5 Summaries of Major Reports

This chapter reprints the summaries of Space Studies Board (SSB) reports that were released in 2012 (or late 2011). Reports are often written in conjunction with other National Research Council boards, including the Aeronautics and Space Engineering Board (ASEB) or the Board on Physics and Astronomy (BPA), as noted.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 35
5 Summaries of Major Reports This chapter reprints the summaries of Space Studies Board (SSB) reports that were released in 2012 (or late 2011). Reports are often written in conjunction with other National Research Council boards, including the A ­ eronautics and Space Engineering Board (ASEB) or the Board on Physics and Astronomy (BPA), as noted. 35

OCR for page 35
36 Space Studies Board Annual Report—2012 5.1 Assessment of a Plan for U.S. Participation in Euclid A Report of the BPA and SSB Ad Hoc Committee on the Assessment of a Plan for U.S. Participation in Euclid Executive Summary NASA has proposed to make a hardware contribution to the European Space Agency’s (ESA’s) Euclid mission in exchange for U.S. membership on the Euclid Science Team and science data access. The Euclid mission will employ a space telescope that will make potentially important contributions to prob- ing dark energy and to the measurement of cosmological parameters. Euclid will image a large fraction of the e ­ xtragalactic sky at unprecedented resolution and measure spectra for millions of galaxies. This report responds to a request from NASA to evaluate whether a small investment in Euclid (around $20 million in hardware) is a viable part of an overall strategy to pursue the science goals of the New Worlds, New Horizons (NWNH) report’s top-ranked large-scale, space-based priority: the Wide-Field Infrared Survey Telescope (WFIRST). WFIRST has a broad, wide-field, near-infrared capability that will serve a wide variety of science pro- grams of U.S. astronomers, including exoplanet research, near-infrared sky surveys, a guest observer program, and dark energy research. In carrying out this study the committee’s intent has been to be clear that this report does not alter NWNH’s plans for the implementation of the survey’s priorities. The Committee on the Assessment of a Plan for U.S. Participation in Euclid concludes that the NASA proposal would represent a valuable first step toward meeting one of the science goals (furthering dark energy research) of WFIRST. While WFIRST dark energy measurements are expected to be superior to Euclid’s, U.S. participation in Euclid will have clear scientific, technical, and programmatic benefits to the U.S. community as WFIRST and Euclid go forward. NASA should make a hardware contribution of approximately $20 million1 to the Euclid mission to en- able U.S. participation. This investment should be made in the context of a strong U.S. commitment to move forward with the full implementation of WFIRST in order to fully realize the decadal science priorities of the NWNH report. In exchange for this small, but crucial contribution, NASA should secure through negotiation with the European Space Agency both a U.S. position on the Euclid Science Team with full data access and the inclu- sion of a team of U.S. scientists in the Euclid Consortium that would be selected by a peer-reviewed process with full data access as well as authorship rights consistent with Euclid policies still to be formulated. NASA should seek independent community review of any financial commitment for hardware expendi- tures beyond $30 million for Euclid. NOTE: “Executive Summary” reprinted from Assessment of a Plan for U.S. Participation in Euclid, The National Academies Press, W ­ ashington, D.C., 2012, p. 1. 1All costs expressed in fiscal year 2012 U.S. dollars unless otherwise specified.

OCR for page 35
Summaries of Major Reports 37 5.2 Assessment of Planetary Protection Requirements for Spacecraft Missions to Icy Solar Systems Bodies A Report of the SSB Ad Hoc Committee on Planetary Protection Standards for Icy Bodies in the Outer Solar System Summary NASA’s exploration of planets and satellites over the past 50 years has led to the discovery of water ice through- out the solar system and prospects for large liquid water reservoirs beneath the frozen shells of icy bodies in the outer solar system. These putative subsurface oceans could provide an environment for prebiotic chemistry or a habitat for indigenous life. During the coming decades, NASA and other space agencies will send flybys, orbiters, subsurface probes, and, possibly, landers to these distant worlds in order to explore their geologic and chemical context and the possibility of extraterrestrial life. Because of their potential to harbor alien life, space agencies will select missions that target the most habitable outer solar system objects. This strategy poses formidable challenges for mission planners who must balance the opportunity for exploration with the risk of contamination by terrestrial microbes that could confuse the interpretation of data from experiments concerned with the origins of life beyond Earth or the processes of chemical evolution. To protect the integrity of mission science and maintain compliance with the mandate of the 1967 Outer Space Treaty to “pursue studies of outer space, including the Moon and other celestial bodies . . . so as to avoid their harmful contamination,”1 NASA adheres to planetary protection guidelines that reflect the most current experimental and observational data from the planetary science and microbiology communities.2 The 2000 National Research Council (NRC) report Preventing the Forward Contamination of Europa3 recom- mended that spacecraft missions to Europa must have their bioload reduced by such an amount that the probability of contaminating a Europan ocean with a single viable terrestrial organism at any time in the future should be less than 10–4 per mission.4 This criterion was adopted for consistency with prior recommendations by the Committee on Space Research (COSPAR) of the International Council for Science for “any spacecraft intended for planetary landing or atmospheric penetration.”5 COSPAR, the de facto adjudicator of planetary protection regulations, adopted the criterion for Europa, and subsequent COSPAR-sponsored workshops extended the 10–4 criterion to other icy bodies of the outer solar system.6,7 In practice, the establishment of a valid forward-contamination-risk goal as a mission requirement implies the use of some method—either a test or analysis—to verify that the mission can achieve the stated goal. The 2000 Europa report recommended that compliance with the 10–4criterion be determined by a so-called Coleman-Sagan calculation.8,9,10 This methodology estimates the probability of forward contamination by multiplying the initial bioload on the spacecraft by a series of bioload-reduction factors associated with spacecraft cleaning, exposure to the space environment, and the likelihood of encountering a habitable environment. If the risk of contamination falls below 10–4, the mission complies with COSPAR planetary protection requirements and can go forward. If the risk exceeds this threshold, mission planners must implement additional mitigation procedures to reach that goal or must reformulate the mission plans. The charge for the Committee on Planetary Protection Standards for Icy Bodies in the Outer Solar System called for it to revisit the 2000 Europa report in light of recent advances in planetary and life sciences and examine the recommendations resulting from two recent COSPAR workshops. The committee addressed three specific tasks to assess the risk of contamination of icy bodies in the solar system. The first task concerned the possible factors that could usefully be included in a Coleman-Sagan formulation of contamination risk. The committee does not support continued reliance on the Coleman-Sagan formulation to estimate the probability of contaminating outer solar system icy bodies. This calculation includes multiple factors of uncertain magnitude that often lack statistical independence. Planetary protection decisions should not rely on the multiplication of probability factors to estimate the likelihood of contaminating solar system bodies with terrestrial organisms unless it can be unequivocally demonstrated that the factors are completely independent and their values and statistical variation are known. NOTE: “Summary” reprinted from Assessment of Planetary Protection Requirements for Spacecraft Missions to Icy Solar Systems Bodies, The National Academies Press, Washington, D.C., 2012, pp. 1-4.

