Affiliation:
1. University of California
2. Jet Propulsion Laboratory
Abstract
It has been well-established that for the extremely large segmented-mirror telescopes (ELTs) currently under construction, segment clocking (in-plane rotation) will result in piston errors between neighboring segments. By contrast, the Keck telescopes utilize a fundamentally different edge sensor geometry, which should in principle render them insensitive to this effect. However, we show that as the result of a systematic internal misalignment of the Keck edge sensors, they in fact suffer from clocking-dependent effects that are remarkably similar to those anticipated for segmented-mirror ELTs. The Keck telescopes thus provide a convenient testbed for studying segment clocking and its associated effects. Analysis of Keck phasing data shows that the segment clocking effects are not random, but systematic and lead to a global segment misalignment mode of striking symmetry in which the primary mirror assumes a terraced structure. This terrace mode has been known for some time at Keck but has only recently been understood to be a direct consequence of segment clocking. A quantitative measurement of terrace mode can be used to diagnose and calibrate segment clocking effects at Keck and for future ELTs.
Funder
Jet Propulsion Laboratory
Subject
Atomic and Molecular Physics, and Optics,Engineering (miscellaneous),Electrical and Electronic Engineering
Cited by
1 articles.
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