The Webb Update #2 - November 2006
Welcome to the second issue of the Webb update, a quarterly newsletter to update the community about the James Webb Space Telescope (JWST). JWST will be the next flagship astrophysics mission for NASA and is 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
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In this newsletter:
"Meet JWST" Reception at Seattle AAS Meeting
Northrop Grumman Space Technology (NGST) is hosting a "Meet JWST" reception at the upcoming AAS meeting in Seattle. All participants are invited to the reception to meet many of the people responsible for the development of the JWST mission. The reception will be held in the lobby of the convention hotel at 6-7pm on Monday evening, January 8. Tours of the JWST full scale model will be held during the reception and throughout the four day AAS meeting.
NGST, GSFC, and the JWST Science Working Group have organized presentations immediately after the reception, on JWST's scientific promise and the technology challenges. These will include introductions by Alexis Livanos, NGST President, and Ed Weiler, GSFC Director. John Mather, JWST Senior Project Scientist, will speak on Lessons Learned from COBE and the scientific promise of JWST. Bob Giampaoli, NGST Chief Engineer, will describe the challenges of deploying the JWST optics and sunshield. Mark Clampin, Observatory Project Scientist, will present the status of the key enabling technologies. Comments and questions will be welcome.
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Astrophysics in the Next Decade: JWST and Concurrent Facilities
NASA and the STScI are hosting an international conference on the science of JWST, ALMA, and other major approved facilities
and instruments in the next decade. Approximately 30 invited speakers will discuss the observational and theoretical questions that will be
addressed by these powerful new capabilities. The conference will be held at the Starr Pass Marriott in Tucson Arizona on September 24-27, 2007.
The agenda for the meeting and registration details will be distributed in January-February 2007. For additional information, please contact
Peter Stockman (stockman@stsci.edu).
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John Mather receives 2006 Nobel Prize in Physics
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In December, John Mather, the JWST Senior Project Scientist will travel to Stockholm to be awarded the 2006 Nobel Prize in Physics with George Smoot of the University of California at Berkeley for their discovery of the blackbody form and anisotropy of the cosmic microwave background radiation. Mather and Smoot worked together on the Cosmic Background Explorer (COBE) mission, which measured the spectrum and anisotropy of the cosmic microwave background (CMB), and discovered the infrared background.
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Mather first proposed the COBE in 1974, less than a decade after the discovery of the CMB. After passing through several different concepts, including as an instrument on the Infrared Astronomical Satellite (IRAS), and a shuttle-borne version, COBE was launched aboard a Delta rocket in 1989 with three instruments. Mather was the overall project scientist for the mission, as well as the principal investigator (PI) of the Far-Infrared Absolute Spectrophotometer (FIRAS), which measured the spectrum of the CMB to be a nearly-perfect blackbody of 2.725 +/- 0.001 K. George Smoot was the PI of the Differential Microwave Radiometer (DMR), which found anisotropies in the CMB of about one part in 100,000. Mike Hauser was the PI of the Diffuse Infrared Background Experiment (DIRBE), which measured the cosmic infrared background. Most of the COBE satellite was built at Goddard Space Flight Center.
The COBE mission ended in 1993, and most of the scientific results appeared over the next few years. In 1996, Mather became the study scientist for the Next Generation Space Telescope, which was later renamed JWST.
The 2006 Nobel Prize for COBE follows on to the 1978 Prize in physics which was given to Arno Penzias and Robert Wilson for the discovery of the CMB. Since there is no separate Nobel Prize for astronomy, only a few astronomers have won the physics prize. Examples include Riccardo Giacconi, who won in 2002 for creating the field of X-ray astronomy, and Subramanyan Chandrasekhar and William Fowler who won in 1983 for stellar and chemical evolution. Mather has worked for Goddard for more than 30 years, and is the first NASA civil servant to win the Nobel Prize. Mather and Smoot will split the $1.4M prize, but both have decided to donate the money to charity.
For links and press releases associated with this award, please visit this page.
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Backplane Stability Test Article Completes Test
by Jon Arenberg, BSTA conductor and Deputy Observatory Systems Engineer (NGST)
The JWST program has completed test and data collection operation on the Backplane Stability Test Article (BSTA). The BSTA is a section of the current flight back plane design containing three full scale primary mirror bays, and is approximately 2.5m by 2.8 m in size. The BSTA was tested at cryogenic temperatures in the X-ray Calibration Facility (XRCF) chamber at the George C. Marshall Space Flight Center from August to October of 2006.
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The test consisted of multiple cycles over the flight backplane operational range of temperature range from 30-60K. The out-of-plane distortions of the BSTA were measured and recorded by an Electronic Speckle Pattern Interferometer (ESPI). The measurement resolution for the motions was of the order of ones of nanometers over this very large structure. The deformation measurements will be compared to predictions to show the predictability of the backplane. Predictability is a key element in making that case for the technological readiness of the flight backplane.