OCR for page 35
38 Space Studies Board Annual Report—2012 The second task given to the committee concerned the range of values that can be estimated for the terms appearing in the Coleman-Sagan equation based on current knowledge, as well as an assessment of conservative values for other specific factors that might be provided to the implementers of missions targeting individual bodies or classes of objects. The committee replaces the Coleman-Sagan formulation with a series of binary (i.e., yes/no) decisions that consider one factor at a time to determine the necessary level of planetary protection. The committee proposes the use of a decision-point framework that allows mission planners to address seven hierarchically orga- nized, independent decision points that reflect the geologic and environmental conditions on the target body in the context of the metabolic and physiological diversity of terrestrial microorganisms. These decision points include the following: 1. Liquid water—Do current data indicate that the destination lacks liquid water essential for terrestrial life? 2. Key elements—Do current data indicate that the destination lacks any of the key elements (i.e., carbon, hydrogen, nitrogen, phosphorus, sulfur, potassium, magnesium, calcium, oxygen, and iron) required for terrestrial life? 3. Physical conditions—Do current data indicate that the physical properties of the target body are incompat- ible with known extreme conditions for terrestrial life? 4. Chemical energy—Do current data indicate that the environment lacks an accessible source of chemical energy? 5. Contacting habitable environments—Do current data indicate that the probability of the spacecraft contact- ing a habitable environment within 1,000 years is less than 10–4? 6. Complex nutrients—Do current data indicate that the lack of complex and heterogeneous organic nutrients in aqueous environments will prevent the survival of irradiated and desiccated microbes? 7. Minimal planetary protection—Do current data indicate that heat treatment of the spacecraft at 60°C for 5 hours will eliminate all physiological groups that can propagate on the target body? Positive evaluations for any of these criteria would release a mission from further mitigation activities, although all missions to habitable and non-habitable environments should still follow routine cleaning procedures and micro- bial bioload monitoring. If a mission fails to receive a positive evaluation for at least one of these decision points, the entire spacecraft must be subjected to a terminal dry-heat bioload reduction process (heating at temperatures >110°C for 30 hours) to meet planetary protection guidelines. Irrespective of whether a mission satisfies one of the seven decision points, the committee recommends the use of molecular-based methods to inventory bioloads, including both living and dead taxa, for spacecraft that might contact a habitable environment. Given current knowledge of icy bodies, three bodies present special concerns for planetary protection: Europa, Jupiter’s third largest satellite; Enceladus, a medium-size satellite of Saturn; and Triton, Neptune’s largest satellite. Missions to other icy bodies present minimal concern for planetary protection. The advantage of the decision framework over the Coleman-Sagan approach lies in its simplicity and in its abandoning of the multiplication of non-independent bioload reduction factors of uncertain magnitude. At the same time, the framework provides a platform for incorporating new observational data from planetary exploration mis- sions and the latest information about microbial physiology and metabolism, particularly for psychrophilic (i.e., cold-loving microbes) and psychrotolerant microorganisms. The committee’s third task concerned the identification of scientific investigations that could reduce the uncer- tainty in the above estimates and assessments, as well as technology developments that would facilitate implemen- tation of planetary protection requirements and/or reduce the overall probability of contamination. The committee recognizes the requirement to further improve knowledge about many of the parameters embodied within the deci- sion framework. Areas of particular concern for which the committee recommends research include the following: • Determination of the time period of heating to temperatures between 40°C and 80°C required to inactivate spores from psychrophilic and psychrotolerant bacteria isolated from high-latitude soil and cryopeg samples, as well as from psychrotolerant microorganisms isolated from temperate soils, spacecraft assembly sites, and the spacecraft itself. • Studies to better understand the environmental conditions that initiate spore formation and spore germina- tion in psychrophilic and psychrotolerant bacteria so that these conditions/requirements can be compared with the characteristics of target icy bodies.

OCR for page 35
Summaries of Major Reports 39 • Searches to discover unknown types of psychrophilic spore-formers and to assess if any of them have toler- ances different from those of known types. • Characterization of the protected microenvironments within spacecraft and assessment of their microbial ecology. • Determination of the extent to which biofilms might increase microbial resistance to heat treatment and other environmental extremes encountered on journeys to icy bodies. • Determination of the concentrations of key elements or compounds containing biologically important ele- ments on icy bodies in the outer solar system through observational technologies and constraints placed on the range of trace element availability through theoretical modeling and laboratory analog studies. • Understanding of global chemical cycles within icy bodies and the geologic processes occurring on these bodies that promote or inhibit surface-subsurface exchange of material. • Development of technologies that can directly detect and enumerate viable microorganisms on spacecraft surfaces. REFERENCES 1  United Nations, Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, . Including the Moon and Other Celestial Bodies, U.N. Document No. 6347, Article IX, January 1967. 2. M. Meltzer, When Biospheres Collide: A History of NASA’s Planetary Protection Programs, NASA SP-2011-4234, NASA, Washington, D.C., 2011. 3  National Research Council, Preventing the Forward Contamination of Europa, National Academy Press, Washington, . D.C., 2000. 4  National Research Council, Preventing the Forward Contamination of Europa, National Academy Press, Washington, . D.C., 2000. 5  The recommendation to accept the 10–4 criterion was made at the 7th COSPAR meeting in May 1964 (see COSPAR, . Report of the Seventh COSPAR Meeting, Florence Italy, COSPAR, Paris, 1964, p. 127, and, also, COSPAR Information ­Bulletin, No. 20, November, 1964, p. 25). The historical literature does not record the rationale for COSPAR’s adoption of this standard. Subsequent policy changes restricted the 10–4 standard to Mars missions (COSPAR, “COSPAR Planetary Protection Policy (20 October 2002; As Amended to 24 March 2011),” COSPAR, Paris, p. A1, available at http://cosparhq.cnes.fr/Scistr/ PPPolicy%20(24Mar2011).pdf. 6  COSPAR Panel on Planetary Protection, COSPAR Workshop on Planetary Protection for Outer Planet Satellites and . Small Solar System Bodies, European Space Policy Institute, Vienna, Austria, 2009. 7  COSPAR Panel on Planetary Protection, COSPAR Workshop on Planetary Protection for Titan and Ganymede, . COSPAR, Paris, France, 2010. 8 . C. Sagan and S. Coleman, Spacecraft sterilization standards and contamination of Mars, Astronautics and Aeronautics 3(5), 1965. 9  C. Sagan and S. Coleman, Decontamination standards for martian exploration programs, pp. 470-481 in National . Research Council, Biology and the Exploration of Mars, National Academy of Sciences, Washington, D.C., 1966. 10  J. Barengoltz, A review of the approach of NASA projects to planetary protection compliance, IEEE Aerospace Con- . ference, 2005, doi:10.1109/AERO.2005.1559319.

OCR for page 35
40 Space Studies Board Annual Report—2012 5.3 Earth Science and Applications from Space: A Midterm Assessment of NASA’s Implementation of the Decadal Survey A Report of the SSB Ad Hoc Committee on the Assessment of NASA’s Earth Science Program Summary Understanding the complex, changing planet on which we live, how it supports life, and how human activities affect its ability to do so in the future is one of the greatest intellectual challenges facing humanity. It is also one of the most important challenges for society as it seeks to achieve prosperity, health, and sustainability.1 The 2007 National Research Council report Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond (referred to in this report as the “2007 decadal survey” or “2007 survey”) called for a renewal of the national commitment to a program of Earth observations in which attention to securing practi- cal benefits for humankind plays an equal role with the quest to acquire new knowledge about the Earth system.2 The decadal survey recommended a balanced interdisciplinary program that would observe the atmosphere, oceans, terrestrial biosphere, and solid Earth and the interactions between these Earth system components to advance under­ standing of how the system functions for the benefit of both science and society. NASA responded positively to the decadal survey and its recommendations and began implementing most of them immediately after the survey’s release. Although its budgets have never risen to the levels assumed in the sur- vey, NASA’s Earth Science Division (ESD) has made major investments toward the missions recommended by the survey and has realized important technological and scientific progress as a result. Several of the survey missions have made significant advances, and operations and applications end users are better integrated into the mission teams. The new Earth Venture competitive solicitation program has initiated five airborne missions and is currently reviewing proposals submitted in response to an orbital stand-alone mission solicitation. At the same time, the Earth sciences have advanced significantly because of existing observational capabilities and the fruit of past investments, along with advances in data and information systems, computer science, and enabling technologies. Three missions already in development prior to the decadal survey—the Ocean Surface Topography Mission (OSTM), Aquarius, and the Suomi National Polar-orbiting Partnership (NPP)3—have since been successfully launched and promise significant benefits to research and applications. The potential for the science community to make use of space-based data for research and applications has never been greater. Finding: NASA responded favorably and aggressively to the 2007 decadal survey, embracing its overall recom- mendations for Earth observations, missions, technology investments, and priorities for the underlying science. As a consequence, the science and applications communities have made significant progress over the past 5 years. However, the Committee on Assessment of NASA’s Earth Science Program found that, for several reasons, the survey vision is being realized at a far slower pace than was recommended. Although NASA accepted and began implementing the survey’s recommendations, the required budget assumed by the survey was not achieved, greatly slowing implementation of the recommended program. Launch failures, delays, changes in scope, and growth in cost estimates have further hampered the program. In addition, the National Oceanic and Atmospheric Administration (NOAA) has significantly reduced the scope of the nation’s future operational environmental satellite series, omit- NOTE: “Summary” reprinted from Earth Science and Applications from Space: A Midterm Assessment of NASA’s Implementation of the Decadal Survey, The National Academies Press, Washington, D.C., 2012, pp. 1-14. 1From National Research Council, Earth Science and Applications from Space: Urgent Needs and Opportunities to Serve the Nation, The National Academies Press, Washington, D.C., 2005, p. 1. 2National Research Council, Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond, The National Academies Press, Washington, D.C., 2007. 3On January 24, 2012, NASA’s National Polar-orbiting Operational Environmental Satellite System Preparatory Project, launched on Octo- ber 28, 2011, was renamed the Suomi National Polar-orbiting Partnership in honor of the late Verner E. Suomi, a renowned meteorologist from the University of Wisconsin considered by many to be “the father of satellite meteorology.” See http://www.nasa.gov/mission_pages/ NPP/news/suomi.html.

