exploration in the 21st Century, John F. Kennedy Space Center, Florida, April 15, 2010, http://www.whitehouse.gov/the-press-office/remarks-president-space-exploration-21st-century. 11 National Science and Technology Council, Presidential Decision Directive/NSC-49/NSTC-8, September 14, 1996, available at http://www.fas.org/spp/military/docops/national/nstc-8.htm. 12 Public Law 111-267, October 11, 2010. 13 National Research Council, Managing Space Radiation Risk in the New Era of Space Exploration, The National Academies Press, Washington, D.C., 2008. 14 Steve Davison, NASA Headquarters, “Crew Health, Medical, and Safety: Human Research Program,” briefing to NRC Committee on Human Spaceflight Technical Panel, March 27, 2013. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-5

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(when the Sun’s magnetic field provides substantial protection), the permissible durations are much less, approaching 6 months in many cases. It is also probable that other factors, such as non-carcinogenic effects of GCR, musculoskeletal degeneration in zero g, ocular impairment, or psycho-social effects could further limit permissible mission durations. Although NASA’s Human Research Program is working efficiently to quantify the health risks of deep space exploration, remaining uncertainties are considerable. In addition, the number of potential health impacts of HSF continues to expand. Ocular impairment and increased intracranial pressure were only identified as a potentially serious problem in 2011,15 and the potential for microgravity to adversely affect the development of endothelial cells, which line the interior of blood vessels, was only identified in 2013.16 These issues only relate to health effects likely to limit permissible cruise durations and do not address additional risks that astronauts will face, say, from environmental factors such as dust or perchlorates from lunar or martian soil, respectively. The impact of psychosocial factors on long-duration spaceflight has also been an issue of significant concern for some time.17 Finally, it is worth noting that just the number of evidence books which the Human Research Program has accumulated (more than 30) highlights the complexity of assessing the safety of long- duration human spaceflight.18 For distant destinations, limitations on the duration of human exploration missions impose minimum spacecraft velocities that will be hard to achieve. Example mission designs for Mars suggest that chemical propulsion (the only technology that has been used for HSF) might enable getting humans to Mars orbit and back, if significant progress is made in storing cryogenic propellants for long periods with minimal loss. Other types of propulsion systems, such as solar electric propulsion (SEP), nuclear electric propulsion (NEP), and nuclear thermal propulsion (NTP), could be used to support a human mission to the Mars surface. However, developing high-power, operational systems using any of these concepts would be a major undertaking. The development challenges associated with any solar system destinations beyond the Earth- Moon system, Earth-Sun Lagrange points, near-Earth asteroids, and Mars are profoundly daunting, involve huge masses of propellant, and have budgets measured in trillions of dollars.19 4.2.2 Design Reference Missions With an initial reconnaissance of the Moon completed, the maturation of the ISS, and robotic exploration of Mars supporting NASA’s search for signs of past or present life elsewhere in the solar system, human exploration of Mars seems to be a logical goal for U.S. HSF, given its prominence in the national space policies of multiple administrations, including the current one. To achieve a human mission to the Mars surface, advanced capabilities and new technologies will be needed. NASA has outlined the challenge of a Mars surface mission with the Mars Design Reference Architecture (DRA) 15 J. Fogarty et al., The Visual Impairment Intracranial Pressure Summit Report, NASA/TP–2011-216160, NASA Johnson Space Center, October 2011. 16 S. Versari et al., The challenging environment on board the International Space Station affects endothelial cell function by triggering oxidative stress through thioredoxin interacting protein overexpression: The ESA-SPHINX experiment, Journal of the Federation of American Societies for Experimental Biology 27:4466-4475, 2013. 17 Institute of Medicine, Chapter 5 in Safe Passage: Astronaut Care for Exploration Missions, The National Academies Press, Washington, D.C., 2001. 18 Evidence books are collections of risk reports and journal articles that address a particular human health issues. A list of Human Research Program evidence books appears at http://humanresearchroadmap.nasa.gov/Evidence/, retrieved April 20, 2014. 19 R. McNutt et al., Human missions throughout the outer solar system: Requirements and implementations, Johns Hopkins APL Technical Digest 28(4):373-388, 2010. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-6

