James Webb Space Telescope’s giant mirror assembly unveiled

BBC : The main feature of the James Webb Space Telescope (JWST)—its 6.5-m-wide gold-coated primary mirror—has been completed and its segment covers removed for the first time. Under construction at NASA’s Goddard Space Flight Center in Maryland, the JWST is to succeed the Hubble Space Telescope as the premier space observatory of the next decade. Its main mirror, which is composed of 18 hexagonal beryllium segments, is about seven times as large as that of the Hubble. To protect the surfaces of the mirror segments from dust and scratches, each had a cover over it. Now that those covers have been removed, the entire structure will be flipped 180 degrees to attach the telescope’s scientific instruments. After environmental testing, the JWST will be shipped to NASA’s Johnson Space Center in Texas for final testing. The spacecraft bus and a giant deployable sunshield will then be attached. If all goes to plan, the final assembly will launch in 2018 from the European Spaceport in French Guiana.