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A Constrained Space Exploration Technology Program: A Review of NASA’s Exploration Technology Development Program 3 Gaps in the Scope of the Exploration Technology Development Program The Exploration Technology Development Program (ETDP) is the successor of the human and crosscutting space technology and advanced development programs that have been a part of NASA since its creation. At this time, the ETDP is the primary broad-based space technology program in the agency. Other, historically smaller programs that have existed alongside the general space technology program have either a specific focus or limited funding mechanisms. These include the programs developing technology for science missions in the Science Mission Directorate, space communications technology in the Space Operations Mission Directorate, and hypersonic reentry technology in the Aeronautics Research Mission Directorate, as well as the work being done under the Innovative Partnerships Program (which includes the Small Business Innovation Research [SBIR] Program and the Small Business Technology Transfer [STTR] Program). Given its role as the successor of the broad-based space technology program, it is important that the ETDP invest in a representative portfolio of the space technologies needed to continue the nation’s leadership in space exploration. The role of NASA as a developer of space technology is clearly articulated in the agency’s governing policy documents. The National Aeronautics and Space Act of 1958 (as amended) calls for NASA to “materially contribute” to “the preservation of the role of the United States as a leader in aeronautical and space science and technology and in the application thereof to the conduct of peaceful activities within and outside the atmosphere.” The Vision for Space Exploration (VSE) calls for NASA to “develop the innovative technologies, knowledge, and infrastructures both to explore and to support decisions about the destinations for human exploration.”1 The ETDP’s responsibilities for and burden of husbanding the civil space technology of the nation must be considered in light of these empowering charters and of the fact that the ETDP is the primary space technology program in NASA. Except as noted above (regarding technology for science missions, space communications, hypersonics, and programs fundable as SBIR and STTR), if the ETDP does not support a particular area of space engineering and technology research and development, there is likely no other NASA-wide program that acts as a source of support for it. Two questions are thus pertinent when assessing the scope of the ETDP: 1 The Vision for Space Exploration initiative was announced by President George W. Bush on January 14, 2004, and is outlined in National Aeronautics and Space Administration (NASA), The Vision for Space Exploration, NP-2004-01-334-HQ, NASA, Washington, D.C., 2004.
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A Constrained Space Exploration Technology Program: A Review of NASA’s Exploration Technology Development Program Do ETDP-funded activities adequately support the development of the elements of the currently envisioned Constellation Program?2 Does ETDP fund a robust program of technology development necessary, as stated in the VSE, “to explore and to support decisions about the destinations for human exploration” and to preserve the “role of the United States as a leader in aeronautical and space science and technology,” as stated in the National Aeronautics and Space Act of 1958? The second of these questions is discussed in Chapter 4; the first is addressed below. Finding on the Scope of the ETDP: The range of technologies covered in the 22 ETDP projects will, in principle, enable many of the early endeavors currently imagined in NASA’s Exploration Systems Architecture Study architecture,3 but not the entire VSE. However, as discussed below, the committee did identify two gaps in which the ETDP’s portfolio could be strengthened: integration of the human system and nuclear thermal propulsion. The first gap represents the interplay of the ETDP and the Human Systems element of the Advanced Capabilities office. The second reflects a historical struggle by NASA to determine the appropriate timing of the development of the potentially beneficial NTP technology and system. INTEGRATION OF THE HUMAN SYSTEM During its assessment, the committee observed that the “human system” was generally not systematically considered in the early requirements, research, design definition, testing, and development of the 22 projects of the ETDP. These human-centered health and human factor requirements are well described in two documents: NASA’s Bioastronautics Roadmap,4 and the National Research Council’s (NRC’s) Safe Passage: Astronaut Care for Exploration Missions.5 The requirements are further documented as flow-down requirements for and from the Exploration Systems Mission Directorate (ESMD).6 Described in a 2006 NRC study, NASA’s Bioastronautics Roadmap is “the framework used to identify and assess the risks of crew exposure to the hazardous environments of space.”7 The Bioastronautics Roadmap was created to facilitate and support the successful accomplishment of the three following design reference missions: A one-year mission to the International Space Station, A month-long stay on the lunar surface, and A 30-month round-trip journey to Mars. The more recent Human Research Program Requirements Document (HRP-47052)8 describes six mission scenarios—a short Earth orbital mission; an International Space Station (ISS) 6-month mission; an ISS 12-month mission; a short-duration lunar sortie; a long-duration lunar mission; and a Mars mission—in determining risk 2 See Appendix F for descriptions of the currently envisioned components of the Constellation Program. 3 National Aeronautics and Space Administration, Exploration Systems Architecture Study—Final Report, NASA-TM-2005-214062, NASA, Washington, D.C., November 2005. 4 See http://bioastroroadmap.nasa.gov. Accessed May 7, 2008. 5 National Research Council, Safe Passage: Astronaut Care for Exploration Missions, National Academy Press, Washington, D.C., 2001. 6 National Aeronautics and Space Administration, Human Research Program Requirements Document, Human Research Program, HRP-47052, Revision A, NASA Johnson Space Center, Houston, Tex., July 2007. 7 National Research Council, A Risk Reduction Strategy for Human Exploration of Space: A Review of NASA’s Bioastronautics Roadmap, The National Academies Press, Washington, D.C., 2006, p. 2. 8 National Aeronautics and Space Administration, Human Research Program Requirements Document, Human Research Program, HRP-47052, Revision A, NASA Johnson Space Center, Houston, Tex., July 2007.