OCR for page 35
Summaries of Major Reports 41 ting observational capabilities assumed by the decadal survey to be part of NOAA’s future capability and failing to implement the three new missions recommended for NOAA implementation by the survey (the Operational GPS Radio Occultation Mission, the Extended Ocean Vector Winds Mission, and the NOAA portion of CLARREO). Thus, despite recent and notable successes, such as the launches of OSTM, Aquarius, and Suomi NPP, the n ­ ation’s Earth observing capability from space is beginning to wane as older missions fail and are not replaced with sufficient cadence to prevent an overall net decline. Using agency estimates for the anticipated remaining lifetime of in-orbit missions and counting new missions formally approved in their enacted budgets, the committee found that the resulting number of NASA and NOAA Earth observing instruments in space by 2020 could be as little as 25 percent of the current number (Figure S.1).4 This precipitous decline in the quantity of Earth science and appli­ cations observations from space undertaken by the United States reinforces the conclusion in the 2007 decadal survey and its predecessor, the 2005 interim report, which declared that the U.S. system of environmental satellites is at risk of collapse.5 The committee found that a rapid decline in capability is now beginning and that the needs for both investment and careful stewardship of the U.S. Earth observations enterprise are more certain and more urgent now than they were 5 years ago. Finding: The nation’s Earth observing system is beginning a rapid decline in capability as long-running mis- sions end and key new missions are delayed, lost, or canceled. The projected loss of observing capability could have significant adverse consequences for science and society. The loss of observations of key Earth system components and processes will weaken the ability to understand and forecast changes arising from interactions and feedbacks within the Earth system and limit the data and information available to users and decision makers. Consequences are likely to include slowing or even reversal of the steady gains in weather forecast accuracy over many years and degradation of the ability to assess and respond to natural hazards and to measure and understand changes in Earth’s climate and life support systems. The decrease in capa- bility by 2020 will also have far-reaching consequences for the vigor and breadth of the nation’s space-observing industrial and academic base, endangering the pipeline of Earth science and aerospace engineering students and the health of the future workforce. CHALLENGES TO IMPLEMENTATION AND OPPORTUNITIES TO IMPROVE ALIGNMENT WITH THE DECADAL SURVEY Although there have been a number of successes, NASA’s Earth science program has suffered multiple set- backs and other external pressures that are, in many cases, beyond the control of program management. Foremost among these is a budget profile that is not sufficient to execute the 2007 decadal survey’s recommended program. In addition, some of the survey-recommended missions have proved more challenging than anticipated, and others envisioned synergies that are not readily achieved via the suggested implementation. The ESD budget has been further strained as a result of mandates from Congress (e.g., the addition of the approximately $150 million TIRS [Thermal Infrared Sensor] to the Landsat Data Continuity Mission) and the interjection of administration priorities (e.g., the Climate Continuity missions6) without the commensurate required funding. Finding: Funding for NASA’s Earth science program has not been restored to the $2 billion per year (in fiscal year [FY] 2006 dollars) level needed to execute the 2007 decadal survey’s recommended program. Congress’s failure to restore the Earth science budget to a $2 billion level is a principal reason for NASA’s inability to realize the mission launch cadence recommended by the survey. 4Figure S.1 is an updated version of a similar chart produced by the 2007 decadal survey. Using agency estimates for the anticipated remain- ing lifetime of in-orbit missions and counting new missions only if they have been formally approved in enacted agency budgets, Figure S.1 indicates that the number of missions could decline from 23 in 2012 to only 6 in 2020, and the number of NASA and NOAA Earth-observing instruments in space could decline from a peak of about 110 in 2011 to approximately 20 in 2020. A more optimistic scenario based on the Climate-Centric Architecture put forth to leverage anticipated augmented funding to support administration priorities is also shown in Figure S.1; however, this plan, which has not been fully funded, also projects a precipitous decline in observing capabilities. 5National Research Council, Earth Science and Applications from Space: Urgent Needs and Opportunities to Serve the Nation, 2005. 6NASA, “Responding to the Challenge of Climate and Environmental Change: NASA’s Plan for a Climate-Centric Architecture for Earth Observations and Applications from Space,” June 2010. Available at http://science.nasa.gov/media/medialibrary/2010/07/01/Climate_­ Architecture_Final.pdf.

OCR for page 35
42 Space Studies Board Annual Report—2012 Missions In‐Orbit or Planned and Funded Optimistic Scenario 30 25 Earth Observing Missions Number of NASA/NOAA  20 15 10 5 0 Year Instruments In‐Orbit or Planned and Funded Optimistic Scenario 140 120 Earth Observing Instruments Number of NASA/NOAA  100 80 60 40 20 0 Year FIGURE S.1  Number of operating (2000-2011) and planned (2012-2020) NASA and NOAA Earth observing missions (top) and instruments (bottom). Shown in blue are missions that are funded and have a specified launch date in NASA or NOAA budget submissions. Thus, the blue curve does not count missions (and associated instruments) that have been proposed or planned but are not yet funded or selected. Shown in pink is an “optimistic scenario” based on the Climate-Centric Architecture put forth to leverage anticipated augmented funding to support administration priorities that makes the following assumptions: GRACE-FO launches in 2016, PACE launches in 2019, ASCENDS launches in 2020, SWOT launches in 2020, EV-2 launches in 2017, SAGE-3 instrument launches in 2014, OCO-3 instrument launches in 2015, and EV-I instruments are launched every year starting in 2017 (plans are for EV-I instruments to be delivered for integration yearly; this assumes they also launch yearly). NOTE: Mission lifetimes for on-orbit missions are taken from estimates provided by NASA and NOAA; the NASA estimates are based on mission team estimates of remaining mission lifetime as provided (and reviewed by the Technical Panel) during the Senior Review process. Acronyms are defined in Appendix G. SOURCE: NASA and NOAA data. The committee concluded that in the near term, budgets for NASA’s Earth science program will remain incom- mensurate with programmatic needs. However, even as NASA strives to “do more with less,” it is confronted with challenges, including limited access to affordable medium-class launch vehicles—the mainstay of Earth observation programs—and significant growth in the cost to develop instruments and spacecraft, a consequence, in part, of how NASA manages its space missions. These challenges (discussed further in Chapter 3) have hindered implementa- tion of the envisioned balanced Earth system science program. With respect to cost growth, the committee found

OCR for page 35
Summaries of Major Reports 43 that decadal survey missions have thus far not been managed with sufficient consideration of the scope and cost outlined in the 2007 decadal survey in either an absolute or a relative sense. Chapter 4 offers recommendations to establish and manage mission costs. Recommendation: •   ASA’s Earth Science Division (ESD) should implement its missions via a cost-constrained N a ­ pproach, requiring that cost partially or fully constrain the scope of each mission such that real- istic science and applications objectives can be accomplished within a reasonable and achievable future budget scenario. F  urther, recognizing that survey-derived cost estimates are by necessity very approximate and that subsequent, more detailed analyses may determine that all of the desired science objectives of a particular mission cannot be achieved at the estimated cost, •  NASA’s ESD should interpret the 2007 decadal survey’s estimates of mission costs as an expression of the relative level of investment that the survey’s authoring committee believed appropriate to advance the intended science and should apportion funds accordingly, even if all desired science objectives for the mission might not be achieved. T  o coordinate decisions regarding mission technical capabilities, cost, and schedule in the context of overarch- ing Earth system science and applications objectives, the committee also recommends that •   ASA’s ESD should establish a cross-mission Earth system science and engineering team to advise N NASA on execution of the broad suite of decadal survey missions within the interdisciplinary con- text advocated by the 2007 decadal survey. The advisory team would assist NASA in coordinating decisions regarding mission technical capabilities, cost, and schedule in the context of overarching Earth system science and applications objectives.7,8 The cost of executing survey-recommended missions has increased, in part because of the lack of availability of a medium-class launch vehicle. To control costs and to optimize the use of scarce fiscal resources, the 2007 decadal survey recommended mostly small- and medium-class missions that could utilize relatively low-cost small- or medium-class launch vehicles (e.g., Pegasus, Taurus, and Delta II). However, the Taurus launch vehicle has failed in its past two launches, and the Delta II is being phased out as the commercial sector focuses on heavier-lift launch vehicles, which are substantially more expensive to procure. Use of such heavy-lift launch vehicles is not generally cost-effective for Earth science missions; indeed, the excess capability and high cost of these vehicles encourage designers to grow their payloads to better match the launcher’s capabilities, which encourages growth in scope and cost. The lack of a reliable and low-cost medium-capability launch vehicle thus directly threatens programmatic robustness. The committee offers the following finding and recommendation concerning the cost and availability of medium-class launch vehicles (see the section “Access to Space” in Chapter 3): Finding: Lack of reliable, affordable, and predictable access to space has become a key impediment to imple- menting NASA’s Earth science program. Furthermore, the lack of a medium-class launch vehicle threatens programmatic robustness. 7The team, similar to the Payload Advisory Panel established by NASA to assist in implementation of its Earth Observing System (EOS), would draw its membership from the scientists and engineers involved in the definition and execution of survey missions as well as the nation’s scientific and engineering talent more broadly. (The Payload Advisory Panel was composed of the EOS Interdisciplinary Science Investigation principal investigators and was formally charged with examining and recommending EOS payloads to NASA based on the scientific require- ments and priorities established by the Earth science community at large. See NASA, Earth Observing System (EOS) Reference Handbook, G. Asrar and D.J. Dokken, eds., Earth Science Support Office, Document Resource Facility, Washington, D.C., 1993.) 8The committee believes that NASA is best positioned to determine whether this advisory panel should be constituted as a Federal Advisory Committee Act-compliant advisory body.

