James Webb Space Telescope receives final mirrors

Space.com : The $8.8 billion James Webb Space Telescope (JWST), the planned replacement for the Hubble Space Telescope, has reached a major milestone with the arrival at NASA’s Goddard Space Flight Center of the final three mirrors. A total of 18 hexagonal mirrors will combine to form a single, 6.5-m-diameter mirror, with small motors attached to each piece so that adjustments to the telescope’s focus can be made after launch. The mirrors as well as JWST‘s four primary scientific instruments are all in the large clean room in which the telescope will be assembled. The mirrors are made of beryllium and coated with gold, and each one weighs 20 kg. JWST will operate in the IR, and because it will collect seven times the amount of light as Hubble, it will be able to peer much farther into space. The telescope is still on schedule to launch in 2018 and will be placed 1.5 million km away from Earth, where it will unfurl a large sunshade to prevent the Sun’s light from affecting the images it collects.