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5.0, which lays out the major mission requirements for a Mars surface landing and exploration. 20 The DRA 5.0 report summarizes the tradeoffs between energy expenditure, surface time, and cruise duration for a human mission to Mars’ surface. However, Mars is not the only potential destination beyond LEO. A number of scientifically and technically interesting destinations exist between Earth and the surface of Mars. Additionally, missions to such intermediate destinations may serve to demonstrate capabilities and improve technologies needed for the Mars surface mission. NASA and others have examined these potential destinations,21,22 and reasonable mission concepts have been formulated. Design Reference Missions (DRMs) are point designs that provide an overview of how a mission goal could be achieved. DRMs serve two purposes during initial conceptual design. First, they provide an overview of the mission and the mission needs, which can then be used to flow down requirements to supporting systems. Second, they provide a benchmark that can be used for comparison with alternative mission concepts for achieving mission goals. This study used a set of representative DRMs to define the three pathways and to assist in evaluating the challenges of expanding HSF beyond LEO as far as the “horizon goal” of a human mission to the Mars surface. DRMs to other feasible destinations, such as the Earth-Moon L1 point and the Earth-Sun L1 and L2 points,23 could also have been used, but pathways using the selected DRMs are sufficient to assess the full scope of the technical and affordability challenges faced by human space exploration. The definition of the DRMs are based on recent publications from NASA (for the ARM,24 Lunar Surface Outpost,25 Asteroid in Native Orbit,26 Mars’s Moons,27 and Mars Surface28 DRMs) as well as the ISECG Global Exploration Roadmap29 (for the Earth- Moon L2, Lunar Surface Sortie, and Lunar Surface Outpost DRMs).30 20 B. Drake, “Design Reference Architecture 5.0,” http://www.nasa.gov/pdf/373665main_NASA-SP-2009- 566.pdf, 2009. 21 NASA, Human Spaceflight Exploration Framework Study, Washington, D.C., January 11, 2012, http://www.nasa.gov/pdf/ 509813main_Human_Space_Exploration_Framework_Summary-2010-01-11.pdf. 22 Chris Culbert and Scott Vangen, NASA Human Space Flight Architecture Team, “Human Space Flight Architecture Team (HAT) Technology Planning,” NASA Advisory Council briefing, March 6, 2012, http://www.nasa.gov/pdf/629951main_CCulbert_HAT_3_6_12=TAGGED.pdf. 23 Lagrangian points, also referred to as L-points or libration points, are five relative positions in the coorbital configuration of two bodies, one of them with a much smaller mass than the other. At each of these points, a third body with a mass that is much smaller than either of the first two will tend to maintain a fixed position relative to the two larger bodies. In the case of the Earth-Moon system, L1 is a position between the Moon and Earth where a spacecraft could be placed, and L2 is a position beyond the Moon that would be similarly fixed in orientation to the Earth and Moon. 24 NASA, “Asteroid Initiative Related Documents,” http://www.nasa.gov/content/asteroid-initiative-related- documents/. 25 L. Toups and K. Kennedy, “Constellation Architecture Team-Lunar Habitation Concepts,” in AIAA Space 2008 Conference and Exposition, American Institute of Aeronautics and Astronautics, 2008, http://arc.aiaa.org/doi/abs/10.2514/6.2008-7633. 26 B.G. Drake, “Strategic Considerations of Human Exploration of near-Earth Asteroids,” paper presented at the Aerospace Conference, 2012 IEEE, March 3-10, 2012. 27 D. Mazanek et al., “Considerations for Designing a Human Mission to the Martian Moons,” paper presented at the 2013 Space Challenge, California Institute of Technology, March 25-29, 2013. 28 B. Drake, “Design Reference Architecture 5.0,” 2009, http://www.nasa.gov/pdf/373665main_NASA-SP- 2009-566.pdf. 29 International Space Exploration Coordination Group (ISECG), The Global Exploration Roadmap, NASA, Washington, D.C., August 2013, https://www.globalspaceexploration.org/. 30 Detailed analyses of the DRMs that in some cases added to or modified the information from these sources was performed to assure that each DRM was based on a consistent set of assumptions concerning, for example, the performance of major system elements. As indicated, the Lunar Outpost DRM is based on information from NASA and the ISECG. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-7

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The DRMs presented below are notional and representative of possible missions, but are neither comprehensive nor finalized designs. These DRMs for each major destination beyond LEO, demonstrate the challenges associated with various pathways to human exploration of Mars. The DRMs below can be divided into two groups: cislunar and deep space missions. Cislunar missions include both missions to the vicinity of the Moon as well as lunar surface missions. These missions have the advantage of remaining in close proximity to Earth, reducing mission risk by allowing for abort contingencies with a relatively quick return to Earth.31Cislunar missions would also cost substantially less and be more affordable than deep space missions. Autonomy requirements are also reduced because of short time delays in communications between spacecraft and Earth. Cislunar missions that do not include a lunar landing also minimize propulsive requirements by avoiding interactions with strong gravitational bodies. Lunar surface missions provide a good analogy for Mars surface operations and constraints on hardware and human physiology to help prove capabilities for future missions. Deep space missions include the horizon goal of a human mission to the Mars surface as well as missions to asteroids in their native orbits and missions to the moons of Mars. The asteroid and Mars moons missions would allow for the demonstration of spacecraft vehicles and systems and validate the ability to sustain human health during long-duration missions similar in scale to a Mars surface mission. 4.2.2.1 The Space Launch System and the Design Reference Missions The Space Launch System (SLS) is a heavy-lift launch vehicle under development by NASA to support human space exploration beyond LEO. The need for a heavy-lift launch vehicle has been noted in many blue ribbon studies of HSF. The planned SLS payload capacity (70 to 130 metric tons MT, depending on which version of SLS is being discussed) and large shroud would reduce the number of launches required for human exploration missions beyond LEO. The Falcon Heavy launch vehicle, currently under development by SpaceX, will have a payload capacity of up to 53 MT. The Augustine study suggested that human exploration could be accomplished with a 50 MT launch system if the architecture relied on advanced capabilities such as in-space refueling and expandable habitats.32 Smaller alternatives to SLS would require more launches, more time in orbit, and more docking events, which might reduce mission reliability. The impact on costs is hard to predict. On the one hand, the increased launch rate and the potential for commonality with other existing systems using smaller vehicles might lead to reduced development and operational costs for the launch vehicle. On the other hand, the development cost for other mission elements would increase because of the need for additional technologies and interface hardware. In addition, increasing the amount of on-orbit assembly would tend to increase operational costs. For simplicity and consistency of presentation, the analysis in this report of all of the DRMs has presumed the use of SLS as the launch vehicle. The business model and schedule for SLS are almost totally driven by the projected costs and the flat budget profile established for the SLS program. A system such as SLS that is derived from mature systems could reach full operational capability in less time and at less total cost than currently planned if the funding profile resembled that for a normal development. Much of the necessary design work was done under the Constellation program. Before that, space shuttle-derived vehicles had been proposed several times, with considerable preliminary design work. Nonetheless, the designs for the SLS were announced in September 2011 with a projected development cost of $12 billion through first flight in late 2017 (including ground-based infrastructure), plus an additional $6 billion for development of the Orion 31 For some emergencies, such as a subsystem failure that would doom a Mars-bound crew, a safe return from cislunar space might be possible. However, for other emergencies, such as an acute medical emergency, the quicker return from cislunar space would still be problematic. 32 Review of U.S. Human Space Flight Plans Committee, Seeking a Human Spaceflight Program Worthy of a Great Nation, 2009. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-8

