World's largest space telescope completes cryogenic testing
NASA's James Webb Space Telescope, which would be the largest-ever space telescope when launched in 2019, has completed its final phase of the 100-day vacuum testing at -266ÂºC. The tests included an alignment check of Webb's 18 primary mirrors, to make sure the gold-plated, hexagonal segments act like a single mirror. The $8.8 billion telescope took 20 years to build.