OCR for page 35
44 Space Studies Board Annual Report—2012 R  ecommendation: NASA should seek to ensure the availability of a highly reliable, affordable medium- class launch capability. Another impediment to effective and efficient implementation of the 2007 decadal survey is the lack of a ­national strategy for establishment and management of Earth observations from space. This problem was recognized in the decadal survey report, which stated (as quoted in this midterm assessment report), The committee is concerned that the nation’s institutions involved in civil Earth science and applications from space (including NASA, NOAA, and USGS) are not adequately prepared to meet society’s rapidly evolving Earth information needs. Those institutions have responsibilities that are in many cases mismatched with their authorities and resources: institutional mandates are inconsistent with agency charters, budgets are not well matched to emerging needs, and shared responsibilities are supported inconsistently by mechanisms for cooperation. These are issues whose solutions will require action at high levels of the federal government.9 Such a strategy is perhaps even more important in an era of severe fiscal constraint. Not only is such a strategy important for optimizing NASA’s and the nation’s resources dedicated to Earth system science, but also it is critical to meeting national needs for the results of Earth system science, including the understanding of climate change and land use. The decadal survey recommended that “the Office of Science and Technology Policy, in collabora- tion with the relevant agencies and in consultation with the scientific community, should develop and implement a plan for achieving and sustaining global Earth observations. This plan should recognize the complexity of differing agency roles, responsibilities, and capabilities as well as the lessons from the implementation of the Landsat, EOS, and NPOESS programs.”10,11 Despite this and other subsequent calls from the community for this national strategy, only a preliminary plan has been outlined.12 A more complete plan for achieving and sustaining global Earth observations remains to be presented or funded. However, the recently released NASA Climate-Centric Architecture plan13 includes a set of Climate Continuity missions, tacitly recognizing for the first time NASA’s role in sustained observations associated with climate (see the section “Lack of a National Strategy for Establishment and Management of Earth Observa- tions from Space” in Chapter 3). Finding: The 2007 decadal survey’s recommendation that the Office of Science and Technology Policy develop an interagency framework for a sustained global Earth observing system has not been implemented. The com- mittee concluded that the lack of such an implementable and funded strategy has become a key, but not the sole, impediment to sustaining Earth science and applications from space. Chapter 4 discusses a number of items that should be considered in the formulation of such a national strategy. In addition to cost control measures, the committee considered other ways for ESD to maximize the value of its limited resources. These include the possible augmentation of the Earth Venture-class program discussed below, and use of alternative and/or synergistic platforms or novel flight architectures (including suborbital platforms as previously mentioned), as well as seeking value-added international partnerships. Alternative platforms such as balloons and aircraft (piloted and unpiloted), hosted payloads, small satellites, the International Space Station, and flight formations (for example, the Afternoon Constellation, or “A-Train”) provide NASA with a diverse portfolio 9National Research Council, Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond, 2007, p. 61. 10National Research Council, Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond, 2007, p. 14. 11Following a major restructuring in 2010, the joint NOAA-Air Force procurement of the polar-orbiting satellite system called NPOESS was ended. The NOAA portion of the NPOESS program is now the Joint Polar Satellite System (JPSS). See, U.S. House of Representatives, “From NPOESS to JPSS: An Update on the Nationís Restructured Polar Weather Satellite System,” Hearing Charter, Committee on Science, Space and Technology, Subcommittee on Investigations and Oversight and the Subcommittee on Energy and Environment, September 23, 2011, available at http://science.house.gov/hearing/joint-hearing-investigations-and-oversight-energy-and-environment-subcommittees-polar. 12See “Achieving and Sustaining Earth Observations: A Preliminary Plan Based on a Strategic Assessment by the US Group on Earth Obser- vations,” Office of Science and Technology Policy, September 2010, available at http://www.whitehouse.gov/sites/default/files/microsites/ostp/ ostp-usgeo-report-earth-obs.pdf (accessed November 2011). 13NASA, “Responding to the Challenge of Climate and Environmental Change: NASA’s Plan for a Climate-Centric Architec- ture for Earth Observations and Applications from Space,” available at http://science.nasa.gov/media/medialibrary/2010/07/01/Climate_ Architecture_Final.pdf.

OCR for page 35
Summaries of Major Reports 45 of options for exploring different and, where appropriate, less costly ways of conducting Earth observations and measurements (see the section “Alternative Platforms and Flight Formations” in Chapter 4). Finding: Alternative platforms and flight formations offer programmatic flexibility. In some cases, they may be employed to lower the cost of meeting science objectives and/or maturing remote sensing and in situ observing technologies. Large uncertainties are typical when attempting to factor international partner missions into long-term plans for U.S. Earth observation missions. Nevertheless, the committee found that ESD has made admirable efforts in securing such partnerships (see the section “International Partnerships” in Chapter 4). Finding: NASA has made considerable efforts to secure international partnerships to meet its science goals and operational requirements. STATUS OF PROGRAM ELEMENTS IN NASA’S EARTH SCIENCE PROGRAM In its assessment of NASA’s Earth science program, the committee examined the major individual ­programmatic elements within NASA’s ESD and also considered the overall program’s effectiveness in realizing the ­ bjectives o of the 2007 decadal survey.14 In particular, the committee reviewed the following program elements and also com- mented on NASA’s Climate Continuity missions. The program elements described in this summary are elaborated on in Chapter 2, where they are listed in the same order as they are here: •  Extended missions—missions whose operations have been extended beyond their nominal lifetime; •  Missions in the pre-decadal survey queue—missions that the decadal survey assumed would be launched as precursors to the decadal survey missions; •  Decadal survey missions—new missions recommended by the 2007 decadal survey; •  Climate Continuity missions; •  Earth Venture missions—a class of smaller missions recommended by the decadal survey; •  Applied Sciences Program; •  Suborbital (Earth Science) Program; •  Technology development; and •  Research and analysis. Extended Missions Extended missions (missions that operate and provide data beyond their originally planned and funded mission lifetimes) continue to provide a wealth of observations and measurements of benefit to society and to the Earth science community. Data from extended missions are critical to the operations of users such as NOAA’s National Weather Service; they also provide information of fundamental importance to advance Earth science research. Overall, the committee strongly supports the process of the NASA Earth Science Senior Review that evaluates these missions and makes recommendations concerning their funding and continuation. Missions in the Pre-Decadal Survey Queue The committee supports NASA’s efforts to fly out its pre-decadal survey mission queue, also referred to as “foundational” missions. Unfortunately, delays, changes in scope, and launch failures15 have hindered progress in implementing the pre-decadal survey mission queue. 14A full listing of all the findings and recommendations in the 2007 decadal survey, as well as responses to each of those from NASA in 2009 and updated responses presented to the committee in April 2011, is available in Appendix E. 15Two important NASA missions—Glory and Orbiting Carbon Observatory (OCO)—were lost because of launch vehicle failures. Lack of reliable, affordable, and predictable access to space has now become a key impediment to implementing NASA’s Earth science program.

