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 then to the first reusable winged, crewed spaceplane, which the United States operated for 3 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. 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 them 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.

The complex mix of historic achievement and uncertain future made the task1 faced by this 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 the ones 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 leading to 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 each year in 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

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1 The committee’s statement of task is given in Appendix A.

2 Including six committee meetings, four Technical Panel meetings, three Public and Stakeholder Opinion Panel meetings, 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.



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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 then to the first reusable winged, crewed spaceplane, which the United States operated for 3 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. 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 them 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. The complex mix of historic achievement and uncertain future made the task 1 faced by this committee extra­ ordinarily 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 the ones 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 labors 2 as presented here provide a map leading to 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 each year in 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 1  Thecommittee’s statement of task is given in Appendix A. 2  Includingsix committee meetings, four Technical Panel meetings, three Public and Stakeholder Opinion Panel meetings, 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. 8

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OVERVIEW OF ANALYSIS AND FINDINGS 9 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 that the United States does best. Throughout this chapter, which gives an overview of the committee’s most important conclusions and historical background related to the relevant issues, the recommendations and conclusions are in boldface type. The com- mittee justifies and quantifies them in the later chapters. 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 it 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. That does not mean that there are no benefits: W.B. Cameron wrote that “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 interest in 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 does not have 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, of which the most distant and difficult 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 principles and decision rules to get there. In the course of developing its findings, the committee identified some important issues that the nation will need to grapple with if it chooses 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. Although those partners expressed interest in aspects of the asteroid-redirect mission (ARM), the committee detected a concern that ARM would divert U.S. resources and attention from an eventual return to the Moon. Of the several pathways examined, the one that 3  In this report, future inflation is projected to be 2.5 percent per year, which is consistent with “2013 NASA New Start Inflation Index for FY14,” http://www.nasa.gov/sites/default/files/files/2013_NNSI_FY14(1).xlsx. 4  President Kennedy, 2 days after Yuri Gagarin’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, 1963, pp. 122-123. 5 W.B. Cameron, Informal Sociology: A Casual Introduction to Sociological Thinking, Random House, New York, 1963.

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10 PATHWAYS TO EXPLORATION does not include a meaningful return to the Moon—that is, extended operations on the lunar surface—has higher development risk than the others. • Continued operation of the ISS beyond 2020 will have a near-term effect on the pace that 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 committed to operating the ISS jointly through 2020, and the United States 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 its ISS space and resources a national laboratory, which proponents say will require extension of the ISS beyond 2020 or even 2024 to increase the probability that the research and development (R&D) conducted there will provide substantial returns, including promised commercial benefits. Continued operation will compete with new programs beyond LEO, and this will aggravate the problems of funding. At the same time, the committee recognizes that much work remains to determine physiological tolerance to and countermeasures for the microgravity environments that will be experienced for long periods 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 and conducting the medical studies in LEO needed to execute human exploration of Mars 2 or 3 decades from now. • The prohibition of NASA’s 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 developments in a program that marches steadily and strategically toward what might eventually become a lead role among the nations in spaceflight. In contrast with 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 that has been inconsistent: regarding China as a potential partner in some activities and as a threat in others. The committee is concerned that current U.S. law is impeding the nation’s ability to collaborate with China when appropriate whereas traditional U.S. international partners have not imposed such restrictions on themselves. The remainder of this chapter looks at past, present, and prospective human spaceflight from a number of perspectives, all of which inform the committee’s final considerations of a sustainable program. The next section begins with a historical trajectory of space policy with regard to human spaceflight and ends with the current situation. Section 1.3 then assesses the international context in terms of current partnerships and the capabilities of nonpartner nations, such as China. Section 1.4 summarizes the enduring questions and rationales for human spaceflight offered over time and is followed by a summation of the opinions of the U.S. public and stakeholders in human spaceflight.6 Section 1.6 discusses strategic approaches to a sustainable human spaceflight program beyond LEO that is based on what the committee calls a pathways approach, The chapter concludes by summarizing 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 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 period up to 2030, so 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 considered 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 possibility that 6  Sections 1.2–1.5 summarize the extensive and detailed analyses of enduring questions, value propositions, and stakeholder and public opinions that are offered in Chapters 2 and 3.

