Computer Science – Performance
Scientific paper
Nov 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aas...198.5125a&link_type=abstract
American Astronomical Society, 198th AAS Meeting, #51.25; Bulletin of the American Astronomical Society, Vol. 33, p.1176
Computer Science
Performance
Scientific paper
How should a Giant Segmented Mirror Telescope be built? For given primary mirror area, higher performance (sharper images and better sensitivity to extra-solar planets) can be realized in a configuration with two independent elements rather than a single dish. In our 20/20 telescope concept, two 21 m diameter telescopes (equivalent to a 30 m single dish) can be operated independently or moved around a 100 m track for operation as an interferometer. The individual foci at f/11 have 12 arcminute, seeing-limited fields. Correction to the diffraction limit (0.01 arcsec at 1 micron wavelength) will be made with adaptive secondary mirrors. For interferometry, the telescopes will be driven in tandem to keep the desired baseline, perpendicular to the source. The beams will be combined at a cryostat positioned midway between. In Fizeau mode, a much larger field of view is achieved than for conventional, fixed-element, Michelson interferometers, 30 arcsec at 2.2 microns, and the resolution of 2-7 mas, (depending on baselines used) is higher than the 15 mas for a 30 m dish. The 20/20 telescope will have the sensitivity to detect Earthlike planets of the nearest stars, through its very efficient implementation of Bracewell nulling interferometry. To minimize performance degradation from segmentation, each 21 m primary will be made from just 7 rigid segments, each like a primary mirror of the Large Binocular Telescope. The adaptive secondary mirrors will be similarly segmented, for detailed correction of wind-induced phase steps at the primary segment boundaries. Very low thermal background is projected because the adaptive correction is made at the secondary mirrors and interferometric beam combination takes place in a cryostat after just one additional Nasmyth flat reflection. Hydrostatic bearings will be used for smooth translation around the 100 m track. Each telescope with f/0.7 primary weighs 850 tons, with lowest resonant frequency > 5.5 Hz, comparable to current 8 m class telescopes. Wind and weather protection is provided by closely-fitting, Keck-sized co-moving enclosures. A separate service building will be provided for assembly, aluminization and instrument installation.
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