OCR for page 35
66 Space Studies Board Annual Report—2012 Implementation of a program to advance space weather and climatology will require funding well above what the survey committee assumes will be available to support its research-related recommendations to NASA (see Table S.1). The committee emphasizes that implementation of an initiative in space weather and climatology should proceed only if it does not impinge on the development and timely execution of the recommended research program. RECOMMENDED PROGRAM, DECISION RULES, AND AUGMENTATION PRIORITIES FOR NASA Recommended Program The committee’s recommended program for NASA Heliophysics Division is shown in Figure S.1. As detailed in Chapter 6, the plan restores the medium-class Explorers and, together with small-class Explorer missions and Missions of Opportunity, achieves the recommended minimum mission cadence. The plan also begins the DRIVE initiative as early in the decade as budgets allow, with full implementation achieved by mid-decade. However, fund- ing constraints affect the restoration and recommended rebalance of heliophysics program elements such that full realization of the survey committee’s strategy is not possible until after 2017 (Figure S.1). Decision Rules to Ensure Balanced Progress is Maintained The recommended program for NASA cost-effectively addresses key science objectives. However, the survey committee recognizes that the already tightly constrained program could face further budgetary challenges. For example, with launch planned in 2018, the Solar Probe Plus project has not yet entered the implementation phase when expenditures are highest.7 Significant cost growth in this very important, but technically challenging, mission beyond the current cap has the potential to disrupt the overall NASA heliophysics program. To guide the allocation of reduced resources, the committee recommends the following decision rules intended to provide flexibility and efficiency if funding is less than anticipated, or should some other disruptive event occur. These rules, discussed in greater depth in Chapter 6, maintain progress toward the top-priority, system-wide science challenges identified in this survey. The decision rules should be applied in the order shown to minimize disruption of higher-priority program elements:  ecision Rule 1. Missions in the STP and LWS lines should be reduced in scope or delayed to accomplish D higher priorities (Chapter 6 gives explicit triggers for review of Solar Probe Plus).  ecision Rule 2. If further reductions are needed, the recommended increase in the cadence of Explorer mis- D sions should be scaled back, with the current cadence maintained as the minimum.  ecision Rule 3. If still further reductions are needed, the DRIVE augmentation profile should be delayed, with D the current level of support for elements in the NASA research line maintained as the minimum. Augmentations to Increase Program Value The committee notes that the resources assumed in crafting this decadal survey’s recommended programs are barely sufficient to make adequate progress in solar and space physics; with reduced resources, progress will be inadequate. It is also evident that with increased resources, the pace at which the nation pursues its program could be accelerated with a concomitant increase in the achievement of scientific discovery and societal value. The com- mittee recommends the following augmentation priorities to aid in implementing a program under a more favorable budgetary environment:  ugmentation Priority 1. Given additional budget authority early in the decade, the implementation of the A DRIVE initiative should be accelerated. 7 On January 31, 2012, Solar Probe Plus passed its agency-level confirmation review and entered what NASA refers to as mission definition or Phase B of its project life cycle.

OCR for page 35
Summaries of Major Reports 67 $1,000 $900 Enabling Budget $800 FY2012 Budget $700 LWS - GDC Annual Budget (RY$million) $600 Solar Probe Plus $500 STP - DYNAMIC STP - IMAP $400 Existing LWS Existing Explorer Augmentation $300 STP Future Explorer $200 DRIVE Existing Explorer $100 Research $0 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 FIGURE S.1  Heliophysics budget and program plan by year and category from 2013 to 2024. The solid black line indicates the funding level from 2013 to 2022 provided to the committee by NASA as the baseline for budget planning, and the dashed black line extrapolates the budget forward to 2024. After 2017 the amount increases with a nominal 2 percent inflationary factor. Through 2016 the program content is tightly constrained by budgetary limits and fully committed for executing exist- ing program elements. The red dashed “Enabling Budget” line includes a modest increase from the baseline budget starting in 2017, allowing implementation of the survey-recommended program at a more efficient cadence that better meets scientific and societal needs and improves optimization of the mix of small and large missions. From 2017 to 2024 the Enabling Budget grows at 1.5 percent above inflation. (Note that the 2024 Enabling Budget is equivalent to growth at a rate just 0.50 percent above inflation from 2009.) GDC, the next large mission of the LWS program after SPP, rises above the baseline curve in order to achieve a more efficient spending profile, as well as to achieve deployment in time for the next solar maximum in 2024. NOTE: LWS refers to missions in the Living With a Star line and STP refers to missions in the Solar-Terrestrial Probes line.  ugmentation Priority 2. With sufficient funds throughout the decade, the Explorer line should be further aug- A mented to increase the cadence and funding available for missions, including Missions of Opportunity.  ugmentation Priority 3. Given further budget augmentation, the schedule of STP missions should advance to A allow the third STP science target (MEDICI) to begin in this decade.  ugmentation Priority 4. The next LWS mission (GDC) should be implemented with an accelerated, more A cost-effective funding profile.

OCR for page 35
68 Space Studies Board Annual Report—2012 EXPECTED BENEFITS OF THE RECOMMENDED PROGRAM Implementation of the survey committee’s recommended programs will ensure that the United States maintains its leadership in solar and space physics and, the committee believes, lead to significant—even transformative—­ advances in scientific understanding and observational capabilities (Table S.3). In turn, these advances will support critical national needs for information that can be used to anticipate, recognize, and mitigate space weather effects that threaten to human life and the technological systems society depends on. TABLE S.3  Fulfilling the Science Goals of the Decadal Survey Advances in Scientific Understanding and Observational Capabilities Goals Advances due to Twin Radiation Belt Storm Probes will observe Earth’s radiation belts from separate locations, finally 2, 4 Implementation of the resolving the importance of temporal and spatial variability in the generation and loss of trapped existing program radiation that threatens spacecraft. The Magnetospheric Multiscale mission will provide the first high-resolution, three-dimensional 2, 4 measurements of magnetic reconnection in the magnetosphere, by sampling small regions where magnetic field line topologies reform. Solar Probe Plus will be the first spacecraft to enter the outer atmosphere of the Sun, repeatedly 1, 4 sampling solar coronal particles and fields to understand coronal heating, solar wind acceleration, and formation and transport of energetic solar particles. Solar Orbiter will provide the first high-latitude images and spectral observations of the Sun’s magnetic 1, 4 field, flows, and seismic waves, relating changes seen in the corona to local measurements of the resulting solar wind. The 4-meter Advanced Technology Solar Telescope will resolve structures as small as 20 km, 1, 4 measuring the dynamics of the magnetic field at the solar surface down to the fundamental density length scale and in the low corona. The Heliophysics Systems Observatory will gather a broad range of ground- and space-based All observations and advance increasingly interdisciplinary and long-term solar and space physics science objectives. New starts on programs The DRIVE initiative will greatly strengthen our ability to pursue innovative observational, theoretical, All and missions to be numerical, modeling, and technical advances. implemented within the Solar and space physicists will accomplish high-payoff, timely science goals with a revitalized All next decade Explorer program, including leveraged Missions of Opportunity. The Interstellar Mapping and Acceleration Probe, in conjunction with the twin Voyager spacecraft, will 2, 3, 4 resolve the interaction between the heliosphere, our home in space, and the interstellar medium. A new funding line for mid-size projects at the National Science Foundation will facilitate long- All recommended ground-based projects, such as COSMO and FASR, by closing the funding gap between large and small programs. New starts on missions The Dynamical Neutral Atmosphere-Ionosphere Coupling mission’s two identical orbiting 2, 4 to be launched early in observatories will clarify the complex variability and structure in near-Earth plasma driven by lower the next decade atmospheric wave energy. The Geospace Dynamics Constellation will provide the first simultaneous, multipoint observations of 2, 4 how the ionosphere-thermosphere system responds to, and regulates, magnetospheric forcing over local and global scales. Possible new start this The Magnetosphere Energetics, Dynamics, and Ionospheric Coupling Investigation will target 2, 4 decade given budget complex, coupled, and interconnected multi-scale behavior of the magnetosphere-ionosphere system augmentation and/or by providing global, high-resolution, continuous three-dimensional images and multi-point in situ cost reduction in other measurements of the ring current, plasmasphere, aurora, and ionospheric-thermospheric dynamics. missions

