Optical testing and verification methods for the James Webb Space Telescope Integrated Science Instrument Module element

Abstract

NASA's James Webb Space Telescope (JWST) is a 6.6m diameter, segmented, deployable telescope for cryogenic IR space astronomy (~40K). The JWST Observatory includes the Optical Telescope Element (OTE) and the Integrated Science Instrument Module (ISIM) that contains four science instruments (SI) and the fine guider. The SIs are mounted to a composite metering structure. The SI and guider units were integrated to the ISIM structure and optically tested at the NASA Goddard Space Flight Center as a suite using the Optical Telescope Element SIMulator (OSIM). OSIM is a full field, cryogenic JWST telescope simulator. SI performance, including alignment and wavefront error, were evaluated using OSIM. We describe test and analysis methods for optical performance verification of the ISIM Element, with an emphasis on the processes used to plan and execute the test. The complexity of ISIM and OSIM drove us to develop a software tool for test planning that allows for configuration control of observations, associated scripts, and management of hardware and software limits and constraints, as well as tools for rapid data evaluation, and flexible re-planning in response to the unexpected. As examples of our test and analysis approach, we discuss how factors such as the ground test thermal environment are compensated in alignment. We describe how these innovative methods for test planning and execution and post-test analysis were instrumental in the verification program for the ISIM element, with enough information to allow the reader to consider these innovations and lessons learned in this successful effort in their future testing for other programs.

Optics technology for large-aperture space telescopes: from fabrication to final acceptance tests

“…The JWST team has developed very extensive tests to create the cryogenic environment that the telescope will experience when used on orbit [209]. The system level tests are first completed on the science instrument assembly [210] and finally planned as a full system [211], where multiple test methods will be implemented to reduce the risk during the test. However, due to the very large aperture of the telescope and gravity deformation of the light-weight mirrors, a full-scale test of the system is not possible.…”

Cryo-vacuum testing of the JWST Integrated Science Instrument Module

“…A strong advantage of the TPT is that it is structured so that updated information about OSIM pointing or the brightness of a light source can be input so as to propagate automatically to all other planned tests using that pointing or source. See Antonille et al (2016) 15 for a more detailed description of these impressive software tools.…”

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.…”