THE ATACAMA Large Millimeter Array

Implications of a Potential Descope

Committee to Review the Science Requirements for the Atacama Large Millimeter Array

Committee on Astronomy and Astrophysics

Board on Physics and Astronomy

Space Studies Board

Division on Engineering and Physical Sciences

NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES

THE NATIONAL ACADEMIES PRESS
Washington, D.C.
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The Atacama Large Millimeter Array: Implications of a Potential Descope THE ATACAMA Large Millimeter Array Implications of a Potential Descope Committee to Review the Science Requirements for the Atacama Large Millimeter Array Committee on Astronomy and Astrophysics Board on Physics and Astronomy Space Studies Board Division on Engineering and Physical Sciences NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES THE NATIONAL ACADEMIES PRESS Washington, D.C. www.nap.edu

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The Atacama Large Millimeter Array: Implications of a Potential Descope 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 was supported by the National Science Foundation. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the organizations or agencies that provided support for the project. Cover: An artist’s conception of the completed Atacama Large Millimeter Array (ALMA). Each of ALMA’s 64-antenna dishes will measure 39 feet (12 meters) wide. The ALMA antennas will be movable. At its largest, the array will measure 10 miles (14 kilometers) wide, and at its smallest, only 500 feet (150 meters). The ALMA correlator, or specialized computer that combines the information received by the antennas, will perform an astounding 16,000 million-million (1.6 × 1016) operations per second. When completed (in 2011), ALMA will be the largest and most capable imaging array of telescopes in the world. Image courtesy of National Radio Astronomy Observatory and Associated Universities, Inc.; computer graphics by European Southern Observatory. International Standard Book Number 0-309-09694-4 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; and Board on Physics and Astronomy, National Research Council, NA-922, 500 Fifth Street, N.W., Washington, DC 20001; Internet http://www.national-academies.org/bpa. Copyright 2005 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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The Atacama Large Millimeter Array: Implications of a Potential Descope 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. Wm. A. Wulf 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. Wm. A. Wulf are chair and vice chair, respectively, of the National Research Council. www.national-academies.org

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The Atacama Large Millimeter Array: Implications of a Potential Descope COMMITTEE TO REVIEW THE SCIENCE REQUIREMENTS FOR THE ATACAMA LARGE MILLIMETER ARRAY ROGER D. BLANDFORD, Stanford University, Chair DONALD C. BACKER, University of California at Berkeley JOHN E. CARLSTROM, University of Chicago SARAH E. CHURCH, Stanford University LENNOX L. COWIE, University of Hawaii AARON S. EVANS, State University of New York, Stony Brook DAVID J. HOLLENBACH, NASA-Ames Research Center ANTHONY C. READHEAD, California Institute of Technology MARK J. REID, Harvard-Smithsonian Astrophysical Observatory DAVID N. SPERGEL, Princeton University Staff DONALD C. SHAPERO, Director, Board on Physics and Astronomy BRIAN D. DEWHURST, Study Director DAVID B. LANG, Research Assistant CELESTE A. NAYLOR, Senior Project Assistant

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The Atacama Large Millimeter Array: Implications of a Potential Descope COMMITTEE ON ASTRONOMY AND ASTROPHYSICS ROGER D. BLANDFORD, Stanford University, Co-chair C. MEGAN URRY, Yale University, Co-chair CHARLES ALCOCK, University of Pennsylvania DONALD C. BACKER, University of California at Berkeley LARS BILDSTEN, University of California at Santa Barbara THOMAS BOGDAN, National Center for Atmospheric Research ALEXEI FILIPPENKO, University of California at Berkeley TIMOTHY M. HECKMAN, Johns Hopkins University DAVID J. HOLLENBACH, NASA-Ames Research Center CHRYSSA KOUVELIOTOU, National Space Science and Technology Center STEPHAN MEYER, University of Chicago EVE OSTRIKER, University of Maryland MARK J. REID, Harvard-Smithsonian Astrophysical Observatory SCOTT TREMAINE, Princeton University JEAN L. TURNER, University of California at Los Angeles CHARLES E. WOODWARD, University of Minnesota Staff DONALD C. SHAPERO, Director, Board on Physics and Astronomy JOSEPH K. ALEXANDER, Director, Space Studies Board BRIAN D. DEWHURST, Senior Program Associate CELESTE A. NAYLOR, Senior Project Assistant

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The Atacama Large Millimeter Array: Implications of a Potential Descope BOARD ON PHYSICS AND ASTRONOMY BURTON RICHTER, Stanford University, Chair ANNEILA I. SARGENT, California Institute of Technology, Vice Chair ELIHU ABRAHAMS, Rutgers State University JONATHAN BAGGER, Johns Hopkins University GORDON A. BAYM, University of Illinois at Urbana-Champaign RONALD C. DAVIDSON, Princeton University WILLIAM EATON, National Institutes of Health RAYMOND FONCK, University of Wisconsin ANDREA M. GHEZ, University of California at Los Angeles LAURA H. GREENE, University of Illinois at Urbana-Champaign FRANCES HELLMAN, University of California at San Diego ERICH P. IPPEN, Massachusetts Institute of Technology MARC A. KASTNER, Massachusetts Institute of Technology CHRISTOPHER F. MCKEE, University of California at Berkeley JULIA M. PHILLIPS, Sandia National Laboratories THOMAS N. THEIS, IBM T.J. Watson Research Center C. MEGAN URRY, Yale University CARL E. WIEMAN, University of Colorado/JILA Staff DONALD C. SHAPERO, Director

