NASA have been busy with the construction of the James Webb Space Telescope, the successor to the Hubble telescope, and have released a few tasty images of the telescope being put together. At least, they are tasty if, like me, you enjoy making your own astronomy equipment.

The James Webb telescope is a lot larger than Hubble. The HST has a primary mirror with a diameter of 2.4 metres. The mirror on the JWST is a multi segment 6.5 metre design. This means that is has a light gathering power around one thousand times the power of the telescope I have in my observatory. This mirror is designed to work in the visible and near infra-red wavelengths. The James Webb telescope is intended to work more in the infra-red, hence the pretty gold mirrors, which reflects infra-red well. The mirror segments themselves are made of beryllium coated in a thin layer of gold. My telescope on the other hand is made of rather more mundane plate glass covered with a thin layer of aluminium. Unlike domestic mirrors, the reflecting surface of a telescope mirror is always on the front, not the back.

Although we are familiar with the visible light images from Hubble, imaging in the infra-red is far more interesting for science. Infra-red light allows us to see through the dust and murk in outer space which sometimes hides scientific targets. Most land based telescopes have to work in the visible and near infra-red spectrum because the water vapour in the Earth’s atmosphere tends to absorb a lot of the infra-red light.

In another departure from Hubble, the James Webb telescope will not be parked in the conventional low-earth orbit. To shield the detectors from infra-red light from the Sun, the JWST will be parked in an orbit around the L2 Lagrangian point on the other side of the Earth from the Sun. Thus the Earth acts as a giant sun screen. This makes telescope operation much easier, but does have the downside that no servicing missions are possible with current technology. The Lagrangian points are regions in space where the gravitational attraction of large orbiting bodies (i.e. the Sun and the Earth) is cancelled out - making quite a nice hideout for a spaceship.

This image shows us part of the mirror assembly at the testing facility. Before committing the telescope to launch, each part of the assembly must be tested by cryogenically cooling and then heating the telescope to test how it will respond to the extreme conditions found in space.

I enjoyed this shot of the engineers working on the mirror segments. IT is quite funny that you see a mundane object like a litter bin (bottom left) next to all the high technology.

Image credit: (NASA/Emmett Given)