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JWST Mirror Progress
by Lee Feinberg, Optical Telescope Element Manager
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It has been a busy and successful period in the development and manufacturing of the lightweight primary mirror segments for JWST. This past June, the final step towards mirror flight readiness (or "TRL-6" in NASA-speak) was achieved. A flight mirror was exposed to 3-axis loads that enveloped the predicted flight vibro-acoustic levels and measurements indicated the mirror did not distort within the very small measurement error of the test.
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In addition to this achievement, manufacturing work on the flight segments continues to go well. Axsys Technologies made great progress on the light-weighting and front surface machining of the flight mirror segments. In fact, 14 of the 18 flight segments have now completed machining at Axsys Technologies and 13 of these have been delivered to L-3 Communications/SSG-Tinsley in Richmond, California for grinding and polishing (one is at Ball Aerospace for vibro-acoustic testing). A total of 6 flight mirrors are in early stages of grinding at Tinsley and the Engineering Design Unit (EDU) is nearly complete with the grinding phase and will soon be ready for polishing. The EDU continues to serve as a process pathfinder and, just like at Axsys, the EDU lessons learned at Tinsley are being applied to flight mirrors. In addition, process improvements made on the EDU during the grinding phases at Tinsley were highly successful and we're optimistic that the flight mirrors can be made ahead of schedule, at least during those same grinding phases of the process.
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JWST WFS&C (Wavefront Sensing and Control) Progress
by Bill Hayden, OTE Systems Engineer
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The James Webb Space Telescope architecture includes a 6.5 meter diameter telescope having a segmented primary mirror that will deploy after it launches. To perform like a single monolithic mirror, a wavefront sensing and control subsystem is required to sense and then correct any errors in the optics. Demonstrating the wavefront sensing and control subsystem algorithms, to flight-readiness on NASA's technology readiness scale, is a key requirement for the NASA Headquarters' technology review scheduled for January 2007. Ball Aerospace has engineered a scaled telescope testbed which is traceable to the flight telescope so that wavefront sensing and control can be developed and demonstrated in a high-fidelity environment. A testbed telescope image is shown in the figure on the right.
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Each of the 9 distinct alignment processes - the algorithms - needed to align the deployed telescope into a high-performance
astronomical telescope have been designed and demonstrated on the testbed.
Sequentially applying this set of algorithms is what we call the
Commissioning Process. The final technology development step is to systematically step through each process and compare the results to
predefined criteria. The last process is the Fine Phasing algorithm, the outcome of which produces a sharp, clear image or, in NASA jargon,
a coherent point spread function that is near the diffraction limit. The figure below illustrates recent results from Fine Phasing on the testbed.
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Image Caption: Optical performance: (l) Stacked incoherent Point Spread Function (PSF) contains random small tip/tilt and piston errors occurring before Fine Phasing; (r) phased PSF clearly indicates coherent addition and success of closed loop fine phasing. (FWHM is Full Width, Half Maximum)
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The NASA and Ball teams have agreed on the test criteria which include 3 critical measurements. The first compares the fine phasing algorithm results to a calibrated interferometer - the industry standard in measuring optical systems; the second compares the completion of the 9 contiguous commissioning steps to the best possible testbed performance; and the third measures the algorithm's capability to get sharp imaging over its entire large field of view, which is critical to the 5 instruments sharing that field of view. The tests started in mid-October and will finish by early December. Results to-date suggests that this will be very successful.
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ISIM Passes its Preliminary Design Review
by Pam Sullivan, ISIM Manager
T
he JWST Project accomplished a major milestone in October as the Integrated Science Instrument Module (ISIM) successfully completed its preliminary design review (PDR). ISIM is one of three elements of the Webb Observatory - the others being the Telescope and Spacecraft - and ISIM is the first to reach this milestone. ISIM contains some of the most challenging design aspects of the Observatory, including cryogenic optics and structures, ultra-low-noise infrared detectors, and high-rate data systems. The completion of the ISIM preliminary design phase gives high confidence that the proposed design will meet its performance requirements.
ISIM is comprised of the four JWST Science Instruments: the Near-Infrared Camera (NIRCam), the Near-Infrared Spectrograph (NIRSpec), the Mid-Infrared Instrument (MIRI), and the Fine Guidance Sensor/Tunable Filter (FGS/TF). ISIM also includes critical subsystems needed to support the instruments such as the structure that aligns the instruments to the telescope and the electronics that retrieve the science data from the instruments. The Goddard Space Flight Center leads the ISIM development, and is responsible for the overall design, integration, and test. Instruments are provided by the University of Arizona and Lockheed Martin (NIRCam), the European Space Agency (NIRSpec), the Canadian Space Agency (FGS/TF), and a team of JPL and a European Consortium of space agencies (MIRI).
The ISIM PDR was held on October 24-26 at the Goddard Space Flight Center. Members from all of the partner organizations were in attendance. The review was conducted by an independent team of 22 subject-matter experts, who judged the ISIM design against a detailed list of success criteria established in Goddard procedural guidelines. The review team concluded unanimously that the objectives of the PDR had been satisfied.
ISIM now moves into the final, critical design phase. Key to this phase of the program is the development of engineering test unit hardware, which will validate performance predictions and manufacturing techniques in order to reduce technical and schedule risk.
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