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Proceedings Paper

Laser metrology for ultra-stable space-based coronagraphs
Author(s): Joel A. Nissen; Alireza Azizi; Feng Zhao; Shannon Kian G. Zareh; Shanti R. Rao; Jeffrey B. Jewell; Dustin Moore
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Paper Abstract

Sensing starlight rejected from a coronagraph is essential in stabilizing the telescope pointing and wavefront drift, but performance is degraded for dim stars. Laser Metrology (MET) provides a different, complementary sensing method, one that can be used to measure changes in the alignment of the optics at high bandwidth, independent of the magnitude of the host star. Laser metrology measures changes in the separation of optical fiducial pairs, which can be separated by many meters. The principle of operations is similar to the laser metrology system used in LISA-Pathfinder to measure the in-orbit displacement between two test masses to a precision of ~10 picometers. In closed loop with actuators, MET actively maintains rigid body alignment of the front-end optics, thereby eliminating the dominant source of wavefront drift. Because MET is not photon starved, it can operate at high bandwidth and feed-forward secondary-mirror jitter to a fast-steering mirror, correcting line-of-sight errors. In the case of a segmented, active primary mirror, MET provides six degrees of freedom sensing, replacing edge sensors. MET maintains wavefront control even during attitude maneuvers, such as slews between target stars, thereby avoiding the need to repeat time-consuming speckle suppression. These features can significantly improve the performance and observational efficiency of future large-aperture space telescopes equipped with internal coronagraphs. We evaluate MET trusses for various proposed monolithic and segmented spacebased coronagraphs and present the performance requirements necessary to maintain contrast drift below 10-11.

Paper Details

Date Published: 5 September 2017
PDF: 8 pages
Proc. SPIE 10398, UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts VIII, 103980I (5 September 2017); doi: 10.1117/12.2274704
Show Author Affiliations
Joel A. Nissen, Jet Propulsion Lab. (United States)
Alireza Azizi, Jet Propulsion Lab. (United States)
Feng Zhao, Jet Propulsion Lab. (United States)
Shannon Kian G. Zareh, Jet Propulsion Lab. (United States)
Shanti R. Rao, Jet Propulsion Lab. (United States)
Jeffrey B. Jewell, Jet Propulsion Lab. (United States)
Dustin Moore, Jet Propulsion Lab. (United States)

Published in SPIE Proceedings Vol. 10398:
UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts VIII
Howard A. MacEwen; James B. Breckinridge, Editor(s)

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