These 4-foot wide hexagonal mirrors will unfold once the telescope reaches orbit and operate like a single 21-foot wide reflector. Each mirror is comprised of super-lightweight beryllium (though they still tip the scales at 88 pounds apiece). Plus, they will have to withstand negative 400 degree temperatures while shifting less than 38 nanometers over the life of the telescope, otherwise they might throw the delicate optics out of phase.
"After a tremendous amount of work by an incredibly dedicated team across the country, it is very exciting to start the primary mirror segment installation process" Lee Feinberg, James Webb Space Telescope optical telescope element manager at Goddard, said in a statement. "This starts the final assembly phase of the telescope." The Goddard team expects to have the rest of the mirrors installed by the end of next year.
[Image Credit: NASA / Chris Gunn]