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Multi-Purpose Crew Vehicle (MPCV).33,34 Orion is the crew capsule being developed in concert with SLS and is intended to support human space exploration beyond LEO. Since then NASA’s budget uncertainty has increased, putting both the launch date and the cost at high risk.35 4.2.2.2 Asteroid Redirect Mission The Asteroid Redirect Mission (ARM) envisions a crew of two briefly interacting with a 7- to 10- meter asteroid while avoiding the longer travel times and environment required to reach an asteroid in its native orbit. A precursor robotic mission utilizing advanced SEP would be sent to a near-Earth asteroid with appropriate mass and orbital properties. Depending on the mission concept ultimately selected, the robotic spacecraft would either capture a small asteroid in entirety or retrieve a boulder from the surface of a larger asteroid36 and then transport its payload to an orbit in the lunar vicinity. Following the multiyear asteroid redirect mission phase, the crew would be launched on the SLS with the Orion capsule, both of which are currently under development, rendezvous with the returned asteroid, and dock to the attached robotic spacecraft. The mission is ultimately constrained by the current capability planned for the Orion capsule, but a two-person crew could spend up to 6 days at the asteroid collecting samples during extra vehicular activity (EVA) before returning to Earth. 4.2.2.3 Earth-Moon L2 The Earth-Moon L2 reference mission23 would demonstrate long-term human habitation and operations in deep space. To achieve this goal, a habitation module and supporting systems would be developed, built, and launched using an SLS. The spacecraft would transit to either an Earth-Moon Lagrange point or, alternatively, a stable lunar orbit. This minimal space station would be capable of supporting a crew of four or more for a minimum of 6 months. The crew would reach the habitat using the SLS and Orion systems. The primary goal would be to provide technologies and techniques that could enable crews to survive and function on long-duration deep space missions while still maintaining a mission abort capability with a quick return to Earth. Other activities, such as observations of the far side of the Moon or support to lunar surface activities, could occur. This mission will require a significant improvement in the reliability and sustainability (i.e., operation without resupply) of closed-loop environmental control and life support systems (ECLSS) compared to the ECLSS on the ISS. In addition, radiation exposure from SPE during extended stays outside of Earth’s magnetosphere will have to be mitigated under mass and volume constraints (no mitigation of GCR currently appears to be practical). The ISECG has proposed a mission of this type. 37 33 NASA, “NASA Announces Design For New Deep Space Exploration System,” Press Release 11-301, September 14, 2011. 34 M.S. Smith, “New NASA Crew Transportation System to Cost $18 Billion Through 2017,” posted September 14, 2011, updated December 5, 2011, http://www.spacepolicyonline.com/news/. 35 M.K. Matthews, “New NASA rocket faces delays,” Orlando Sentinel, September 6, 2013 (quoting NASA Deputy Administrator Lori Garver). 36 NASA is currently studying two missions concepts for robotic the ARM mission. The reference robotic mission concept would capture a small asteroid. The alternate mission concept would capture a boulder. 37 ISECG, The Global Exploration Roadmap, 2013. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-9

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4.2.2.4 Lunar Surface Sortie The Lunar Surface Sortie reference mission would leverage substantial pre-positioned assets in lunar orbit, similar to the proposal for lunar exploration in The Global Exploration Roadmap recently updated by the ISECG.38 It would be a 28-day mission on the lunar surface for a crew of four. Predeployed pressurized lunar surface mobility units would be positioned using SLS launch vehicles and reusable lunar ascent/descent vehicles. The crew would be launched within an Orion system and rendezvous with a permanent lunar orbit facility. This facility would serve as the staging point for the crew and the ascent/descent stage. Access to the lunar surface would be provided by a reusable ascent/descent vehicle, which would be augmented by a low-cost disposable deceleration stage. Scientific exploration would be conducted using surface mobility units that also operate as habitation units for the duration of the surface stay. Exploration range would be limited to a reasonable return distance to the ascent/descent stage. Beyond the attendant lunar surface science, this DRM demonstrates surface operations, surface habitation, and surface mobility required for partial gravity environments where dust and other potential contaminants are present. 4.2.2.5 Lunar Surface Outpost The Lunar Surface Outpost DRM is an extension of the Lunar Surface Sortie mission, requiring the deployment of long-duration surface assets. Using a similar architecture of SLS cargo deployment launches, reusable lunar ascent/descent vehicles, staging orbital facility, and disposable propulsion stages, surface assets for a long-duration installation are delivered. The additional assets extend the potential mission duration from the 28-day sortie to as much as 6 months. The mobile assets would allow for extended sortie missions from the outpost to scientifically diverse sites, while the outpost itself would be used for scientific experimentation and testing of Mars-focused technologies, such as extended high- power generation system and operations planning for long-duration surface stays. 4.2.2.6 Asteroid in Native Orbit The Asteroid DRM is a deep space mission beyond cislunar space for a crew of four to a near- Earth asteroid. The asteroid for the mission is selected based on scientific interest (or relevance to planetary defense) and Earth-asteroid alignment to allow the crew to transfer to and from the asteroid within a 270-day total mission duration. An Orion vehicle, a deep-space propulsion unit, a deep-space habitation module, and a space exploration vehicle would be launched on SLS vehicles and rendezvous in LEO before the transfer to the asteroid. Upon arrival at the asteroid following a 60 to 130 day transit, the crew would transfer to the space exploration vehicle and perform close-proximity operations and EVAs to collect samples and perform experiments on the asteroid. After a 14-day mission at the asteroid, the crew would return to Earth in the space habitat on a 70- to 160-day journey before performing a direct entry within the Orion vehicle. This DRM features deep-space habitation capability beyond 180 days, deep space navigation, low-gravity foreign-body exploration, and potentially important scientific returns. 4.2.2.7 Mars’s Moons The Mars Moons DRM is similar to the Asteroid DRM in that it is an exploration of a low- gravity body in deep space using space exploration vehicles and EVAs for crewed exploration. The major 38 ISECG, The Global Exploration Roadmap, 2013. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-10

