National Academies Press: OpenBook
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×

LIMITING FUTURE COLLISION
RISK TO SPACECRAFT

AN ASSESSMENT OF NASA’S METEOROID
AND ORBITAL DEBRIS PROGRAMS

 

Committee for the Assessment of NASA’s Orbital Debris Programs

Aeronautics and Space Engineering Board

Division on Engineering and Physical Sciences

NATIONAL RESEARCH COUNCIL

OF THE NATIONAL ACADEMIES

 

THE NATIONAL ACADEMIES PRESS
Washington, D.C.
www.nap.edu

Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×

THE NATIONAL ACADEMIES PRESS    500 Fifth Street, N.W.    Washington, DC 20001

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 committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

This study is based on work supported by Contract NNH10CC48B between the National Academy of Sciences and the National Aeronautics and Space Administration. Any views or observations expressed in this publication are those of the authors and do not necessarily reflect the views of the agency that provided support for the project.

International Standard Book Number-13: 978-0-309-21974-7
International Standard Book Number-10: 0-309-21974-4

Cover: Design by Tim Warchocki.

Copies of this report are available free of charge from:

Aeronautics and Space Engineering Board
National Research Council
500 Fifth Street, N.W.
Washington, DC 20001

Additional copies of this report are available from the National Academies Press, 500 Fifth Street, N.W., Lockbox 285, Washington, DC 20055; (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area); Internet, http://www.nap.edu.

Copyright 2011 by the National Academy of Sciences. All rights reserved.

Printed in the United States of America

Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×

THE NATIONAL ACADEMIES

Advisers to the Nation on Science, Engineering, and 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. Ralph J. Cicerone 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 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. Charles M. Vest is 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. Harvey V. Fineberg 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. Ralph J. Cicerone and Dr. Charles M. Vest are chair and vice chair, respectively, of the National Research Council.

www.nationalacademies.org

Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×

OTHER RECENT REPORTS OF THE AERONAUTICS AND SPACE ENGINEERING BOARD

An Interim Report on NASA’s Draft Space Technology Roadmaps [prepublication version] (Aeronautics and Space Engineering Board [ASEB], 2011)

Preparing for the High Frontier—the Role and Training of NASA Astronauts in the Post-Space Shuttle Era [prepublication version] (ASEB, 2011)

Recapturing a Future for Space Exploration: Life and Physical Sciences Research for a New Era [prepublication version] (Space Studies Board [SSB] with ASEB, 2011)

Summary of the Workshop to Identify Gaps and Possible Directions for NASA’s Meteoroid and Orbital Debris Programs (ASEB, 2011)

Advancing Aeronautical Safety: A Review of NASA’s Aviation Safety-Related Research Programs (SSB with ASEB, 2010)

Capabilities for the Future: An Assessment of NASA Laboratories for Basic Research (Laboratory Assessments Board with ASEB, 2010)

Defending Planet Earth: Near-Earth-Object Surveys and Hazard Mitigation Strategies: Final Report (SSB with ASEB, 2010)

Final Report of the Committee to Review Proposals to the 2010 Ohio Third Frontier (OTF) Wright Projects Program (WPP) (ASEB, 2010)

America’s Future in Space: Aligning the Civil Space Program with National Needs (SSB with ASEB, 2009)

Approaches to Future Space Cooperation and Competition in a Globalizing World: Summary of a Workshop (SSB with ASEB, 2009)

An Assessment of NASA’s National Aviation Operations Monitoring Service (ASEB, 2009)

Final Report of the Committee for the Review of Proposals to the 2009 Engineering and Physical Science Research and Commercialization Program of the Ohio Third Frontier Program (ASEB, 2009)

Fostering Visions for the Future: A Review of the NASA Institute for Advanced Concepts (ASEB, 2009)

Near-Earth Object Surveys and Hazard Mitigation Strategies: Interim Report (SSB with ASEB, 2009)

Radioisotope Power Systems: An Imperative for Maintaining U.S. Leadership in Space Exploration (SSB with ASEB, 2009)

Assessing the Research and Development Plan for the Next Generation Air Transportation System: Summary of a Workshop (ASEB, 2008)

