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How Snow Keeps the World’s Most Powerful Space Telescope Squeaky Clean

CO2 snowflakes are being tested for use with Hubble’s successor

Correspondent

May 13, 2015

If you like Hubble, you'll love its successor, the James Webb Space Telescope. The gigantic scope, which is being prepared for an October 2018 launch, will feature relatively lightweight mirrors nearly three times the size of Hubble’s. And technicians are using an unexpected substance — snow — to keep those mirrors squeaky clean.

The technique harnesses the power of particles. Here’s how it works: scientists blow high-speed liquid CO2 at the mirror, which then freezes and creates snowflakes. As the snowflakes hit the mirror, they give their momentum to other particles (dusts, contaminants and other gunk) on the surface. Snow flies off the mirror along with everything else. Best of all, the snow is so gentle that it doesn’t scratch the pricey mirrors.

The snow treatment is being tested out in Goddard Space Flight Center’s clean room on some beryllium mirror segments that will reflect the light of far-off stars. In order to watch galaxies up to 13 billion light years away, the mirrors must be free of dust and other contamination. Now, engineers are practicing a technique known as “snow cleaning” on mirror surfaces to make sure they’ve perfected it before they assemble the telescope.

A bit of snow feels just about right for the telescope, which will withstand frigid temperatures in space. In fact, it’s being built in a clean room that can simulate temperatures of -384.1 Fahrenheit. But the snow cleaning is just an Earth-bound system — there won't be any snow makers on the telescope. The technique will be used only if the actual mirrors get contaminated while they’re tested and installed.

Goddard isn’t the only facility that makes it snow — other observatories use the technique, too, and snow cleaning can be found in labs and other places that need super-clean surfaces. It’s even gaining popularity among art conservators, who are using it to clean sensitive surfaces like sculptures that can’t stand up to solvents.

(h/t io9)