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distinguishing factor is the location of the low-gravity body. A crewed mission to both Phobos and Deimos in Mars orbit would include many elements of a crewed mission to Mars, but without the challenge of the entry, descent, and landing (EDL) and ascent from Mars. The mission first attains Mars orbit insertion and then uses orbital maneuvering units to spend up to 60 days at Phobos and Deimos. The mission length would increase from 1 year or less for asteroid missions to almost 2 years for the Mars Moons mission. The increase in mission duration and the higher propulsive requirements result in the need for an advanced in-space propulsion system. The current design baseline is NTP, although as of the end of 2013, NASA is still examining the propulsion trade space. Two space exploration vehicles and small propulsion stages for martian orbital maneuvering would be predeployed at Mars using an advanced propulsion stage. The crew would rendezvous with their long-duration, deep-space habitat and advanced propulsion stage in LEO, having been launched on SLS, before transferring to Mars. The habitat would need to protect the crew from the deep space environment for most of the 700-day mission, with the exception of the 2 months in Mars orbit. The in-space duration for this mission is more than three times that expected for the Mars Surface mission, and deep-space habitation and logistics for a 700-day in-space mission may not be feasible, depending on the challenges of GCRs. 4.2.2.8 Mars Surface The horizon goal for HSF is the human exploration of the Mars surface. Numerous concepts for surface exploration missions have been described in various documents; the analysis in this report is based on NASA’s Mars DRA 5.0. The mission is based on three different vehicles traveling to Mars, as shown in Figure 4.1. Multiple SLS launches will be required to place both the cargo and crewed portion of the mission in LEO. The cargo portion of the mission would use two vehicles to carry support equipment and travel to Mars during a planetary alignment prior to the crew transit.39 This will allow verification that the support equipment has arrived successfully and the crew’s ascent vehicle has landed on Mars with sufficient time to use in situ resources to harvest propellant. The mission concept relies on the crew landing on Mars in proximity to the predeployed ascent vehicle and its support equipment. The cargo mission transfers will occur on a minimal-energy 350-day trajectory and be captured into Mars orbit using aerocapture technology. One of the predeployed vehicles will then perform aero-assisted EDL and initiate preliminary robotic efforts to prepare the landing site for the crewed mission. The second predeployed vehicle waits in Mars orbit for the arrival of the crewed vehicle. The crewed portion of the mission would depart in a long-duration habitat from a LEO staging point using NTP on a 6-month transfer to Mars orbit. The crewed system will be propulsively captured into Mars orbit and rendezvous with the predeployed vehicle. The crew of six then transfers to the predeployed vehicle containing the surface habitat, which will transfer them to the planet’s surface. The EDL system will land the habitat in close proximity to the predeployed assets, and the crew is then able to conduct mobile scientific exploration of Mars. The Mars surface mission lasts for approximately 500 days before the crew boards the ascent stage and returns to the deep-space habitat and propulsion system that remained in Mars orbit. The surface assets continue autonomous missions and data collection for possible use by future Mars exploration crews. Upon crew transfer to the deep-space habitat, which has been in standby mode, the crew jettisons the ascent vehicle and returns to Earth on another 6-month transfer and a direct Earth entry using the Orion vehicle.40 39 Transit times and propulsion requirements for missions to Mars are minimized when Earth and Mars are favorably aligned in their orbits. This alignment occurs every 26 months or so. 40 The DRA 5.0 architecture outlined here is for the long-surface-duration, so-called “conjunction” mission. Given the orbital mechanics of Earth and Mars, a second, short-stay “opposition” class mission is also possible. This PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-11

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NASA’s effort to enhance HSF capabilities that could support missions to a wide range of destinations, in anticipation of a future commitment to initiate a flight program to one or more specific destinations. The first flight of an SLS launch vehicle (EM-1) is scheduled for 2017, with a second flight (EM- 2) to follow in 2021.95 Both of these vehicles will have a payload capacity of 70 MT to LEO. Upgrades to the SLS could increase the payload capacity to 130 MT or more. Additional information on the SLS program appears above in section “Heavy-Lift Launch Vehicles.” The main components of the Orion MPCV are the launch abort system, the crew module, and the service module. Orion will have a crew capacity of four, and it will serve as the primary crew vehicle for launch and return to Earth. It will be capable of conducting rendezvous, docking, and EVA activities. The Orion’s maximum mission length will depend on the capabilities of the service module, which will provide consumables needed to sustain the crew. The first uncrewed test flight is scheduled to take place in 2014 using a Boeing Delta IV Heavy launch vehicle. The second flight will take place in 2017 as part of the first SLS flight, EM-1. The first crewed flight of the Orion will take place in 2021 on SLS flight EM-2. The service module for the first Orion flight will be provided by NASA. The service module for the second Orion flight (EM-1) will be provided by the European Space Agency (ESA) as part of its cost- sharing obligation to the United States as an ISS partner. The design of the ESA service module will be based on the design of the Automated Transfer Vehicle that has flown to the ISS several times. The Exploration Ground Systems Program is developing new and refurbished launch site infrastructure to support integration, launch, and recovery operations for the SLS and Orion MPCV flight systems. NASA’s Kennedy Space Center has established a single office to manage the Exploration Ground Systems Program and the 21st Century Ground Systems Program. The latter is intended to improve NASA’s ability to support non-NASA launch customers from government and industry. 4.3.2.2 Exploration Research and Development NASA’s Exploration Research and Development program area consists of the Human Research Program and Advanced Exploration Systems Program. The Human Research Program is concerned with investigating, understanding, preventing and mitigating risks to human health and performance associated with long-duration space missions. Areas of particular interest include exposure to space radiation, emergency medical care in space, psychosocial issues associated with the effects of confinement and isolation, and the effects of microgravity on the human body. This program makes extensive use of the ISS to conduct experiments and analyze data on astronaut health in the microgravity environment. The Space Radiation NASA Research Announcement engages the external scientific community to provide better understanding and risk reduction of the space radiation hazard faced by spaceflight crews on exploration missions. This research announcement and associated NASA research is critically aligned to U.S. deep space exploration objectives. The Advanced Exploration Systems Program is developing new capabilities and operational concepts to improve safety, reduce risk, and lower the cost of HSF missions beyond LEO. The scope of this program includes crew mobility, habitat systems, vehicle systems, and operations robotic technology for precursor missions. Activities include the demonstration and evaluation of prototype systems during test on the ground and in space on the ISS. The program is also cooperating with the Science Mission Directorate to develop instruments and concepts for robotic precursor missions that would collect data on potential destinations for human exploration missions. 95 These dates appear to be flux as this report was in its final preparation but the dates shown here are those reported by NASA in January 2014. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-67

