The enormous potential of a next generation optical/infrared (O/IR) telescope was recognized by the National Research Council's (NRC) Astronomy and Astrophysics Survey Committee (AASC), which recommended the construction of a 30-m, filled-aperture, segmented mirror O/IR telescope - the Giant Segmented Mirror Telescope (GSMT) - as its highest priority large project among recommended ground-based initiatives. In its decadal report Astronomy and Astrophysics in the New Millennium (National Academy Press, 2001), the AASC urges rapid development of GSMT in order that this facility be in place early in the next decade. This would enable full exploitation of both the decadal survey's highest priority initiative, the James Webb Space Telescope (JWST), and the powerful Atacama Large Millimeter Array (ALMA).
The decadal survey further recommends an optimum path toward a GSMT for the US community through a partnership between the US national observatory and one or more independent observatories. Such a partnership has the advantage of providing full community representation during the design and construction phase of GSMT, ensuring that the design is optimized to meet the scientific aspirations of the entire astronomy community. Additionally, this partnership would provide broad, merit-based access to this frontier facility during its operation phase.
AURA RESPONSE: CREATION OF THE NEW INITIATIVES OFFICE
In response to the decadal survey, AURA formally established a New Initiatives Office (NIO) in January 2001 as a joint venture drawing from the strengths inherent in the two ground-based institutions managed by AURA: the National Optical Astronomy Observatory (NOAO) and the Gemini Observatory.
The principal mission of the NIO is to enable the successful creation of a GSMT to which there is broad astronomy community access, in a time frame contemporary with ALMA and JWST.
NIO's activities are guided by a broadly representative advisory committee comprising both national and international scientific leaders and key "stakeholders" who have a strong incentive to ensure that investments in NIO are well-aligned with long-term community interests.
| John Casani | Jet Propulsion Laboratory |
| Alan Dressler | Carnegie Observatory |
| Richard Ellis | Caltech |
| Robert Fugate | Starfire Optical Range |
| Jay Gallagher | University of Wisconsin |
| Bob Gehrz | University of Minnesota |
| Roberto Gilmozzi | European Southern Observatory |
| Riccardo Giovanelli | Cornell University |
| Bob Kirshner | Harvard-Smithsonian, CfA |
| Rolf Kudritzki | University of Hawaii |
| TBD | Herzberg Institute of Astrophysics |
| Joe Miller | University of California |
| Jerry Nelson | University of California |
| Larry Ramsey | Pennsylvania State University |
| Chuck Steidel | Caltech |
| Alfonso Serrano | CONACyT Mexico |
In structuring its initial activities, NIO has embarked on three parallel efforts:
- To develop an initial understanding of the key science that drives GSMT performance goals and requirements. Chapter 2 represents the culmination of a year-long effort to engage a broad cross section of the community in defining the discovery spaces opened by a next generation telescope, and in analyzing a representative sample of science enabled by a GSMT in the following areas: origin of large scale structure; galaxy formation; stellar populations and formation of stars and planetary systems; and high dynamic range science.
- To address technical challenges common to all extremely large telescopes (ELTs). There has
been an extraordinary worldwide effort to explore multiple concepts for a next generation
ELT, ranging from fixed elevation analogs of the Arecibo radio telescope to a 100-m baseline
binocular telescope to a 30-m diameter analog of the Keck telescope. Although each has
peculiar technical challenges, all must address: (1) selection of a site with excellent
properties; (2) characterization of predicted telescope disturbances, particularly wind loading;
(3) design and modeling of complex, hierarchical control systems; (4) design of adaptive
optics (AO) systems; and (5) design of instruments that can take advantage of the power of
GSMT. Chapter 5 describes our recent technology development
activities, which are summarized below:
- In collaboration with several other ELT groups, NOAO and Gemini staff are carrying out an extensive program of site characterization involving: (1) remote sensing studies to identify promising candidate sites; (2) development and construction of a turbulence profilometer capable of evaluating altitude dependence of turbulence in the atmosphere; (3) development and deployment of site testing instruments at specific sites; (4) modeling of atmospheric turbulence above candidate sites using computational fluid dynamics; and (5) measurements of variations of the atmospheric sodium layer, an important factor in understanding the efficacy of laser guide stars.
- NIO staff have gained significant insight into wind loading of large telescopes by analyzing an extensive set of wind pressure and velocity measurements made at Gemini South in collaboration with researchers from the University of Massachusetts at Lowell. These results are being extended by computational fluid dynamics studies undertaken at the University of Arizona and Tennessee State University.
- Working with the Gemini AO group, NIO has developed an innovative modeling capability that can simulate the performance of very-high-order, multi-conjugate laser guide star AO systems on ELTs. This modeling capability can produce realistic simulations of delivered point spread functions for AO systems with up to 105 actuators utilizing multiple deformable mirrors, and a specified number of natural guide stars and laser beacons.
