The construction of the replacement for the ageing Hubble Space Telescope is finally complete.
The James Webb Space Telescope will launch sometime in the next two years, NASA has announced.
"Today we're celebrating the fact that our telescope is finished, and we're about to prove that it works," says John Mather, astrophysicist and senior project scientist.
"We've done two decades of innovation and hard work, and this is the result - we're opening up a whole new territory of astronomy."
James Webb was the head of NASA through the John F Kennedy and Lyndon Johnson administrations, overseeing the Mercury and Gemini programmes.
The telescope that bears his name costs US$8.8 billion. It features a 6.5m mirror, the largest ever sent into space, with seven times the surface area of that on the Hubble.
It also has an infrared camera that will allow it to peer back at some of the universe's earliest galaxies. It'll also be able to analyse the atmospheres of exoplanets it finds, looking for signs of extraterrestrial life.
The James Webb telescope is so powerful, it could spot a bumblebee at a distance of the moon - in visible light and by the heat its body emits.
It was meant to launch in 2014 and cost US$5 billion, and was nearly cancelled at one point.
Unlike Hubble, it likely won't be able to be fixed if something goes wrong after launch - so NASA knows it has to get everything just right.