Optics for the 20/20 telescope

We present a plan for making the optics of a 21 m telescope that builds on advances in mirror design and fabrication developed for the Large Binocular Telescope and other large telescopes. The 21 m telescope, with a fast f/0.7 primary mirror made of only seven large honeycomb-sandwich segments and an adaptive secondary mirror with matching segments, is much stiffer than other designs and offers simpler and more accurate wavefront control. It can be a powerful stand-alone telescope, or one of a pair that move on a circular track to achieve coherent imaging with baselines up to 120 m (the 20/20 telescope). Each segment of the 21 m primary mirror is similar to an 8.4 m LBT primary, and each segment of the 2.1 m adaptive secondary mirror is similar to an LBT secondary. The off-axis segments of both mirrors can be made with the same methods and equipment currently used at the Steward Observatory Mirror Lab, and can be polished with the same stressed-lap polishing system used for the LBT mirrors. A change in algorithm to accommodate the asymmetric surface is required, but no new hardware development is needed because the lap bending is similar to that for the LBT mirrors. Each segment can be measured interferometrically, with a combination reflective and diffractive null corrector producing an accurate template wavefront and alignment references for the segments.

[1]  James Roger P. Angel,et al.  20 and 30 m telescope designs with potential for subsequent incorporation into a track-mounted pair (20/20 or 30/30). , 2003, SPIE Astronomical Telescopes + Instrumentation.

[2]  Roger Angel,et al.  The 20/20 telescope: MCAO imaging at the individual and combined foci , 2002 .

[3]  Alfred Vidal-Madjar,et al.  The Magellan project , 1982 .

[4]  James H. Burge,et al.  Measurement of large convex aspheres , 1997, Other Conferences.

[5]  James H. Burge,et al.  Optical test alignment using computer generated holograms , 2002 .

[6]  John M. Hill,et al.  The Large Binocular Telescope project , 2004, SPIE Astronomical Telescopes + Instrumentation.

[7]  Jose M. Sasian,et al.  Design, tolerancing, and certification of a null corrector to test 8.4-m mirrors , 1999, Optical Systems Design.

[8]  James H. Burge,et al.  Optical fabrication of the MMT adaptive secondary mirror , 2000, Astronomical Telescopes and Instrumentation.

[9]  Hubert M. Martin,et al.  Optical issues for giant telescopes with extremely fast primary mirrors , 2003, SPIE Astronomical Telescopes + Instrumentation.

[10]  Casting 6.5-meter mirrors for the MMT conversion and Magellan , 1994, Astronomical Telescopes and Instrumentation.

[11]  Jerry Nelson,et al.  Design concepts for the California Extremely Large Telescope (CELT) , 2000, Astronomical Telescopes + Instrumentation.

[12]  Brian Cuerden,et al.  Primary mirror system for the first Magellan telescope , 2000, Astronomical Telescopes and Instrumentation.

[13]  John M. Hill,et al.  Toward first light for the 6.5-m MMT Telescope , 1997, Other Conferences.

[14]  Warren B. Davison,et al.  Machine for complete fabrication of 8-m class mirrors , 1994, Astronomical Telescopes and Instrumentation.

[15]  James H. Burge,et al.  Null test optics for the MMT and Magellan 6.5-m f/1.25 primary mirrors , 1994, Astronomical Telescopes and Instrumentation.

[16]  James Roger P. Angel,et al.  Design and Analysis of 20m track mounted and 30m telescopes , 2003, SPIE Astronomical Telescopes + Instrumentation.

[17]  Philippe Dierickx,et al.  Progress of the OWL 100-m telescope conceptual design , 2000, Astronomical Telescopes + Instrumentation.