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OVERVIEW OF ANALYSIS AND FINDINGS 11 over the half-century considered, advances in science and technology in bioengineering, artificial intelligence, and other fields may come far more quickly and unpredictably than the advances contemplated for the human spaceflight pathways proposed in this report. Breakthroughs in these other realms 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 that is titled “Great Nations Dare” and is 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, and so on), there has almost always been a nationalistic competitive element that helped in obtaining resources for these expensive adventures. The committee was charged 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 every major accomplish- ment but rather to highlight the principal changes and shifts in civil space policy—especially as related to human spaceflight—that drove the program at the highest level. Early 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, which was signed on July 29, 1958, and led to the formation of NASA.9 In response to 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 the original act and 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: • T  he “expansion of human knowledge of phenomena in the atmosphere and space.” • I  mproving the “usefulness, performance, speed, safety, and efficiency” of rockets and spacecraft. • T  he “development and operation of [robotic and crewed] vehicles.” • T  he “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.” •  ooperation with the Department of Defense as required. C •  Cooperation 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.” 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 in the vehicles. Here, regions can refer to position, to orbital energy (velocity), or both. The committee defines as human exploration ambiguous cases in which humans are in martian or lunar orbit telerobotically conducting surface operations 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, reproduced in full in John M. Logsdon, editor, with L.J. Lear, J. Warren-Findley, R.A. Williamson, and D.A. Day, Exploring the Unknown: Selected Docu- ments in the History of the U.S. Civil Space Program, Volume I: Organizing for Exploration, NASA, Washington, D.C., 1995, pp. 334-345. 10  “National Security Council, NSC 5814, ‘U.S. Policy on Outer Space,’ June 20, 1958” in Exploring the Unknown, Volume I, 1995, pp. 345-359.

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12 PATHWAYS TO EXPLORATION •  o make effective use of the scientific and engineering resources in the country in cooperation with T interested agencies. On the basis of those objectives, 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, 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 in a major policy speech on May 25, 1961, in which President 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 pro- gram to achieve the Moon-landing goal.12 In the following 2 years, NASA’s budget increased by 89 percent and 101 percent.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 objective 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 perform- ing increasingly complex human space missions that involved 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. It culminated in the landing of Apollo 11 astronauts Neil Armstrong and Edwin “Buzz” Aldrin on the Moon on July 20, 1969, and thus fulfilled President Kennedy’s mandate. After five further landings (and 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 heavily invested in a new program whose origins date back to the report of the Space Task Group (STG) headed by Vice President Agnew. In its report, The Post-Apollo Space Program: Directions for the Future, which was delivered to President Nixon in September 1969, 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 priority afforded Apollo, President Nixon contended that “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 President 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 has remained. In January 1972, President Nixon announced the development of a partially reusable crewed vehicle, the space shuttle. That 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 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 Inter- est (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. 14  Space Task Group, The Post-Apollo Space Program: Directions for the Future, September 1969, available in NASA Historical Reference Collection, History Office, NASA Headquarters, Washington, D.C., http://www.hq.nasa.gov/office/pao/History/taskgrp.html. 15  Roger D. Launius, “NASA and the Decision to Build the Space Shuttle, 1969-72,” The Historian 57.1 (September 1994): 17-34.

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OVERVIEW OF ANALYSIS AND FINDINGS 13 FIGURE 1.1  John Glenn climbs into the Mercury capsule, which 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. 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, as follows: 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 that 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 President Nixon’s announcement, to a partially reusable, more expensive, and, as would become evident later, less safe system. After some 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 16  John M. Logsdon, “The Evolution of U.S. Space Policy and Plans,” in Exploring the Unknown, 1995, 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 echoed 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.”

