Although it is still two years away from launch, the James Webb Space Telescope recently passed a number of important project milestones.
Touted as the most powerful space telescope ever built, the Webb telescope will provide images of the first galaxies ever formed and study planets around distant stars. It is a joint project of NASA, the European Space Agency and the Canadian Space Agency.
So far this month, the team working on the telescope have completed the installation of its mirrors, making it optically complete, and completed cryogenic testing on its science cameras and spectrographs.
"Optical completeness means that all of the telescope mirrors have been installed," said Lee Feinberg, the Optical Telescope Element Manager.
"We can now say ‘we have a telescope’—it’s a huge milestone many years in the making."
The telescope's 25 square metre primary mirror consists of 18 hexagonal concave segments, a secondary rounded, convex mirror, a tertiary concave mirror, and a moveable turning flat mirror called the fine steering mirror.
Its primary mirror segments and secondary mirror are made of beryllium, which was selected for its stiffness, light weight and stability at cryogenic temperatures. Bare beryllium is not very reflective of near-infrared light, so each mirror is coated with about 3 g of gold to enable it to efficiently reflect infrared light, which is what the Webb telescope's cameras see.
The cameras themselves have recently completed nearly four months of final cryo testing and monitoring at NASA'a Space Environment Simulator in Maryland, which duplicates the vacuum and extreme temperatures of space.
"We needed to test these instruments against the cold because one of the more difficult things on this project is that we are operating at very cold temperatures," said NASA's Cryogenic Test Lead Begoña Vila.
"We needed to make sure everything moves and behaves the way we expect them to in space. Everything has to be very precisely aligned for the cameras to take their measurements at those cold temperatures which they are optimised for."
All 18 mirrors are now in place on the Webb telescope. Photo: NASA/Chris Gunn