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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 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 opinions, findings, conclusions, or recommendations 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.

Cover: Design by Tim Warchocki. Image of the Carina Nebula captured by the NASA/ESA Hubble Space Telescope, courtesy of NASA, ESA, and M. Livio, the Hubble Heritage Team and the Hubble 20th Anniversary Team (STScI). Back Cover: NASA Global Hawk courtesy of NASA/Lori Losey.

International Standard Book Number-13: 978-0-309-31354-4
International Standard Book Number-10: 0-309-31354-6

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Copyright 2012 by the National Academy of Sciences. All rights reserved.

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