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1 Overview of Analysis and Findings 1.1 INTRODUCTION The United States has publicly funded its human spaceflight program continuously for more than a half-century, through three wars and a half dozen recessions, from the early Mercury and Gemini suborbital and Earth orbital missions, to the Apollo lunar landings, and thence to the first reusable winged, crewed spaceplane, which the United States operated for three decades. Today the United States is the major partner in a massive orbital facility—the International Space Station (ISS)—which is becoming the focal point for the first tentative steps in commercial cargo and crewed orbital spaceflights. And yet, the long-term future of human spaceflight beyond the ISS is unclear. Pronouncements by multiple presidents of bold new U.S. ventures to the Moon, to Mars, and to an asteroid in its native orbit, summarized in Section 1.2 of this chapter, have not been matched by the same commitment that accompanied President Kennedy’s now fabled 1961 speech—namely, the substantial increase in NASA funding needed to make it happen. In the view of many observers, the human spaceflight program conducted by the U.S. government today has no strong direction and no firm timetable for accomplishments. This complex mix of historic achievement and uncertain future made the task1 faced by the committee extraordinarily difficult. In responding to the task the committee assessed the historically stated rationales for human spaceflight as rigorously as possible given the available knowledge base, with the intent of identifying a set of “enduring questions” akin to those that motivate strategic plans for scientific disciplines. The committee also sought to describe the value and “value proposition” of the program; to solicit and interpret stakeholder and public opinion; and to provide conclusions, recommendations, and decision rules that can guide future human spaceflight programs pursued or led by this country. The fruits of the committee’s labors2 as presented here provide a map toward a human spaceflight program that can avoid some of the ills and false starts of the past. However, to set course on such an endeavor, the nation will need its investment in the human spaceflight program to grow annually over the coming decades. To continue on the present course—pursuit of an exploration system to go beyond low Earth orbit (LEO) while simultaneously operating the ISS through the middle of the next decade as the major partner, all under a budget profile that fails even to keep pace with inflation3—is to invite failure, disillusionment, and the loss of the longstanding international perception that human spaceflight is something the United States does best. Throughout this chapter, which gives an overview of the committee’s most important conclusions as well as historical background to the relevant issues, the recommendations and conclusions 1 The committee’s statement of task is given in Appendix A. 2 Six committee meetings, four Technical Panel meetings, three Public and Stakeholder Opinion Panel meetings, site visits to Johnson Space Center, Kennedy Space Center, and Marshall Space Flight Center (the key NASA human spaceflight centers), a call to the public for white papers, stakeholder interviews, a public discussion on Twitter, and participation in international conferences. 3 In this report, future inflation is projected to be 2.5 percent per year, consistent with “2013 NASA New Start Inflation Index for FY14,” http://www.nasa.gov/sites/default/files/files/2013_NNSI_FY14(1).xlsx. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-1

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are highlighted in bold. The committee justifies and quantifies these in the chapters that follow. The essential cornerstones of the committee’s findings can be summarized as follows:  The rationales for human spaceflight are a mix of the aspirational and the pragmatic. The primary rationale for the Apollo program was to demonstrate in an unambiguous but peaceful way the technological supremacy of the United States over the Soviet Union by beating the Russians to the Moon.4 The rationale for Apollo took place not only against a backdrop of Cold War potential for nuclear war but also in the midst of an existential conflict between two fundamentally different economic systems, a conflict that is now over. Quantification of the value of human spaceflight to the nation today, in terms of economic return or increased quality of life, is difficult. This does not mean that there are no benefits: W.B. Cameron wrote “not everything that can be counted counts, and not everything that counts can be counted.”5  The level of public interest in space exploration is modest relative to other public policy issues. As Chapter 3 documents, public opinion about space has been generally favorable over the past 50 years, but much of the public is inattentive to space exploration, and spending on space exploration is not a high priority for most of the public.  The horizon goal for human space exploration is Mars. In Chapter 4 the committee shows that there is a small set of plausible goals for human space exploration in the foreseeable future, the most distant and difficult of which is a landing by human beings on the surface of Mars. All long- range space programs, by all potential partners, for human space exploration converge on this goal.  A program of human space exploration beyond LEO that satisfies the pathway principles defined below is not sustainable with a human spaceflight budget that increases only enough to keep pace with inflation. As shown in Chapter 4, the current program to develop launch vehicles and spacecraft for flight beyond LEO cannot be sustained with constant buying power over time, in that it cannot provide the flight frequency required to maintain competence and safety, does not possess the “stepping-stone” architecture that allows the public to see the connection between the horizon goal and near-term accomplishments, and may discourage potential international partners. In the section “Pathway Principles and Decision Rules,” below, the committee outlines a “pathways” approach, which requires the United States to settle on a definite pathway to the horizon goal and adhere to certain principles and decision rules to get there. In the course of developing its findings, the committee identified some specific important issues that the nation will need to grapple with should it choose to embark on a renewed effort in deep space exploration involving humans:  The nation’s near-term goals for human exploration beyond LEO are not aligned with those of our traditional international partners. The committee heard from representatives of international partners that their near-term goal for human spaceflight was lunar surface operations. They also made it clear that they could not undertake such a program on their own, and were relying on the United States to play a leadership role in human exploration of the Moon. While these partners expressed interests in aspects of the asteroid redirect mission (ARM), the committee detected in its discussions with representatives an underlying concern that ARM would divert U.S. resources and attention from an eventual return to the Moon. Of the several pathways examined, the one 4 President Kennedy, 2 days after Yuri Gargarin’s historic flight into space on April 12, 1961, said in a meeting to NASA and cabinet officers, “If somebody can just tell me how to catch up … there’s nothing more important.” H. Sidey, John F, Kennedy, President, Atheneum Press, New York, pp. 122-123. 5 W.B. Cameron, Informal Sociology: A Casual Introduction to Sociological Thinking, Random House, 1963. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-2

