Radiation Hazards to Crews of Interplanetary Missions

Biological Issues and Research Strategies

Task Group on the Biological Effects of Space Radiation

Space Studies Board

Commission on Physical Sciences, Mathematics, and Applications

National Research Council

NATIONAL ACADEMY PRESS
Washington, D.C.
1996



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--> Radiation Hazards to Crews of Interplanetary Missions Biological Issues and Research Strategies Task Group on the Biological Effects of Space Radiation Space Studies Board Commission on Physical Sciences, Mathematics, and Applications National Research Council NATIONAL ACADEMY PRESS Washington, D.C. 1996

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--> NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committees responsible for the report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is interim president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce Alberts and Dr. William A. Wulf are chairman and interim vice chairman, respectively, of the National Research Council. Support for this project was provided by Contract NASW 4627 and Contract NASW 96013 between the National Academy of Sciences and the National Aeronautics and Space Administration. Copyright 1996 by the National Academy of Sciences. All rights reserved. Copies of this report are available from Space Studies Board National Research Council 2101 Constitution Avenue, N.W. Washington, D.C. 20418 Printed in the United States of America

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--> TASK GROUP ON THE BIOLOGICAL EFFECTS OF SPACE RADIATION RICHARD SETLOW, Brookhaven National Laboratory, Chair JOHN F. DICELLO, Johns Hopkins University School of Medicine R.J. MICHAEL FRY, Oak Ridge National Laboratory JOHN B. LITTLE, Harvard University School of Public Health R. JULIAN PRESTON, Chemical Industry Institute of Toxicology JAMES B. SMATHERS, University of California, Los Angeles ROBERT L. ULLRICH, University of Texas Medical Branch, Galveston SANDRA J. GRAHAM, Study Director SHOBITA PARTHASARATHY, Research Assistant VICTORIA P. FRIEDENSEN, Former Senior Program Assistant CATHY GRUBER, Senior Program Assistant

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--> SPACE STUDIES BOARD CLAUDE R. CANIZARES, Massachusetts Institute of Technology, Chair MARK R. ABBOTT, Oregon State University JOHN A. ARMSTRONG,* IBM Corporation (retired) JAMES P. BAGIAN, Environmental Protection Agency DANIEL N. BAKER, University of Colorado LAWRENCE BOGORAD, Harvard University DONALD E. BROWNLEE, University of Washington JOHN J. DONEGAN, John Donegan Associates, Inc. GERARD W. ELVERUM, JR., TRW Space and Technology Group ANTHONY W. ENGLAND, University of Michigan DANIEL J. FINK,* D.J. Fink Associates, Inc. MARTIN E. GLICKSMAN, Rensselaer Polytechnic Institute RONALD GREELEY, Arizona State University BILL GREEN, former member, U.S. House of Representatives NOEL W. HINNERS,* Lockheed Martin Astronautics Company ANDREW H. KNOLL, Harvard University JANET G. LUHMANN, University of California, Berkeley JOHN H. McELROY,* University of Texas, Arlington ROBERTA BALSTAD MILLER, CIESIN BERRIEN MOORE III, University of New Hampshire KENNETH H. NEALSON, University of Wisconsin MARY JANE OSBORN, University of Connecticut Health Center SIMON OSTRACH, Case Western Reserve University MORTON B. PANISH, AT&T Bell Laboratories (retired) CARLÉ M. PIETERS, Brown University MARCIA J. RIEKE, University of Arizona JOHN A. SIMPSON, Enrico Fermi Institute ROBERT E. WILLIAMS, Space Telescope Science Institute MARC S. ALLEN, Director *   Former member.

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--> COMMISSION ON PHYSICAL SCIENCES, MATHEMATICS, AND APPLICATIONS ROBERT J. HERMANN, United Technologies Corporation, Co-chair W. CARL LINEBERGER, University of Colorado, Co-chair PETER M. BANKS, Environmental Research Institute of Michigan LAWRENCE D. BROWN, University of Pennsylvania RONALD G. DOUGLAS, Texas A&M University JOHN E. ESTES, University of California, Santa Barbara L. LOUIS HEGEDUS, Elf Atochem North America, Inc. JOHN E. HOPCROFT, Cornell University RHONDA J. HUGHES, Bryn Mawr College SHIRLEY A. JACKSON, U.S. Nuclear Regulatory Commission KENNETH H. KELLER, University of Minnesota KENNETH I. KELLERMANN, National Radio Astronomy Observatory MARGARET G. KIVELSON, University of California, Los Angeles DANIEL KLEPPNER, Massachusetts Institute of Technology JOHN KREICK, Sanders, a Lockheed Martin Company MARSHA I. LESTER, University of Pennsylvania THOMAS A. PRINCE, California Institute of Technology NICHOLAS P. SAMIOS, Brookhaven National Laboratory L.E. SCRIVEN, University of Minnesota SHMUEL WINOGRAD, IBM T.J. Watson Research Center CHARLES A. ZRAKET, MITRE Corporation (retired) NORMAN METZGER, Executive Director

