Coarse alignment of the James Webb Space Telescope secondary and primary mirrors without a fine guidance sensor

Raymond H. Wright

doi:10.1117/12.2632086

27 August 2022 Coarse alignment of the James Webb Space Telescope secondary and primary mirrors without a fine guidance sensor

Raymond H. Wright

Author Affiliations +

Proceedings Volume 12180, Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave; 121803X (2022) https://doi.org/10.1117/12.2632086
Event: SPIE Astronomical Telescopes + Instrumentation, 2022, Montréal, Québec, Canada

Conference Poster

Abstract

Launched December 25th 2021 to its final destination at the Sun-Earth Lagrange Point 2, JWST will revolutionize the way the universe is seen back to the early universe beginnings. During the six month commissioning phase of the mission, there were various activities performed which aligned the segmented telescope from eighteen unique Point Spread Functions (PSFs) to a single PSF. One of these steps is to globally align the Secondary Mirror (SM) Assembly (SMA) to the 18 Primary Mirror Segment Assemblies (PMSA) in the primary mirror. This alignment process happens in two phases, and they are named Global Alignment 1 (GA1) and Global Alignment 2 (GA2). A successful completion of GA1 entails coarsely aligning the SM and each PMSA to achieve an RMS Wavefront Error (WFE) less than 200nm. This is accomplished by generating PMSA wavefront maps which are used to determine a correction in the SM using Phase Retrieval and Decomposition. One of the requirements is that the Fine Guidance Sensor (FGS) can guide on a segment during the exposures, minimizing the impacts of motion blur on the images. This paper details a contingency method on how global alignment can be achieved using the observatories star trackers for guiding. The star trackers line of sight (LOS) stability and pointing stability performance are intended for coarse guiding whereas FGS provides fine guiding. It is expected that motion blur will increase should the observatory use coarse guiding during the GA1 exposures. Within the paper, we detail the maximum motion thresholds needed to achieve the desired placement of the SM, as well as exposure methods which can be used to handle motions that exceed the thresholds.

Citation Download Citation

Raymond H. Wright "Coarse alignment of the James Webb Space Telescope secondary and primary mirrors without a fine guidance sensor", Proc. SPIE 12180, Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave, 121803X (27 August 2022); https://doi.org/10.1117/12.2632086

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

;

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE