This photo from NASA shows two engineers from Exelis Inc. of Rochester, N.Y. demonstrating how to perform “snow cleaning” on a test telescope mirror for the James Webb Space Telescope. The cleaning took place at NASA’s Goddard Space Flight Center in Greenbelt, Md.
The snow cleaning is performed by shooting carbon dioxide snow at the surface of the mirror. This method enables engineers to clean the telescope mirrors without scratching them.
Jim Collins, Contamination Control Engineer at Exelis, is one of the workers pictured in the photo. In an exclusive interview with Controlled Environments, he gives details on the process.
“For the James Webb Space Telescope, we’re integrating and aligning the primary mirror segments under the backplane,” he says. “Since we’re handling the mirrors at this level of integration, [NASA] approached us to look into the effectiveness of the snow cleaning method on their primary mirrors.”
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The Exelis team worked in two cleanroom facilities at Goddard. Pictured in the photo is the ISO 6 facility. The other, where the integration is taking place, is an ISO 7 cleanroom.
“The process itself has two main cleaning techniques,” says Collins. “One is particle removal through momentum transfer with the snow particles hitting the surface and sweeping them off. The other is more of a solvent process — in this particular case, the process we focused on was trying to remove particles through the physical method of impacting the particles and sweeping them from the surface through momentum transfer.”
Collins says that the equipment pictured in the photo was brought to the Goddard facility by Exelis, and NASA provided some help once it got there. “We started this effort with some small development tests at our facility in Rochester. We took our equipment down to NASA and they supplied the gas for the CO2 and the mirror for the cleaning.”
Gary Matthews, Director of Universe Exploration at Exelis, explains the technology to Controlled Environments: “Snow cleaning is a technology that we’ve used on several occasions. It’s typically used for things like optical coating.” He also notes that ground-based telescopes utilize the snow cleaning technology quite a bit.
Collins adds, “In the contamination control world and the aerospace industry, snow cleaning is not uncommon but it’s typically only used for very sensitive surfaces or very sensitive paints that have specific thermal or texture profiles, where physical contact would have a negative effect on the performance of that part.”
Matthews says that there are risks involved with working on an assembled piece of equipment – with the money investment involved, negative consequences would be very bad for the space program, therefore Exelis takes great care with their tasks. “The challenge here is using this technology on an assembled piece of equipment and on the telescope itself,” he says. “We try to quantify the risks as we move forward.”
The Webb telescope is the scientific successor to NASA’s Hubble Space Telescope. It will be the most powerful space telescope ever built. With a mirror seven times as large as Hubble’s and infrared capability, Webb will be capturing light from 13.5 billion light years away. To do this, its mirror must be kept super clean.
NASA’s “Webb Cam” offers a real-time look inside the cleanroom where the Webb Telescope is being housed: http://www.jwst.nasa.gov/
Webb is an international project led by NASA with its partners, the European Space Agency, and the Canadian Space Agency.
Image credit: NASA/Chris Gunn