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The Webb Update #1 - July 2006

Welcome to the Webb update! This is the first issue of a quarterly newsletter to update the community about the James Webb Space Telescope (JWST), planned for launch in 2014. The Space Telescope Science Institute also maintains an archive of the HST newsletters, which have regular discussions of the JWST progress. These are available at

A text version of this newsletter is emailed to a subscriber list when it is released. If you would like to subscribe to the email newsletter, please visit our main Newsletter page for information on how to subscribe.

In this newsletter:

Space Science Reviews Paper on JWST Capabilities

by Jonathan Gardner, Deputy Senior Project Scientist

JWST artist conception

The design of JWST is guided by four science themes: (1) The End of the Dark Ages: First Light and Reionization; (2) The Assembly of Galaxies; (3) The Birth of Stars and Protoplanetary Systems; and (4) Planetary Systems and the Origins of Life. These science themes, the observations that can address them, and the planned capabilities of JWST are described in a paper that was recently accepted for publication in the journal Space Science Reviews. The paper is available as a preprint from

Most (85%) of the science that JWST does after launch will be determined by future Time Allocation Committees in response to proposals, just like HST. The SSR paper contains four chapters with detailed discussions of the four science themes, along with representative observations that would address them. Another chapter describes the design of JWST, including the observatory, the instruments and the plans for operations. Lists of filters and instrument sensitivities will be useful for planning future observations. This paper, along with the JWST website, provides a nearly complete description of the science and implementation of JWST.

JWST Observatory Update

by Mark Clampin, Observatory Scientist

The JWST team is making rapid progress on the fabrication of the telescope optics. This is important because the beryllium primary mirror segments drive the schedule for the whole mission. The primary mirror consists of 18 hexagonal mirror segments, fabricated from beryllium which is very stable at JWST’s nominal operating temperature. All of the Be mirror billets have now been fabricated by Brush-Wellman, yielding the 18 mirror segments required for JWST.

figure 1

Figure 1 (at left) shows an example of the Be mirror blank once it is cut from the Be billet. (It is being prepared for shipment at Brush-Wellman.) The next stage of mirror processing is the light weighting process undertaken at Axsys in Culman, Alabama, where the mirror blanks are machined to remove excess material from the mirror blanks.

The resulting hexagonal honeycomb structure on the rear surface of the mirror is shown in Figure 2 (right). All eighteen mirror blanks are being machined, with the first three mirror blanks having been completed.

figure 2

The engineering pathfinder mirror and the first two flight mirrors are complete and have been delivered to Tinsley for the final phase, mirror figuring. Mirror figuring work has already started on the pathfinder mirror. In the last month an important milestone was been completed with the successful vibration testing of the first flight mirror, mounted on its flight actuators and backplane assembly. The test basically demonstrated that the mirror segment did not change its figure after being subjected to launch loads.

figure 3

A picture of the flight mirror assembly is shown in Figure 3 (left), which this time includes the mirror blank, the six degree-of-freedom actuator assemblies and the strong back structure. The JWST Project's central philosophy is to complete all technology demonstrations early so that all technical risks have been retired, as the project moves into the construction phase. In the next few months we will report on each of our technology demonstrations in turn, and their importance to the success of JWST.

Project Status

by John Mather, Senior Project Scientist

JWST mirrors

The current planned cost for JWST is $2.4 B from now to launch, and about $1B for 10 years of operations. The JWST project has been subjected to exhaustive scrutiny by experts who are not part of the Project or of Goddard, and are chartered by NASA Headquarters to be skeptical and complete. The technical review panels concluded that the project is well-managed and making good progress, and that the basic designs are sound. The independent cost estimate agreed with the Project's cost estimate within 5%. Both estimates are made on the basis of extremely detailed lists of parts and subsystems, with discussions of technical maturity and heritage. The Chandra observatory, which had extremely challenging optics as well, was built by the same prime contractor and had comparable total development costs. JWST's planned budget peaks in 2008, ramping down rapidly after that.

The JWST project has worked to reduce or eliminate many of the future cost risks to the project. All the contracts are in place every part of the observatory; the last international agreement (for NASA to accept the ESA contribution of an Ariane 5 launch vehicle) has been completed. By January 2007, the project will show that every technological development is ready for detailed design and flight production by flight-like testing. Approximately half of the observatory has now reached the Preliminary Design Review stage (no showstoppers), while critical design reviews are now being held for the science instruments. This level of maturity is important because each of these areas (contracts, technology, mass, etc.) has caused major overruns on other missions during the mission construction phase.