The first six of 18 segments that will form NASA's James Webb Space Telescope's primary mirror for space observations completed final cryogenic（冷冻的） testing this week. The ten week test series included two tests cycles where the mirrors were chilled down to -379 degrees Fahrenheit, then back to ambient temperature（环境温度） to ensure the mirrors respond as expected to the extreme temperatures of space. A second set of six mirror assemblies will arrive at Marshall in late July to begin testing, and the final set of six will arrive in the fall.

The X-ray and Cryogenic Facility at NASA's Marshall Space Flight Center in Huntsville, Ala. provides the space-like environment to help engineers measure how well the telescope will image infrared sources once in orbit.

Each mirror segment measures approximately 4.3 feet (1.3 meters) in diameter to form the 21.3 foot (6.5 meters), hexagonal（六边的） telescope mirror assembly critical for infrared observations. Each of the 18 hexagonal-shaped mirror assemblies weighs approximately 88 pounds (40 kilograms). The mirrors are made of a light and strong metal called beryllium（铍） , and coated with a microscopically thin coat of gold to enabling the mirror to efficiently collect infrared light.