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that does not include a meaningful return to the Moon—that is, extended operations on the lunar surface—has higher development risk than the other pathways.  Continued operation of the ISS beyond 2020 will have a near-term effect on the pace NASA can sustain in exploration programs beyond LEO, but it also affords an opportunity for extended studies related to long-term exposure to microgravity. The United States and its international partners are jointly committed to operating the ISS through 2020, with the United States having recently proposed extension to 2024. In its presentations to the committee, NASA made clear its desire to operate the complex facility through 2028. In addition, the United States has designated half of its ISS space and resources as a National Laboratory, which proponents say will require extension of the ISS beyond 2020 or even 2024 in order to increase the probability that the research and development (R&D) conducted there provides substantial returns, including promised commercial benefits. Continued operation will compete with new programs beyond LEO, aggravating the problems of funding. At the same time, the committee recognizes that much work remains to determine physiological tolerance to and countermeasures for the lengthy microgravity environments that will be experienced on flights to and from Mars, and the ISS is the platform on which to do this work. There is thus a tension between moving beyond the ISS to the exploration of deep space at a safe and sustainable pace on the one hand and, on the other, conducting the medical studies in LEO needed to execute human exploration of Mars two or three decades hence.  The prohibition on NASA speaking to Chinese space authorities has left open opportunities for collaboration that are being filled by other spacefaring nations. The recent docking of a piloted Chinese vessel to a new orbital module, and the first robotic rover operations by China on the Moon, are the latest in a program that marches steadily and strategically toward what might eventually become a lead role among the nations in spaceflight. In contrast to the failure-prone early histories of the U.S. and USSR human spaceflight programs, China has proceeded methodically, deliberately, and with little in the way of visible failure. The U.S. government’s response to this has been inconsistent, regarding China as a potential partner in certain areas and a threat in others. The committee is concerned that current U.S. law is impeding the nation’s ability to collaborate with China where appropriate, while traditional U.S. international partners have not imposed on themselves such restrictions. The remainder of Chapter 1 explores the past, present, and prospects of human spaceflight from a number of different perspectives, all of which inform the committee’s final considerations of a sustainable program. The committee begins with a historical trajectory of space policy in regard to human spaceflight and ends with the current situation (Section 1.2). The chapter then assesses the international context (Section 1.3), in terms of current partnerships and the capabilities of non-partner nations such as China. Section 1.4 summarizes the enduring questions and rationales for human spaceflight offered over time, and it is followed by a summation (Section 1.5) of the opinions of the U.S. public and stakeholders in human spaceflight.6 Then, Chapter 1 closes with a section (Section 1.6) on strategic approaches to a sustainable human spaceflight program beyond LEO based on what the committee calls a “pathways approach” as described later in this chapter. The chapter concludes by summarizing (Section 1.7) the requirements for undertaking such an effort and the consequences of embarking on a new program of deep space exploration without adequate funding. The committee formulates a set of Pathways Principles and Decision Rules to guide the program, and offers two examples of how the pathways approach might be used to design a human spaceflight program. The report reviews and rearticulates why the nation might 6 Sections 1.2 through 1.5 summarize the extensive and detailed analyses of enduring questions, value propositions, and stakeholder and public opinions offered in Chapters 2 and 3, respectively. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-3

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choose to move forward and lays out an approach that is responsive to the enduring questions and rationales that are developed and analyzed here. Although the statement of task mentions two time horizons, one extending to 2023 and the other to 2030, the committee has not attempted to separate recommendations for the two horizons. The pathways approach described here requires integrated programs that will span the entire time period up to 2030, so that any attempt to divide the time window into a “before” and “after” 2023 is artificial. In fact, in developing and exercising the pathways approach, the committee of necessity had to consider a time horizon extending into the middle of this century, well beyond the year 2030 specified in the task statement. The committee therefore acknowledges the real possibility that over the half century considered, advances in science and technology in bioengineering, artificial intelligence, and other disciplines may come far more quickly and unpredictably than the advances contemplated for the human spaceflight pathways proposed in this report. Breakthroughs in these other disciplines could serve to solve many of the large obstacles to exploration beyond LEO. In particular, the line between the human and the robotic may be blurred more profoundly than simple linear extrapolations predict. In such an eventuality, exploration of the “last frontier” of space might well occur in a more rapid and far-reaching way than is envisioned in this report; indeed, whether it would still be accurately described as “human exploration”7 is unknowable. 1.2 U.S. SPACE POLICY PAST AND PRESENT The U.S. Space and Rocket Center near NASA’s Marshall Space Flight Center includes an exhibit entitled “Great Nations Dare,” an immersion into the history of exploration.8 It is a fitting reminder, at the place where the massive Saturn V moon rocket was developed and built, that history is replete with examples of nations and societies that were at the forefront of exploration for brief periods and sooner or later lost their momentum. Although the specific reasons for exploration have varied (expansion of power, trade routes, precious metals, spreading religion, etc.), there was almost always a nationalistic competitive element that helped in obtaining resources for these expensive adventures. The committee was charged as part of its task (see Appendix A) to consider the goals of NASA as set forth in its founding legislation and the legislative acts and policy directives that followed. The committee provides below a brief history of U.S. human spaceflight efforts and brings the story up to the present day. The goal is not to chronicle each and every major accomplishment but rather to highlight the principal changes and shifts in civil space policy—especially as it relates to human spaceflight—that drove the program at the highest level. The early history of space exploration was driven largely by competition between nations. The program’s effective birth can be traced back to the National Aeronautics and Space Act signed on July 29, 1958, which led to the formation of the National Aeronautics and Space Administration (NASA).9 Precipitated by the shock of the launch of the Soviet Sputnik satellite on October 4, 1957, U.S. policy makers were mobilized into creating and consolidating a federal infrastructure in support of space activities. Once NASA officially opened its doors on October 1, 1958, its initial activities were guided by 7 For the purposes of this report, human exploration of space is defined as flight into regions of space beyond LEO in which humans are actually present in the vehicles. Here, “regions” can refer to position, to orbital energy (velocity), or both. The committee defines ambiguous cases where humans are in martian or lunar orbit by virtue of telerobotically conducting surface operations as human exploration because of the astronauts’ proximity to the target and their remoteness from Earth. 8 “‘Great Nations Dare’ Exploration Technology Exhibit,” http://www.nasa.gov/centers/marshall/news/exhibits/great_nations.html, accessed January 19, 2014. 9 National Aeronautics and Space Act of 1958, Public Law 85-568, 72 Stat., 426. Signed by the President on July 29, 1958 in Exploring the Unknown: Selected Documents in the History of the U.S. Civil Space Program, Volume I: Organizing for Exploration, eds. John M. Logsdon et al. (Washington, DC: NASA, 1995), 334-345. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-4

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the original act as well by the Eisenhower administration’s preliminary U.S. policy for outer space.10 The Space Act laid out eight objectives of the U.S. civilian space program:  The “expansion of human knowledge of phenomena in the atmosphere and space”;  Improving the “usefulness, performance, speed, safety, and efficiency” of rockets and spacecraft;  The “development and operation of [robotic and crewed] vehicles”;  The “establishment of long-range studies of … (a) the benefits to be gained (b) opportunities for and (c) problems involved, in the use aerospace activities for peaceful and scientific purposes;  “The preservation of the role of the United States as a leader in aeronautical and space science and technology”  Cooperation with the Department of Defense as required;  “Collaboration by the United States with other nations and groups of nations in work done pursuant to this Act and in peaceful application of the results, thereof”;  To make effective use of the scientific and engineering resources in the country in cooperation with interested agencies. Based on these, NASA prepared a formal long-range plan in December 1959 (“The Long Range Plan of the National Aeronautics and Space Administration”). The original plan featured a balanced program of science, applications, and human space exploration with the possibility of human flight to the Moon “beyond 1970.”11 Hopes for a long and stable space policy were, however, thrown into doubt with the continuing successes of the Soviet space program, in particular, with the launch of the first human being into space in 1961. Cosmonaut Yuri Gagarin’s historic flight on April 12, 1961, set into motion a series of events that culminated with a major policy speech on May 25, 1961, in which President John F. Kennedy called for landing an American on the Moon before the end of the decade and returning him safely to Earth. Driven by the need to reassert U.S. confidence in the arena of space, President Kennedy’s decision (and considerable congressional support for it) set NASA on a crash program to achieve the Moon landing goal.12 In the following 2 years, NASA’s budget increased 89 percent and 101 percent, respectively.13 Over the course of a decade, NASA became a large federal bureaucracy with an associated contractor workforce whose primary (although not sole) goal was to develop the capabilities for human spaceflight with the proximate and primary goal of landing humans on the Moon—only to see its share of the federal budget and horizons shrink with the end of Apollo. Through the 1960s, NASA implemented the highly successful Mercury and Gemini programs as a lead-up to the Apollo project. The first American astronaut to enter orbit, John Glenn, was launched aboard the Mercury Friendship 7 vehicle (Figure 1.1). With Mercury and Gemini, NASA centers gained critical experience in performing increasingly complex human space missions involving extravehicular activity, rendezvous and docking, and long-duration flight. Despite the setback of the tragic Apollo 1 fire in early 1967, when three astronauts were killed during a ground test at Cape Kennedy, the program progressed by leaps and bounds, culminating in the landing of Apollo 11 astronauts Neil Armstrong and Edwin “Buzz” Aldrin on the Moon on July 20, 1969, thus fulfilling President Kennedy’s 10 “National Security Council, NSC 5814, ‘U.S. Policy on Outer Space,’ June 20, 1958” in Exploring the Unknown, Volume I, 345-359. 11 “NASA Long Range Plan, 1959,” http://www.senate.gov/artandhistory/history/resources/pdf/ NASALongRange1959.pdf. 12 The classic work on the Kennedy decision is John M. Logsdon’s The Decision to Go to the Moon: Project Apollo and the National Interest (MIT Press, Cambridge, Mass., 1970). See also the more recent John F. Kennedy and the Race to the Moon (Palgrave Macmillan, New York, 2010). 13 Figures taken from Logsdon, John F. Kennedy and the Race to the Moon, 2010. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-5

