Optical Alignment and Test of the James Webb Space Telescope Integrated Science Instrument Module

Abstract

The James Webb Space Telescope (JWST) is a 6.6 m diameter, segmented, deployable telescope for cryogenic IR space astronomy (~40 K). The JWST observatory architecture includes the optical telescope element (OTE) and the integrated science instrument module (ISIM) element that contains four science instruments (SI) including a guider. The SI's and Guider are mounted to a composite metering structure with outer dimensions of 2.1 times 2.2 times 1.9 m. The SI and guider units are integrated to the ISIM structure and optically tested at NASA/Goddard Space Flight Center as an instrument suite using an OTE SIMulator (OSIM). OSIM is a high-fidelity, cryogenic JWST telescope simulator that features a 1.5 m diameter powered mirror. The SIs are aligned to the structure's coordinate system under ambient, clean room conditions using laser tracker and theodolite metrology. Temperature-induced mechanical SI alignment and structural changes are measured using a photogrammetric measurement system at ambient and cryogenic temperatures. OSIM is aligned to the ISIM mechanical coordinate system at the cryogenic operating temperature via internal mechanisms and feedback from alignment sensors in six degrees of freedom. SI performance, including focus, pupil shear and wavefront error, is evaluated at the operating temperature using OSIM. We describe the ambient and cryogenic optical alignment, test and verification plan for the ISIM element.