OCR for page 35
Summaries of Major Reports 69 5.7 Technical Evaluation of the NASA Model for Cancer Risk to Astronauts Due to Space Radiation A Report of the SSB Ad Hoc Committee for Evaluation of Space Radiation Cancer Risk Model Summary At the request of NASA, the National Research Council’s (NRC’s) Committee for Evaluation of Space ­Radiation Cancer Risk Model1 reviewed a number of changes that NASA proposes to make to its model for estimat- ing the risk of radiation-induced cancer in astronauts. The NASA model in current use was last updated in 2005, and the proposed model would incorporate recent research directed at improving the quantification and understanding of the health risks posed by the space radiation environment. NASA’s proposed model is defined by the 2011 NASA report Space Radiation Cancer Risk Projections and Uncertainties—2010 (Cucinotta et al., 2011). The com­ ittee’s m evaluation is based primarily on this source, which is referred to hereafter as the 2011 NASA report, with mention of specific sections or tables cited more formally as Cucinotta et al. (2011). The overall process for estimating cancer risks due to low linear energy transfer (LET)2 radiation exposure has been fully described in reports by a number of organizations. They include, more recently: • The “BEIR VII Phase 2” report from the NRC’s Committee on Biological Effects of Ionizing Radiation (BEIR) (NRC, 2006);3 • Studies of Radiation and Cancer from the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 2006), • The 2007 Recommendations of the International Commission on Radiological Protection (ICRP), ICRP Publication 103 (ICRP, 2007); and • The Environmental Protection Agency’s (EPA’s) report EPA Radiogenic Cancer Risk Models and Projections for the U.S. Population (EPA, 2011). The approaches described in the reports from all of these expert groups are quite similar. NASA’s proposed space radiation cancer risk assessment model calculates, as its main output, age- and gender-specific risk of e ­ xposure-induced death (REID) for use in the estimation of mission and astronaut-specific cancer risk. The model also calculates the associated uncertainties in REID. The general approach for estimating risk and uncertainty in the proposed model is broadly similar to that used for the current (2005) NASA model and is based on recommendations by the National Council on Radiation Pro- tection and Measurements (NCRP, 2000, 2006). However, NASA’s proposed model has significant changes with respect to the following: the integration of new findings and methods into its components by taking into account newer epidemiological data and analyses, new radiobiological data indicating that quality factors differ for leukemia and solid cancers, an improved method for specifying quality factors in terms of radiation track structure concepts as opposed to the previous approach based on linear energy transfer, the development of a new solar particle event (SPE) model, and the updates to galactic cosmic ray (GCR) and shielding transport models. The newer epidemio- logical information includes updates to the cancer incidence rates from the life span study (LSS) of the Japanese atomic bomb survivors (Preston et al., 2007), transferred to the U.S. population and converted to cancer mortality rates from U.S. population statistics. In addition, the proposed model provides an alternative analysis applicable to lifetime never-smokers (NSs). Details of the uncertainty analysis in the model have also been updated and revised. NASA’s proposed model and associated uncertainties are complex in their formulation and as such require a very clear and precise set of descriptions. The committee found the 2011 NASA report challenging to review largely because of the lack of clarity in the model descriptions and derivation of the various parameters used. The commit- NOTE: “Summary” reprinted from Technical Evaluation of the NASA Model for Cancer Risk to Astronauts Due to Space Radiation, The National Academies Press, Washington, D.C., 2012, pp. 1-8. 1Biographical information about the members of the committee is presented in Appendix B. 2See Appendix C, “Glossary and Acronyms,” for definitions of terms and acronyms. 3The BEIR VII Phase 2 report is the most recent in a series of reports by NRC committees dealing with ionizing radiation; these are widely known as the BEIR reports.

OCR for page 35
70 Space Studies Board Annual Report—2012 tee requested some clarifications from NASA throughout its review and was able to resolve many, but not all, of the ambiguities in the written description. PROPOSED MODEL—OVERALL CONCLUSION In considering NASA’s proposed model as a whole, the committee noted that the general approach to estimating cancer risks from exposure to low-LET radiation follows that utilized by ICRP, NCRP, EPA, and BEIR VII, and as such is state of the art. The specific data incorporated into NASA’s proposed model are generally appropriate, with some exceptions, noted below, relating to new data that have become available since the development of the model or additional data sets that were already available and not selected for use by NASA. There remains a need for develop- ment of additional data to enhance the current approach and to reduce uncertainty in the model; specific needs have been identified by the committee. The committee has some concerns about specific model components, particularly related to the change to an “incidence-mortality” approach for calculating mortality and to the risk-transfer approach used by NASA. The question of the effectiveness of the combination of the several modules into the proposed inte- grated model was most appropriately answered by the committee’s observing of a live demonstration by NASA of the application of the model for assessing risk to astronauts under some selected specific mission conditions. This demonstration showed that the model was indeed an integrated one—something that was not immediately apparent from the rather complex descriptions provided in the 2011 NASA report. The committee’s overall evaluation is that NASA’s proposed model represents a definite improvement over the current one. However, the committee urges that the necessary improvements identified in the specific recommendations provided below be incorporated before the proposed integrated model is implemented. NASA’s proposed model is composed of a number of components or modules that separately address highly distinct aspects of radiation risk and uncertainty. The committee assessed each of the individual components of the model as well as the integrated model as a whole. The key results of its evaluations are summarized below. Possible improvements to components of the model and to the integrated model are provided, together with recommenda- tions for addressing gaps in the model. In some cases, specific research is identified that could help NASA address gaps and/or uncertainties in its proposed model for cancer risk projections. The specific research identified is not necessarily a comprehensive list but is intended to include efforts that would have a significant impact and at the same time would be feasible to undertake within the short to medium term (less than 5 years). The recommendations provided in this Summary address those areas for which the committee perceived more substantial gaps or issues. The model components are discussed in more detail in the main body of the report (see Chapter 2), which contains advice in addition to the major recommendations and conclusions. It is the integrated model that will actually be implemented by NASA, and so it is also assessed in detail in Chapter 2 of this report, particularly with regard to the integration methodology. PROPOSED MODEL—ASSESSMENT OF COMPONENTS Tissue-Specific Particle Spectra The committee considers that the radiation environment and shielding transport models used in NASA’s pro- posed model are a major step forward compared to previous models used. This is especially the case for the statistical solar particle event model. The current models have been developed by making extensive use of available data and rigorous mathematical analyses. The uncertainties conservatively allocated to the space physics ­ arameters (i.e., p environment and shielding transport models) are deemed to be adequate at this time, considering that the space physics uncertainty is only a minor contributor to the overall cancer risk assessment. Although further research in this area could reduce the uncertainty, the law of diminishing returns may prevail. Given the above considerations, the committee does not recommend any specific research to improve the pro- posed model for tissue-specific particle spectra at this time. However, in this report the committee has identified sev- eral specific research areas that could improve the proposed environment models for tissue-specific particle spectra, including additional statistical analysis of the radial dependence of SPE intensity and solar-cycle dependence of SPE frequency and extreme events. The estimates could be further improved by adding physics-based studies of particle transport using the current picture of the heliosphere and its magnetic fields. Particle transport in the interplanetary medium is determined by its electric and magnetic fields. Theoretical and numerical studies of particle trajectories

