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Proceedings Paper

Optical assessment of the James Webb Space telescope primary and secondary mirror cryogenic alignment with a Hartmann test
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Paper Abstract

The James Webb Space Telescope is a large, deployable telescope that will operate at cryogenic temperatures at the Earth-Sun Lagrange 2 point. The Webb Optical Telescope Element (OTE) consists of 18 actively controlled Primary Mirror Segment Assemblies (PMSAs), an actively controlled Secondary Mirror Assembly (SMA), and an Aft-Optics Subsystem (AOS) that contains a fixed Tertiary Mirror and a Fine Steering Mirror. The OTE is combined with the Integrated Science Instrument Module (ISIM) to create the full optical train called OTIS (OTE and ISIM).

OTIS has recently undergone cryogenic vacuum testing in Chamber A at Johnson Space Center in Houston, TX. A key outcome of this test was to verify there is adequate range of motion in PMSA and SMA actuators to align them to AOS/ISIM under flight-like conditions. The alignment state of the PMSAs and SMA was measured using photogrammetry and cross-checked optically using a variation of a classical Hartmann test. In the “Pass-and-a-Half” (PAAH) configuration, fiber sources near the Cassegrain focus propagate light through the full optical train and small tilts on the PMSAs create an array of spots on the science instrument detectors, mimicking the effect of a Hartmann mask. Comparison of measured and modeled spot arrays provides the alignment state of the SMA and the global tilt of the primary mirror. This paper will discuss the methodology, testing, and analysis performed to measure the alignment state of OTIS using the Hartmann method and verify the primary and secondary mirrors can be successfully aligned on orbit to meet performance requirements.

Paper Details

Date Published: 10 July 2018
PDF: 14 pages
Proc. SPIE 10706, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation III, 107061Q (10 July 2018); doi: 10.1117/12.2312201
Show Author Affiliations
Laura E. Coyle, Ball Aerospace & Technologies Corp. (United States)
Taylor S. Chonis, Ball Aerospace & Technologies Corp. (United States)
Koby Z. Smith, Ball Aerospace & Technologies Corp. (United States)
J. Scott Knight, Ball Aerospace & Technologies Corp. (United States)
D. Scott Acton, Ball Aerospace & Technologies Corp. (United States)
Joseph M. Howard, NASA Goddard Space Flight Ctr. (United States)
Lee D. Feinberg, NASA Goddard Space Flight Ctr. (United States)


Published in SPIE Proceedings Vol. 10706:
Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation III
Ramón Navarro; Roland Geyl, Editor(s)

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