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Proceedings Paper

Design issues for the active control system of the California Extremely Large Telescope (CELT)
Author(s): Gary A. Chanan; Jerry E. Nelson; Catherine Mayumi Ohara; Edwin Sirko
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Paper Abstract

We explore the issues in the control and alignment of the primary mirror of the proposed 30 meter California Extremely Large Telescope and other very large telescopes with segmented primaries (consisting of 1000 or more segments). We show that as the number of segments increases, the noise in the telescope active control system (ACS) increases, roughly as (root)n. This likely means that, for a thousand segment telescope like CELT, Keck-style capacitive sensors will not be able to adequately monitor the lowest spatial frequency degrees of freedom of the primary mirror, and will therefore have to be supplemented by a Shack-Hartmann-type wavefront sensor. However, in the case of segment phasing, which is governed by a `control matrix' similar to that of the ACS, the corresponding noise is virtually independent of n. It follows that reasonably straightforward extensions of current techniques should be adequate to phase the extremely large telescopes of the future.

Paper Details

Date Published: 2 August 2000
PDF: 10 pages
Proc. SPIE 4004, Telescope Structures, Enclosures, Controls, Assembly/Integration/Validation, and Commissioning, (2 August 2000); doi: 10.1117/12.393941
Show Author Affiliations
Gary A. Chanan, Univ. of California/Irvine (United States)
Jerry E. Nelson, Univ. of California/Santa Cruz (United States)
Catherine Mayumi Ohara, Univ. of California/Irvine (United States)
Edwin Sirko, Univ. of California/Irvine (United States)

Published in SPIE Proceedings Vol. 4004:
Telescope Structures, Enclosures, Controls, Assembly/Integration/Validation, and Commissioning
Thomas A. Sebring; Torben Andersen, Editor(s)

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