The JWST mirror system includes 18 gold-coated, ultrasmooth, 4.2-foot (1.3 meters) hexagonal mirror segments that comprise the 21.3-foot (6.5 m) primary mirror. When launched, it will be the largest mirror ever flown in space. [Photos: Building the James Webb Space Telescope]
Down on the floor where the packaged mirrors are ready for shipping to NASA, labels such as "do not stack…this side up" and "critical space flight hardware" are visible.
A folding scheme allows the primary mirror segments to fit atop Europe’s Ariane 5 launcher for their eventual unfolding in space. Aligning the mirror segments and adjusting the primary mirror’s curvature will occur over approximately two months.
It has taken about eight years to complete the fabrication of the mirrors, said Paul Lightsey, a Ball mission systems engineer for the optical system on JWST.
"We actually have a real nice success story," Lightsey told SPACE.com. "We’ve been able to show how long it took to polish the first mirror, then each successive mirror. By the time we got up to the later mirrors, we were taking half the time than it took for the first mirror."
Working together as one mirror, those 18 beryllium mirror segments are adjusted by computer-controlled actuators. They adjust each of the mirror segments to correct any errors and are key to giving JWST the power to produce high-quality, sharp images.
"One of the difficulties in making mirrors is to make the curvature exactly what you want," Lightsey said. JWST's mirrors can be pushed and pulled a little to get the curvature right, as well as moved up, down and sideways, he said.