Roamy here. Some positive news from NASA this week is that six of the 18 mirrors for the James Webb Space Telescope were delivered to Marshall for cryogenic testing this week.
The X-ray and Cryogenic Facility (XRCF) will cool the mirror segments down to deep space temperature, -220 degrees Celsius (-364 degrees F), and they will check for any distortions that would ruin the image. The tolerance for these mirrors is 20 nanometers. That’s 1/10,000th the thickness of a human hair or 1/20th of the shortest wavelength of light you can see.
I worked on various coatings on beryllium in 1991 – 1992. Beryllium is light and strong, but you have to be careful machining and handling it, because of the risk of lung damage by berylliosis. Given the size of what they are building, that weight savings is necessary.
The James Webb Space Telescope is 6.5 meters (21 feet, 4 inches) across. Some more on the manufacturing of the mirrors here, and I promise a future post on the sunshield.