The primary mirror on NASA’s James Webb Space Telescope has an approximate diameter of 6.5 meters.
Webb’s mirror is made from 18 hexagonal segments of gold-coated beryllium. The segments fold for launch and unfold in space, forming a much larger collecting surface than could fit inside the launch vehicle’s fairing as one rigid mirror.
Webb observes primarily in infrared light. Its large mirror helps it collect faint radiation from distant galaxies and stars, while a five-layer sunshield protects the telescope from heat and light produced by the Sun, Earth and Moon. The observatory operates near the Sun–Earth L2 point, about 1.5 million kilometers from Earth.
The 2.4-meter figure belongs to the Hubble Space Telescope, so it is a frequent comparison error. Webb’s mirror is not a single solid disk; its 18 segments work together as one aligned optical system.