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 2013.
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 http://sco.stsci.edu/newsletter
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
|
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
http://arxiv.org/abs/astro-ph/0606175.
|
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 JWSTÕs 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 (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. |
|
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.
|
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
|
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.
