This Newsletter can also be found at:
http://www.jwst.nasa.gov/newsletter7.html
OPTICAL TELESCOPE ELEMENT CRITICAL DESIGN REVIEW SUCCESSFULLY COMPLETED
by Lee Feinberg
The Optical Telescope (OTE) Element Critical Design Review (CDR) was
completed successfully on October 5th-9th at Northrop Grumman in Redondo
Beach, California. The review board concluded that the CDR was passed
and identified 3 liens that will be closed out by the Mission CDR.
Leading up to the CDR, many OTE subsystem CDRs were completed over the
summer. This included reviews of the deployment systems for the primary
mirror and secondary mirror and the large composite backplane that holds
the primary mirror segments. The OTE CDR comes as the primary mirror
segment engineering design unit nears its very final polishing. Before
the end of this calendar year, the mirror will be shipped for a second
cryogenic test to assure the polishing of mirror deformations has been
successful and then it will go on to coating. The OTE team is now
focused on supporting the mission CDR and fabrication and assembly of
the OTE.
ONE-THIRD SCALE SUNSHIELD TESTING
by Mark Clampin
The James Webb Space Telescope’s sunshield is designed to shield the
telescope from the sun, and allow the telescope to cool to its 50K
operating temperature (Figure 1). The sunshield assembly is built from
five large Kapton membranes (similar to the Mylar used in party
balloons.) Think of five candy wrappers, each the size of a tennis
court. To understand how the sunshield will perform in its task of
cooling the telescope, Northrop Grumman will perform a thermal test of a
one-third scale sunshield assembly this month. One of the five membranes
to be used in this test is shown in Figure 2. The test will allow the
sophisticated models that predict JWST’s temperature profile to be
compared to real test data. This represents one of the last schedule
milestones to be completed prior to the Sunshield's Critical Design
Review in January 2010.
INTEGRATED SCIENCE INSTRUMENT MODULE STRUCTURE ARRIVES AT GSFC
by Matt Greenhouse
The Integrated Science Instrument Module (ISIM) is the science
instrument payload of the JWST. It is a distributed system with
subsystems located throughout the observatory. Its cryogenic portion
consists of:
• Four science instruments described at:
http://jwst.gsfc.nasa.gov/instruments.html,
• A fine guidance sensor that is used to control telescope pointing
during science observations,
• An optical metering structure that supports the instruments,
• A thermal transition harness system that connects the instruments to
control electronics both on the cold side of the observatory and in the
warm spacecraft,
• A command and data handling computer system, and
• Flight software.
For a technical description of the ISIM see: Greenhouse, M. A., et al.,
2006, Proc. SPIE 6265, 33.
The ISIM structure is a high precision M55J-954-6 cynate ester composite
material that affords a high stiffness to mass ratio and a low cryogenic
expansion coefficient to yield high optical alignment stability with
repeated thermal cycling to 40K and through the launch load environment
to orbit. The JWST application is the first time that this composite
material has been used as a cryogenic optical metering structure.
The flight model structure is now in Goddard’s large cleanroom for
integration with secondary structure and kinematic mounts that interface
the ISIM to the JWST telescope. Fit checks with Engineering Test Unit
science instruments and other testing will occur at Goddard during 2010.
A press release about the arrival of the ISIM's structure at GSFC can be
found at: http://www.nasa.gov/topics/universe/features/webb_shape.html;
as well as a movie of the structure being placed into the GSFC clean
room: http://www.jwst.nasa.gov/videos_instruments.html.