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FIGURE 1.1 John Glenn climbs inside the Mercury capsule he dubbed “Friendship 7” on February 20, 1962, before launching into space. SOURCE: Courtesy of NASA, “Glenn Launch Highlighted Changing World,” February 17, 2012, http://www.nasa.gov/topics/history/features/Glenn-50thKSC.html#.U34ERyhhu6I. FIGURE 1.2 Eugene Cernan, Apollo 17 commander, was the last human to walk on the Moon, finishing up the third of three moonwalks on December 13, 1972. SOURCE: Courtesy of NASA. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-6

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FIGURE 1.3 Space shuttle concepts. SOURCE: Courtesy of NASA; available at http://history.nasa.gov/SP- 4219/Chapter12.html. mandate. After five further landings (plus Apollo 13, which failed to land), the Apollo program ended in 1972 (Figure 1.2). Equipment left over from Apollo was used for the long-duration Skylab project in 1973-1974 and the Apollo-Soyuz Test Project (ASTP) in 1975. By the time ASTP was implemented, NASA was already heavily invested in a new program whose origins date back to the report of the Space Task Group (STG) headed by Vice President Spiro Agnew and delivered to President Richard M. Nixon in September 1969. In its report, The Post-Apollo Space Program: Directions for the Future, the STG endorsed a NASA proposal for “a balanced manned and unmanned space program conducted for the benefit of all mankind” that could include missions to Mars, a space station, and the construction of a space shuttle for routine access to Earth orbit (Figure 1.3).14 In response, however, President Nixon issued a major statement on the U.S. space program in March 1970 that downgraded the STG’s objectives. Arguing against the very high level of priority afforded Apollo, Nixon contended “space expenditures must take their place within a rigorous system of national priorities.” In effect, such an approach has guided U.S. civilian space policy for the past four decades. By the time Nixon left the White House, the NASA budget had fallen from its peak of nearly 4 percent of the total federal budget to less than 1 percent, which is essentially where it remained for the subsequent 40 years. 14 “Space Task Group Report, 1969,” http://www.hq.nasa.gov/office/pao/taskgrp.html. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-7

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FIGURE 1.4 Space shuttle Columbia launch. SOURCE: Courtesy of NASA. STS-1 Shuttle Mission Imagery, S81- 30462 (April 12, 1981), http://spaceflight.nasa.gov/gallery/images/shuttle/sts-1/html/s81-30462.html. In January 1972, President Nixon announced the development of a partially reusable crewed vehicle, the space shuttle. This decision was the outcome of a complicated set of negotiations over post- Apollo goals in human spaceflight that included a possible Earth-orbiting space station, a Mars mission, and a space shuttle.15 Because the administration lacked enthusiasm for the station and the Mars option proved too ambitious and expensive, leading NASA officials believed, in the words of space policy scholar John Logsdon, NASA had to get a go-ahead for the shuttle in 1971 if NASA were to maintain its identity as a large development organization with human spaceflight as its central activity. The choice of whether or not to approve the space shuttle thus became the de facto policy decision on the kind of civilian space policy and program the United States would pursue during the 1970s and beyond.”16 (Two decades later, the Columbia Accident Investigation Board (CAIB) would call this approach “straining to do too much with too little.”17) With further budget cuts and compromises, the original fully reusable space shuttle concept was downgraded, by the time of Nixon’s announcement, to a partially reusable, more expensive, and, as would become evident later, less safe system. 15 Roger D. Launius, “NASA and the Decision to Build the Space Shuttle, 1969-72,” The Historian 57.1 (September 1994): 17-34. 16 John M. Logsdon, “The Evolution of U.S. Space Policy and Plans,” in Exploring the Unknown, p. 384. 17 “NASA—Report of Columbia Accident Investigation Board,” http://www.nasa.gov/columbia/home/CAIB_Vol1.html. (see especially, pp. 102-105, and 209). CAIB’s comment a similar comment made by the Augustine commission in 1990 that NASA “is trying to do too much and allowing too little margin for the unexpected.” PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-8