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14 PATHWAYS TO EXPLORATION 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. 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 the launch of numerous satellites and interplanetary probes, deployment of the Hubble Space Telescope, a vast array of scientific experiments in Earth orbit, and 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 for the Russian space station Mir and later the ISS. More than 350 astronauts—most from NASA but also from other nations, agencies, and corporations—flew on the space shuttle. Despite those successes, the Space Shuttle Program was plagued by two fatal disasters, involving STS-51L

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OVERVIEW OF ANALYSIS AND FINDINGS 15 FIGURE 1.3  Space shuttle concepts. SOURCE: Courtesy of NASA; available at http://history.nasa.gov/SP-4219/Chapter12.html.

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16 PATHWAYS TO EXPLORATION 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.

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OVERVIEW OF ANALYSIS AND FINDINGS 17 Challenger in 1986 and STS-107 Columbia in 2003, that killed all seven crew members on each mission. After Challenger, President Reagan announced that all commercial and Department of Defense payloads would be shifted off the space shuttle; this relieved the program of one of its original rationales as an all-purpose launch system for satellites.18 Safety concerns eventually came to dominate discussions of 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 adminis- tration 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 and to exploit the commercial potential of space. In January 1984, in his State of the Union speech, President 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 substantial cost overruns, changing 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” and emphasized U.S. lead- ership 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. In its 1987 report titled 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.” With a focus 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 However, lukewarm support from Congress and events outside the United States changed the landscape of U.S. space policy before those recommendations could even be fully considered. 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, which would be followed by human missions to the Moon but, in the words of President Bush, “this time, back to stay” and later “a manned mission to Mars.” The president suggested that such missions had historical precedent, such as the voyages of Columbus and the Oregon Trail.22 Lack of congressional support, however, left the SEI dead by the time President George H. W. Bush left the White House. A new advisory report in December 1990, the so-called Augustine Report, Report of the 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 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, 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, 1986, http://history.nasa.gov/painerep/begin.html. 21  Leadership and America’s Future in Space: A Report to the Administrator, August 1987, http://history.nasa.gov/riderep/cover.htm. 22  NASA, “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.

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18 PATHWAYS TO EXPLORATION 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. A joint station was perceived as an ideal vehicle to achieve those aims.25 In his State of the Union address in January 1994, President 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 missions culminated in docking and visiting missions to Mir starting 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 and completed 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 Automated Transfer Vehicle, ATV), Japan (the H-II Transfer Vehicle, HTV), and 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 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 the “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 the new initiative, called Project Constellation, it did not enjoy across-the-board sup- port. 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 pro- gram, as defined, could not be executed without substantial increases in funding. Eventually, in February 2010, President 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 over the decades, especially after 1969. They all include a space program that would advance long-range technologies (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 commercial investment opportunities; improve affordability; support national security; and expand international collaboration. All the panels have sug- gested that Mars be the ultimate goal of human spaceflight with return to the lunar surface as an intermediate step. 24  Vice President’s Space Policy Advisory Board, A Post Cold War Assessment of U.S. Space Policy: A Task Group Report, December 1992, available at http://history.nasa.gov/33080.pt1.pdf and http://history.nasa.gov/33080.pt2.pdf. 25  In June 1992, President 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 signed on November 1, 1993, 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. 27  NASA, “President Bush Offers New Vision for NASA,” http://www.nasa.gov/missions/solarsystem/bush_vision.html, January 14, 2004.