OCR for page 35
Summaries of Major Reports 71 would certainly result in improved transport models and smaller uncertainties in the environmental estimates, but would involve a major effort and a change in modeling approach. NASA would need to weigh the added value of such an approach to its model outputs. Cancer Risk Projection Model for Low-LET Exposures Epidemiology Data A major change proposed in NASA’s model is to use the “incidence-mortality” approach used by BEIR VII (NRC, 2006) for the development of a REID. For this approach, risk coefficients from LSS cancer incidence models are converted into cancer mortality risks. A major reason for the use of the LSS cancer incidence data is that these are likely to be more accurate with respect to diagnosis than are mortality data, which suffer from misclassification of causes on death certificates. The approach results in considerable changes in the REID estimates, particularly in the pattern with age at exposure, and the committee considers this to be an improvement for site-specific cancer mortality estimation. Recommendation: Before NASA implements its proposed major change to the “incidence-mortality” a ­ pproach, the committee recommends that NASA conduct more research into the specific patterns of the underlying epidemiological biases that drive these changes. The committee also highlights a specific problem with the method of estimating the mortality probability from the ratio of cancer mortality to incidence as developed by the BEIR VII report published by the National Research Council in 2006 and proposed for use by NASA. In response, the committee recommends that NASA consider alternative methods for improved estimation of mortality probabilities for each cancer site. For example, as presented in its 2011 report EPA Radiogenic Cancer Risk Models and Projections for the U.S. Population, the Environmental Protection Agency has developed an alternative approach for breast cancer mortality estimation, and this could serve as a suitable approach to be applied by NASA. Transfer of Cancer Risk Estimates from the Japanese to the U.S. Population Because underlying cancer incidence rates for some cancer sites differ greatly between the Japanese and the U.S. populations, risk estimates based on an excess relative risk (ERR) model can give REID values very different from those based on an excess absolute risk (EAR) model. A number of organizations and committees (ICRP, the National Council on Radiation Protection and Measurements [NCRP], BEIR VII) have recommended that a site- specific weighted average of the ERR and EAR models be used. The proposed NASA approach follows BEIR VII (NRC, 2006) in calculating a weighted average with uncertain weights and generally follows the recommended BEIR VII weights. Recommendation: Because there are some deviations in NASA’s proposed model from the weights recom- mended by BEIR VII for the excess relative risk and excess absolute risk models, the committee recommends that NASA provide additional justification for these alternative weights. Dose and Dose Rate Effectiveness Factor A dose and dose rate effectiveness factor (DDREF) value is applied, when appropriate, to reduce the LSS- based cancer risk coefficients for protracted exposures. A median value of 1.75 was selected by NASA for its proposed model, based on an assessment made by the National Institutes of Health (NIH) for a previous estimate and its uncertainty (NIH, 2003). For its proposed model, NASA assumed that the DDREF applies only to low-LET radiations and consequently that there is no dependence of space radiation risks on dose rate. Differences in risks between space radiation charged particles and gamma rays at low dose rate are encompassed entirely within the quality factor, QF, discussed below. A number of publications issued since the NIH report are relevant to this issue, and although these were discussed in the 2011 NASA report, they were not used by NASA in its choice of DDREF or in the associated uncertainty analysis. These studies include the Mayak workers study (Shilnikova et al., 2003), the third analysis of the United Kingdom’s National Registry for Radiation Workers (Muirhead et al., 2009), and

OCR for page 35
72 Space Studies Board Annual Report—2012 the 15-country nuclear workers study (Cardis et al., 2007), together with the review of these studies and comparison with the life span study by Jacob et al. (2009). Conclusion: Although the proposed NASA approach for estimating a DDREF describes a number of limi- tations in these newer epidemiological studies and in the BEIR VII DDREF methodology, the justification given for preferring the older approach taken by the National Institutes of Health in 2003 is that it is close to the average of various recommended values of slightly less than 2. The use of this average value is somewhat problematic, given that the recommended values used to derive this average are not independent and thus applying equal weights to these is not justifiable. Recommendation: The committee agrees with the use of an uncertainty approach for estimating DDREF, but it recommends that NASA use a central value and distribution that better accounts for the recent epide- miological and laboratory animal data. Risk Models for Never-Smokers The issue of the smoking status of astronauts and the potential implications for risk projections for smoking- related cancers are important, and it is appropriate that this should be investigated. Most astronauts are non-smokers, which would likely lower the risk projections for astronauts compared to estimates for the general population (a mix of never- and ever-smokers). Recommendation: The proposed NASA approach for estimating lung cancer risks for astronauts who are never-smokers is limited and does not consider competing risks. Thus, the committee recommends that the NASA approach be developed further, given the important impact that it has on reducing estimated risk. The revised approach should use survival probabilities for competing risks that are specific to never-smokers. F ­ urther, the committee recommends that NASA make no changes at this time in the proposed model to i ­ nclude other smoking-related cancers. The data are not sufficiently robust for use in the modification of the REID estimate. Uncertainties in Low-LET Cancer Risk Model and Overall Uncertainties in Cancer Risk Projections for High-LET Exposures The 2011 NASA report addresses risk estimates and their uncertainties associated with exposure to low-LET radiation. Uncertainties are important because risk protection involves the use of safety factors, and NASA sets radiation permissible exposure limits (PELs) based on the 95 percent confidence limit that takes into account the uncertainties in risk projection models (NASA, 2005). Uncertainty Limits and Methodology Conclusion: Uncertainty limits on radiation-related risk reflect information about anticipated environmental radiation dose levels and accumulated knowledge about the relationship between radiation dose and cancer risk. For the approach used by NASA, more information, if available, might reduce statistical uncertainty and, assuming that the new information did not increase the central risk estimate, lower the upper 95 percent uncertainty bound criterion used by NASA to evaluate the acceptability of activity-related mortality risk. Maximum Likelihood and Empirical Bayes Estimates In the 2011 NASA report’s description of the proposed model, the discussion of the use of a maximum likeli- hood estimate (MLE) and/or empirical Bayes (EB) estimate of site-specific ERR per sievert is ambiguous with respect to the specific approach that was used in specific instances. For example, the site-specific EB estimate of ERR per sievert for kidney cancer (0.40) would be similar to the MLE (also 0.40 for this particular organ site), with a lower estimated standard error (0.19) compared to the MLE standard error of 0.32.

OCR for page 35
Summaries of Major Reports 73 Recommendation: On the assumption that the empirical Bayes approach has been used in NASA’s proposed model, the committee recommends that the authors ensure that the off-diagonal covariance information has been taken into account. If the EB approach has not been used, either this fact should be stated in the text of the 2011 NASA report (Cucinotta et al., 2011) or the references to the EB approach should be removed from the text. Uncertainty in the Value of the Quality Factor The uncertainty analysis in NASA’s proposed model reveals that the value of the quality factor (QF, as defined in NASA’s proposed model) is the largest contributor to the uncertainty of REID, introducing about a 3.4-fold uncertainty in risk. Additional analysis by NASA (Cucinotta et al., 2011) using its proposed model finds that this component could be reduced to a 2.8-fold uncertainty if two of the track structure parameters were constrained to a fixed algebraic relationship to one another (such that the Z*2/β2 position of the maximum value of QF is held fixed). In this context, the committee notes that different values of QF are used for leukemia and solid cancers based on recent studies using animal tumor models. Conclusion: According to NASA’s proposed model, the observation that the use of a fixed relationship b ­ etween two track structure parameters reduces the uncertainty is a potentially valuable finding that may provide a method to reduce uncertainty in estimations of the risk of exposure-induced death. However, little indication is given in the 2011 NASA report as to why such a fixed position might be justified or expected. The committee suggests that further investigations into the validity and usefulness of this approach would be worthwhile. Radiation Quality and Track Structure Risk Cross Section The main parameter used to specify radiation quality is Z*2/β2, where Z* is the effective charge number of the particle and β its speed relative to the speed of light. Z*2/β2 replaces LET used in the conventional quality factor definition, and also by NASA in its current model. However, three additional empirical parameters (κ, Σ0/αγ, and m) are introduced to define the quality factor-risk relationships as a function of Z*2/β2. For NASA’s proposed model, values for these parameters have been selected by comparison with experimentally observed variations in relative biological effectiveness (RBE) for different types of radiation for various cellular biological effects and for selected cancer types. While this approach is broadly appropriate for the proposed model parameters, the committee was ­unable to determine from the 2011 NASA report or from inquiries how the particular parameter values were selected. Recommendation: The committee recommends that NASA make a detailed comparison of the relative biological effectiveness versus Z*2/β2 dependence of the experimental data with the proposed form and p ­ arameters of the quality factor, QF, equation in order to improve the transparency of the basis for the selection of the proposed parameter values for the model and to provide guidance for future research to test, validate, modify, and/or extend the parameterization. This analysis needs to include the defined selection of different values for parameters κ and Σ0/αγ for ions of Z ≤ 4 compared to all ions of higher charge. Conclusion: In the proposed model, different maximum values of quality factor, QF, are assumed for leuke- mia (maximum 10) and for solid tumors (maximum 40). This is a change from the current NASA risk model. The committee agrees that it is reasonable to make such a distinction on the basis of the limited animal and human data available. Effective Dose NASA’s proposed model defines a quantity that is analogous to “effective dose” as defined by ICRP, but it uses different gender-specific sets of normalized tissue weighting factors (wT) to match the estimated risks to the various tissues in representative space radiation environments. NASA proposes to use this as a summary quantity for mission operational purposes and, in NASA’s proposed model, it is simply termed “effective dose.” Effective dose is, strictly speaking, a quantity defined by ICRP that includes the ICRP-defined specification of numerical values for weighting

