Ambient optomechanical alignment and pupil metrology for the flight instruments aboard the James Webb Space Telescope

Abstract

The James Webb Space Telescope science instruments are in the final stages of being integrated into the Integrated Science Instrument Module (ISIM) element. Each instrument is tied into a common coordinate system through mechanical references that are used for optical alignment and metrology within ISIM after element-level assembly. In addition, a set of ground support equipment (GSE) consisting of large, precisely calibrated, ambient, and cryogenic structures are used as alignment references and gauges during various phases of integration and test (I&T). This GSE, the flight instruments, and ISIM structure feature different types of complimentary metrology targeting. These GSE targets are used to establish and track six degrees of freedom instrument alignment during I&T in the vehicle coordinate system (VCS). This paper describes the optomechanical metrology conducted during science instrument integration and alignment in the Spacecraft Systems Development and Integration Facility (SSDIF) cleanroom at NASA Goddard Space Flight Center (GSFC). The measurement of each instrument's ambient entrance pupil location in the telescope coordinate system is discussed. The construction of the database of target locations and the development of metrology uncertainties is also discussed.

Fine guidance sensor/near-infrared imager and slitless spectrograph on James Webb Space Telescope: pupil alignment methodology and metrology

“…Instrument and OSIM PAR calibration data were then used to calculate actual pupil coordinates resulting in the onorbit shear values as in Table 3, including gravity release estimates. Ambient and cryo temperature ISIM pupil methodology and metrology is described in [10], [12], [13] and [14]. …”