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OVERVIEW OF ANALYSIS AND FINDINGS 33 majority agreement when the question was asked that way either. The most commonly mentioned loss was national prestige, which was mentioned by only one-fourth of respondents. And 15 percent said that nothing would be lost. 1.5.2.2  Stakeholder Views on a Course for the Future Respondents were asked to consider what goals a worthwhile and feasible U.S. human space exploration pro- gram might work toward over the next 20 years. They were presented with a list of possible projects that NASA could pursue and asked to indicate how strongly they favored or opposed each of them. The options were presented with approximate overall costs to provide some context for the scale of the projects. Overall, the option that received the most “strongly favor” responses was continuing with LEO flights until 2020 (the survey was done before the U.S. administration’s proposal to its partners to continue ISS operations through 2024). A majority of respondents favored four programs (either “strongly” or “somewhat”): LEO flights to the ISS until 2020, extending the ISS to 2028, conducting orbital missions to Mars to teleoperate robots on the surface, and returning to the Moon to explore more of it with short visits. Those who said that they were involved in space-related work, and in particular those who were involved in human spaceflight-related work, were gener- ally more likely to favor most programs strongly than those who were not so involved, but continuing with LEO flights to the ISS until 2020 was the option that received the most “strongly favor” responses in all three groups. Those who were under 40 years old were generally more likely to favor most projects strongly than those who were 40 years old and over. Continuing with LEO flights to the ISS until 2020 and extending the ISS to 2028 were the two options with the most “strongly favor” responses among respondents who were under 40 years old, and they were followed by establishing outposts on the Moon and landing humans on Mars. Respondents were asked to rate the importance of several possible projects or activities for NASA over the next 20 years. The stakeholders were grouped into three categories—those who were not involved in space-related work, those who were involved in nonhuman space-related work, and those who were involved in human space- related work. The three groups differed in their views about what NASA should be doing over the next 20 years. For example, the stakeholders who were involved in human space-related work were more likely than stakeholders in the other two categories to say that it was very important to make the investment needed to sustain a vigorous program of human spaceflight (see Table 3.18). Still, majorities in all three groups thought it very important to make the investment needed to sustain a vigorous program of robotic space exploration. The two groups of stake- holders who were not involved in human spaceflight were more likely than those who were involved in human spaceflight to support improving orbital technologies, such as weather and communication satellites. Finally, substantial minorities of all three stakeholder groups (at least 40 percent) rated expanding space collaboration with other countries as very important. The stakeholders had clear views about the role of NASA versus the private sector. More than 90 percent thought that NASA should take the lead in space exploration for scientific research, but nearly 85 percent said that the private sector should take the lead in space travel by private citizens, and more than two-thirds said that the private sector should take the lead in economic activities in space. Nearly half thought that NASA should take the lead in establishing an off-planet human presence, but almost one-third said that neither NASA nor the private sector should do this. 1.5.2.3  Summary of Stakeholder Survey Results For space exploration in general, “expanding knowledge and scientific understanding” emerged as the rationale that was shared by the overwhelming majority of the respondents. However, when restricted to human spaceflight, no single rationale garnered agreement from a majority of the respondents. Support for human spaceflight appears to decline steadily with age, although it is important to note that due to the panel’s intentional focus on policy leaders, the respondents to the survey tended to be older overall than the general population. Support for human spaceflight goes up with involvement in work related to human space exploration. There are also differences among the stakeholder groups in their support for human spaceflight: support was lowest among the nonspace scientists and highest among the advocates and popularizers.

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34 PATHWAYS TO EXPLORATION 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 a fundamental question: What type of human spaceflight program would be responsive to those factors? The 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 the 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 that it 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 important, because major new spaceflight programs have lead times of years (sometimes a decade) between a decision to pursue a program and first flight, delaying a decision until near the end of the ISS’s lifetime will guarantee a long gap in any human spaceflight activity—just as the termination of the Space Shuttle has led to a hiatus in U.S. capability to take astronauts up and bring them back to Earth. Chapter 4 argues that SLS and Orion flight rates that are too far below historical norms will not be sustainable over the course of an exploration pathway that spans decades. That will be the case for the first two launches of SLS, which are the only ones scheduled. 65 Hence, the committee has concluded the following: 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 the essential nature of a sustainable program. 1.6.1  Horizon Goal: Mars Within the limits of foreseeable technologies, there are a small number of places that humans can go beyond LEO, and only two that 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 with likely future technologies (Chapter 4). Mars is a goal most compatible with the committee’s endur- ing questions, and the intrinsic fascination that Mars has held in the popular imagination for well over a century makes it an attractive target. Such a program in 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 that Mars is the horizon goal of human space exploration. The committee has concluded the following: 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 technological failures and accidents or by the vagaries of the political process and economic scene. 64  Much of the technical discussion in this section is derived from the deliberations of the Technical Panel, which are described in detail in Chapter 4. 65  The first two launches of SLS are planned to occur 4 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 4 years the Apollo program conducted 12 launches and the Space Shuttle Program conducted 17. 66  Essentially, the region of gravitational influence that a body exerts on the space around it.

