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California Extremely Large Telescope CELT Report Number 34 California Extremely Large Telescope Conceptual Design for a Thirty-Meter Telescope June 2002 University of California California Institute of Technology The California Extremely Large Telescope Conceptual Design for a Thirty-Meter Telescope Participants Preface Executive Summary 1. Introduction and Overview 2. Scientific Motivation 3. Telescope Performance Specifications 4. Optical Design 5. Primary Mirror 6. Secondary and Tertiary Mirrors 7. Telescope Structure 8. Optics Alignment 9. Adaptive Optics 10. Scientific Instrumentation 11. Expected Image and Wavefront Quality 12. Observatory Dome and Facilities 13. Site Selection 14. Computer Software and Hardware For thousands of years astronomy has captured the imagination of all civilizations. In 1669 Vermeer vividly portrayed the astronomer’s technology, discipline, and sense of awe. i Participants Greg Ames (Blueline Eng.) Doug MacMartin (CIT) Jean Aubrun (ACSD) Terry Mast (UCSC) Mike Bolte (UCSC) Keith Matthews (CIT) Brian Bauman (LLNL) Bruce Macintosh (LLNL) Gary Brack (JPL) Ian McLean (UCLA) Matthew Britton (CIT) Maureen McLean (UCSC) Jerry Cabak (UCO/Lick) Steve Medwadowski (SJM Eng.) Gary Chanan (UCI) Heather Mietz (UCO/Lick) Judy Cohen (CIT) Joe Miller (UCSC) Al Conrad (WMKO) Bob Minor (LBNL) Dave Cowley (UCSC) Richard Murray (CIT) Deborah Culmer (UCSC) Jerry Nelson (UCSC) Richard Dekany (CIT) Scot Olivier (LLNL) George Djorgovski (CIT) Carol Osborne (UCSC) Richard Ellis (CIT) Steve Padin (CIT) Don Gavel (LLNL) Andreas Quirrenbach (UCSD) Andrea Ghez (UCLA) Wal Sargent (CIT) Kirk Gilmore (UCO/Lick) Alan Schier (Pilot Group) James Graham (UCB) Matthias Schoeck (UCI) Raja Guhathakurta (UCSC) Gerry Smith (WMKO) Steve Gunnels (Paragon Eng.) Gary Sommargren (LLNL) Stan Hermann (Vertex/RSI) Chuck Steidel (CIT) Bill Irace (JPL) Keith Taylor (CIT) Richard Jared (LBNL) Tom Tombrello (CIT) Mike Jura (UCLA) Mitchell Troy (JPL) Shri Kulkarni (CIT) David Tytler (UCSD) Lee Laiterman (UCSC) Steve Vogt (UCSC) James Larkin (UCLA) Dave Woody (CIT) Hilton Lewis (WMKO) Ken Lorell (ACSD) ii Preface For many centuries the exploration of the world by courageous discoverers profoundly influenced the development of civilization. The discovery of new lands and new societies brought pivotal changes to our world. Whether it was the discoveries of Polynesian adventurers crossing the Pacific Ocean or European explorers in the New World, the desire to explore and understand the unknown is a fundamental trait of the human race. In many respects the scientists of the 20th century were the modern equivalent of these explorers. Venturing into the microscopic world of the atom and the vast reaches of the universe, they made discoveries that had as profound an impact on the development of civilization as those of the early explorers of our planet. Entering the 21st century, we stand on the threshold of dramatic astronomical explorations. The universe has been a source of interest, inspiration, and wonderment since the earliest times. Today, newspapers and magazines are filled with exciting new discoveries of astronomy because they appeal to something fundamental in human nature. People are eager to know about the universe in which we live, how it began and how it evolved to its present state; and to understand our place in it. We want to know: • Why is the space of the universe filled with galaxies? • Why are galaxies filled with stars? • Why are stars surrounded by planets? • Is the existence of life an extremely rare event or common in the universe? We are beginning to answer some of these questions with existing telescopes on the ground and in space. The next generation of astronomical instruments will dramatically improve our ability to find answers to these questions that have intrigued human beings for thousands of years. Scientists at the University of California and the California Institute of Technology propose to design, build, and operate a 30-meter telescope that will be an extraordinarily powerful tool for exploring the universe. It will see farther into space and farther back in time than any instruments currently in use. It will give us unprecedented access to exquisite details of physical processes on both small and large scales and over most of the age of the universe. • We expect to see galaxies at their birth, when the first stars formed in the universe and started the processes which resulted in the world on which we live. • We expect to further understand the evolution of galaxies from birth to the present. • We expect to have detailed views of stars and solar systems in the process of formation. • We expect to observe directly planets in orbits around other stars, planets that may be the abodes of life. All this and much more will be possible because of the enormous light-gathering power and extremely high spatial resolution of a 30-meter telescope. The same scientists who conceived of and very successfully led the creation of the two largest telescopes in the world at the Keck Observatory are now prepared and eager to lead