Webb Telescope Completes First Round of Mirror Tests

The first six of 18 segments that will form the James Webb Space Telescope’s primary mirror has undergone final cryogenic testing.

The 10-week series included two test cycles where the mirrors were chilled down to -379 °F, then back to ambient temperature to ensure that they respond as expected to the extreme temperatures of space.

After completing final cryogenic testing this week at Marshall Space Flight Center, engineers and technicians guided six mirror segments for the James Webb Space Telescope off the rails. (Image: Emmett Given, NASA)

Each mirror segment, measuring ~1.3 m in diameter, will form part of the 6.5-m hexagonal telescope mirror assembly critical for infrared observations. Each of the 18 hexagonal mirror assemblies weighs approximately 40 kg. The mirrors are made of beryllium and coated with a microscopically thin coat of gold to enable efficient IR collection.

The X-ray and Cryogenic Facility at NASA’s Marshall Space Flight Center in Huntsville, Ala., provided the spacelike environment that helped engineers measure how well the telescope will image IR sources once it is in orbit.

A second set of six mirror assemblies will arrive at Marshall in late July for testing, and the final set of six will arrive in the fall.

The telescope is a combined project of NASA, the European Space Agency and the Canadian Space Agency. Northrop Grumman is the prime contractor under NASA's Goddard Space Flight Center in Greenbelt. Ball Aerospace & Technologies Corp. in Boulder, Colo., is responsible for mirror development, and L-3 Tinsley Laboratories Inc. in Richmond, Calif., is responsible for mirror grinding and polishing.

For more information, visit: www.nasa.gov/goddard