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--> Foreword Astronauts who venture beyond the protection of Earth's atmosphere and magnetosphere risk exposure to levels of radiation far exceeding those on Earth. Of all the risks they face, this one is probably the most straightforward to control—by providing adequate shielding. However, because shielding adds weight, cost, and complexity to space vehicles, it is very important for designers to have a good, quantitative understanding of the true risk and its degree of certainty. This report assesses our understanding of radiation hazards in space. It also considers the additional research needed to reduce the areas of uncertainty, research that must be completed prior to undertaking the detailed design of a vehicle carrying crew members into space for periods of extended exposure. The report finds that it will take more than a decade of research to answer even the narrowest set of key questions, although happily the needed studies can all be conducted on the ground rather than in space. The nation has backed away from a specific timetable for human exploration of the moon and Mars. Yet it seems plausible that such expeditions will be mounted sometime in the first quarter of the 21st century, especially given the recent resurgence of interest in possible life on Mars from the study of meteorites. It becomes clear, when the lengthy time scale of the research is also taken into account, that the present report is indeed timely and should receive prompt consideration by NASA planners. CLAUDE R. CANIZARES, CHAIR SPACE STUDIES BOARD

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--> Preface The study that is the subject of this report was initiated as a result of a series of discussions between the leaders of NASA's Office of Life and Microgravity Sciences and Applications (OLMSA), NASA's Life and Biomedical Sciences Division (LBSAD), and the Space Studies Board's Committee on Space Biology and Medicine (CSBM). In order to address concerns within NASA and CSBM regarding the many uncertainties in the understanding of radiation hazards to the crew of long-duration missions in space, CSBM formed an expert task group on radiation biology and physics whose members had no direct involvement with NASA's radiation programs. A CSBM member with the appropriate expertise was appointed to lead the group. The Task Group on the Biological Effects of Space Radiation (TGBESR) was asked to review current knowledge on the effects of long-term exposure to radiation in a space environment and to consider NASA radiation shielding requirements for orbital and interplanetary spacecraft. The task group was charged with assessing the adequacy of NASA planning for the protection of humans from radiation in those environments and with making recommendations regarding needed research and/or new shielding requirements. Where feasible, the task group would also provide NASA with radiation safety guidelines. Early in the study the task group was informed by NASA that plans for the international space station were at such an advanced stage that any recommendations affecting shielding of orbital craft could not be implemented by the agency. The task group therefore decided to concentrate on the radiation hazards of interplanetary missions. Further, at the urging of NASA, the task group has attempted to provide reasonable estimates of time lines for completing the radiation research it has recommended. Although the recommendations of the task group are published here as a separate and independent report of TGBESR, it is the intent of CSBM that this report will also form the basis of a section in a space life sciences strategy report being prepared by CSBM for publication at a later date. During the course of this study the task group was briefed extensively by representatives of OLMSA and LBSAD regarding NASA's planning for deep-space missions and projections for radiation shielding. The task group also received in-depth technical briefings on the status of NASA's radiation research and the agency's current understanding of radiation hazards, and it consulted a wide range of technical documentation. When verification or additional details of prior research were needed, task group members made direct queries to the pertinent investigators in the radiation research community. A number of individuals who assisted the task group by supplying information deserve special thanks for their contributions: Harry Holloway, Frank Sulzman, and Walter Schimmerling of NASA headquarters; John Wilson of NASA Langley Research Center; Amy Kronenberg of Lawrence Berkeley National Laboratory; and Gregory Nelson of the Jet Propulsion Laboratory.

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--> Contents     Executive Summary   1 1   Introduction   5     Statement of Problem   5     Contributions and Use of Past Radiation Research   7     Current Understanding of Biological Effects of Radiation   8     Types of Effects   8     Effects Induced by Protons   8     Effects Induced by Heavy Ions   9     References   11 2   Issues of Concern to NASA: Discussion and Conclusions   13     Types of Particles and Their Energies   14     Galactic Cosmic Rays   14     Solar Particles   15     Secondary Particles   18     Estimates of Uncertainty in Radiation Risk Factors   18     Conclusions   18     Biological Effects of Radiation   19     Early Effects   19     General Considerations   19     Early Systemic Effects   20     Skin   20     Fertility   21     Other Organ Systems   21     Conclusions   21     Late Effects   21     General Considerations   21     Cancer and Uncertainty in Estimates of Its Induction   22     Central Nervous System   24     Cataracts   27     Heritable Effects   28

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-->     Variation in Susceptibility to Radiation Across Subject Types   28     DNA Repair   29     Repair of Oxidative Damage and Double-Strand Breaks   29     Other Studies   30     Conclusion   31     Loss of Research Programs   31     References   32 3   How to Reduce Risk and the Uncertainty in Risk Estimates   35     Shielding   35     Recommendations for Research to Better Determine Shielding Requirements   35     Knowledge Base Development   35     Shielding Approaches   36     Cost of Research vs. Cost of Excess Shielding   38     Radioprotective and Chemoprotective Drugs and Diet   38     Crew Selection   39     Optimal Time for Flight   39     Solar Particle Event Warning System   40     Flares   40     Coronal Mass Ejections/Interplanetary Shocks   40     Conclusions   40     References   40 4   Priority Research Questions and Strategies   42     Higher-Priority Research Questions   42     Lower-Priority Research Questions   47     Time Scale of Research   50     What Will Still Remain Unknown, and What Risk Does This Represent?   54     References   54 5   Other Issues   55     Need for Animal Use   55     Experimental Techniques and New Data Required   56     Ground-vs. Space-based Research   56     Plants and Food Supply   57     References   57     Appendixes         A Acronyms and Abbreviations   61     B Glossary   63     C Beam Sources   69     D Previous Advice of the National Research Council Regarding the BEVALAC Facility   72