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After some initial delays, the space shuttle began flying on April 12, 1981, when the first orbiter, Columbia, lifted off on a successful 2-day mission with astronauts John Young and Robert Crippen (Figure 1.4). With the launch of 135 missions from 1981 to 2011, the Space Shuttle Program saw the use of five orbiters: Columbia, Challenger, Discovery, Atlantis, and Endeavour. Key achievements of the program included launching numerous satellites and interplanetary probes, deploying the Hubble Space Telescope, conducting a vast array of scientific experiments in Earth orbit, and carrying out several crucial servicing missions to Hubble. In its later years, the space shuttle served as a ferry vehicle (both up and down) for crews and supplies to the Russian space station Mir and subsequently to the ISS. More than 350 astronauts, the majority from NASA but also from other nations, agencies, and corporations, flew on the space shuttle. Despite these successes, the Space Shuttle Program was plagued by two fatal disasters, on STS-51L Challenger in 1986 and STS-107 Columbia in 2003, killing all seven crew members on each mission. After Challenger, President Ronald Reagan announced that all commercial and Department of Defense payloads would be shifted off the space shuttle, thus relieving the program of one of its original rationales as an all-purpose launch system for satellites.18 Safety concerns eventually came to dominate discussions on the potential continuation of the Space Shuttle Program. In January 2004, President George W. Bush effectively set into motion the process by which the program came to a definitive end in 2011. Although the Space Shuttle Program was finally concluded, the United States continued to have a permanent presence in space through its participation in the ISS. The roots of the station program date back to the administration of President Reagan, when NASA leadership advanced the idea of a large space station in Earth orbit as a way to underscore U.S. leadership in space activity as well as to exploit the commercial potential of space. In January 1984, in his State of the Union speech, Reagan directed “NASA to develop a permanently manned space station and to do it within a decade.” The design of the new station evolved through a number of iterations in the 1980s, driven largely by significant cost overruns, evolving requirements, and the repercussions of the Challenger accident in 1986.19 In May 1986, the National Commission on Space, chartered by Congress, issued a major report, Pioneering the Space Frontier, that recommended “a pioneering mission for 21st century America,” emphasizing U.S. leadership in space activities, including missions to the Moon (by about 2005) and Mars (by about 2015). The report for the first time acknowledged the importance of maintaining U.S. leadership in a global economy with rising economic powers in Asia.20 The Challenger disaster, however, interrupted that expectation, and yet another task force followed, this one commissioned by NASA and chaired by astronaut Sally K. Ride, producing a report in 1987 entitled Leadership and America’s Future in Space. The commission recommended a “strategy of evolution and natural progression … [that] would begin by increasing our capabilities in transportation and technology—not goals in themselves, but as the necessary means to achieve our goals in science and exploration.” While focusing on capabilities for the first time, the goal for the United States would, once again, be human missions to the Moon and Mars to be carried out individually or in collaboration with other nations. The objective was unequivocally stated: “There is no doubt that exploring, prospecting, and settling Mars should be the ultimate objective of human space exploration. But America should not rush headlong toward Mars; we should adopt a strategy to continue an orderly expansion outward from Earth.”21 Unfortunately, lukewarm support from Congress, as well as events outside the United States changed the landscape of U.S. space policy before these recommendations could even be considered. 18 “Statement on the Building of a Fourth Shuttle Orbiter and the Future of the Space Program, August 15, 1986,” from Public Papers of Ronald Reagan, 1986, accessed at http://www.reagan.utexas.edu/archives/speeches/1986/081586f.htm. 19 W.D. Kay, “Democracy and super technologies: The politics of the space shuttle and Space Station Freedom,” Science, Technology and Human Values 19.2(April):131-151, 1994. 20 National Commission on Space, Pioneering the Space Frontier: The Report of the National Commission on Space: An Exciting Vision of Our Next Fifty Years in Space, http://history.nasa.gov/painerep/begin.html, 1986. 21 Leadership and America’s Future in Space: A Report to the Administrator, August 1987, http://history.nasa.gov/riderep/cover.htm. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-9

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As the Cold War came to a close, President George H.W. Bush announced the Space Exploration Initiative (SEI) in July 1989, on the 20th anniversary of the first Moon landing. The SEI called for continuing investment in what, after Challenger, was named “Space Station Freedom,” followed by human missions to the Moon, but, in the words of the President Bush, “this time, back to stay,” and then further on, “a manned mission to Mars.” The president suggested that such missions had historical precedent such as the voyages of Columbus or the Oregon Trail.22 Lack of congressional support, however, left the SEI dead by the time the first President Bush left the White House. A new advisory report in December 1990, the Augustine Report (Report on Advisory Committee on the Future of the U.S. Space Program), said that NASA was currently “overcommitted in terms of program obligations relative to resources available—in short, it [was] trying to do too much.”23 The end of the Cold War provided a new set of opportunities. With the Freedom space station program over budget and on the verge of cancellation, NASA proposed combining its elements with elements of the post-Soviet (Russian) space station program, known as Mir, to create an international space station. A December 1992 study (A Post Cold War Assessment of U.S. Space Policy)24 called for the United States to “develop a ‘cooperative strategy’ as a central element of its future approach to overall space policy.” International collaboration with the Russians had already moved to the fore by this time, driven largely by geopolitical issues, especially the need to prevent Russian engineers from working for hostile nations and having Russia join the Missile Technology Control Regime (MTCR). A joint station was perceived as an ideal vehicle to achieve these aims.25 In his State of the Union address in January 1994, Newly elected President Bill Clinton announced the plan to build such a station—which became the ISS—with Russian partners.26 As a result, NASA implemented the Shuttle-Mir program, in which the space shuttle carried Russian cosmonauts into orbit. These culminated in docking and visiting missions to Mir beginning with STS-71 in 1995. Soon, U.S. astronauts, beginning with Norman E. Thagard, spent long tours aboard Mir. Although marred by a number of accidents (including a fire and a collision, both unrelated to the space shuttle), the experience proved critical to the beginning of joint operations with Russia on the ISS. The ISS, whose first element was launched into orbit in 1998, is a joint project among the space agencies of the United States, Russia, Europe (collectively and through individual nations), Japan, and Canada. Since the arrival of Expedition 1 at the ISS on November 2, 2000, it has been continuously occupied, constituting the longest continuous human presence in space; astronauts from at least 15 different nations have visited the station since then, completing more than 35 expeditions in orbit. For most of the first decade or so, the bulk of station servicing was carried out by the space shuttle, but since the end of the Space Shuttle Program, cargo and crew deliveries have been taken over by vehicles from Russia (Soyuz TMA and Progress M), Europe (the ATV), Japan (the HTV), or commercial contractors (Dragon and Cygnus). Since the summer of 2011, only Soyuz can carry crews to the ISS, and in fact the United States has no independent capability to launch crews into orbit, an outcome set into motion by the space shuttle Columbia accident in 2003. In investigating the larger structural, institutional, and cultural causes of the accident, the CAIB noted that there had been “a failure of national leadership” in not replacing the aging space shuttles and 22 “Space Exploration Initiative,” http://history.nasa.gov/sei.htm [accessed January 19, 2014]. 23 “Report of the Advisory Committee on the Future of the U.S. Space Program,” December 1990, http://history.nasa.gov/augustine/racfup1.htm. 24 A Post Cold War Assessment of U.S. Space Policy, 1992. 25 In June 1992, George H.W. Bush and Boris Yeltsin signed an agreement calling for, among other things, increased collaboration between the United States and Russia. NASA and the Russian Space Agency soon ratified a 1-year contract that included consideration of increased Russian participation in a U.S. space station program. 26 The United States and Russia agreed to cooperate in human spaceflight on September 2, 1993. A formal agreement was signed on November 1, 1993 that brought the Russian Space Agency as a partner with NASA on the new station. See Space Station: Impact of the Expanded Russian Role on Funding and Research, GAO Report to the Ranking Minority Member, Subcommittee on Oversight of Government Management, Committee on Governmental Affairs, U.S. Senate, June 1994, http://archive.gao.gov/t2pbat3/151975.pdf. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-10

