NASA’s James Webb Space Telescope has reached a major milestone: completion of the coating process for the mirrors that will fly aboard the premier observatory of the next decade.
Quantum Coating Inc., of Moorestown, NJ, began applying the high-reflectance gold coating in June 2010 to a test mirror segment.
|The first six flight-ready James Webb Space Telescope's primary mirror segments are prepped to begin final cryogenic testing at NASA's Marshall Space Flight Center in Huntsville, AL.|
The microscopically thin layer of gold was selected for its ability to properly reflect infrared light from the mirrors into the observatory’s science instruments. The coating—about 0.12 ounce of gold on each segment—allows the telescope's “infrared eyes” to observe extremely faint objects in infrared light, reports Quantum Coating, an avionics optical coating technology provider founded in 1990.
‘Spectacularly New Technology’
The Webb telescope—the $8.7 billion successor to the Hubble Space Telescope—has 21 mirrors, with 18 mirror segments working together as one large 21.3-foot (6.5-meter) primary mirror. The other three segments will be used elsewhere in the telescope. The mirror segments are made of beryllium, selected for its stiffness, light weight and stability at cryogenic temperatures.
Webb’s mission is to observe the most distant objects in the universe.
“Finishing all mirror coatings on schedule is another major success story for the Webb telescope mirrors,” said Lee Feinberg, NASA Optical Telescope Element manager for the Webb telescope at Goddard Space Flight Center in Greenbelt, MD. “These coatings easily meet their specifications, ensuring even more scientific discovery potential for the Webb telescope.”
John Mather, the telescope's senior project scientist, told SPACE.com: “It represents not just the coating event but the completion of a huge engineering project. The mirrors are spectacularly new technology.”
The most powerful space telescope ever built, the Webb is designed to provide images of the first galaxies ever formed and to explore planets around distant stars. It is a joint project of NASA, the European Space Agency and the Canadian Space Agency.
Mirror manufacturing began eight years ago with blanks made out of beryllium. Several of the smaller mirrors in the telescope—the tertiary mirror and the fine steering mirror—were coated in 2010. The secondary mirror was finished earlier this year.
The coating process capped two years of development by QCI to create a coating for NASA that would meet performance goals for uniformity, cryogenic cycling, durability, stress, reflectance and other characteristics. Under a contract with Ball Aerospace and Northrop Grumman, QCI also constructed a new facility and clean room to coat the large mirror segments.
‘Without a Single Failure’
The coating process involves heating gold to its liquid point—more than 2,500 degrees Fahrenheit (1,371 degrees Celsius)—and allowing it to evaporate onto the mirror's optical surface. The resulting coatings are 120 nanometers—about a millionth of an inch, or 200 times thinner than a human hair.
“We faced many technical challenges on the Webb mirror coating program,” said Ian Stevenson, director of coating at Quantum Coating. “One of the most daunting was that all flight hardware runs had to be executed without a single failure.”
A NASA video offers more details about the coating project.
The mirror segments recently were shipped to Ball Aerospace in Boulder, CO, where actuators are being attached to help move the mirror. From there, the segments travel to the X-ray and Calibration Facility at NASA's Marshall Space Flight Center in Huntsville, AL, to undergo a final test in which they are chilled to -400 degrees Fahrenheit (-240 degrees Celsius). The last batch of six flight mirrors should complete the test by the end of this year.