Production of 8.4 m segments for the Giant Magellan Telescope

H. M. Martin, R. G. Allen, J. H. Burge, D. W. Kim, J. S. Kingsley, K. Law, R. D. Lutz, P. A. Strittmatter, P. Su, M. T. Tuell, S. C. West, P. Zhou

Research output: Chapter in Book/Report/Conference proceedingConference contribution

35 Scopus citations


Production of segments for the Giant Magellan Telescope is well underway at the Steward Observatory Mirror Lab. We report on the completion of the first 8.4 m off-axis segment, the casting of the second segment, and preparations for manufacture of the remaining segments. The complete set of infrastructure for serial production is in place, including the casting furnace, two 8.4 m capacity grinding and polishing machines, and a 28 m test tower that incorporates four independent measurement systems. The first segment, with 14 mm p-v aspheric departure, is by some measures the most challenging astronomical mirror ever made. Its manufacture took longer than expected, but the result is an excellent figure and demonstration of valuable new systems that will support both fabrication and measurement of the remaining segments. Polishing was done with a 1.2 m stressed lap for smoothing and large-scale figuring, and a series of smaller passive rigid-conformal laps for deterministic figuring on smaller scales. The interferometric measurement produces a null wavefront with a 3-element asymmetric null corrector including a 3.8 m spherical mirror and a computer-generated hologram. In addition to this test, we relied heavily on the new SCOTS slope test with its high accuracy and dynamic range. Evaluation of the measured figure includes simulated active correction using both the 160-actuator mirror support and the alignment degrees of freedom for the off-axis segment.

Original languageEnglish (US)
Title of host publicationModern Technologies in Space- and Ground-Based Telescopes and Instrumentation II
StatePublished - 2012
EventModern Technologies in Space- and Ground-Based Telescopes and Instrumentation II - Amsterdam, Netherlands
Duration: Jul 1 2012Jul 6 2012

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


OtherModern Technologies in Space- and Ground-Based Telescopes and Instrumentation II


  • Active optics
  • Aspheres
  • Giant Magellan Telescope
  • Off-axis
  • Optical fabrication
  • Optical testing
  • Telescopes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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