Presentation, analysis, and simulation of active alignment strategies for the James Webb Space Telescope

Abstract

This paper presents three characteristics in the simulated active alignment strategy of the James Webb Space Telescope. The first includes the analysis and comparison of a baseline active alignment strategy with a damped least squares strategy. This baseline utilizes prior knowledge by means of direct human operator interaction to engage sets of telescope compensators to target specific aberration signatures. The baseline is compared to a damped least-squares strategy that utilizes simultaneous engagement of all telescope compensators without explicit human operator interaction to achieve a least-squares telescope compensation. Second, we discuss how the active alignment of the JWST is encapsulated in a linear optical model developed at the Space Telescope Science Institute. This linear optical model provides a framework for an efficient and robust description of the optical control properties of the JWST and clearly articulates the necessity for having a multi-instrument multifield wavefront sensing strategy to overcome control system non independence and the effects of non-common path errors in the main wavefront sensing camera. Finally, we present analytical results that explicitly map the telescope wavefront responses to the telescope control modes, and we present Monte-Carlo optical performance simulation results that demonstrate the efficacy of the damped least-squares active alignment and the priorknowledge active alignment schemes.

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

“…Already, the first signs of active optics implementations in space projects can be found. For instance, the JWST will include active optics in order to adjust phasing of its large segmented deployable primary mirror and correct for line of sight variations [226], while the future NASA mission Wide Field Infrared Survey Telescope will include deformable mirrors in its coronagraph to correct for wavefront error instabilities in order to reach the extreme contrast required [227]. ESA initiated studies are also making the case for use of active correction loops for Space-based Astronomy [218] future large missions.…”