NNTT's Next Generation: Harmonizing a Quartet of Large Telescopes
Thomsen, Dietrick E., Science News
The National New Technology Telescope (NNTT) is the National Optical Astronomy Observatories' (NOAO's) entry in what may be the coming generation of large telescopes. The NNTT, a proposed multiple-mirror telescope, would employ four separate mirrors to act together to simulate a single mirror 15 meters across, or to act separately. At a recent meeting in Houston of the American Astronomical Society, the NNTT's planners announced significant developments in its design, and the director of the project, Jacques M. Beckers, described successful tests of a new method for making the mirrors act in concert.
The plan, as it has evolved since 1984 when NOAO decided that the NNTT should be a multiple-mirror telescope, envisions four mirrors, each of 7.5 meters diameter, hung in a common altitude-azimuth mounting. In this mounting the telescope rotates in horizontal and vertical planes. The more usual equatorial mounting, in which the telescope rotates vertically and in the plane of the celestial equator, makes it easier to follow stars across the sky. However, the telescope has to be hung at an angle to the vertical, and in the case of an arrangement as bulky as the NNTT, an equatorial mounting would impose torques and shears that the system couldn't sustain. As does the housing of the existing Multiple Mirror Telescope, the entire building housing the NNTT would rotate horizontally (telescopes usually rotate inside their buildings).
Each of the 7.5-meter mirrors would be bigger than any telescope mirror would be bigger than any telescope mirror now existing. Earlier concepts of the NNTT had generally foreseen a larger number of smaller mirrors, but recent progress in spin-casting of large mirrors, pioneered by Roger Angel of the University of Arizona in Tucson (SN: 2/16/85, p. 106), has made the larger mirrors seem practical.
Together the four mirrors would simulate a single mirror 15 meters across, for imaging purposes. …