- NIO staff have (1) developed a model that resolves control functions of the point design telescope into control systems that are separable in bandwidth and spatial frequency, and (2) begun simulations of the response of the telescope to dynamic disturbances.
- Optical designs have been developed for four potential AO systems that will enable delivery of high quality, near-diffraction-limited imaging at wavelengths as short as 1 micron. Key areas have been highlighted for continued technology development activities.
- Conceptual designs have been developed for a range of instruments that address the representative science cases. These innovative concepts demonstrate that practical instrument designs are quite feasible, while highlighting areas where technology development is needed.
- To create a point design based on the initial performance goals emerging from analysis of
key science problems. The point design is viewed as a tool that can be used to help:
- Identify fundamental technical challenges and their solution paths
- Understand the complex interplay among science-driven performance requirements, instrumentation, system level design issues, and the design of key subsystems
- Evaluate the dynamic performance of a complete telescope under simulated conditions of wind-buffeting and turbulence via integrated modeling
- Identify cost drivers and key cost-performance trade areas
- Develop the analytical models and tools critical to next-step studies
The point design is described in detail in Chapter 4.
AURA'S STRATEGIC PLAN
Both JWST and ALMA will be operational early in the next decade. Our estimates indicate that creation of GSMT, including initial development studies, design, construction, and commissioning, will take at least 10 years, assuming funding at an optimal rate. If GSMT is to be contemporary with JWST and ALMA, work needs to start immediately. Toward that end, AURA has developed a strategic plan that takes into account funding realities and assumes that the most expeditious path toward a GSMT involves partnerships (1) to initiate the design for GSMT and its major instruments, (2) to build the telescope and instruments, and (3) to operate the telescope. The plan's key elements are:
- Working with the US and international astronomical communities to define (1) the science context for GSMT in the era of ALMA and JWST, (2) a set of science requirements that reflects the consensus of scientific priorities, and (3) a "merit function" to guide system design choices to optimize GSMT performance in the context of a design-to-cost effort. Tasks (2) and (3) will be carried by the NSF's GSMT Science Working Group, supported by NIO staff.
- Promoting and funding development of enabling technologies for GSMT (e.g., AO components, advanced gratings).
- Actively promoting parallel study efforts aimed at exploring common technical problems and pooling resources with interested parties to accelerate necessary studies of GSMT technology, fabrication, and instrumentation issues.
- Continuing vigorous investment in site, wind loading, and AO studies critical to enabling the success of all GSMT design efforts.
- Investing in the sophisticated tools (integrated modeling; modeling of AO systems; parametric cost estimating; design-to-cost protocol) that are essential for optimizing GSMT performance per dollar invested and for minimizing life cycle costs.
- Vigorously advocating National Science Foundation (NSF) investment in AO and other technologies key to enabling GSMT performance via facilitation "roadmaps" that express broad community consensus regarding key areas for funding. Investment in these areas early in this decade can both accelerate "first light" on a GSMT and ensure that US community interests are represented in setting the requirements and designing GSMT.
- Investing in a formal GSMT design project supported through the NOAO budget and by one or more US or international partner institutions.
- Investing in GSMT instrumentation, supported through the NOAO budget, and developed via partnership arrangements.
- Investing in GSMT operations through the NOAO budget.
This strategy recognizes explicitly that the NSF is presently committed to initiating other major projects, including ALMA and ATST (Advanced Technology Solar Telescope), and calls for a significant investment from the NOAO base budget in order to initiate broad community participation in GSMT design efforts. Furthermore, AURA assumes that NSF participation in GSMT will be through a partnership involving NOAO and other national or international collaborators. It also recognizes the essential importance of proactively involving the community at all stages of the GSMT program, from setting the science goals to operating GSMT.
AURA'S COMMITMENT
AURA is committed to ensuring that the US astronomy community is fully engaged in planning, building, and operating a next generation ground-based O/IR telescope, in service of fulfilling the recommendation of the AASC decadal survey that the community be represented at all phases in the evolution of a GSMT project, and able to gain access to GSMT through an "effective national observatory." Indeed, these goals were paramount in establishing the NIO.
In the immediate future, AURA will continue to ensure that the efforts of the NIO are directed toward: (1) involving the community deeply in developing a science-based set of performance goals for GSMT; (2) supporting technology development studies with general applicability to multiple ELT design efforts; (3) investing in technical and analytical "tools" necessary for the successful design of GSMT; and (4) exploring public/private and US/international partnerships aimed at achieving full GSMT operations during the prime mission phase of JWST. In doing so, it will seek advice from the NIO Advisory Committee and work in close collaboration iwth the NSF GSMT SWG.
AURA will work to: (1) proactively serve as a "fair broker" in bringing elements of the community together to explore and define the partnerships needed to realize a GSMT; (2) develop community consensus regarding plausible funding paths to enable public participation in a GSMT project; and (3) articulate that consensus vigorously at appropriate levels in the federal government in a continuing effort to ensure timely funding of the design, construction, and operation of GSMT.
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November 2002
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