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also lamented a lack of “strategic vision” in civilian space activities. As a result, in January 2004, President George W. Bush, in a major speech, outlined a plan to extend “human presence across the solar system, starting with a human return to the Moon by the year 2020, in preparation for human exploration of Mars and other destinations.”27 Despite considerable investments in this new initiative, called Project Constellation, it did not enjoy across-the-board support. A new Augustine Commission conducted a major review of human spaceflight and issued a report (Seeking a Human Spaceflight Program Worthy of a Great Nation) in October 2009 that noted that the Constellation program, as defined, could not be executed without significant increases in funding. Eventually, in February 2010, President Barack Obama announced that the program would be canceled. The NASA Authorization Act of 2010, signed on October 11, 2010, effectively terminated the program. It is worth noting that all the blue ribbon and advisory panels formed to recommend a course of action for human spaceflight (or, more broadly, U.S. space policy) have focused on a set of key goals that are surprisingly uniform across the decades, especially after 1969. They all include a space program that would advance long-range technologies (both for daily life and ultimately for human missions to Mars); develop sensible mission architectures (with a proper balance of human and robotic systems); promote science, technology, engineering, and mathematics education; maintain U.S. leadership in a competitive global environment; open up commercial investment opportunities; improve affordability; support national security; and expand international collaboration. All of these panels have suggested that Mars be the ultimate goal of human spaceflight, with return to the lunar surface as an intermediate step. The Obama administration issued a new national space policy in June 2010.28 The document adheres to six very broad goals: energize domestic industry, expand international collaboration, strengthen stability in space, increase resilience of mission-essential functions, perform human and robotic missions, and improve capabilities to conduct science and study the Earth’s resources. With respect to “space science, exploration, and discovery” and human spaceflight in particular, the document notes that the Administrator of NASA shall:  Set far-reaching exploration milestones. By 2025, begin crewed missions beyond the moon, including sending humans to an asteroid. By mid-2030s, send humans to orbit Mars and return them safely to Earth.  Continue the operation of the [ISS] … likely to 2020; and  Seek partnerships with the private sector to enable safe, reliable, and cost-effective commercial spaceflight capabilities and services for the transport of crew and cargo to and from the ISS. While the National Space Policy offers general guidelines, de facto work on human spaceflight is reliant on the considerations laid out in three consecutive NASA Authorization Acts issued in 2005, 2008, and 2010, each of which added to, clarified, and updated many of NASA’s immediate goals in light of the winding down of the Space Shuttle Program, the end of construction of the ISS, and plans for human exploration beyond LEO. The committee notes below only those provisions of the acts related to human spaceflight. The 2005 Act (signed into law on December 30, 2005) codified President George W. Bush’s Vision for Space Exploration (VSE), specifically, its call for a sustained human presence on the Moon that would begin with precursor robotic missions. It also authorized collaboration with international partners. At the time, the goal was to launch a new crewed spacecraft, the Crew Exploration Vehicle, in 2014, continue work on the ISS during the ensuing decade, and return U.S. astronauts to the Moon by 27 NASA, “President Bush Offers New Vision for NASA,” http://www.nasa.gov/missions/solarsystem/bush_vision.html, January 14, 2004. 28 National Space Policy of the United States of America, June 28, 2010, http://www.whitehouse.gov/sites/default/files/national_space_policy_6-28-10.pdf. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-11

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1.6 A STRATEGIC APPROACH TO A SUSTAINABLE PROGRAM OF HUMAN SPACEFLIGHT64 Having laid out past and current space policy, explored the international setting, articulated the enduring questions and rationales, and examined public and stakeholder opinions, the committee draws from all this information to ask a fundamental question: What type of human spaceflight program would be responsive to these factors? This committee argues that it is a program in which humans operate beyond LEO on a routine basis, in other words, a sustainable human exploration program beyond LEO. It is not the role of this committee to recommend whether the nation should move forward with such a program at this time. However, it is important to recognize that the assembly of the ISS is now essentially complete, and the ISS has a finite lifetime. If the nation does not decide soon whether to embark on human space exploration beyond LEO, it will de facto begin ramping down its human spaceflight activities in the early 2020s as preparations for the closeout of ISS begin. More importantly, because major new spaceflight programs have lead times of years (sometimes a decade) between the decision to pursue the program and first flight, delaying a decision to near the end of the ISS’s lifetime will guarantee a long gap in any human spaceflight activity—just as the termination of Space Shuttle has led to a hiatus in U.S. capability to take astronauts up and bring them back to Earth. In Chapter 4 the report argues that SLS and Orion flight rates that are too far below historic norms will not be sustainable over the course of an exploration pathway that spans decades. This will be the case for the first two launches of the SLS, which are the only launches scheduled.65 Hence, the committee has concluded: If the nation deems continuity in human spaceflight to be a desirable national objective, it must decide now on whether to pursue a sustainable program of human space exploration, and on the nature of such a program. In what follows the committee outlines what the essential nature of a sustainable program would be. 1.6.1 Horizon Goal: Mars Within the limits of foreseeable technologies, there are a limited number of places humans can go beyond LEO and only two of them have significant gravitational wells:66 the Moon and Mars. Mars is the farthest practical exploration “horizon” for the foreseeable future—the most distant goal that is consistent with human physiological limits under likely future technologies (Chapter 4). Mars is a goal most compatible with the committee’s enduring questions, and the intrinsic fascination that Mars has held in the popular imagination for well more than a century makes it an attractive target. Such a program under any realistic funding scenario requires a sustained effort for several decades, and it would address the enduring questions. There is a consensus in national space policy, international coordination groups, and the public imagination for Mars as the horizon goal of human space exploration. The committee has concluded: A sustainable program of human deep space exploration must have an ultimate, “horizon” goal that provides a long-term focus that is less likely to be disrupted by major 64 Much of the technical discussion and figures in this section derive from the deliberations of the Technical Panel which are described in detail in Chapter 4. 65 The first two launches of the SLS are planned to occur four years apart, in 2017 and 2021. In contrast, beginning with the first flights of the Saturn V launch vehicle and the Space Shuttle, respectively, during the subsequent four years the Apollo program conducted 12 launches and the Space Shuttle Program conducted 17. 66 Essentially, the region of gravitational influence a body exerts on the space around it. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-28

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technological failures and accidents along the way and the vagaries of the political process and economic scene. 1.6.2 Stepping Stones Between LEO and the martian surface are regions of space, essentially operational theatres, with stepping stone destinations that are reachable with foreseeable advances in the state of the art of key capabilities. These operational theaters include:  Cislunar space, which encompasses missions to the Earth-Moon L2 point,67 lunar orbit, and the lunar surface (both lunar sorties with relatively short stays and lunar outposts with extended stays);  Near-Earth asteroids (NEAs) in their native orbits; and  Mars, which encompasses a Mars flyby mission as well as missions to the moons of Mars, Mars orbit, and the surface of Mars. Missions to various destinations within these operational theatres could provide the necessary challenges, adventures, and diverse patterns of activity and utilization to sustain a program that addresses the enduring questions. The challenges of human spaceflight beyond LEO are driven in part by increased requirements for propulsive energy and by longer mission durations. For example, Figure 1.9 shows how mission duration and delta-V, which is a measure of propulsive energy requirements, vary for missions in each operational theater. The size and placement of the regions associated with each mission in Figure 1.9 are determined by a number of factors, such as mission selection, orbital constraints, and specific destination. The delta-V for the Mars missions is highly variable, depending on the year of the mission; an exploration system design for the lowest delta-V values shown will only be capable of visiting Mars once every 15 years or so, while one with a higher delta-V capability allows visits every other year. Similarly, improving the propulsive capabilities of a near-Earth asteroid (NEA) orbital transfer vehicle would increase launch opportunities and the diversity of targets. As propulsive energy requirements and/or mission durations increase, so does mission cost and risk. Increasing mission duration increases the risk of component failures, it increases radiation exposure of systems and crew, and it exacerbates many other technical, physiological, and psychological risks. Human exploration missions to cislunar space have the advantage of variable mission durations (from as little as two weeks to six months or more, as desired) and modest delta-V requirements. Missions to most NEAs would require substantially more delta-V than cislunar missions, with typical mission durations of six months to a year. The delta-V requirements for missions to Mars orbit or to the moons of Mars with a stay time of 500 days at the destination are comparable to the delta-V requirements for missions to the lunar surface, but the Mars missions would last about 900 days. A Mars surface mission with a stay time of 500 days would require more delta-V than either the cislunar missions or the other 500-day Mars missions. Missions to Mars with stay times of 30 days would have a shorter mission duration than their 500-day counterparts, but they would also require more delta-V because such missions need to use a less- favorable Earth-Mars orbital alignment. 67 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. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-29