A Constrained Space Exploration Technology Program: A Review of NASA’s Exploration Technology Development Program (ASEB, 2008)

Launching Science: Science Opportunities Provided by NASA’s Constellation System (SSB with ASEB, 2008)

Managing Space Radiation Risk in the New Era of Space Exploration (ASEB, 2008)

NASA Aeronautics Research: An Assessment (ASEB, 2008)

Review of NASA’s Exploration Technology Development Program: An Interim Report (ASEB, 2008)

Science Opportunities Enabled by NASA’s Constellation System: Interim Report (SSB with ASEB, 2008)

United States Civil Space Policy: Summary of a Workshop (SSB with ASEB, 2008)

Wake Turbulence: An Obstacle to Increased Air Traffic Capacity (ASEB, 2008)

Limited copies of ASEB reports are available free of charge from

Aeronautics and Space Engineering Board
National Research Council
The Keck Center of the National Academies
500 Fifth Street, N.W., Washington, DC 20001
(202) 334-2858/aseb@nas.edu
www.nationalacademies.org/aseb.html

Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×

COMMITTEE FOR THE ASSESSMENT OF NASA’S ORBITAL DEBRIS PROGRAMS

DONALD J. KESSLER, NASA (retired), Chair

GEORGE J. GLEGHORN, TRW Space and Technology Group (retired), Vice Chair

KYLE T. ALFRIEND, Texas A&M University

MICHAEL J. BLOOMFIELD, Oceaneering Space Systems

PETER BROWN, University of Western Ontario

RAMON L. CHASE, Booz Allen Hamilton

SIGRID CLOSE, Stanford University

JOANNE IRENE GABRYNOWICZ, National Center for Remote Sensing, Air, and Space Law, University of Mississippi

ROGER E. KASPERSON, Clark University

T.S. KELSO, Analytical Graphics, Inc.

MOLLY K. MACAULEY, Resources for the Future

DARREN S. McKNIGHT, Integrity Applications, Inc.

WILLIAM P. SCHONBERG, Missouri University of Science and Technology

Staff

PAUL JACKSON, Program Officer, Study Director

LEWIS B. GROSWALD, Research Associate

JOHN F. WENDT, Senior Program Officer

CATHERINE A. GRUBER, Editor

ANDREA M. REBHOLZ, Program Associate

DALAL NAJIB, Christine Mirzayan Science and Technology Policy Graduate Fellow

RACHAEL ALEXANDROFF, Lloyd V. Berkner Space Policy Intern

KATIE DAUD, Lloyd V. Berkner Space Policy Intern

MICHAEL H. MOLONEY, Director, Aeronautics and Space Engineering Board

Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×

AERONAUTICS AND SPACE ENGINEERING BOARD

RAYMOND S. COLLADAY, Lockheed Martin Astronautics (retired), Chair

LESTER LYLES, The Lyles Group, Vice Chair

ELLA M. ATKINS, University of Michigan

AMY L. BUHRIG, Boeing Commercial Airplanes Group

INDERJIT CHOPRA, University of Maryland, College Park

JOHN-PAUL B. CLARKE, Georgia Institute of Technology

RAVI B. DEO, EMBR

VIJAY DHIR, University of California, Los Angeles

EARL H. DOWELL, Duke University

MICA R. ENDSLEY, SA Technologies

DAVID GOLDSTON, Harvard University

R. JOHN HANSMAN, Massachusetts Institute of Technology

JOHN B. HAYHURST, Boeing Company (retired)

WILLIAM L. JOHNSON, California Institute of Technology

RICHARD KOHRS, Independent Consultant

IVETT LEYVA, Air Force Research Laboratory, Edwards Air Force Base

ELAINE S. ORAN, Naval Research Laboratory

ALAN G. POINDEXTER, Naval Postgraduate School

HELEN R. REED, Texas A&M University

ELI RESHOTKO, Case Western Reserve University

EDMOND SOLIDAY, United Airlines (retired)