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The Atacama Large Millimeter Array: Implications of a Potential Descope SPACE STUDIES BOARD LENNARD A. FISK, University of Michigan, Chair GEORGE A. PAULIKAS, The Aerospace Corporation (retired), Vice Chair DANIEL N. BAKER, University of Colorado ANA P. BARROS, Duke University RETA F. BEEBE, New Mexico State University ROGER D. BLANDFORD, Stanford University RADFORD BYERLY, JR., University of Colorado JUDITH A. CURRY, Georgia Institute of Technology JACK D. FARMER, Arizona State University JACQUELINE N. HEWITT, Massachusetts Institute of Technology DONALD INGBER, Harvard Medical Center RALPH H. JACOBSON, The Charles Stark Draper Laboratory (retired) TAMARA E. JERNIGAN, Lawrence Livermore National Laboratory MARGARET G. KIVELSON, University of California at Los Angeles CALVIN W. LOWE, Bowie State University HARRY Y. McSWEEN, JR., University of Tennessee BERRIEN MOORE III, University of New Hampshire NORMAN NEUREITER, Texas Instruments (retired) SUZANNE OPARIL, University of Alabama, Birmingham RONALD F. PROBSTEIN, Massachusetts Institute of Technology DENNIS W. READEY, Colorado School of Mines ANNA-LOUISE REYSENBACH, Portland State University ROALD S. SAGDEEV, University of Maryland CAROLUS J. SCHRIJVER, Lockheed Martin Solar and Astrophysics Laboratory HARVEY D. TANANBAUM, Smithsonian Astrophysical Observatory J. CRAIG WHEELER, University of Texas, Austin A. THOMAS YOUNG, Lockheed Martin Corporation (retired) Staff JOSEPH K. ALEXANDER, Director

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The Atacama Large Millimeter Array: Implications of a Potential Descope Preface The prioritized list of instruments recommended in the 1991 astronomy and astrophysics decadal survey included the Millimeter Array (MMA): … an array of telescopes operating at millimeter wavelengths [that] would provide high-spatial- and high-spectral-resolution images of star-forming regions and distant star-burst galaxies. With spatial resolution of a tenth of an arcsecond at a wavelength of 1 mm, the MMA would bring new classes of objects into clear view for the first time.1 With the addition of an equal contributing European partner, plans for the MMA have since evolved into the Atacama Large Millimeter Array (ALMA), a proposed array of 64 transportable 12-meter antennas capable of enabling transformational science. This project has been accepted by the National Science Board for inclusion in the National Science Foundation’s (NSF’s) Major Research Equipment and Facilities Construction queue. Increases in cost driven primarily by an increase in commodity prices have forced the NSF to consider reducing the number of antennas. 1   National Research Council, The Decade of Discovery in Astronomy and Astrophysics, National Academy Press, Washington, D.C., 1991, pp. 4-5.

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The Atacama Large Millimeter Array: Implications of a Potential Descope The Committee to Review the Science Requirements for the Atacama Large Millimeter Array (the ALMA Committee) was established by the National Research Council under the Board on Physics and Astronomy and the Space Studies Board with oversight and guidance from the Committee on Astronomy and Astrophysics in March 2005 at the request of NSF’s Astronomy Division. The committee was charged with assessing the following issues related to a possible descope of the ALMA array to 40 or 50 12-meter antennas: What would be the impact on the attainability of the technical performance specifications? What would be the loss of speed, image quality, mosaicing ability,2 and point-source sensitivity? What would be the impact on the scientific reach of the project? Would ALMA still be sufficiently transformational in terms of its scientific potential to warrant continued support by the United States? Is there a particular threshold in the number of antennas below which ALMA would suffer a degradation in its performance sufficiently serious that it would not merit the scientific priority accorded it in the 1991 survey of astronomy and astrophysics? The membership of the ALMA Committee was designed to bring together experts in millimeter- and centimeter-wave interferometry, as well as experts in the scientific areas ALMA will address, to consider the charge. The committee expresses its appreciation to the following individuals for their contributions to its work and the completion of this report: Robert Dickman (NSF), Jean Turner (UCLA), Mark Holdaway (NRAO), Ewine van Dishoeck (Leiden Observatory), and Al Wooten (NRAO). 2   Mosaicing refers to the mapping of areas larger than the field of view of a single antenna, by using multiple pointings, up to a thousand in extreme cases.

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The Atacama Large Millimeter Array: Implications of a Potential Descope 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 National Research Council’s Report Review Committee. 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: Michael Davis, SETI Institute, Paul F. Goldsmith, Cornell University, Eve C. Ostriker, University of Maryland, Joseph H. Taylor, Jr., Princeton University, William J. Welch, University of California at Berkeley, and David J. Wilner, Harvard-Smithsonian Center for Astrophysics. Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to en-

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The Atacama Large Millimeter Array: Implications of a Potential Descope dorse 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 Jacqueline N. Hewitt of MIT. Appointed by the National Research Council, she 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.

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The Atacama Large Millimeter Array: Implications of a Potential Descope Contents     Summary   1 1   Introduction   3 2   Technical Performance Specifications   7 3   Performance Degradation   13 4   The Threshold for Transformational Science   17 5   Minimum Number of Antennas   21     Appendixes         A  Letter of Request   25     B  ALMA Level-1 Science Requirements   29

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