Some JWST hardware nears completion amid reviews
BY STEPHEN CLARK
Posted: January 17, 2011
BOULDER, Colo. -- Contractors and instrument teams working on the James Webb Space Telescope will deliver critical pieces of the observatory this year, despite growing anxiety over the mission's ultimate launch date and price tag.
Although key components of the telescope will be finished by the end of 2011, integration of those parts, construction of the spacecraft bus and years of testing are still to come.
The mission has been mired in budget and schedule trouble since NASA formally green-lighted the project in 2008, and problems were brewing even before then. The rising costs caught the attention of Congress this year, when Sen. Barbara Mikulski, D-Md., requested an independent review of the budget difficulties, which were threatening other high-priority science probes and the future of NASA's astronomy program.
Chaired by John Casani, a respected veteran NASA engineer and project manager, the review panel concluded the earliest JWST could launch is September 2015. The board predicted the project's life-cycle cost would be at least $6.5 billion.
Before the report's release in November, NASA was estimating the mission's cost around $5.1 billion and forecasting a launch in June 2014.
The panel indicted NASA's budgeting practices, particularly within the JWST project, but Casani defended achievements in the early stages of technical development.
About $3 billion has been spent on JWST so far.
Technical progress is evident in laboratories in the United States and Europe, where engineers are getting ready to ship significant parts of the telescope to NASA's Goddard Space Flight Center in Greenbelt, Md.
But delays are just as clear. According to schedules laid out eight years ago, JWST was supposed to be yielding new cosmic discoveries right now. Instead, agency managers are grappling with rising costs as engineers struggle to meet tough schedules with evaporating cash.
The Casani report said NASA needed to commit $250 million more to JWST in both 2011 and 2012, just to achieve a launch date in September 2015. Elizabeth Robinson, NASA's chief financial officer, told Congress last month she doesn't expect that funding to materialize this year.
NASA is doing an internal bottoms-up assessment of the program to get its own funding and schedule estimates.
Richard Howard, the JWST program director at NASA Headquarters, told an agency advisory committee last month that he hopes to have a new project baseline by February for independent review. Final NASA approval would come a few months later, when the 2011 and 2012 federal budgets are better understood.
"This is our one and last chance to get this right," Howard said Dec. 22. "We have to include all the liens and threats and things maybe we haven't even accounted for yet."
Ball builds space-age mirrors
Ball Aerospace and Technologies Corp. here is overseeing the construction, polishing and testing of the telescope's light-reflecting mirrors.
JWST will be the largest telescope to ever fly in space, eclipsing Hubble, the legendary mission the new observatory is intended to replace. The primary mirror will collect seven times more light than Hubble, according to NASA.
During its launch, the probe's mirror will be folded like a piece of Japanese origami art. The structure will later unfurl not just the mirror, but also a solar panel, a heat-blocking sunshield the size of a tennis court and an array of support structures.
"James Webb doesn't look like a conventional telescope," said Mark Bergeland, the JWST program manager at Ball Aerospace. "There are two reasons for that. One is it's too large to fit in any launch vehicle. It's just too big. The second reason is it's a cryogenic telescope. We have a sunshield that has the spacecraft side always facing the sun. The telescope side is always facing deep space."
The JWST primary mirror will stretch 6.5 meters, or 21.3 feet, in diameter when fully deployed. Hubble's mirror is 2.4 meters, or nearly 7.9 feet, across.
"The primary mirror reflecting aperture is one of the measures of goodness of a telescope," Bergeland said.
Unlike other telescopes, JWST's primary mirror is composed of 18 six-sided segments. Technicians treat telescope mirrors with special care and precision. Errors in the polishing of a mirror can distort imagery and ruin science results, so Hubble and other astronomy missions use a lone rigid reflecting surface in the interest of reliability.
Incoming light will first bounce off JWST's primary mirror, then pass through geometrically-perfect secondary mirror, and tertiary and fine steering mirrors before finally reaching the spacecraft's four instruments.
Such a complex design necessitates flawless construction.
The primary mirror segments are made of beryllium, a durable, yet lightweight, material known for its conduction of heat and electricity. In the first phase of construction, Brush Wellman Inc., a Ball subcontractor based in Ohio, each section of the mirror starts off as a blank weighing about 550 pounds, according to Bergeland.
Those are just the first two stops in the mirrors' cross-country journey. Mirror components go through Ohio, Alabama, California, Colorado, New Jersey, Maryland and French Guiana on their way to space.
The big challenge is getting 18 mirror segments, each manufactured separately, to work as one unit in space a million miles from Earth at a temperature of 40 Kelvin, or nearly -390 degrees Fahrenheit. A five-layer sunshield will pop open once the probe reaches space to block sunlight and keep the optics system cold.
The telescope has to be cooled to such temperatures to detect distant infrared light sources such as cold star-forming dust clouds and ancient galaxies.
At those cryogenic temperatures, materials inside the telescope, including the mirrors themselves, will contract. That introduces another challenge for engineers.
"One of the unique challenges for JWST, because it's a cryogenic telescope, we know that when we go cold, those mirrors are going to change shape," Bergeland said. "You take anything down to -390 degrees (Fahrenheit), and it will distort and warp. The nice thing about beryllium is it does that predictably."
Developers are putting the mirrors through a series of cryogenic tests to subject the structures to the ultra-cold conditions they will experience in space.
"Think of it as a topographic map of how it distorts," Bergeland said. "We can map the highs and lows."
