Fabrication of mirrors for the Magellan Telescopes and the Large Binocular Telescope

Martin, Hubert M.; Allen, Richard G.; Burge, James H.; Dettmann, Lee R.; Ketelsen, Dean A.; Miller, Stephen Matteo; Sasián, José M.

doi:10.1117/12.458606

Cited by 30 publications

(13 citation statements)

References 10 publications

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“…Move mirror segments to optimize wavefront: a. translate in radial direction b. rotate about segment center (clocking) (There is NO ALLOWANCE for axial spacing adjustment to compensate power.) 4. Bend mirrors to correct other shape errors, including power.…”

Section: Error Analysis For Gmt Interferometrymentioning

confidence: 99%

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Design and analysis for interferometric measurements of the GMT primary mirror segments

et al. 2006

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The Giant Magellan Telescope (GMT) uses seven 8.4-m diameter segments to create a giant primary mirror, 25 meters across with focal ratio f /0.7. The off-axis segments will be difficult to measure accurately, as they have 14.5 mm departure from the nearest fitting sphere! The test configuration adopted uses a large 3.75-m powered mirror to fold the light path and provide most of the aspheric correction, with a smaller mirror and computer generated hologram (CGH) providing the additional correction. These optics will be aligned to a vibration-insensitive interferometer using a combination of optical references created by the CGH and metrology with a laser tracker. Some key challenges for this system are presented here including, the system alignment, the large fold mirror, and the mechanical structure. Analysis of the optical test shows that it will meet GMT specifications, including the difficult requirement that the separate segments have matching radius of curvature. Additional corroborative testing will be performed to assure that the mirror segments are correctly figured.

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Section: Error Analysis For Gmt Interferometrymentioning

confidence: 99%

“…4 We use an interferometer with null lens at the center of curvature of the mirror under test. 5 The null lens that compensates the aspheric departure consists of a set of lens elements that are aligned using axisymmetry.…”

Section: Heritage For Measuring Large Aspheric Mirrorsmentioning

confidence: 99%

Design and analysis for interferometric measurements of the GMT primary mirror segments

et al. 2006

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“…The mirror on the polishing machine is shown in Figure 1. More details of the optical fabrication process are provided by Martin et al (2002). After polishing, the mirror will be integrated onto the support system in the telescope cell before being transported to the mountain.…”

Section: First Primary Mirrormentioning

confidence: 99%

Large Binocular Telescope project

Hill

Salinari

2003

SPIE Proceedings

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The Large Binocular Telescope (LBT) Project is a collaboration between institutions in Arizona, Germany, Italy, and Ohio. The first of two 8.4-meter borosilicate honeycomb primary mirrors for LBT is being polished at the Steward Observatory Mirror Lab this year. The second of the two 8.4-meter mirror blanks waits its turn in the polishing queue. The baseline optical configuration of LBT includes adaptive infrared secondaries of a Gregorian design. The F/15 secondaries are undersized to provide a low thermal background focal plane which is unvignetted over a 4-arcminute diameter field-of-view. These adaptive secondary mirrors with 672 voice-coil actuators are now in the early stages of fabrication. The interferometric focus combining the light from the two 8.4-meter primaries will reimage the two folded Gregorian focal planes to three central locations for phased array imaging. The telescope elevation structure accommodates swing arm spiders which allow rapid interchange of the various secondary and tertiary mirrors as well as prime focus cameras. The telescope structure accommodates installation of a vacuum bell jar for aluminizing the primary mirrors in-situ on the telescope. The telescope structure was fabricated and pre-assembled in Italy by Ansaldo-Camozzi in Milan. The structure was disassembled, packed and shipped to Arizona. The enclosure was built on Mt. Graham and is ready for telescope installation.

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“…The disadvantages of an off-axis telescope have traditionally been the additional cost of mirror fabrication and a slight increase in the weight of the support structure for the same stiffness. However the development of the computercontrolled stressed-lap polishing technique has greatly facilitated the production of fast, aspheric off-axis surfaces 23 , leading to a relatively small marginal cost increase over a conventional design.…”

Section: Off-axis Telescopesmentioning

confidence: 99%

LAPCAT: the Large Antarctic Plateau Clear-Aperture Telescope

et al. 2006

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We present a proposal for an 8.4 metre off-axis optical/IR telescope to be located at Dome C, Antarctica. LAPCAT will use a mirror identical to the offset segment recently cast for the Giant Magellan Telescope (GMT) as a completely unobscured f/2.1 primary. With a cooled deformable Gregorian secondary in a dewar following prime focus, LAPCAT will allow for diffraction-limited imaging with only a single reflecting surface at ~ 220K, and thus the lowest possible thermal background obtainable on earth. The exceptionally low atmospheric turbulence above Dome C enables very high contrast imaging in the thermal infrared, and diffraction limited imaging extending to optical wavelengths (20 mas at 800 nm, where Strehl ratios > 60% are projected). As an example, a deep 5 µm exoplanet imaging survey to complement current radial velocity methods could take advantage of both the low background and pupil remapping methods for apodization enabled by the clear aperture. Many new, young, giant planets (≥ 3M J at 1 Gyr) would be detected in orbits ≥ 5 AU out to 20 pc. By providing a test bed for many of the GMT technologies in an Antarctic environment, LAPCAT also paves the way for the eventual construction of a second GMT at Dome C. Such a telescope would have unparalleled capabilities compared both to other ELTs in temperate sites and to JWST.

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Fabrication of mirrors for the Magellan Telescopes and the Large Binocular Telescope

Cited by 30 publications

References 10 publications

Design and analysis for interferometric measurements of the GMT primary mirror segments

Design and analysis for interferometric measurements of the GMT primary mirror segments

Large Binocular Telescope project

LAPCAT: the Large Antarctic Plateau Clear-Aperture Telescope

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