Telescope to look for earliest light

Although the James Webb Space Telescope isn’t scheduled to be launched on an Ariane 5 rocket from French Guiana until October 2018, NASA announced that the 18th and final primary mirror segment was recently installed on what will be the biggest and most powerful space telescope. Each segment required almost a year to process, including 6,600 hours of machining time, heat treatment and inspection. The infrared telescope has a 6.5m (21.3′) primary mirror and a 0.74m-dia. (2.4′) secondary mirror, and, compared to 2.4m-dia. (7.9′) Hubble Space Telescope, the JWST will have nearly three times higher resolution in the infrared.

Technicians perform optical tests on the James Webb Space Telescope. Image courtesy NASA.

The stated mission goals of the JWST are to:

• Search for the first galaxies or luminous objects formed after the big bang;
• determine how galaxies evolved from their formation;
• observe the formation of stars from the first stages of the formation of planetary systems; and
• measure the physical and chemical properties of planetary systems and investigate the potential for life in those systems.

The mirror segments are made of ultralightweight beryllium and will unfold and adjust to shape after launch, NASA reported. Each hexagonal-shaped segment measures about 1.3m (4.2′) across and weighs about 40kg (88 lbs.). Once polishing is completed for each segment, a 100nm-thick coating of gold is applied via vacuum vapor deposition to improve the mirror’s ability to reflect infrared light. About 3g (0.106 oz.) of pure gold, total, is deposited on the mirrors.