Greenbelt, MD--The James Webb Space Telescope (JWST) reached a mission-readiness landmark yesterday, when its first primary-mirror segment was cryo-polished to its required prescription as measured at operational cryogenic temperatures. This achievement sets the stage for a successful polishing process for the remaining 18 flight mirror segments. (When in space, the cold part of the JWST will operate at a temperature of 35 K; the telescope will be a showcase of leading-edge technologies.)
Northrop Grumman Corporation is leading the JWST design-and-development effort for NASA's Goddard Space Flight Center, Greenbelt, Md. "Many predicted it would take us multiple iterations to successfully polish these mirror segments to achieve the correct optical prescription at the telescope's operating temperatures, but we did it on our first try," said Scott Willoughby, JWST program manager for Northrop Grumman Aerospace Systems. "All our budgets and schedules are based on this and it's a confirmation of the basic plan we proposed ten years ago."
Cryogenic polishing, or cryo-null figuring, ensures that when the mirror reaches its operating temperature, its shape will conform to the proper optical prescription required for it to accurately image stars and galaxies in the IR. The engineering-development unit mirror, which will be used as a flight spare, was cryotested in the X-Ray and Cryogenic Facility (XRCF) at NASA's Marshall Space Flight Center (Huntsville, AL). More testing is planned as the telescope is built up from the segments.
Testing with more than one set of null optics
Principal optical contractor Ball Aerospace will conduct separate verification tests using different computer-generated-hologram (CGH) null tools. NASA Goddard will use its own testing equipment and measurement methods in its clean room; testing at Johnson Space Flight Center will use a reflective null tool manufactured by optical integration and test partner ITT; and polishing partner Tinsley Labs will make measurements using their own independent method of calibrating their CGH null tools.
The JWST is currently expected to launch in 2014.