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Martian Moons 30 Day Stay 30 km/s delta-v Mars Surface < 30 Day Stay More NEAs Few Mars Surface NEAs 500 Days Martian Moons 20 km/s delta-v 500 Days Moon: Moon: Mars Orbit Mars Orbit Lunar Sortie Lunar Outpost 30 Day Stay 500 Days Cis-Lunar: Cis-Lunar: Mars Flyby ARM L2 Outpost 10km/s delta-v ISS 0km/s delta-v 0 mission 200 mission 400 mission 600 mission 800 mission days days days days days FIGURE 1.9 Comparison of human spaceflight destinations and missions in terms of mission duration and round- trip propulsive energy requirements from Earth in terms of delta-V (velocity changes). SOURCE: Chart developed for the Committee on Human Spaceflight by the Aerospace Corporation using multiple sources, including design reference missions (DRMs) generated by NASA and the ISECG (Human Spaceflight Exploration Framework Study, NASA, January 11, 2012, Washington, D.C., http://www.nasa.gov/pdf/509813main_Human_Space_Exploration_ Framework_Summary-2010-01-11.pdf; Human Space Flight Architecture Team (HAT) Technology Planning, Report to NASA Advisory Council March 6, 2012, Washington, D.C., http://www.nasa.gov/pdf/629951main_ CCulbert_HAT_3_6_12=TAGGED.pdf; B.G. Drake, “Strategic Considerations of Human Exploration of near-Earth Asteroids,” paper presented at the Aerospace Conference, 2012 IEEE, March 3-10, 2012; 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; International Space Exploration Coordination Group, “The Global Exploration Roadmap,” NASA, Washington, D.C., August 2013, https://www.globalspaceexploration.org/; D.A. Tito, G. Anderson, J.P. Carrico, J. Clark, B. Finger, G.A. Lantz, M.E. Loucks, et al. “Feasibility Analysis for a Manned Mars Free-Return Mission in 2018,” paper presented at the Aerospace Conference, 2013 IEEE, March 2-9, 2013; J. Connolly, “Human Lunar Exploration Architectures,” presentation to Annual Meeting of the Lunar Exploration Analysis Group, October 24, 2012, http://www.lpi.usra.edu/meetings/leag2012/presentations/). Additional information on the Design Reference Missions appears in Chapter 4. For these reasons and others, a Mars surface mission is the most difficult goal in terms of the time required to overcome all the technological and physiological factors associated with it. In particular, unlike other missions under consideration, a human mission to the Mars surface would require an entry, descent, and landing (EDL) system to land massive payloads and crew on the surface of Mars. This is a major cost, schedule, and risk item. The committee has concluded: Given the magnitude of the technical and physiological challenges, should the nation decide to embark on a human exploration program whose horizon goal is Mars, NASA would need to begin to focus right away on the high-priority research and technology investments that PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-30

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would develop the capabilities required for human surface exploration of Mars. As discussed in Chapter 4, the most challenging of these will be (1) entry, descent, and landing for Mars; (2) in-space propulsion and power; and (3) radiation safety (radiation health effects and amelioration). NASA’s current proposal for the next step in deep space exploration—to retrieve a small asteroid and tow it into a retrograde lunar orbit for examination by astronauts—is with respect to the realm of human operations the least demanding of the operating theaters. But, as argued in Chapter 4, if humans are eventually to land and operate for extended periods of time on Mars, the capabilities required are best developed and tested on the lunar surface as well as in cislunar space. And they are best developed in a way such that significant milestones are accomplished early and at regular intervals in the program— milestones that meaningfully and progressively enhance the capabilities of humankind for space exploration. NASA and outside experts told the committee that the current administration regards the lunar surface as the purview of other nation’s space programs and that it is not of interest to the U.S. human exploration program. This argument is made despite the barely touched scientific record of the earliest solar system that lies hidden in the lunar crust,68 despite its importance as a place to develop the capabilities required to go to Mars, and despite the fact that the technical capabilities and operational expertise of Apollo belong to our grandparent’s generation. The history of exploration of our own globe carries a lesson that the ones who follow the first explorers are the ones to profit from the accomplishment. Such a lesson would suggest that the United States relook at its disinterest in the lunar surface as a site for human operations. The pathways approach outlined below and its application, detailed in Chapter 4, support the view of this committee that the Moon, and in particular its surface, have significant advantages over other targets as an intermediate step on the road to the horizon goal of Mars. The committee does not recommend either a capabilities-based or flexible-path approach, approaches where no specific sequence of destinations is specified (see Chapter 4). Instead, as discussed below, the committee will recommend a “pathways approach” to human space exploration: a specific sequence of intermediate accomplishments and destinations normally of increasing difficulty and complexity leading to an ultimate (horizon) goal with technology feed-forward from one mission to subsequent missions. When properly planned, funded, and executed, a pathways approach will enable taxpayers to see progress as missions explore significant destinations, and it will support a manageable level of development risk and an operational tempo that ensures retention of critical technical capability, proficiency of operators, and effective utilization of infrastructure. Also a pathways approach would include technology development that addresses mission requirements and integration, placing crew and launch vehicles into a system architecture that includes key components such as radiation safety; advanced in-space propulsion and power; and entry, descent and landing technologies for Mars. Chapter 4 describes the process by which pathways to a human Mars-surface mission might be developed. Each of the three example pathways could be attempted using a budget-limited approach that would not require a significant bump in funding as Apollo did. However, the budget-limited scenarios feature a very low operational tempo (at best, one piloted mission every 2.4 years), which is much lower than that of any previous successful U.S. human spaceflight program. The committee has concluded: NASA can sustain a human space exploration program with meaningful milestones that simultaneously reasserts U.S. leadership in space while allowing ample opportunity for substantial international collaboration when that program  Has elements that are built in a logical sequence, and 68 See, for example, R.M. Canup and K. Righter, eds., Origin of the Earth and the Moon, University of Arizona Press, Tucson Ariz., 2000; National Research Council, The Scientific Context for Exploration of the Moon, National Academy Press, Washington, D.C., 1997. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-31

