James Webb Space Telescope mirror
A mirror at Goddard Space Flight Center

The James Webb Space Telescope (JWST) which is currently under development is the successor of Hubble Space Telescope. 

It is also known as the Next Generation Space Telescope is named after the NASA administrator James E.Webb who played an important role in Apollo program. The telescope is a joint project by NASA, European Space Agency and Canadian Space Agency.

The James Webb Space Telescope comprises of 21 mirrors which include primary mirror segments, secondary mirror, tertiary mirror, and fine steering mirror.

Mirrors of James Webb Space Telescope

The primary mirror has a diameter of 6.5m and is a gold-coated beryllium reflector. The primary mirror has 18 hexagonal mirror segments that provide a large collecting area on the telescope.

Unlike the primary mirror, the secondary mirror is round one. It is convex and it bulges towards the light source. 

The secondary mirror has the finest surface finish and it won't change its design under extremely cold temperatures. The secondary mirror is mounted on a tripod above the primary mirror.

James Webb and Hubble Space Telescope

The tertiary mirror and fine steering mirror are located inside an assembly near the center of the primary mirror. All the mirrors used in the telescope are made up of beryllium which is suited for stiffness, lightweight and can withstand cryogenic temperatures.

Beryllium does not efficiently reflect infrared light, so it is coated with gold to improve its reflecting properties. The James Webb Space Telescope once launched into space, it will start providing images of distant planets and very first galaxies formed in the universe.

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