level). Assuming the current status of the projects, the dates for full operations of the two telescopes (defined as including three instruments and the adaptive optics system) were estimated as spring 2024 for GMT, and between summer 2025 and summer 2030 for TMT depending on assumptions about segment manufacture and delivery. The telescope projects estimated their annual operations costs (including facility and instrument upgrades) as being $36 million for GMT and $55 million for TMT. Although the committee did not analyze these estimates in detail, they are far below the usual rule of thumb for large projects (10 percent of construction costs per year); should the projects go forward, their operations costs will need to be scrutinized in considerable detail. The committee did not evaluate the cost estimate or risks for the E-ELT, but the ESO estimate is 1 billion with a start of operations in 2018.

The two U.S.-led projects, GMT and TMT, are in fairly advanced states of design. GMT has already cast one of its six off-axis mirrors, which is currently being polished. TMT has cast, polished, and mounted an on-axis segment and is in the process of polishing an off-axis segment. Furthermore, through a combination of private and international partnerships, both projects have made considerable progress on their financing. The question, now, is whether or not the federal government can afford to become a partner in one of these projects and, if so, which one. The arguments for federal partnership are strong. First, the science case for a GSMT is highly compelling, and a federal share will ensure access to observing time for all U.S. astronomers, not just those associated with partner institutions.23 This is a principle that is similar to the Telescope System Instrumentation Program (TSIP) program philosophy that has been so successfully implemented with respect to existing privately operated telescopes. Second, partnership can greatly enhance and improve these projects by bringing a much larger experience base and resources to them. This will be particularly important during the operations phase when funds to run the telescopes must be found and new and expensive instruments will need to be constructed.

In the committee’s judgment, due to the severe budget limitations, a federal partnership in a GSMT will be limited to a minority role with one project. For the construction phase, a potential MREFC funding wedge opens up in the second half of the decade (after ALMA, ATST, and LSST have passed their peak funding) that would allow for a federal share in a GSMT to be supported by the MREFC line by the end of this decade. For the operations phase, in the optimistic budget-

23

Institutional members as of May 2010 were, for GMT, Astronomy Australia Limited, the Australian National Observatory, Carnegie Institution for Science, Harvard University, Korea Astronomy and Space Science Institute, Smithsonian Astrophysical Observatory, Texas A&M University, the University of Texas at Austin, and the University of Arizona, and for TMT were the Association of Canadian Universities for Research in Astronomy, California Institute of Technology, and the University of California.



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