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OVERVIEW OF ANALYSIS AND FINDINGS 35 1.6.2  Stepping Stones Between LEO and the martian surface are regions of space, essentially operational theaters, that have stepping- stone destinations that are reachable with foreseeable advances in the state of the art for key technologies. Those 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. • Mars, which encompasses a Mars flyby mission and missions to the moons of Mars, Mars orbit, and the surface of Mars. Missions to various destinations within those operational theaters could provide the necessary challenges, adventures, and diverse patterns of activity and use to sustain a program that addresses the enduring questions. The challenges of human spaceflight beyond LEO are created 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. These factors vary greatly for NEAs, which populate a wide variety of orbits. The figure uses all of the NEA objects in the NHATS database. 68 The number of known NEAs is increasing at a rate of approximately 1,000 per year, but only a small fraction of NEAs are known to have orbits that may be suitable for a human mission, and many of those are nonetheless unsuitable destinations for human exploration because of other characteristics, such as spin rate, that are harder to determine and remain unknown for most asteroids, even after their orbits are quantified.69 The delta-V for the Mars missions is highly variable and depends on the year of the mission; an exploration system design for the lowest delta-V values shown will be capable of visiting Mars only once every 15 years or so, whereas a design for a higher delta-V capability would allow visits every other year. Similarly, improving the propulsive capabilities of an NEA orbital-transfer vehicle would increase launch opportunities and the diversity of targets. As propulsive energy requirements or mission durations increase, so do mission cost and risk. Increasing mission duration increases the risk of component failures, increases radiation exposure of systems and crew, and 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 2 weeks to 6 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 6 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 with 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 be shorter 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. For those 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) 67  Lagrangian points, also referred to as L points or libration points, are five relative positions in the co-orbital configuration of two bodies, one of them with a much smaller mass than the other. At each of those points, a third body 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. 68  Near-Earth Object Human Space Flight Accessible Targets Study (NHATS). Table of Accessible Near-Earth Asteroids, http://neo.jpl. nasa.gov/cgi-bin/nhats. 69  E.V. Ryan and W.H. Ryan, “Physical Characterization Studies of Near-Earth Object Spacecraft Mission Targets,” Advanced Maui Optical and Space Surveillance Technologies Conference, Maui, Hawaii, 2012, http://www.amostech.com/TechnicalPapers/2013/POSTER/RYAN.pdf.

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36 PATHWAYS TO EXPLORATION Fewer NEAs More NEAs Martian Moons 30 Day Stay 30 km/s delta-v Mars Surface < 30 Day Stay Mars Surface 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  General comparison of human spaceflight destinations and missions in terms of mission duration and round-trip propulsive energy requirements from Earth in delta-V (velocity changes). SOURCE: Chart developed for the Committee on Human Spaceflight by the Aerospace Corporation on the basis of multiple sources, including design reference missions (DRMs) generated by NASA and the International Space Exploration Coordination Group (Human Spaceflight Exploration Frame- work Study, NASA, January 11, 2012, Washington, DC, 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, DC, 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 informa- tion on the Design Reference Missions appears in Chapter 4. system to land massive payloads and crew. That is a major cost, schedule, and risk item. The committee has con- cluded the following: 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 would develop the capabilities required for human surface exploration of Mars. As discussed in Chapter 4, the most challenging of these will be entry, descent, and landing for Mars; in-space propulsion and power; and radiation safety (radiation health effects and amelioration).