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4.3.2.3 Commercial Spaceflight Anticipating the termination of space shuttle operations in 2011, in 2006 NASA began the process of partnering with industry to foster the development of commercial systems to transport cargo and crew to and from the ISS. The development of commercial cargo launch systems is complete, as evidenced by successful demonstration and operational flights to ISS by SpaceX and Orbital Sciences Corporation. SpaceX and Orbital are under contract to provide a total of 20 cargo flights to ISS, and funding for commercial cargo activities has been transferred from Exploration to Operations in the NASA HEOMD budget. As of April 2014, SpaceX had completed three ISS resupply missions using its Falcon 9 launch vehicles and Dragon capsules. Orbital completed its first resupply mission in January 2014 using its Antares launch vehicle and Cygnus capsule. NASA is continuing to support the development of commercial crew capabilities (to transport astronauts to the ISS and return them to Earth) with three industry partners: Boeing, SpaceX, and Sierra Nevada. NASA has financial agreements with these companies to provide a total of up to $1.1 billion for all three companies over a 2-year period. Subsequent agreements are expected to result in crewed flights to the ISS starting no earlier than 2017. The main impact on NASA of the commercial crew program is to mitigate the current complete dependence on Russia for crew transport. It is too early to know if this approach will reduce costs. What is certain, however, is that the U.S. industrial base capable of supporting HSF has been stabilized and expanded by the commercial cargo and commercial crew programs. This will most probably provide NASA additional capabilities in the future, and may enable the establishment of a space-based economy that is not completely dependent on NASA, much as the commercial imaging and communications satellite industries are no longer dependent on NASA. It is well to note, however, that such a commercial space- based economy, heavily utilizing HSF, is highly speculative at this point. 4.3.2.4 Space Technology Mission Directorate The Exploration Technology Development Program is developing technologies to support human exploration beyond Earth orbit, with a focus on advanced technologies that have a long development time. The scope of this program includes advanced technologies for SEP, ECLSS, ISRU, EDL, storage and transfer of cryogenic fluids in space, and robotic systems to improve crew safety and effectiveness. The Exploration Technology Development Program consumes about one-third of STMD’s budget. STMD also funds three other programs:  Crosscutting Space Technology Development Program  Small Business Innovation Research/Small Business Technology Transfer Program  Partnership Development and Strategic Integration Program Each of these programs supports HEOMD as well as the Science Mission Directorate and the Aeronautics Research Mission Directorate. The Crosscutting Space Technology Development Program develops technology that is broadly applicable to the needs of future NASA science and exploration missions as well as the needs of other federal agencies and industry. Various elements of this program investigate technologies across a wide range of maturity levels, from conceptual studies through flight demonstrations. Areas of interest include, for example, advanced manufacturing technologies, nanotechnology, and synthetic biology. In addition, this program conducts technology demonstration missions to validate selected technologies that have successfully competed ground testing. Technology demonstration missions are currently being developed for low-density supersonic decelerators, laser communications, deep space atomic clocks, and solar sails. The Small Business Innovation Research/Small Business Technology Transfer Program is intended to increase the participation of small businesses in NASA research and technology development and to facilitate the commercial application of NASA research results. The 2012 solicitation for this PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-68

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program encompassed a broad scope of topics including, for example, the reduction of airframe noise and drag; the development and use of launch vehicles, in-space propulsion systems, and space habitats; and advanced space telescopes for astrophysics and Earth science. The Partnership Development and Strategic Integration Program coordinates technology development activities throughout NASA and takes the lead for NASA’s technology transfer and commercialization activities. 4.3.2.5 NASA Infrastructure The United States had a fairly rudimentary space program when the Apollo program started. As a result, in addition to developing the required technology, the supporting infrastructure for testing, assembly, launch, etc. had to be created ab initio. Some of this infrastructure, such as the Vehicle Assembly Building and the Pad 39 Complex (A and B) at Kennedy Space Center, was repurposed after Apollo. Even so, NASA carries a very large set of aging infrastructure. NASA’s Office of the Inspector General (OIG), the Government Accounting Office (GAO), and the National Research Council have each reported on NASA infrastructure with worrisome observations.96 NASA’s OIG determined that approximately 80 percent of NASA facilities are more than 40 years old and that maintenance costs for these facilities amount to more than $24 million per year, and ongoing shortfalls in maintenance are adding to an already substantial backlog in deferred maintenance. 97 Carrying costs such as these represent latent threats to the development of newer infrastructure that will be needed to support human exploration beyond LEO. For example, some of the infrastructure to develop and test fission surface power and NEP systems will undoubtedly be extremely challenging to plan, permit, fund, and construct. 4.3.3 Commercial Programs A wide range of corporations are developing advanced launch vehicles, capsules, and space habitats to support traditional customers such as the commercial satellite industry, NASA, and DOD. However, some of the new initiatives to provide orbital and suborbital flight capabilities are focused on new markets such as space tourism or transportation to a privately developed space station, should one be constructed. Some of the new transportation systems are being developed by aerospace companies such as Boeing and Orbital Sciences Corporation, which have substantial spaceflight experience. Others are being developed by relatively new ventures such as Bigelow Aerospace, Blue Origin, SpaceX, Virgin Galactic, and XCOR Aerospace. In some cases, the development of new vehicles has been aided by NASA (to support the development of commercial cargo and crew space transportation systems, for example). In other cases, development programs have relied entirely on private funding. In all cases, however, these companies have invested heavily toward the objective of making commercial HSF profitable, and market- based evidence indicates that there is a sustainable path forward for at least some of these initiatives. In fact, many of these companies are making good progress in developing new systems; as noted above, Orbital Sciences Antares launch vehicle and the SpaceX Falcon 9 launch vehicle have entered commercial cargo service, and a space habitat developed by Bigelow Aerospace will be docked to the ISS in 2015 for a 2-year evaluation period. Looking beyond LEO, some new ventures have been established with the goal of launching privately funded crewed missions to the Moon or Mars and uncrewed missions to asteroids. However, 96 A.D. McNaull, House Space Subcommittee discusses aging NASA infrastructure, FYI: The AIP Bulletin of Science Policy News, Number 145, October 4, 2013. 97 NASA Office of Inspector General, “NASA’s Efforts to Reduce Unneeded Infrastructure and Facilities,” February 12, 2013, http://oig.nasa.gov/audits/reports/FY13/IG-13-008.pdf. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-69

