tech track papers
Categories: 2018, Next Generation Technology
As space based telescopes continue to get larger and larger it has become necessary to split the primary mirror up into multiple segments. This allows for the telescope to be folded up within the launch fairing and deployed once on orbit. While there are obvious advantages with this segmented approach it is not without its technical challenges. One of these challenges is to match the radii of curvature (RoC) for all segments, thus allowing them to act as a single large mirror. Errors in the RoC matching will add to the total wavefront error of the telescope and therefore must be minimized. There are several methods which can be employed for RoC matching. Examples include RoC actuation, RoC precision polishing, and deformable or fixed compensation optics. This paper focuses on the method and results utilized by the James Webb Space Telescope (JWST), that of RoC actuation. This method carries with it many attractive advantages such as the relaxation of RoC polishing requirements and thus polishing time, as well as the ability to perform real-time matching to compensate for changing environmental conditions which helps guarantee a fully optimized wavefront. This method was especially advantageous given the 45 Kelvin nominal operational temperature of the Webb Telescope primary mirror. Webb’s primary consists of 18 hexagonal segments, each approximately 1.5 meters point to point and made of optical grade beryllium. A RoC actuation system on each segment uses a single actuator and six struts attached to the back of the mirror. Presented here is the RoC manufacturing methodology, as well as the measured RoC performance of both individual segments and the full primary mirror.
Author: David ChaneyTopic: Next Generation Technology