this exciting new venture. We are confident it will succeed, and the discoveries that flow from this magnificent new instrument will advance our understanding of the universe to a profound new level. iii Executive Summary Following great success in the creation of the Keck Observatory, scientists at the California Institute of Technology and the University of California have begun to explore the scientific and technical prospects for a much larger telescope. The Keck telescopes will remain the largest telescopes in the world for a number of years, with many decades of forefront research ahead after that. Though these telescopes have produced dramatic discoveries, it is already clear that even larger telescopes must be built if we are to address some of the most profound questions about our universe. The time required to build a larger telescope is approximately ten years, and the California community is presently well-positioned to begin its design and construction. The same scientists who conceived, led the design, and guided the construction of the Keck Observatory have been intensely engaged in a study of the prospects for an extremely large telescope. Building on our experience with the Keck Observatory, we have concluded that the large telescope is feasible and is within the bounds set by present-day technology. Our reference telescope has a diameter of 30 meters, the largest size we believe can be built with acceptable risk. The project is currently designated the California Extremely Large Telescope (CELT). CELT will have nine times the collecting area of a Keck telescope. This tremendous gain in light gathering ability will allow imaging and spectroscopy of the faintest and most distant known objects in the universe and will provide a powerful complement to any future space-based telescopes. Because of the travel time of light, a large telescope is a time machine that allows travel into the distant past by observing objects at great distances. The 30-meter telescope will allow scientists to study in detail for the first time the era when the matter of the universe first began to collect into the organized structures of stars and galaxies. Many of the characteristics of the world we see around us today, including the conditions for the existence of life, result directly from the processes that took place in the early universe. The 30-meter telescope will provide the crucial measurements needed for understanding this era. CELT will also allow the direct detections of planets orbiting other stars, observations that are crucial for our understanding of the formation of planetary systems that may well be the locations of extraterrestrial life. Many other important and exciting scientific questions can be addressed only by using a telescope of this size. The 30-meter telescope will unquestionably have a profound impact on our understanding of the universe and our place in it. A major design goal of the project will be to make cost-saving improvements beyond those incorporated in the Keck telescopes. Based on our experience with Keck, a segmented primary mirror is unquestionably the best choice for a telescope of this size. We will study alternative segment polishing and segment support techniques with the aim of greatly reducing the cost of the optics. We will also investigate alternative structural designs, with the aim of reduced cost and improved optics-support performance. Adaptive optics aided by laser beacons will be used to remove the blurring effects of atmospheric turbulence. Adaptive optics will provide a remarkable increase in angular resolution, orders-of-magnitude increase in point source sensitivity, and the ability to detect and spatially resolve even the most distant galaxies. Some of the adaptive optics technology required for the 30-meter telescope is not currently available. However, its rapid development, aided in part by the new NSF Center for Adaptive Optics at UC Santa Cruz, is presently underway. Scientific instruments, such as cameras and spectrometers, are needed to analyze the light collected by the telescope. These instruments, while challenging to build, are feasible and central to the scientific exploitation of the telescope. In addition, we expect that close collaboration with industry will produce a high performance and cost- effective dome design. The site for the 30-meter telescope has not yet been selected. Candidate sites iv will be researched in the near future, and will include Mauna Kea in Hawaii and several sites in Chile. If the telescope is located outside the United States, we expect that scientists in the host country will have some access to the facility. During the past year we have carried out a conceptual design program for CELT. Several engineering design studies have created a solid basis for many of the assumptions in this proposal. We have studied and created conceptual designs for the telescope structure, telescope bearings and drives, stressing fixtures for segment polishing, interferometric testing of segment surfaces, and sensors and actuators for segment active control.
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