OCR for page 35
74 Space Studies Board Annual Report—2012 factors and sex-averaging. If considerably different tissue weighting factors and radiation quality specifications are used and “effective dose” is evaluated without sex-averaging, it is problematic for the resulting quantity still to be termed “effective dose,” and the unit sievert given to its numerical values. The committee believes that the NASA description of the proposed model would be improved by the use of terminology and notation that distinguish NASA-defined quantities (especially the quantity termed “effective dose”) from quantities defined by ICRP. Other Issues Non-Cancer Effects (Tissue Reactions) In its proposed approach to estimating the safe days in deep space, NASA has used a 3 percent REID for f ­ atal cancer as the limit. In its current model, NASA also considers dose limits for non-cancer effects—lens, skin, blood-forming organs, heart, and central nervous system. For example, “career limits for the heart are intended to limit the REID for heart disease to be below approximately 3 to 5 percent, and are expected to be largely age and sex independent” (NASA, 2005, p. 65). It was further assumed by NASA that the limits established would restrict mortality values for these non-cancer effects to less than the risk level for cancer mortality. The cancer and non- cancer risks were not combined into a single REID. More recent data have led ICRP to reconsider the threshold dose values particularly for the cardiovascular system (and cataracts) (see ICRP, 2011). It is concluded by ICRP (2011) that a threshold absorbed dose of 0.5 Gy should be considered for cardiovascular disease (and cataracts) for acute and for fractionated/protracted exposures. It is appreciated by ICRP that these values have a degree of uncertainty associated with them. Conclusion: The revised value for the threshold dose value proposed by ICRP suggests that NASA may need to consider how it might account for cardiovascular disease in its calculations of dose limits. However, it is noted that to date there exists very little of the information on relative biological effectiveness for non-cancer effects that is needed for estimates of risks posed by exposure to space radiation. Delayed Effects Delayed effects pertinent to the assessment of risk principally relate to observations whereby ongoing r ­ adiation-induced genomic instability is expressed, even at long times after radiation exposure. Such effects could have important implications for radiation protection in view of current notions of the multistep mutational processes involved in carcinogenesis. An early induced change in subsequent and ongoing mutation rates in irradiated somatic cells could accelerate this process. Conclusion: There are conflicting reports on the generality of the phenomenon of radiation-induced delayed genomic instability and some question about variation in the susceptibilities of cells from different individuals with regard to this effect. Thus, the committee concludes that it is appropriate that genomic instability not be incorporated into NASA’s proposed model, in agreement with the proposed NASA approach. However, the committee considers that further investigation of the phenomenon is certainly warranted. Non-Targeted Effects Non-targeted effects (NTEs) largely refer to the so-called bystander effects, by which responses can be pro- duced in an unirradiated cell as a result of the transfer of a signal from an irradiated cell. For high atomic number and energy (HZE) radiations, doses that may be received by astronauts are very non-uniform in the sense that some cells will be traversed by the primary particle itself, whereas other cells will not be traversed; thus, an NTE is also a phenomenon that is of considerable interest. Conclusion: Although the 2011 NASA report (Cucinotta et al., 2011) contains an extended discussion on non- targeted effects and their potential impact on risk estimates, NASA appropriately chose not to include these NTEs in its proposed model at this time. Little is known in qualitative or quantitative terms of the contribution

OCR for page 35
Summaries of Major Reports 75 of these NTEs directly related to radiation-induced carcinogenesis, but the committee believes that studies to elucidate any such relevance should be encouraged. Qualitative Differences It is recognized that there are qualitative differences in the nature of the initial energy depositions and hence in initial chemical, biochemical, and biological damages from different types of ionizing radiation. Differences are particularly great between low-LET gamma rays and the wide variety of high-LET heavy ions in space radiation. This may lead to observed differences in responses of cells, tissues, and organisms such as differences in spectra of mutations and chromosome aberrations, altered gene-expression patterns, and different spectra and latencies for carcinogenesis. There is some experimental evidence for qualitative differences at each of the above levels of biological effect. As a result, it may not be entirely appropriate to apply universal values for quality factors as quan- titative scaling factors, based on empirical data such as RBE that assume similar underlying biological processes. The committee notes that this is an area in which experiments quantifying types, frequencies, and latencies of various cancers—for example, lung, colon, and breast cancer, with further study of liver cancer and leukemia—are sorely needed for radiations of varying LET, especially for high-LET particles at low particle fluences such as occur in space. Furthermore, the committee suggests that the tumor studies should be coupled with appropriate m ­ echanistic investigations to provide an understanding of the underlying carcinogenic processes. Probabilistic Risk Assessment The committee notes that the risk projections discussed in NASA’s proposed space radiation cancer risk assess­ ent model and uncertainties are not presented or intended as being based on a probabilistic risk assessment m (PRA) approach. NASA’s proposed model is a health-effects model intended to provide estimates of cancer risk and uncertainties for defined space radiation exposure scenarios. More generally, however, the cancer risk to astronauts is dependent on much more than a defined scenario model of health effects, with engineered barriers, in the space radiation environment. Experience with full-scope PRAs of complex systems indicates the importance of account- ing for the “what can go wrong during actual operations” scenarios, as such scenarios generally drive the overall risk. Thus, the committee suggests that comprehensive, mission-specific PRAs also be considered so as to enable accountability for the “what can go wrong” scenarios in the overall risk projections. REFERENCES Cardis, E., Vrijheid, M., Blettner, M., Gilbert, E., Hakama, M., Hill, C., Howe, G., Kaldor, J., Muirhead, C.R., Schubauer-Berigan, M., and Yoshimura, T., et al. 2007. The 15-Country Collaborative Study of Cancer Risk among Radiation Workers in the Nuclear Industry: Estimates of Radiation-Related Cancer Risks. Radiation Research 167(4):396-416. Cucinotta, F.A., Kim, M.-H.Y., and Chappell, L.J. 2011. Space Radiation Cancer Risk Projections and Uncertainties—2010. NASA/TP-2011- 216155. NASA Johnson Space Center, Houston, Tex. July. EPA (Environmental Protection Agency). 2011. EPA Radiogenic Cancer Risk Models and Projections for the U.S. Population. U.S. Environ- mental Protection Agency, Washington, D.C. ICRP (International Commission on Radiological Protection). 2007. The 2007 Recommendations of the International Commission on ­Radiological Protection. ICRP Publication 103. Ann ICRP 37 (2-4). International Commission on Radiological Protection, Ottawa, Ontario, Canada. ICRP. 2011. Early and Late Effects of Radiation in Normal Tissues and Organs: Threshold Doses for Tissue Reactions in a Radiation Protec- tion Context. Draft Report for Consultation. ICRP Ref 4844-6029-7736. International Commission on Radiological Protection, Ottawa, Ontario, Canada. January 20. Jacob, P., Ruhm, W., Walsh, L., Blettner, M., Hammer, G., and Zeeb, H. 2009. Is cancer risk of radiation workers larger than expected? Occupa­ tional and Environmental Medicine 66:789-796. Muirhead, C.R., O’Hagan, J.A., Haylock, R.G.E., Phillipson, M.A., Willcock, T., Berridge, G.L.C., and Zhang, W. 2009. Mortality and cancer incidence following occupational radiation exposure: Third analysis of the National Registry for Radiation Workers. British Journal of Cancer 100:206-212. NASA (National Aeronautics and Space Administration). 2005. NASA Space Flight Human System Standard, Volume 1: Crew Health. NASA- STD-3001. (Approved 03-05-2007) NASA, Washington, D.C. NCRP (National Council on Radiation Protection and Measurements). 2000. Radiation Protection Guidance for Activities in Low-Earth Orbit. NCRP Report No. 132. NCRP, Bethesda, Md. NCRP. 2006. Information Needed to Make Radiation Protection Recommendations for Space Missions Beyond Low-Earth Orbit. NCRP Report No. 153. NCRP, Bethesda, Md.

OCR for page 35
76 Space Studies Board Annual Report—2012 NIH (National Institutes of Health). 2003. Report of the NCI-CDC Working Group to Revise the 1985 NIH Radioepidemiological Tables. NIH Publication No. 03-5387. Bethesda, Md. NRC (National Research Council). 2006. Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2. The National Academies Press, Washington, D.C. Preston, D.L., Ron, E., Tokuoka, S., Funamoto, S., Nishi N., Soda, M., Mabuchi, K., and Kodama, K. 2007. Solid cancer incidence in atomic bomb survivors: 1958-1998. Radiation Research 168:1-64. Shilnikova, N.S., Preston, D.L., Ron, E., Gilbert, E.S., Vassilenko, E.K., Romanov, S.A., Kuznetsova, I.S., Sokolnikov, M.E., Okatenko, P.V., Kreslov, V.V., and Koshurnikova, N.A. 2003. Cancer mortality risk among workers at the Mayak Nuclear Complex. Radiation ­Research 159(6):787-798. UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation). 2006. Studies of Radiation and Cancer. Report to the General Assembly, with Scientific Annexes A and B. United Nations. New York.