ATST Design Update

Credit: Mark Warner, NSO/AURA/NSF

Home » ATST Design Update
Release Date: June 3, 2004

The Inouye Solar Telescope team has redefined the observatory design. The most significant change is a simplified, single-level coudé lab.

The ATST design has been refined since publication of the 24-page booklet (published in early 2004) describing the project. The ATST construction phase proposal was submitted to the National Science Foundation (NSF) on Jan. 8, 2004. The team has returned to design issues raised by the Concept Design Review (CoDR) in August 2003. The most significant change is a simplified, single-level coudé lab.

Coudé Lab: To simplify the telescope’s interface to the coudé instruments, the team selected a new optical arrangement that feeds the instruments from the center of the rotating lab, rather than the outer edge. The arrangement has one level with the same lab area as the previous two-level lab. The pier diameter was increased from 12 meters to 16.3 meters, resulting in better stability for the telescope. The increased cost is offset by the simpler arrangement. Other benefits include longer paths for instruments, which minimize beam folding, and easier switching between instruments.

Optical Beam Feed: The optical concept that accompanies the new single-level coudé lab involves three mirrors, at very small angles of incidence, in a tower mounted to the center of the rotating lab. The resulting layout produces a 100- to 120-millimeter collimated pupil at the last mirror, which is steerable, to direct the beam to any part of the lab, thereby feeding individual or groups of instruments. The new optical arrangement also places transfer mirrors at useful conjugate locations for future multiconjugate adaptive optics (MCAO) upgrades without requiring additional reflections. With the central grouping of these new beam relay optics, beam conditioning can be accomplished in less space. To make this work, the elevation axis relay optics required a change to one powered mirror. This concept still has the pupil conjugate deformable mirror on the elevation axis. Near-term work will investigate methods of thermally controlling the environment to better match the lab below. This will help avoid some potential problems of deformable mirror performance.

Telescope/Coudé Lab Interface: A major issue discussed at the CoDR was the need to control the interface between the typically colder ambient air of the telescope with that of the controlled air in the laboratory environment at the coudé level. Our baseline plan has a series of changeable windows, but we would like to eliminate these. One concept under consideration is to enclose, insulate, and control the air around the deformable mirror in a plenum extending down through the telescope mount to the coudé lab. Controlled air flow through this plenum, coupled with a horizontally-facing aperture where the telescope light enters the plenum, will provide minimal seeing. We are setting up lab experiments involving air knives, laminar flow systems, and heated boxes to simulate this interface. A high-resolution interferometer will be used to evaluate the various options.

Gregorian Rotator: One of the more difficult tasks that came from the CoDR is the requirement to supply a mechanical image rotator to the Gregorian focus area. We are looking at several options that relay the Gregorian focus to an area that would allow a reasonably sized instrument package. Each has many subtle pros and cons involved with each option, including polarization effects, variable gravity vectors acting on the instruments, and required f-ratios of the beam.

Enclosure: The dome was refined to incorporate larger louvers for ventilation to enhance thermal control of the telescope.

Site Survey: Observations continue at the sites – Haleakala, HA, Big Bear Solar Observatory, CA, and La Palma, The Canary Islands, Spain – selected November 2003 for detailed study. A finalist is to be selected in late 2004.

Upcoming Milestones: Current activities revolve around the preliminary design review later in 2004.

Related Images

Artist's concept depicts the new single-level coude lab that will sit in the base of the ATST observatory. Despite the loss of one level, the coude lab will provide eight instrument positions on hardened pads, the same as in the prior design. The expanded louvers provide up to 2.5 times as much air flow as the previous design.

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Credits

National Solar Observatory (NSO), AURA, NSF

Media Contact:
Evan Pascual
National Solar Observatory Communications Officer
media@nso.edu