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A Constrained Space Exploration Technology Program: A Review of NASA’s Exploration Technology Development Program assessment and vehicle and systems designs. In both documents, lunar surface operations and martian surface operations are identified as research and development (R&D) design drivers. Human health and human factor risks are interdependent with spacecraft and extravehicular activity (EVA) system design risks. Changing one risk can have unanticipated consequences on another risk. A classic example of such unanticipated interactions is well illustrated by the interaction between the mitigation of the risk posed for water contamination aboard the NASA orbiters and consequent thyroid dysfunction in crew members. Iodine was used as the bacteriostatic agent in drinking water aboard the U.S. space shuttle orbiters—a seemingly reasonable approach to water purification. However, the concentration of iodine resulted in a daily iodine intake that far exceeded the recommended daily allowance and was sufficient to cause chemical evidence of thyroid dysfunction (e.g., increases in thyroid-stimulating hormone) in many astronauts and clinical hyper- or hypothyroidism in several astronauts.9 Finding on Integration of the Human System: The committee did not find a high degree of awareness of the interdependencies between the ETDP technology projects and associated human health risks and human design factor considerations. In fact, the Bioastronautics Roadmap, the Safe Passage study, and HRP-47052 were not clearly identified as guiding requirements in the material presented to the committee. In the period that during which study was conducted, NASA formulated a set of evidence books10 related to operationally relevant human health risks. The scope of these risks and associated gaps in knowledge that inform R&D programs is currently under review in another NRC study, and the final list of health risks is potentially subject to change. For this reason, reference is made here to the 2005 Bioastronautics Roadmap rather than to the more recent naming and numbering of human health risks. However, the essential linkages between ETDP projects and human health risks outlined here remain valid. Appendix G shows some of the relationships that exist between various ETDP projects and risks identified in the Bioastronautics Roadmap. Recommendation 1 on the Human System: ETDP project managers should clearly identify the interrelationships between human health and human factor risks and requirements11 on the one hand and technology development on the other and should ensure that those risks and requirements are addressed in their project plans. Each ETDP project manager should be able to show clearly where that project fits within the integrated Exploration Systems Mission Directorate Advanced Capabilities Program (which includes the ETDP, the Lunar Precursor Robotic Program, and the Human Research Program), and this integrated program plan should include all elements necessary to achieve the Vision for Space Exploration. Recommendation 2 on the Human System: Exploration Technology Development Program (ETDP) project managers should systematically include representatives of the Human Research Program on the ETDP technology development teams. For example, the risks associated with EVA suit anthropometric sizing and motion loads should be introduced to both the NASA and the contractor teams as soon as possible. The committee understands that a contractor to build a common launch/entry, EVA, and lunar surface suit is being selected. If the contractor is not familiar with the risks associated with (1) the past history of ill-fitting suits that degrade crew performance at both ends of the 9 Institute of Medicine, Review of NASA’s Longitudinal Study of Astronaut Health, The National Academies Press, Washington, D.C., 2004. 10 National Aeronautics and Space Administration, Human Research Program Evidence Book, NASA Johnson Space Center, Houston, Tex., 2008. 11 As identified in such documents, as appropriate, as NASA, Human Research Program Requirements Document, Human Research Program, HRP-47052, Revision A, NASA Johnson Space Center, Houston, Tex., July 2007; NASA, NASA Space Flight Human Systems Standards, Volumes I and II, NP-2006-11-448-HQ, Washington, D.C.; and the Risk Mitigation Analysis Tool developed under the direction of Jeffrey R. Davis.
