More than 20 years after construction started, the James Webb Space Telescope is nearly ready to go. The successor to the iconic and groundbreaking Hubble is expected to launch in 2020 following in-depth testing.

NASA Administrator Charles Bolden made the announcement at Goddard Space Flight Center, overlooking the massive infrared light collecting mirrors. "Today, we're celebrating the fact that our telescope is finished, and we're about to prove that it works," said John Mather, an astrophysicist and senior project scientist for the telescope. "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."

A mirror segment after being coated with gold.

Mirror segments undergoing cryogenic tests at the X-ray & Cryogenic Facility at Marshall Space Flight Center.

Primary flight mirrors.

The first six primary mirror segments being prepared for final cryogenic acceptance testing.

September 2009 artist conception showing the sun-facing (bottom) view.

September 2009 artist conception showing a 3/4 top view.