NASA is putting the mirrors for its James Webb Space Telescope (JWST) through the ultimate cold test — one that exposes them to temperatures hundreds of degrees below freezing to make sure they will work in space.

Six of the space telescope’s big beryllium mirrors were subjected to temperatures as low as minus 248 degrees Celsius so engineers could measure in extreme detail how their shape deformed as they cooled.

With those measurements in hand, the mirrors will be shipped to Tinsley Corp. in Redmond, Calif., for final surface polishing at room temperature. The next time the mirrors are cooled to cryogenic temperatures, the fine-tuned mirrors should distort, or bend, into the perfect shape.

JWST is slated to launch in 2014 aboard a European Space Agency-provided Ariane 5 rocket to begin scanning the universe in the infrared range of the light spectrum to peer farther back into the universe’s history than ever before. The telescope’s mission is expected to cost about $5 billion.

But first, its vital mirror system must pass their endurance trials.

The ultra-cold tests are being performed at the X-ray and Cryogenic Facility at NASA’s Marshall Space Flight Center in Huntsville, Ala.

These experiments tell scientists how well each mirror handles changes in temperature over a range of environments in space, NASA officials said in a statement.

Ultimately, the James Webb Space Telescope will use a set of 18 connected mirrors to detect infrared light from space. The next set of telescope mirrors are expected to arrive at the testing site in August.