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The Webb Update #5 - September 2008

Welcome to the fifth issue of the Webb Update, a newsletter to update the community about the James Webb Space Telescope.  Webb will be the next flagship astrophysics mission for NASA and is planned for launch in 2014.  A text version of this newsletter is emailed to a subscriber list when it is released. If you would like to receive the email newsletter, please visit our main Newsletter page for information on how to subscribe.

In this newsletter:

Webb Confirmed for Implementation
by Mark Clampin, Observatory Scientist and Peter Stockman, STScI Deputy Project Scientist

On July 10, 2008, NASA confirmed the James Webb Space Telescope, marking the project’s formal transition from the formulation phase to the implementation phase. Confirmation initiates monitoring of the project by Congress. NASA’s decision followed two intensive reviews of the Webb project, the Preliminary Design Review (PDR) in March, and, several weeks later, a second Non-Advocate Review (NAR). The first NAR, dealing specifically with Webb’s new technologies, was held in January 2007.

The Webb design evolved considerably in the run-up to the PDR, as illustrated in the figure.  While the telescope optics and their deployment structures remain the same, the sunshield size and shape have been optimized. For protection during launch, the sunshield will now be stowed on two folding pallets. After launch, booms will extend the sunshield from the pallets. Located at the rear of the sunshield, to neutralize the generated solar-radiation torque, a trim tab will help manage the momentum in the spacecraft’s reaction wheels. The design of the spacecraft bus—which provides support functions, such as avionics, power, and computers—has also evolved, due to the decision to employ a single, long solar array.


Current Webb design. Upper right: the design uses a long, single solar array in a “tail-dragger” configuration. Lower right: the sunshield includes a trim tab to balance the radiation torque. Lower left: the sunshield is stowed on two folding pallets, which remain with the observatory after deployment. Upper left: the optimized sunshield has straight edges ; the deployable optics are unchanged.

The next 12 months will present exciting challenges for the Webb project. Before their final cryo-polishing, the first mirrors intended for flight will be delivered to the Marshall Space Flight Center for testing. The last of the science instruments will complete their Critical Design Reviews (CDRs), and the fabrication of the flight instruments will begin. The CDR for the entire Webb mission will take place in 2009.

The project schedule shows readiness for launch in mid 2013, when an Ariane 5 rocket will lift the Webb observatory into space from the European Space Agency spaceport at Kourou, French Guiana. Science operations—the fun part!—will begin after instrument checkout and the cruise to Webb’s station at L2, the second Earth-Sun Lagrange point.

Webb Primary Mirror Engineering Design Unit in Final Stages of Testing
by Lee Feinberg, Optical Telescope Element Manager

The James Webb Space Telescope Primary Mirror Engineering Design Unit (EDU) recently demonstrated the final manufacturing process at L-3-SSG/Tinsley in Richmond, California.  As shown in the picture, the EDU is a prototype 1.4 meter diameter Beryllium mirror that is identical to the 18 flight mirror segments and is used to check out all mirror manufacturing processes prior to the actual flight mirror processing.  This recent result gives confidence that all manufacturing processes are in place to figure the 18 flight mirrors.  Lessons learned from the EDU have been applied to the flight mirrors improving the performance and processing time and all 18 flight mirrors are well along in their processing at L3-SSG/Tinsley. 

As a result of completing the final manufacturing demonstration, the EDU mirror was sent to Ball Aerospace in Boulder, Colorado where it is now undergoing integration with the hexapod mount assembly and optical testing checkout.  After integration to mount assemblies, flight mirrors will be sent for cryogenic (50 degrees Kelvin) optical testing where the cryogenic distortions will be measured.  After cryogenic testing, mirrors will eventually be returned to Tinsley for final cryogenic polishing.  During final cryogenic polishing, the inverse of the measured cryogenic distortions will be polished into the mirror to assure the mirror works at its cryogenic operating temperature.  Once cryogenic polishing is completed to final specifications, the mirror will be coated and sent for final cryogenic testing.

Engineering Design Unit Primary Mirror Segment

The people shown from left to right are: Chris Alongi (L3-SSG/Tinsley), Amber Zertuche (L-3-SSG/Tinsley), Scott Texter (NGST), Patrick Johnson (L3-SSG/Tinsley), Michael Hirsch (NGST), Lee Feinberg (NASA GSFC), Ben Gallagher (Ball Aerospace).  

Hubble Postdoctoral Fellowship Program to Include Webb

NASA has announced the launch of a new postdoctoral fellowship program, which is an amalgamation of the pre-existing Hubble and Spitzer Fellowship programs.  This new program, to be called the Hubble Postdoctoral Fellowship program, will support outstanding postdoctoral scientists whose research is broadly related to NASA Cosmic Origins scientific goals as addressed by ANY of the missions in this program: the Herschel Space Observatory, Hubble Space Telescope (HST), James Webb Space Telescope (JWST), Stratospheric Observatory for Infrared Astronomy (SOFIA), and the Spitzer Space Telescope.

Applications are solicited for fellowships to begin in the fall of 2009.  The Announcement of Opportunity, which includes detailed program policies and application instructions, is available at the web site: