World's most expensive telescope's parts cleared for use in space

NASA's $8.8-billion James Webb Space Telescope, the world's largest and most expensive one, has successfully passed final thermal vacuum test, making its parts cleared for use in space. The 6.5-metre diameter telescope has 18 gold-coated mirrors and a tennis court-sized sun-shield to gather light and protect its instruments. The telescope, set to launch in 2021, took 20 years to build.