JWST science instrument pupil alignment measurements

Abstract

NASA's James Webb Space Telescope (JWST) is a 6.5m diameter, segmented, deployable telescope for cryogenic IR space astronomy (~40K). 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. OSIM is a full field, cryogenic, optical simulator of the JWST OTE. It is the "Master Tool" for verifying the cryogenic alignment and optical performance of ISIM by providing simulated point source/star images to each of the four Science Instruments in ISIM. Included in OSIM is a Pupil Imaging Module (PIM) -a large format CCD used for measuring pupil alignment. Located at a virtual stop location within OSIM, the PIM records superimposed shadow images of pupil alignment reference (PAR) targets located in the OSIM and SI pupils.The OSIM Pupil Imaging Module was described by Brent Bos, et al, at SPIE in 2011 prior to ISIM testing. We have recently completed the third and final ISIM cryogenic performance verification test before ISIM was integrated with the OTE. In this paper, we describe PIM implementation, performance, and measurement results.

Critical science instrument alignment of the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM)

“…6 Pupil shear is measured in-situ using a combination of two Pupil Alignment References (PARs) and the Pupil Imaging Module (PIM) assembly within OSIM. 7 Light from the OSIM Source Delivery Module (SDM) passes through one of two OSIM PARs (either the "crossed ladder" mask or a simple cross-hair mask shown in Figure 7.) to the SI being tested where it reflects back from a PAR at the SI pupil. The reflected light comes back into OSIM and some fraction passes through the 3 rd fold mirror and is captured by the PIM.…”

JWST MIRI flight performance: Imaging

“…This test was repeated in flight to determine whether the pupil alignment had changed and to check for vignetting. The in-flight measurement showed MIRI remained aligned and met requirements reference inKubalak et al (2016).…”

Metrology for trending alignment of the James Webb Space Telescope before and after ambient environmental testing

“…In the fall of 2016 the ISIM was integrated to the OTE and met its ambient alignment requirements. ISIM had undergone rigorous characterizations and environmental testing on its own 1,2,3,4,5,6 . After ISIM and the OTE (OTIS) were integrated, the OTIS was required to experience both vibration (for three orientations) and acoustics testing.…”