The mirrors go through two phases of automated polishing at Tinsley Laboratories in California. In the first step, Tinsley grinds the mirror to the rough shape required by NASA, then the unit is shipped to the Marshall Space Flight Center for testing, where they are cooled to the temperatures they will see in space.
Engineers observe the mirror segments' response to the frigid conditions, cataloguing their bending and warping for Tinsley to correct in the second round of polishing.
NASA specifies each primary mirror segment be smoothed with variations no larger than 25 nanometers. For comparison, a sheet of paper is about 100,000 nanometers thick.
"If you scaled that mirror to the size of the continental United States, the biggest variation would be about 6 inches," Bergeland said.
The 18 segments are polished to three different specifications. Inner, middle and outer rings each have their own prescriptions, and mirror segments are interchangeable within each ring.
The last step is coating the mirror's optical surface with gold to increase reflectivity in infrared wavelengths. Ball sends the mirrors to Marshall for a final cryogenic test before the end of manufacturing.
"All 18 primary mirror segments are through the first cryogenic test. They're either in final polishing or through final polishing," Bergeland said in December. "We're just clicking them off one-by-one."
The primary mirror won't be fully optimized until the observatory reaches space. Each segment has seven mechanical actuators to tilt, rotate and change its curvature. The telescope's optics will initially correct itself to compensate for launch vibrations, but it has the ability for further adjustments throughout the five-year mission.
"We have to have the capability on each of the individual mirror segments to move them fractions of wavelengths of light-type motions to make these 18 individual segments look like one big mirror," Bergeland said.
All of JWST's mirrors, including the secondary, tertiary and fine steering systems, are on schedule for delivery to Goddard by the end of 2011 for attachment to the observatory's backplane, the composite structure that supports the whole telescope.
ATK is the prime contractor for the backplane, which will also be an attachment point for JWST's science payloads. ITT Geospatial Systems has the contract for integration and testing of the optical telescope element.
Science payloads almost ready for delivery
The mission's instruments will also converge on Goddard this year.
Goddard is building and testing the Integrated Science Instrument Module, or ISIM, the chassis that will cocoon the telescope's suite of cameras. The ISIM will be ready to receive instruments as soon as June 2011, according to Lynn Chandler, a NASA spokesperson.
Scientific and industrial teams from Europe, the United States and Canada all expect to send their sensors to Goddard by the end of 2011.
Marcia Rieke, principal investigator for the NIRCam near-infrared imager, says her instrument is under construction at Lockheed Martin's Advanced Technology Center in Palo Alto, Calif.
The fully-assembled NIRCam instrument should be ready for integrated testing this spring, followed by delivery to Goddard in late 2011, according to Rieke, a researcher from the University of Arizona.
Two payload packages from the European Space Agency are due for delivery in July and August 2011, according to Peter Jensen, ESA's JWST project manager.
EADS Astrium of Germany is waiting for delivery of a final piece of the Near-Infrared Spectrograph, or NIRSpec instrument, early this year. A NASA-supplied focal plane assembly showed defects, so the sensor's European builder is awaiting a spare unit.
Completion and final testing of the Mid-Infrared Instrument, or MIRI, is also pending arrival of a NASA focal plane system. MIRI passed vibration testing last year at Rutherford Appleton Laboratory in the United Kingdom.
MIRI is the coldest of JWST's instruments. Its detectors will be as cold as -447 degrees Fahrenheit, allowing it to see through cosmic dust and into faraway star clusters and galaxies.
NIRSpec and MIRI will both undergo cryogenic cold-temperature testing before they are transported to Goddard, Jensen said.
The Canadian Space Agency's main contribution to JWST is scheduled to be at Goddard by September 2011, according to Chandler. Canada is providing the observatory's Fine Guidance Sensor and a Tunable Filter Camera.
The ISIM's cryogenic proof testing was also finished last year, verifying its structure has the strength to withstand the telescope's operating conditions.
Engineers will spend 2012 and 2013 putting together the observatory's complex telescope element inside a clean room at Goddard. Then comes more testing.
NASA ordered an assessment of JWST testing plans last year to see if some of the checks could be streamlined or requirements could be relaxed.
The test assessment team found some time could be cut from the telescope and instrument test schedules at Goddard and the Johnson Space Center in Houston. Project managers could save up to six months by optimizing testing, the engineering review concluded.
"This reduction could shorten the critical path, avoiding significant cost growth," the test assessment team wrote in its report.
Although shortened testing would increase the uncertainty of JWST's flight characteristics, there would be a "negligible difference" in the odds of unacceptable performance, according to engineers.
Northrop Grumman Corp., JWST's prime contractor, oversees the mission's design and development. The California-based company will also construct the observatory's spacecraft bus, which contains nuts-and-bolts items like rocket fuel, reaction wheels, solar panels, communications antennas and computers.
Production of the JWST spacecraft hasn't even started yet. Planners front-loaded the project timeline with the most challenging work first, and Northrop Grumman and NASA consider the spacecraft bus a low-risk development.
But in a time of tight schedules, NASA is looking at beginning some of the spacecraft work sooner. Such a decision would reduce schedule risk, according to Howard.
"We need to look at what makes sense in terms of what we can bring back to the left in the schedule for the spacecraft element," Howard said.
Without money now, officials caution JWST's launch could move even later.
"Funding in the early part of this program is key to bring a launch date in that's earlier than early '16 or late '15," Howard said.