tech track papers
Categories: 2018, Technology Test Updates
The James Webb Space Telescope (JWST) project is an international collaboration led by NASA’s Goddard Space Flight Center (GSFC) in Greenbelt, MD. The Webb Telescope is NASA’s flagship observatory that will operate nearly a million miles away from Earth at the L2 Lagrange point. Webb’s optical design is a three-mirror anastigmat with four main optical systems; 1) the eighteen active Primary Mirror Segment Assemblies (PMSA), 2) a single active Secondary Mirror Assembly (SMA), 3) an Aft-Optics Subsystem (AOS) consisting of a Tertiary Mirror and Fine Steering Mirror, and 4) an Integrated Science Instrument Module (ISIM) consisting of the various instruments for the Webb Telescope. Webb’s optical system has been designed to accommodate a significant amount of alignment capability and risk with the PMSAs and SMA having rigid body motion available on-orbit for alignment to the essentially fixed AOS and ISIM optical systems.
Two critical pieces of information for the ground-test of such a large, segmented, active telescope is to 1) ensure that the relative alignment of the fixed optical sub-systems (AOS & ISIM) meet expectations, and that 2) the active components of the system (PMSAs & SMA) have adequate range of motion to align to the fixed optical subsystems once on-orbit. Addressing these two critical system parameters, a novel approach utilizing single-image phase retrieval of highly aberrated ground-test images combined with spatial metrology was developed to assess the relative alignment of the fixed optical sub-systems, and an innovative technique combining the classical optical Hartmann test with the active primary mirror segments was developed to assess the relative optical alignment of the PMSAs and SMA to the AOS & ISIM. This paper presents the methodology and results of these approaches implemented on the James Webb Space Telescope during cryogenic thermal vacuum testing at Johnson Space Center in Houston, TX.
Author: Koby SmithTopic: Technology Test Updates