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none of these more ambitious endeavors have evidenced substantial funding or vehicle development activities. This is not surprising because exploration missions beyond LEO would be extremely expensive, they would need to overcome substantial technical risks, and the time to produce a positive return on investment would be well beyond the normal time horizon of corporate business plans. The largest of the new commercial vehicles under development, the SpaceX Falcon Heavy, would be able to launch robotic missions to Mars, but it would have limited capabilities to support HSF beyond LEO, unless the U.S. committed itself to on-orbit assembly, replenishment, fuel depots, etc. Given the congressional mandate to develop SLS, this seems unlikely. Smaller launch vehicles currently in service or under development would be less suitable. This is not surprising given the very limited market for such capabilities and the fact that NASA is developing its own launch vehicle, the SLS, for HSF beyond LEO. 4.3.4 Department of Defense Research and development of new technology and capabilities in other government agencies beside NASA could benefit future HSF programs. Most prominently, DOD is highly invested in improving the capabilities and reducing the costs of their space-related activities. Launch costs are of particular interest. The U.S. Air Force recently announced that it will allow new launch vehicle providers, such as Space X, to pursue certification to launch national security payloads. On the other hand, there has been little overt DOD interest in SLS—an effort that has been and will continue to be leveraged by NASA. DOD research agencies such as the Defense Advanced Research Projects Agency (DARPA), the Air Force Research Laboratory, and the Naval Research Laboratory are also advancing the state of the art of space technologies at various levels of maturity, from basic building blocks such as advanced materials and power generation technologies to complex in-space demonstrations of systems such as automated rendezvous and docking. Specific examples include the DARPA Fast Access Spacecraft Testbed, which facilitated the development of solar arrays with higher power and less mass; the DARPA Orbital Express missions, which demonstrated automated rendezvous and docking as well as the transfer of (non- cryogenic) fluids between two spacecraft; and the Air Force Research Laboratory’s research into advanced thermal protection systems. Research focused on terrestrial applications can also contribute to future HSF missions. For example, some of the medical and behavioral advances to improve the performance and safety of soldiers on the battlefield may help assure the health of astronauts on long-duration missions. Advances in robotics technology for military applications may contribute to the development of advanced robotics by NASA. In addition, technology developed for the Army’s Human Universal Load Carrier could enable NASA to develop advanced spacesuits that reduce the forces and torques that the wearer must exert during EVA operations. 4.3.5 International Activities There are a growing number of nations that have substantial human exploration programs, including ongoing system or technology development programs that could possibly contribute directly to future NASA human space activities. Programs of greatest note are being conducted by Russia, ESA, Japan, and China. In addition, Canada is an active partner in the ISS program, and India has a long-term plan for human space exploration. Altogether, 38 nations have had their nations’ astronauts fly in space. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-70

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As noted in Chapter 2, human space exploration enhances international stature and national pride, and this seems to be a key motivation for emerging space powers to enter and expand their activities in this area.98 Like the United States, Russia’s current human space program is focused on supporting the ISS. Russia has a long-term space policy, and, as discussed in the media, they have the capabilities to develop technologies and systems in support of human exploration program beyond LEO, particularly with regard to nuclear propulsion, power systems, and human exploration. The Russian nuclear development facilities would likely require a major refurbishment before they could support a major new development effort. Like the United States, nearly all of Russia’s work in the development of space nuclear systems took place decades ago. The ESA’s HSF program is focused on supporting the ISS. ESA is conducting cargo flights to the ISS and exploring options for a crewed spacecraft, and it is also committed to developing a service module for Orion MPCV. The service module will incorporate technology from the ESA’s Automated Transfer Vehicle, which has been used for ISS resupply. Chinese astronauts (also known as yŭhángyuán or taikonauts) are viewed domestically as symbols of Chinese cultural and technological prominence. China’s HSF program is focused on LEO missions. China intends to develop a modular space station and a crewed lunar exploration program, although details of the technologies and systems being developed for these missions are not publically available. NASA is prohibited by law from bilateral cooperation with the Chinese, so the U.S. and Chinese space programs are proceeding independently. This policy, while driven by congressional sentiment, denies the U.S. partnership with a nation that will probably be capable of making truly significant contributions to international collaborative missions. It may be time to reexamine whether this policy serves the long-term interests of the United States. India and Japan are separately considering options for developing a crewed spacecraft to be launched on indigenous rockets. 99 The Global Exploration Roadmap from the ISECG’s 2013 roadmap includes a single reference mission scenario that leads to a human mission to the Mars surface. This scenario “reflects the importance of a stepwise evolution of critical capabilities which are necessary for executing increasingly complex missions to multiple destinations. . . . The roadmap demonstrates how initial capabilities can enable a variety of missions in the lunar vicinity, responding to individual and common goals and objectives, while contributing to building the partnerships required for sustainable human space exploration.”100 The 12 space agencies and countries who authored the ISECG Global Exploration Roadmap101 continue to support human exploration beyond LEO. 4.3.6 Robotic Systems 4.3.6.1 Robotic Science and Exploration Robotic space exploration, which is driven by science objectives, has greatly expanded knowledge of the solar system, including its origin and evolution. Robotic missions involving orbiters, landers, and rovers have discovered extensive evidence of past warm and wet conditions on Mars. The 98 Mindell et al., “The Future of Human Spaceflight: Objectives and Policy Implications in a Global Context,” American Academy of Arts and Sciences, Cambridge, Mass., 2009. 99 Mindell et al., “The Future of Human Spaceflight: Objectives and Policy Implications in a Global Context,” American Academy of Arts and Sciences, Cambridge, Mass., 2009. 100 ISECG, The Global Exploration Roadmap, 2013. 101 Ibid. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-71

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evidence includes lake systems, alkali flats, and volcanic vents.102 The possibility that Mars may contain evidence of past life is a driving scientific reason for continued interest in exploring and understanding the red planet, for both robotic and human missions. Other targets of interest for human and/or robotic expeditions include asteroids, Earth’s Moon, and the two moons of Mars, Phobos and Deimos. Analysis of lunar material brought back by Apollo and by robotic missions launched by the Soviet Union, as well as subsequent robotic orbital missions to the Moon, indicate that the Moon was created when a Mars- sized planetesimal impacted Earth early in its history.103 Earth-based observations and robotic exploration of asteroids shows a plethora of evolutionary states, from primitive bodies to remnants of iron-nickel cores of impact-disrupted objects.104 Phobos and Deimos are particularly interesting because these two small bodies appear to be composed of very primitive materials that are quite different than the inferred average composition of Mars.105 Given the high scientific interest in Mars, the Moon, asteroids, and the moons of Mars, there will be continued interest in additional robotic missions to the Moon and beyond. Robotic science missions provide information about the environmental, terrain, and surface properties, and other information that is essential to the safety and effectiveness of crewed missions. For example, radiation data collected by the MSL mission en route to Mars and on the ground (by the Curiosity rover) are providing NASA with more accurate information about the nature and level of radiation that astronauts would encounter during a human mission to the Mars surface. Evolutionary improvements in the capabilities of robotics would enable robotic servicing of spacecraft as well as robotic precursor missions to conduct ground operations at a landing site before a crewed lander arrives. Currently, experiments on the ISS are testing the ability of robotic systems to refuel and repair spacecraft. Ground operations could include exploration of potentially hazardous terrains and environments near landing sites, and a robotically operated ISRU system on the surface of Mars could generate needed supplies of oxygen from the carbon dioxide atmosphere, some of which could be converted to water using hydrogen brought from Earth. After the crew arrives on the surface, robotic systems could relieve the crew from menial tasks, such as housekeeping. In addition, surface exploration could be conducted as a cooperative effort involving humans and robotic systems. For example, robots capable of traversing hazardous terrain might be used to explore the safest paths for humans to sample strata on the walls of canyons and crater rims, or they could be commanded to conduct reconnaissance and sampling if the terrain proved to be too difficult for humans to explore. 4.3.6.2 A Game-Changing Vision of Robotics As observed elsewhere in this chapter, visionaries in the late 1940s correctly presumed that humans would eventually travel to the Moon, but the approaches they envisioned (a single, huge rocket that would make the round trip) did not match the approach that actually happened. In part, that was because more practical approaches were developed in the constrained resource environment of a real program, and in part because there were tremendous technological advances unforeseen by the earlier visionaries, particularly with regard to digital computers. Although the fundamental technology of chemical propulsion has hardly advanced in the past 50 years, the capability of computers has continued to advance at an exponential pace with no end in sight. The capabilities of sensor technologies has also exploded. Inexpensive consumer devices now have more 102 J.P. Grotzinger et al., A habitable fluvio-lacustrine environment at Yellowknife Bay, Gale Crater, Mars, Science 343, doi:10.1126/science.1242777. 103 D.J. Stevenson, “Origin of the moon—The collision hypothesis, Annual Review of Earth and Planetary Sciences 15(1):271-315, 1987. 104 H.Y. McSween, Jr., Meteorites and their Parent Planets (2nd ed.), Oxford University Press, 1999. 105 A. Fraeman et al., Spectral absorptions on Phobos and Deimos in the visible/near infrared wavelengths and their compositional constraints, Icarus 229:196-205, doi:10.1016/j.icarus.2013.11.021. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-72

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computing power, sensor resolution, and programmability than was available to NASA in the midst of Apollo. One particular manifestation of the exponential increase in computational capability, sensor quality, and mechatronics (which combines mechanical, electrical, and control technologies) is the field of robotics. Industrial robots are commonplace. Self-driving cars, which in the recent past were the subject of highly speculative, cutting edge experiments, are now under commercial development. Robots are seriously contemplated as an answer to demographic crises in Western societies, where eldercare will require significantly capable, highly autonomous systems capable of complex interactions with humans. The most common response to the criticism that HSF is extremely expensive is that humans’ capacity for contextual reasoning and problem solving is indispensable in exploration scenarios. Nonetheless, much more has been learned about our solar system by relatively primitive robots than by human explorers. Similarly, oceanographic research, until recently in decline because of the prohibitive costs of ship-based oceanography, is undergoing a revolution through the use of autonomous systems that can gather data in larger quantities and much less expensively than conventional ocean expeditions. Even in the culturally resistant domain of warfare, where it has been assumed that human presence is mandatory, uncrewed aircraft, uncrewed submersibles (to detect and destroy mines), and other robotic systems are increasingly taking the place of humans for dangerous missions. In coming decades, advances in robotic capabilities may likewise present new options for space exploration, opening new pathways that are technologically achievable and can be implemented affordably without incurring unacceptable developmental risk. 4.4 KEY RESULTS FROM THE PANEL’S TECHNICAL ANALYSIS AND AFFORDABILITY ASSESSMENT The following key results arise from the Technical Panel’s technical analysis and affordability assessment, which are detailed in this chapter. 1. Feasible Destinations for Human Exploration. For the foreseeable future, the only feasible destinations for human exploration are the Moon, asteroids, Mars, and the moons of Mars. A human mission to the Mars surface is feasible, although doing so will require overcoming unprecedented technical risk, fiscal risk, and programmatic challenges. Mars is humanity’s horizon destination. 2. Pace and Cost of Human Exploration. Progress in human exploration beyond LEO will be measured in decades with costs measured in hundreds of billions of dollars and significant risk to human life. 3. Human Spaceflight Budget Projections. With current flat or even inflation-adjusted budget projections for human spaceflight, there are no viable pathways to Mars. a. A continuation of flat budgets for human spaceflight is insufficient for NASA to execute any pathway to Mars and limits human spaceflight to LEO until after the end of the ISS program. b. Even with a NASA human spaceflight budget adjusted for inflation, technical and operational risks do not permit a viable pathway to Mars. c. The currently planned crewed flight rate is far below the flight rate of past human spaceflight programs.106 106 Late in the production of this report, NASA leadership told the NASA Advisory Council’s Human Exploration and Operations Committee that as a “repetitive cadence is necessary” for a viable SLS program, SLS would launch every year. While this statement is consistent with the findings of this committee, the “assumed long- term SLS manifest” shown to Human Exploration and Operations Committee did not identify payloads past the EM2 mission currently planned for 2021. Suggestions that military, commercial, and/or science missions will take PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-73