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 Can fund a frequency of flights sufficiently high to ensure retention of critical technical capability, proficiency of operators, and effective utilization of infrastructure. However, a NASA human spaceflight budget that increases with inflation does not permit a viable pathway to Mars (Chapter 4). The program will require increasing the budget by more than the rate of inflation. 1.6.3 Pathway Principles and Decision Rules The pathway approach applies principles and decision rules designed to maximize efficient use of feed-forward systems and subsystems. The cost, scope, and challenges of human spaceflight beyond LEO demand that a set of carefully thought-out principles be applied before any pathway is initiated. Progress toward deep space destinations will be measured on timescales of decades, with costs measured in hundreds of billions of dollars and significant risk to human life. In what follows, the committee is not recommending one pathway over another, but rather proposes such principles by which national leadership might decide on pursuing a given pathway, measure its progress along the pathway, move off the pathway to another, or cease the endeavor altogether. The resulting Pathway Principles are intended to be used to help establish a sustainable long-term course. In the environment of constrained federal budgets for the foreseeable future, the application of these principles should result in a pathway that includes only essential major hardware and mission elements in order to live within expected funding constraints. This approach leaves limited opportunities for major reductions in scope (“descopes”) later, as described in detail in Chapter 4. Therefore, as its highest priority recommendation, the committee recommends: NASA should adopt the following Pathway Principles: I. Commit to design, maintain, and pursue the execution of an exploration pathway beyond low Earth orbit toward a clear horizon goal that addresses the “enduring questions” for human spaceflight. II. Engage international space agencies early in design and development of the pathway on the basis of their ability and willingness to contribute. III. Define steps on the pathway that foster sustainability and maintain progress on achieving the pathway’s long-term goal of reaching the horizon destination. IV. Seek continuously to engage new partners that can solve technical and/or programmatic impediments to pathway progress. V. Create a risk mitigation plan to sustain the selected pathway when unforeseen technical or budgetary problems arise. Such a plan should also include points at which decisions are made to move to a less ambitious pathway (‘off-ramp as defined below”) or stand down the program. VI. Establish exploration pathway characteristics that maximize the overall scientific, cultural, economic, political, and inspirational benefits without sacrificing progress toward the long-term goal, these characteristics being: a. The horizon and intermediate destinations have profound scientific, cultural, economic, inspirational, or geopolitical benefits that justify public investment; b. The sequence of missions and destinations permits stakeholders, including taxpayers, to see progress and develop confidence in NASA being able to execute the pathway; c. The pathway is characterized by logical feed-forward of technical capabilities; PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-32

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d. The pathway minimizes the use of dead-end mission elements that do not contribute to later destinations on the pathway; e. The pathway is affordable without incurring unacceptable development risk; and f. 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. Application of upfront Pathway Principles are made recognizing that a set of operational Decision Rules will also be required and applied as NASA, the administration, and Congress face how to deal with inevitable programmatic challenges along a selected pathway. The Decision Rules this committee has developed provide operational guidance that can be applied as major technical, cost, and schedule issues arise while NASA progresses along a pathway. The Decision Rules have been designed to provide the framework for a sustainable program through the lifetime of the selected pathway. They are designed to allow a program to stay within the constraints accepted and developed when applying the Pathway Principles. The committee recommends: Whereas the overall pathway scope and cost are defined by applying the Pathway Principles, once on a pathway, if and when technical, cost, or schedule problems arise, they should be addressed by the administration, NASA, and Congress by applying the following Decision Rules: A. If the appropriated funding level and projected 5-year budget projection do not permit execution of a pathway within the established schedule, then do not start down that pathway. 69 B. If a budget profile does not permit the chosen pathway, even if NASA is well down it, then take an “off-ramp.” C. If the U.S. human spaceflight program receives an unexpected increase in budget for human spaceflight, NASA, the administration, and Congress should not redefine the pathway such that continued budget increases would be required for the pathway’s sustainable execution, but rather the increase in funds should be applied to retire rapidly significant technology risks or increase operational tempo in pursuit of the pathway’s predefined technical and exploration goals. D. Given that limitations on funding will require difficult choices in the development of major new technologies and capabilities, give priority to those that solve significant existing technological shortcomings, reduce overall program cost, allow for an acceleration of the schedule, and/or reduce developmental or operational risk. E. If there are human spaceflight program elements, infrastructure, and organizations that no longer contribute to progress along the pathway, the human spaceflight program should divest itself of them as soon as possible. 1.6.4 Two Examples: Futures for Human Spaceflight: The Fiscal Challenge Ahead In what follows, the committee provides examples derived from Chapter 4 to demonstrate the fiscal challenge the United States faces in any exploration program beyond LEO. These examples are for illustrative purposes and should not be construed as recommendations regarding options. In each case, the 69 The committee recognizes that budget projections are unreliable, but they are also indispensable. One way to make the use of such projections more robust would be for NASA to conduct sensitivity analysis and evaluate plans against a range of possible 5-year budget projections that may vary by 10 percent or more. This might be done as part of the “Risk Mitigation” plan. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-33

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“sand charts” depict in a linear fashion the annual estimated cost70 of the human spaceflight program, and two budget profiles are shown for reference: a flat budget (constant then-year dollars) and a budget that increases with inflation. 1.6.4.1 Example 1—A Minimalist Program that Ends at L2 The scenario shown in Figure 1.10 provides an example of what could be accomplished with a flat human spaceflight budget. It continues the ISS to 2028, conducts the asteroid redirect mission, and establishes an intermittent human presence at the Earth-Moon “L2” Lagrange point. This scenario could be executed with a budget that is essentially flat from 2015 through 2045. However, no additional missions could be conducted after the L2 missions. Also, by 2045 the entire human spaceflight budget would be consumed by the fixed cost of the SLS and the Orion program, and core research, technology development, and support activities. Because this scenario does not accommodate any missions beyond cislunar space, it violates Pathway Principles I and III. L2 OUTPOST PATHWAYS DRMs ANNUAL COST (THEN-YEAR $) Asteroid Redirect Earth-Moon L2 Human Spaceflight Mission (ARM) Budget Increasing with Inflation (2.5% per year) Flat Budget 2020 2030 2040 2050 Program of Record & Fixed Costs ISS 2028 FIGURE 1.10 Pathway showing a minimalist program that ends at L2. 1.6.4.2 Example 2—A Budget-Driven Pathway Toward Mars that does not satisfy the Principles. The scenario shown in Figure 1.11 was generated to conduct a technical analysis and affordability assessment of a notional pathway to Mars, with a human spaceflight budget that increases at or about the rate of inflation, while also adhering to Pathway Principle VIa and VId by including targets that provide intermediate accomplishments and minimize the use of systems that do not contribute to achieving the horizon goal. Astronauts would explore new destinations at a steady pace: operation at L2 is achieved in 2024, a rendezvous with an asteroid in its native orbit in 2028, and the lunar sortie in 2033. Continuing, a 70 Because of the notional nature of the cost projections in this study, the vertical cost axes on Figure 1.10 and similar figures are not marked with dollar values. However, the committee is confident that the cost projections that are summarized in these figures provide a sound basis for making relative comparisons among the pathways and between the pathways and budget projections. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-34

