The mirror of James Webb is fully deployed. The image was made in Goddard Space Flight Center, as the mirror is being lifted with crane for transfer to the clean room.
Image: NASA
The mirror consists of 18 segments, made from berillium with gold coating. Each segment is 1.3 meter wide and weights 40 kilograms. Fully deployed it is 6.5 meters in diameter.
Image: NASA
James Webb will be launched to the point Lagrange L2 of the Sun-Earth system, located on the line Sun - Earth at 1.5 million kilometers distance from the Earth. This location is chosen, because Earth will shield cooled almost to 7 K (-266 C) sensors from sunlight.
Besides, James Webb has its own shield, covering sensors from Earth's lights. However, 1.5 million kilometers distance means, that in case of malfunctions, repair mission in Hubble style is impossible.
Image: Wikipedia
For this reason, Webb is undergoing very intensive tests, simulating all possible external causes, which may damage its systems. Below are shown vibration tests:
Image: NASA
The launch of James Webb is scheduled at October, 2018, with Ariane 5 rocket
This will be the most powerful space telescope, far outperforming Hubble. Unlike Hubble, it will work in invisible for naked eyes infrared range, so its images will be processed to get custom pictures. If all goes well, we'll see exoplanets in the next 2 - 3 years.