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d. Increasing NASA’s budget to allow increasing the human spaceflight budget by 5 percent per year would enable pathways with potentially viable mission rates, greatly reducing technical, cost, and schedule risk. 4. Potential Cost Reductions. The decadal time scales reflected above are based on traditional NASA acquisition. Acceleration might be possible with significant cost reductions resulting from: a. More extensive use of broadly applicable commercial products and practices b. Robust international cost sharing (that is, cost sharing that greatly exceeds the level of cost sharing with the ISS) c. Unforeseen significant technological advances in the high priority capabilities 5. Highest-Priority Capabilities. The highest-priority capabilities that are needed to enable human surface exploration of Mars are related to: a. Entry, descent, and landing for Mars b. Radiation safety c. In-space propulsion and power 6. Continuity of Goals. Frequent changes in the goals for U.S. human space exploration (in the context of the decades that will be required to accomplish them) dissipate resources and impede progress. 7. Maintaining Forward Progress. Within the current budget scenario, there are only a few actions, all of which would be difficult to take, that can ensure that the U.S. human exploration program keeps moving forward during the next decade following the pathways laid out in this report. These options include the following: a. Aggressively divesting NASA of nonessential facilities and personnel to free up resources for future-oriented programs.107 b. Focusing the use of the ISS to support future exploration beyond LEO, including the use of the ISS as a testbed for technologies and human health. (However, for technical reasons and because the operation of nuclear fission systems in LEO is prohibited, 108 the ISS cannot be used to support development of any of the highest-priority capabilities identified in key result 5.) c. Making substantial research and technology investments in the highest-priority capabilities. d. Maintaining a robust planetary and space science program to engage and maintain the interest of the public in deep space exploration, to advance technological capabilities relevant to human exploration operations in space and on the surface of the Moon and/or Mars, and to better understand space and surface environments. e. Investing in people: developing a workforce with hands-on experience in flight programs. f. Continuing to leverage commercial products and practices to strengthen the industrial base and increase NASA’s efficiency. g. Strengthening international relationships and partnerships with the goal of reducing duplication, exploiting worldwide expertise, and substantially reducing the cost of the total program to the United States. up the slack have been made, but no commitments have been announced. The SLS heavy lift capacity suggests that the cost of payloads appropriate for its use will provide a substantial barrier to increasing the SLS launch rate to once per year. 107 The political difficulty of taking this action suggests that it may require an extraordinary process, akin to NASA’s “real property assessment” of 2004, but using an independent, bipartisan assessment commission and a subsequent up-or-down vote by Congress. 108 United Nations Principles Relevant to the Use of Nuclear Power Sources in Outer Space, UN A/RES/47/68, 1992, available at http://www.un.org/documents/ga/res/47/a47r068.htm. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-74

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Human spaceflight is an extraordinarily challenging endeavor, fraught with daunting technical, political, and programmatic hurdles, and carrying a high degree of physical risk to the explorers who push forward the boundaries of human presence. The scale of U.S. investment in this endeavor is substantial and has remained so for decades, despite periodic financial strictures and without broad and deeply committed public support. The frequently cited rationales for human spaceflight are self-evident to some, unconvincing for others, and there are unlikely to be novel rationales that are more potent. The nation has completed the most ambitious space engineering project ever, the International Space Station, where a group of nations act cooperatively to sustain it and exploit its capabilities. It is a substantial investment by multiple countries, and it is natural to attempt to amortize that investment and retain the capability. Programmatic and budgetary factors led to the completion of ISS just as the main launch system enabling its construction was retired from service, and Congress mandated the development of a new heavy lift launcher, the SLS. In addition, national leadership has called for the United States to venture beyond LEO, where more distant destinations beckon. SLS is but one part of the technology that needs to be developed to enable even a return to the Moon, let alone human visits to near- Earth asteroids, or the vicinity or surface of Mars. And while national leadership has sustained operations in LEO, it seems disinclined to substantially increase the level of investment in human spaceflight. Thus, the HSF program faces a dilemma. Maintaining the ISS and developing SLS leave precious little budgetary maneuvering room to plan the next steps beyond LEO. However, the affordability analysis summarized above has shown that within currently projected HSF budgets, it will be decades before the next significant human spaceflight milestone, even with optimistic assumptions about costs, technology development, and programmatic stability. Probably the most significant single factor in allowing progress beyond LEO is the development of a strong national (and international) consensus about the pathway to be undertaken and sustained discipline in not tampering with that plan over many administrations and Congresses. Without that consensus and discipline, it seems all too likely that the potential of SLS will be wasted, human spaceflight to LEO will become increasingly routine (though still with risk to life), and the horizons of human existence will not be expanded, at least not by the United States. With such a consensus, however, and with strict adherence to the pathways approach and principles outlined in this report, the United States could maintain its historic position of leadership in space exploration and embark on a program of human spaceflight beyond LEO that, perhaps for the first time in the more than half-century of human spaceflight, would be sustainable. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 4-75

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Appendixes

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