James Webb Space Telescope

Webb's main mirror is 6.5 m across and is made of 18 gold-coated segments. It launched on 25 December 2021, and NASA calls it the largest and most complex space telescope ever built.

The mirror folded up to fit inside the rocket and opened in space.

Context

Webb is designed to observe mainly in infrared light, which lets it see through dust and detect very distant objects whose light has been stretched by cosmic expansion. To work well, its instruments must stay extremely cold, so a sunshield about the size of a tennis court blocks heat and light from the Sun, Earth and Moon.

The 6.5-metre primary mirror is made of 18 hexagonal segments of beryllium coated with a thin layer of gold, a metal that reflects infrared light very efficiently. Each segment can be adjusted by tiny actuators, and the team aligned them to work as one mirror after launch. The mirror is much larger than the 2.4-metre mirror of the Hubble Space Telescope.

Webb was launched on an Ariane 5 rocket from French Guiana on 25 December 2021. It then travelled about 1.5 million kilometres to a spot called the second Sun-Earth Lagrange point, where it orbits the Sun in step with Earth. It is too far away for any current crewed mission to repair.

Its first full-colour images were released in July 2022, and it has since studied early galaxies, star formation and the atmospheres of exoplanets.