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A Constrained Space Exploration Technology Program: A Review of NASA’s Exploration Technology Development Program anthropometric spectrum (large and small), (2) the worst-case scenario of the resulting suit design not fitting the anthropometric range of the selected and trained crew population, or (3) the requirement for loads and forces of the suit to accommodate worst-case deconditioned crew members on the surface of the Moon or Mars, or on the ISS, then EVA operations, and therefore mission success, may be significantly compromised. PRESERVING THE OPTION FOR NUCLEAR THERMAL PROPULSION A member of NASA’s Mars Architecture Working Group study briefed the committee on those activities results during the committee’s visit to the Johnson Space Center (JSC). That briefing summarized the trade-offs in technologies that had been considered for a human mission to Mars. For propulsion, the propulsion system selected was nuclear thermal propulsion (NTP). This choice is consistent with advice given in previous Mars mission architecture studies.12,13 In 2005, an NRC committee reported on its examination of the potential benefits of a nuclear thermal rocket (NTR) to enhance uncrewed exploration of the outer solar system and for human exploration: Finding: Nuclear propulsion technologies will likely be used initially for moving relatively large scientific payloads (~1,000s kg) to destinations in the outer solar system and beyond and extremely large payloads (~10,000s kg) in support of human exploration activities in the inner solar system. But it is necessary to investigate nuclear propulsion technologies more thoroughly to determine if they can provide fast, affordable access to the outer solar system and beyond and can move large payloads in the inner solar system cost-effectively and efficiently.14 The basic feasibility of the NTR was demonstrated in the Rover and the Nuclear Engine for Rocket Vehicle Applications (NERVA) programs in the 1960s, which tested an integrated engine/stage system to TRL 6. Because of its high performance, the NTR offers the potential of reduced mass in orbit (one-half to one-third that of chemically propelled systems), freedom from the need to develop aerobraking/aerocapture technologies for Mars, and the option of executing opposition-class missions with a stay on the surface that might extend to a few months. Total round-trip times of less than 500 days are possible for spacecraft that have an initial mass in low Earth orbit equivalent to those of chemically propelled missions lasting 900 days. Shorter trip times translate into reduced radiation doses from cosmic rays, microgravity effects, and psychological stresses associated with being confined in a spacecraft for months at a time. The NERVA engines used fuels clad in graphite that had a tendency to crack, erode, and leak fission products into the exhaust. Such performance is not acceptable in today’s environment. However, one of the alternative fuel forms investigated in the 1960s, tungsten loaded with uranium dioxide, demonstrated the ability to retain radioactivity and did not lead to cracking or to erosion due to thermal loading under the hydrogen flow conditions. Thus, the major issue for fuel development is materials behavior, including cracking, erosion, and thermal expansion. Electrical heating of candidate fuel elements can be accomplished in university or government laboratories—no nuclear conditions need be considered in the early stages of research. Development and demonstration of improved fuel material behavior would be a first, modest-cost step. According to one NASA Glenn Research Center estimate, the cost to develop a flight-ready NTR system is on the order of $3 billion (in 1996 dollars).15 The committee recognizes that constraints on the program may preclude 12 T.P. Stafford, America at the Threshold: Report of the Synthesis Group on America’s Space Exploration Initiative, U.S. Government Printing Office, Washington, D.C., 1991. 13 Space Task Group, “The Post-Apollo Space Program: Directions for the Future,” available in NASA Historical Reference Collection, History Office, NASA, Washington, D.C., September 1969. 14 National Research Council, Priorities in Space Science Enabled by Nuclear Power and Propulsion, The National Academies Press, Washington, D.C., 2006. 15 S.K. Borowski and L.A. Dudzinski, “High Leverage Space Transportation System Technologies for Human Exploration Missions to the Moon and Beyond,” Paper AIAA-96-2810 in 32nd Joint Propulsion Conference Proceedings, American Institute of Aeronautics and Astronautics, Reston, Va., 1996. Also published as NASA-TM-107295, available at http://trajectory.grc.nasa.gov/aboutus/papers/AIAA-96-2810.pdf.
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A Constrained Space Exploration Technology Program: A Review of NASA’s Exploration Technology Development Program the full development of an NTR system at this time, but it believes that NASA should take steps to maintain this technology as a potential option for future decisions. Finding on Nuclear Thermal Rocket Technology: NASA has no project for examining the fundamental issues involved in recovering the nuclear thermal rocket (NTR) technology even though the utility and the technical feasibility of the NTR have been established. Recommendation on Nuclear Thermal Rocket Technology: The Exploration Technology Development Program should initiate a technology project to evaluate experimentally candidate nuclear thermal rocket (NTR) fuels for materials and thermal characteristics. Using these data, the Exploration Systems Mission Directorate should assess the potential benefit of using an NTR for lunar missions and should continue to assess the impact on Mars missions. SUMMARY COMMENTS NASA must couple the human aspects of its mission with its technology development program in order to succeed. NASA could return humans to the Moon without nuclear thermal propulsion technology, but the ability to go beyond the Apollo program would be substantially reduced. Such a reduction would call into question the rationale for exploration provided in the Vision for Space Exploration, the national space policy, and the NASA Authorization Act of 2005 (Public Law 109-155). Adding nuclear thermal propulsion would provide NASA with a technology that would support decisions about future destinations and potentially significantly enhance the capability of NASA’s systems and vehicles. A better integration of the human systems would help to ensure the efficient completion of mission objectives by reducing barriers or obstacles to the human operation of Constellation systems.