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OVERVIEW OF ANALYSIS AND FINDINGS 37 NASA’s current proposal for the next step in deep space exploration—retrieving a small asteroid and towing 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 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 such a way 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 nations’ space programs and that it is not of interest to the U.S. human exploration program. That argument is made despite the barely touched scientific record of the earliest history of the solar system that lies hidden in the lunar crust,70 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 grandparents’ genera­ ion. The history of exploration of our own globe carries the lesson that the ones who follow the first explor- t ers are the ones who profit from the accomplishment. Such a lesson would suggest that the United States relook at its lack of interest 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 the present committee that the Moon and in particular its surface have important 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 a flexible-path approach, in which no specific sequence of destinations is specified (see Chapter 4). Instead, as discussed below, the committee recom- mends a “pathways approach” to human space exploration: a specific sequence of intermediate accomplishments and destinations, normally of increasing difficulty and complexity, that lead to an ultimate (horizon) goal with technology feed-forward from one mission to the next. If it is 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 use of infrastructure. A pathways approach also would include technology development that addresses mission requirements and integration, placing crew and launch vehicles into a system architecture that includes such key components as radiation safety, advanced in-space propulsion and power, and EDL 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 large 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 as follows: NASA can sustain a human space exploration program with meaningful milestones that simultaneously reasserts U.S. leadership in space and allows ample opportunity for substantial international collabora- tion when that program •  as elements that are built in a logical sequence. H •  an fund a frequency of flights sufficiently high to ensure retention of critical technical capability, C proficiency of operators, and effective use 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. 70  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, The National Academies Press, Washington, D.C., 2007.

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38 PATHWAYS TO EXPLORATION 1.6.3  Pathway Principles and Decision Rules The pathways approach applies principles and decision rules that are 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 in decades with costs measured in hundreds of billions of dollars and significant risk to human life. In what follows, the committee does not recommend one pathway over another but rather pro- poses principles by which national leadership might decide on pursuing a given pathway, measure progress along the pathway, move off the pathway to another, or cease the endeavor altogether. The resulting pathway principles are intended to be used in establishing a sustainable long-term course. In the environment of constrained federal budgets for the foreseeable future, the application of the principles should result in a pathway that includes only essential major hardware and mission elements so that it is possible to live within expected funding constraints. This approach leaves limited opportunities for major reductions in scope (“descoping”) later, as described in detail in Chapter 4. Therefore, as its highest-priority recommendation, the committee recommends as follows: NASA should adopt the following pathway principles: I. Commit to designing, maintaining, and pursuing 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 the 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 or programmatic impediments to progress. V. Create a risk-mitigation plan to sustain the selected pathway when unforeseen technical or budgetary problems arise. Such a plan should include points at which decisions are made to move to a less ambitious pathway (referred to as an “off-ramp”) or to 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, namely, 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 to develop confidence in NASA’s ability to execute the pathway. c. The pathway is characterized by logical feed-forward of technical capabilities. 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. 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 use of infrastructure. Upfront pathway principles are applied with recognition that a set of operational decision rules will also be required and applied as NASA, the administration, and Congress face inevitable programmatic challenges along a selected pathway. The decision rules that this committee has developed provide operational guidance that can be applied as major technical, cost, and schedule issues arise as NASA progresses along a pathway. They have been designed to provide a framework for a sustainable program through the lifetime of the selected pathway and to allow a program to stay within the constraints accepted and developed when applying the pathway principles. The committee recommends the following:

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OVERVIEW OF ANALYSIS AND FINDINGS 39 Whereas the overall pathway scope and cost are defined by application of the pathway principles, once a program is on a pathway, technical, cost, or schedule problems that arise should be addressed by the administration, NASA, and Congress by applying the following decision rules: A. If the appropriated funding level and 5-year budget projection do not permit execution of a pathway within the established schedule, do not start down that pathway. 71 B. If a budget profile does not permit the chosen pathway, even if NASA is well along on it, 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 in such a way that continued budget increases are required for the pathway’s sustainable execution; rather, the increase in funds should be applied to rapid retirement of important technology risks or to an increase in operational tempo in pursuit of the pathway’s previously defined technical and exploration goals. D. Given that limitations on funding will require difficult choices in the development of major new technologies and capabilities, give high priority to choices that solve important technological shortcomings, that reduce overall program cost, that allow an acceleration of the schedule, or that reduce developmental or operational risk. E. If there are human spaceflight program elements, infrastructure, or organizations that are no longer contributing to progress along the pathway, the human spaceflight program should divest itself of them as soon as possible. 1.6.4  Two Examples of Futures for Human Spaceflight: The Fiscal Challenge Ahead The committee provides here examples derived from Chapter 4 to demonstrate the fiscal challenge that the United States faces in any exploration program beyond LEO. The examples are for illustrative purposes and should not be construed as recommendations regarding options. In each case, the “sand charts” depict in a linear fashion the annual estimated cost72 of the human spaceflight program. 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 intermit- tent human presence at the Earth–Moon L2 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 by 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. 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 71  The committee recognizes that budget projections are unreliable, but they are also indispensable. One way to make the use of such projec- tions 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. That might be done as part of the risk-mitigation plan. 72  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.

