Engineering
The Design and Implementation of the James Webb Space Telescope
Quick fact
The James Webb Space Telescope's primary mirror is 6.5 meters across—too big for any rocket fairing—so it was built as 18 hexagonal segments that had to unfold and align themselves to within a fraction of a wavelength of light, all while operating at about 40 Kelvin.
Why this is interesting
Imagine a telescope so large it has to be folded like origami to fit inside a rocket. How do you make it unfold perfectly, a million miles from Earth, where no one can fix it?