MICHAEL H. MOLONEY, Director

CARMELA J. CHAMBERLAIN, Administrative Coordinator

TANJA PILZAK, Manager, Program Operations

CELESTE A. NAYLOR, Information Management Associate

CHRISTINA O. SHIPMAN, Financial Officer

SANDRA WILSON, Financial Assistant

Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×

Preface

In 1995, the National Research Council’s (NRC’s) Committee on Space Debris wrote,

The threat that orbital debris poses to international space activities is presently not large, but it may be on the verge of becoming significant. If and when it does, the consequences could be very costly—and extremely difficult to reverse. By contrast, the cost of reducing the growth of the hazard can be relatively low. … The committee believes that spacefaring nations should take judicious, timely steps now to understand the risk and agree on ways to reduce it.1

At that time, no destructive collisions between active spacecraft and debris or meteoroids2 had been recorded. In addition, the amount of debris in orbit did not include the aftermath of the 2009 Iridium-Cosmos collision and the 2007 on-orbit destruction by the Chinese of a weather satellite as part of an anti-satellite test. Both of those events greatly increased the amount of debris in the near-Earth space environment, thus pushing the threat posed by orbital debris even further toward what was described more than 15 years ago as “on the verge of becoming significant.”

In a letter dated April 26, 2010, Bryan O’Connor, NASA’s chief of safety and mission assurance, requested that the NRC conduct a study on NASA’s meteoroid and orbital debris programs. This letter was a direct response to a request from the White House Office of Management and Budget (OMB) and Office of Science and Technology Policy (OSTP) for NASA to engage in a study of the “opportunities for NASA to enhance the benefits delivered by its orbital debris program in the context of a fairly constrained budget environment.” As indicated in the letter, the study’s primary task was to review NASA’s current efforts with regard to meteoroids and orbital debris and provide recommendations as to whether NASA should increase or decrease its efforts or pursue new directions. The full text of the letter is reprinted as Appendix A of this report, and the specific language of the study charge is contained in Appendix B.

To conduct this study, the NRC’s Aeronautics and Space Engineering Board (ASEB) assembled the Committee for the Assessment of NASA’s Orbital Debris Programs, composed of 13 experts with a wide range of experience

___________________

1 National Research Council, Orbital Debris: A Technical Assessment, National Academy Press, Washington, D.C., 1995, p. 9.

2 This report uses the word “meteoroid” according to its precise definition, rather than the term “micrometeoroid,” a colloquialism for “small” meteoroids and an imprecise term that does not cover the full range of sizes of meteoroids. However, to avoid adding a new acronym to the literature and to minimize confusion, the committee retains use of the acronym “MMOD” (micrometeoroid and orbital debris) as a modifier (e.g., MMOD programs).

Page viii Cite
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×

and perspectives. In addition to NASA’s orbital debris programs, the committee also evaluated NASA’s meteoroid program. Donald Kessler, senior scientist (retired) for orbital debris research at NASA, chaired the committee, which included experts in orbital debris, spacecraft engineering, spacecraft shielding, astrodynamics, meteoroids, hypervelocity impacts, space law, space policy, and risk assessment. Biographical sketches of the committee members are given in Appendix C.

Over the course of the study, the committee met in person four times. During its first meeting on December 13-15, 2010, the committee received overview briefings on many of NASA’s relevant programs from the programs’ lead researchers and managers. To better understand the context of its charge, the committee met with representatives from OSTP and OMB. In addition, the committee received non-NASA input from sources such as the European Space Agency and the Aerospace Corporation. The committee’s second meeting was held January 19-21, 2011, at the NASA Johnson Space Center, where the committee was able to interact directly with many of the NASA researchers and managers who work on orbital debris issues. During the meeting, the committee received more detailed briefings regarding NASA’s efforts, particularly those undertaken by NASA’s Orbital Debris Program Office.

The committee’s third meeting was held March 9-11, 2011, and because of the diversity and number of perspectives and entities involved in space activities, was structured primarily as a public workshop to facilitate hearing from the various stakeholders and interested parties in an efficient manner. On May 26, 2011, the committee released Summary of the Workshop to Identify Gaps and Possible Directions for NASA’s Meteoroid and Orbital Debris Programs, a short summary report of the workshop that is reprinted in Appendix F. The committee met for the final time on April 25-27, 2011, in order to develop this final report.

