The largest astronomical mirror to be launched into space has passed its first unfolding test conducted by NASA. A key stage for this juggernaut which will have to be folded down to accommodate itself in an Ariane rocket, in 2021.
This NASA video reveals the unfolding of the main mirror of the James Webb Space Telescope. This 6.5 m diameter mirror, covered with a microscopic layer of gold to improve the reflection of infrared, is the largest ever designed to be sent into space.
The size of the future telescope depends on its size: the larger the mirror, the greater the amount of light absorbed, and therefore the greater the sensitivity of the telescope. The James Webb Space Telescope will succeed the famous Hubble space telescope (whose mirror measures 2.4 m in diameter), to explore galaxies and distant exoplanets.
A foldable mirror in 3 parts
Problem: the mirror was too large to enter the rocket that will take the telescope into space, an Ariane 5. So scientists had to find a way to temporarily reduce its size. They thus designed a mirror made up of 18 hexagons of 1.3 m wide, which can fold in three, the time of the journey, before unfolding and locking once arrived at a destination, at 1.5 million kilometers from Earth. The ambitious maneuver was tested for the first time in a cleanroom in California, with success!
The test was carried out under conditions that reproduce the absence of gravity, and a second will soon be carried out, for safety, before sending the instrument into space, in 2021.