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lunar outpost would be constructed in 2036, and the martian moons would be reached in 2043. Humans would land on Mars at the midpoint of the 21st century. However, this scenario violates Pathway Principle VIf because the flight rate is too low to maintain proficiency (Chapter 4): on average, one crewed mission every 2.1 years, with gaps of up to 5 years with no crewed missions.71 This scenario could be modified to allow higher mission rates (see Chapter 4). However, that would require funding to increase at a rate substantially higher than the rate of inflation for more than a decade, which, in the current fiscal environment, would violate Pathway Principle VIe. Based on the lessons from these and other scenarios presented in Chapter 4, the committee has concluded: As long as flat NASA human spaceflight budgets are continued, NASA will be unable to conduct any human space exploration programs beyond cislunar space. The only pathways that successfully land humans on the surface of Mars require spending to rise above inflation for an extended period. This conclusion could be modified in the case of robust international cost sharing (that is, cost sharing that greatly exceeds the level of cost sharing with the ISS). BUDGET DRIVEN ENHANCED EXPLORATION ANNUAL COST (THEN-YEAR $) Earth-Moon Asteroid in Martian Moons Mars Surface Human Spaceflight L2 Native Orbit Budget Increasing with Inflation (2.5% per year) Flat Budget 2020 2030 2040 2050 Program of Record & Fixed Costs ISS 2028 Lunar Sortie Lunar Outpost FIGURE 1.11 A budget-driven pathway toward Mars. 71 The Enhanced Exploration pathway includes many more SLS launches, for both crewed and uncrewed (cargo) vehicles, than the other two pathways. However, even for the Enhanced Exploration pathway, and even if uncrewed launches are considered, for much of the pathway the total SLS launch rate would be far lower than the Apollo or Space Shuttle programs. In particular, between 2022 and 2030, there would be, on average, one SLS launch every 18 months. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-35

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1.6.5 Risk Tolerance in a Sustained Program of Human Space Exploration A sustained human exploration program beyond LEO, despite all reasonable attention paid to safety, will almost inevitably lead to multiple losses of vehicles and crews over the long term. For each step along the pathway, it will be important for NASA leadership and other stakeholders to discuss risk honestly and establish acceptable levels of risk to mission and crew for deep space missions. At the agency level, the risk discussion will be more detailed, using relative or probabilistic levels to define the risk threshold, inform the design, and set priorities. NASA should make all reasonable effort to manage its technical risk in a way that emphasizes crew safety through use of robust designs, failure tolerance, and safe operations in adverse environments. However, a national failing to acknowledge that there are limits to the ability to mitigate the risks of human exploration inevitably undermines the ability of the program to accomplish high-risk goals and thus precludes a stable, sustainable program of exploration. A nation that chooses to extend human presence beyond the bounds of Earth affirms its commitment to that endeavor and accepts the risk to human life by continuing to pursue the program despite the inevitability of major accidents. 1.7 SUMMARY: A SUSTAINABLE U.S. HUMAN SPACE EXPLORATION PROGRAM Human space exploration requires a long-term commitment by the nation or entity that undertakes it. Therefore the committee has concluded: National leadership and a sustained consensus on the vision and goals are essential to the success of a human space exploration program that extends beyond LEO. Frequent changes in the goals for U.S. human space exploration waste resources and impede progress. The instability of goals for the U.S. program in human spaceflight beyond LEO threatens our nation’s appeal and suitability as an international partner. The United States has had a sustained program of human spaceflight for more than half a century, paradoxically in the face of, at best, lukewarm public support. There has not been a committed, passionate minority large and influential enough to maintain momentum for the kind of dramatic progress predicted by many space experts at the time of Apollo.72 This is a problem that adds to the numerous difficulties— frequent redirection, mismatch of mission and resources, political micromanagement—that have afflicted the U.S. human spaceflight program after Apollo. The committee has concluded: Simply setting a policy goal is not sufficient for a sustainable human spaceflight program, because policy goals do not change programmatic, technical, and budgetary realities. Those who are formulating policy goals need to keep the following factors in mind:  Any defensible calculation of tangible, quantifiable benefits – spinoff technologies, attraction of talent to scientific careers, scientific knowledge, and so on – is unlikely to ever demonstrate a positive return on the massive investments required by human spaceflight.  The arguments that triggered the Apollo investments, national defense and prestige, seem to have especially limited public salience in today’s post-Cold War America.  Although the public is mostly positive about NASA and its spaceflight programs, increased spending on spaceflight is a low priority for most Americans. At the same 72 Aviation Week and Space Technology predicted, in the 1960s, a landing of humans on Mars by the early 1980s. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-36

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time, most Americans do not follow the issue closely, and those who pay more attention are more supportive of space exploration. It serves no purpose for advocates of human exploration to dismiss these realities in an era in which both the citizenry and national leaders are focused intensely on the unsustainability of the national debt, the dramatic growth of entitlement spending, and the consequent downward pressure on discretionary spending, including the NASA budget. With most projections forecasting growing national debt in the decades ahead, there is at least as great a chance that human spaceflight budgets will be below the recent flat trend line as markedly above it. Nevertheless, the committee has concluded: Should the United States decide that the intangible benefits of human spaceflight still justifies major, new, and enduring public investments in human spaceflight, it will need to craft a long-term strategy that will be robust in the face of technical and fiscal challenges. Together with the highest priority recommendation to adopt the pathways approach, the committee offers the following prioritized recommendations as being those most critical to the development and implementation of a sustainable human space exploration program. The committee recommends: NASA should: 1. Commit to design, maintain, and pursue the extension of human presence beyond low Earth orbit (LEO). This step should include: a. Committing NASA’s human spaceflight asset base, both physical and human, to this effort and b. Redirecting human spaceflight resources as needed to include improving program management efficiency (including establishing and managing to appropriate levels of risk), eliminating obsolete facilities, and consolidating remaining infrastructure where possible. 2. Maintain long-term focus on Mars as the “horizon goal” for human space exploration, addressing the enduring questions for human spaceflight: How far from Earth can humans go? and What can humans do and achieve when we get there? 3. Establish and implement the pathway approach so as to maximize the overall scientific, cultural, economic, political, and inspirational benefits of individual milestones and to conduct meaningful work at each step along the pathway, without sacrificing progress toward long-term goals. 4. Vigorously pursue opportunities for international and commercial collaboration in order to leverage financial resources and capabilities of other nations and commercial entities. International collaboration would be open to the inclusion of China and potentially other emerging space powers, as well as traditional International Partners. Specifically, future collaborations on major new endeavors should seek to incorporate: a. A level of overall cost sharing appropriate to the true partnerships that will be necessary to pursue pathways beyond LEO. b. Shared decision making with partners. This should include a detailed analysis, in concert with international partners, of the implications for human exploration of continuing the International Space Station beyond 2024. 5. Engage in planning that includes mission requirements and a systems architecture targeting funded high-priority technology development, most critically: PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-37

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a. Entry, descent, and landing for Mars, b. Advanced in-space propulsion and power, and c. Radiation safety. None of these steps can replace the element of sustained commitment on the part of those who govern the nation, without which neither Apollo nor its successor programs would have occurred. Hard as the above choices may appear, they probably are less difficult or alien to conventional political decision makers than the recognition that human spaceflight—among the longest of long-term endeavors—cannot be successful if held hostage to traditional short-term decision-making and budgetary processes. Asking future presidents to preserve rather than tinker with previously chosen pathways, or asking congresses present and future to aggressively fund human spaceflight with budgets that increase by more than the rate of inflation every year for decades, may seem fanciful. But it is no less so than imagining a magic rationale that ignites and then sustains a public demand that has never existed in the first place. Americans have continued to fly into space not so much because the public strongly wants it to be so, but because the counterfactual—space exploration dominated by the vehicles and astronauts of other nations—seems unthinkable after 50 years of U.S. leadership in space. In reviving a U.S. human exploration program capable of answering the enduring questions about humanity’s destiny beyond our tiny blue planet, we will need to grapple with the attitudinal and fiscal realities of the nation today while staying true to a small but crucial set of fundamental principles for the conduct of exploration of the endless frontier. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 1-38