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40 PATHWAYS TO EXPLORATION 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. 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.

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OVERVIEW OF ANALYSIS AND FINDINGS 41 adhering to pathway principles 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 in 2024, a rendezvous with an asteroid in its native orbit in 2028, and the lunar sortie in 2033; a 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. This scenario violates pathway principle VIf in that the flight rate is too low to maintain proficiency (Chapter 4): on the average, one crewed mission every 2.1 years with gaps of up to 5 years in which there are no crewed missions. 73 This scenario could be modified to allow higher mission rates (see Chapter 4), but 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. On the basis of the lessons learned from those and other scenarios presented in Chapter 4, the committee has concluded the following: 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. That 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). 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 to establish acceptable levels of risk to missions and crews for deep-space missions. At the agency level, the risk discussion will be more detailed and will use relative or probabilistic levels to define the risk threshold, inform the design, and set priorities. NASA should make all reasonable efforts to manage its technical risk in a way that emphasizes crew safety through the use of robust designs, failure tolerant approaches, and safe operations in adverse environments. How- ever, a national failing to acknowledge that there are limits to the ability to mitigate the risks of human explora- tion 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 the following: 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 of human spaceflight beyond LEO threatens our nation’s appeal and suitability as an international partner. 73  Theenhanced-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 that of the Apollo or space shuttle programs. In particular, between 2022 and 2030, there would be an average of one SLS launch every 18 months.

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42 PATHWAYS TO EXPLORATION The United States has had a sustained program of human spaceflight for more than a half-century, para- doxically 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 that was predicted by many space experts at the time of Apollo.74 That is a problem that adds to the numerous difficulties—frequent redirec- tion, mismatch of mission and resources, and political micromanagement—that have afflicted the U.S. human spaceflight program since Apollo ended. The committee has concluded as follows: 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: •  o defensible calculation of tangible, quantifiable benefits—spinoff technologies, attraction of talent N to scientific careers, scientific knowledge, and so on—is likely ever to demonstrate a positive return on the massive investment required by human spaceflight. •  he arguments that triggered the Apollo investment—national defense and prestige—seem to have T especially limited public salience in today’s post–Cold War America. •  lthough the public is mostly positive about NASA and its spaceflight programs, increased spending A on spaceflight has low priority for most Americans. However, 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 those 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 that they will be markedly above it. Nevertheless, the committee has concluded as follows: If the United States decides that the intangible benefits of human spaceflight justify 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: 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. 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? What can humans do and achieve when we get there? 74  Aviation Week & Space Technology in the 1960s predicted a landing of humans on Mars by the early 1980s.

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OVERVIEW OF ANALYSIS AND FINDINGS 43 3. Establish and implement the pathways 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 in addition to traditional international partners. Specifically, future collaborations in major new endeavors should seek to incorporate a.  level of overall cost-sharing that is appropriate to the true partnerships that will be necessary A to pursue pathways beyond LEO. b. Shared decision-making with partners, including 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 that target funded high-priority technology development, most critically a. Entry, descent, and landing for Mars. b. Advanced in-space propulsion and power. c. Radiation safety. None of those 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 less alien for conventional political decision-makers than the rec- ognition that human spaceflight—among the longest-term 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 fund human spaceflight aggressively 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 reali- ties 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.