The committee notes that several topics of interest related to orbital debris were not included in its statement of task, and as such are not full topics in this report. In particular, the committee was not asked to weigh in on the degree of the threat posed by meteoroids and debris, nor was the committee asked to determine which technology or path is best suited for the removal of debris from orbit. In effect, this study is more a review of NASA’s meteoroid and orbital debris programs than an attempt to solve the threat posed by meteoroids and orbital debris.

Although the statement of task refers to a singular NASA program in this field, there are, in fact, numerous program elements spread across NASA mission centers that address MMOD. For the purposes of this report, these elements are referred to as NASA’s MMOD programs, although at times they are referred to separately (i.e., meteoroid program, orbital debris programs) depending on the context.

We sincerely thank the experts who made their time available to the committee and provided necessary data, analyses of that data, and insight into technical, management, and political issues. In addition, the NRC staff played an essential role in requesting information, pulling information together, and organizing meetings and editing this report. Without their organizational skills, this document would not have been possible. We would like to particularly thank Paul Jackson, the study director. His commitment to maintaining focus and spending countless hours leading his team, as well as to resolving issues within the committee, made an essential contribution toward increasing the quality of this report.

Donald J. Kessler, Chair

George J. Gleghorn, Vice Chair

Committee for the Assessment of NASA’s

Orbital Debris Programs

Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×

Acknowledgment of Reviewers

This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the Report Review Committee of the National Research Council (NRC). The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report:

William Ailor, The Aerospace Corporation,

Ravi B. Deo, EMBR,

Eberhard Grün, Max-Planck-Institut fuer Kernphysik,

John L. Junkins, Texas A&M University,

Charles F. Kennel, Scripps Institution of Oceanography and University of California, San Diego,

Robert Kerr, Scientific Solutions, Inc.,

John M. Klineberg, Space Systems/Loral (retired),

Andrew Piekutowski, University of Dayton Research Institute (retired), and

Michael F. Zedd, Naval Research Laboratory.

Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations, nor did they see the final draft of the report before its release. The review of this report was overseen by M. Granger Morgan, Carnegie Mellon University. Appointed by the NRC, he was responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.

Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×

This page intentionally left blank.

Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×
Page R1
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×
Page R2
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×
Page R3
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×
Page R4
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×
Page R5
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×
Page R6
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×
Page R7
Page viii Cite
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×
Page R8
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×
Page R9
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×
Page R10
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×
Page R11
Suggested Citation:"Front Matter." National Research Council. 2011. Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, DC: The National Academies Press. doi: 10.17226/13244.
×
Page R12
Next: Summary »
Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs Get This Book
×
Buy Paperback | $45.00 Buy Ebook | $35.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

Derelict satellites, equipment and other debris orbiting Earth (aka space junk) have been accumulating for many decades and could damage or even possibly destroy satellites and human spacecraft if they collide. During the past 50 years, various National Aeronautics and Space Administration (NASA) communities have contributed significantly to maturing meteoroid and orbital debris (MMOD) programs to their current state. Satellites have been redesigned to protect critical components from MMOD damage by moving critical components from exterior surfaces to deep inside a satellite's structure. Orbits are monitored and altered to minimize the risk of collision with tracked orbital debris. MMOD shielding added to the International Space Station (ISS) protects critical components and astronauts from potentially catastrophic damage that might result from smaller, untracked debris and meteoroid impacts.

Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Program examines NASA's efforts to understand the meteoroid and orbital debris environment, identifies what NASA is and is not doing to mitigate the risks posed by this threat, and makes recommendations as to how they can improve their programs. While the report identified many positive aspects of NASA's MMOD programs and efforts including responsible use of resources, it recommends that the agency develop a formal strategic plan that provides the basis for prioritizing the allocation of funds and effort over various MMOD program needs. Other necessary steps include improvements in long-term modeling, better measurements, more regular updates of the debris environmental models, and other actions to better characterize the long-term evolution of the debris environment.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

    « Back Next »
  6. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  7. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  8. ×

    View our suggested citation for this chapter.

    « Back Next »
  9. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!