Goddard Space Flight Center, Greenbelt, Maryland 20771

ENGINEERING COLLOQUIUM

Monday, May21, 2007 / 3:30 PM, Building 3 Auditorium

Pat McCarthy

"The Magellan Telescope"

ABSTRACT -- Advances in optical fabrication and support technologies, finite element analysis and adaptive optics have opened multiple paths to a next generation of extremely large telescopes (ELTs). Three international consortia are developing concepts for telescopes larger than 20m in diameter. One of these, The Giant Magellan Telescope, a 25m aperture built around seven 8.4m diameter mirror segments. The GMT mirror segments are spun-cast borosilicate glass and six of them are polished into off-axis ellipsoids using a deformable lap. The seven mirrors will work together to provide the collecting area equivalent to that of a filled aperture 22m in diameter and the angular resolution of a filled 24.5m aperture - ten times that of the Hubble Space Telescope. This combination of collecting area and resolving power enables a broad range of exciting science beyond the reach of current facilities. I will describe the scientific frontiers for ELTs and the GMT in particular and focus on studies of extrasolar planets, distant black holes and the first stars and galaxies. Extremely large telescopes and their associated instruments face significant challenges in rejecting wind disturbances, maintaining phase alignment and canceling the effects of atmospheric turbulence. An adaptive secondary mirror, composed of 3mm thin face sheets and more than 7000 voice coil actuators will correct wavefronts distorted by the Earth's atmosphere hundreds of times each second, while powerful lasers will provide artificial beacons as wavefront reference sources. I will describe the technical challenges facing the GMT and explain the rationale for the choice of large segments, an adaptive secondary mirror and a compact and stiff telescope structure.

SPEAKER -- Patrick McCarthy earned his doctorate in astronomy and astrophysics at Berkeley in 1988. He was a Carnegie Fellow and then a Hubble Fellow at the Carnegie Observatories, where he is presently a member of the scientific staff. His research is centered on understanding the formation and evolution of galaxies at high redshift. For the past three years he has served as the chair of the Giant Magellan Telescope Science Advisory Committee and is a member of the GMT Board of Directors. Dr. McCarthy is currently the chair of the Hubble Users Committee.