Webb Update

In April 2010, Webb passed its mission CDR, which was held at Northrop Grumman’s Redondo Beach facility near Los Angeles. Over the course of several days, 1,854 viewgraphs were presented by the leads of all subsystems. The final conclusion was that Webb‘s development is on track, despite its complexity.

Verification of Figuring Method

Ensuring that the primary mirror segments have the correct figure when cooled to the 40 K operating temperature is a major challenge. The segments are polished at room temperature to a shape that is not the desired flight shape, but the mirrors will deform to the correct shape when cooled to flight temperatures. This strategy requires extensive numerical simulations and iterative polishing and testing. In the final stages, the mirror segments circulate around the country: First, they are figured, polished, and measured at Tinsley Laboratories in California. Next, the segments travel to Colorado for the support structures to be installed at Ball Aerospace Technology Corporation. Next, the units travel to Alabama for optical measurements at cryogenic temperatures at the X-Ray and Cryogenic Facility (XRCF) at the Marshall Space Flight Center. Then the cycle is repeated, with further polishing at Tinsley, remounting at Ball, and retesting at Marshall, until the required optical figure is achieved.

As of January 2010, this complex process of figuring Webb’s primary mirror segments was tested and verified, when a flight spare successfully completed this polishing and testing cycle. Many lessons were learned on this pathfinder program, which should substantially reduce the polishing andtesting times for the remaining segments. Many of the segments are ready for testing at the XRCF.