It could revolutionize our understanding of the universe.

On Wednesday, NASA announced construction on the James Webb Telescope is now complete- and it will now undergo rigorous testing ahead of its 2018 launch.

Unlike the Hubble Telescope, which captures its images from orbit around Earth, the Webb Telescope will travel one million miles into space to take its pictures.

"These are technologies that did not exist when this telescope was conceived and when it was agreed that we would do this, the technology still did not exist," said NASA Administrator Charles Bolden.

The Webb Telescope is large – much bigger than Hubble.

"It's gigantic. This beautiful gold telescope is seven times the collecting area of the Hubble Telescope," said Dr. John Mather, NASA Senior Astrophysicist. “If you were a bumble bee hovering at the distance of the moon, we would be able to see you."

Boulder-based Ball Aerospace built the 18 large mirrors, which will enable the Webb Telescope to capture new images of galaxies far beyond our current view.

"We are going to discover things with this telescope that we don't even know to ask. What are those questions going to be that we learn to ask because of this instrument that we couldn't think of today," Allison Barto, who is the telescope’s program manager at Ball, told 9NEWS earlier this year.

Webb will be able to capture images on a different spectrum than Hubble and that could lead to new discoveries, like looking for things on faraway planets.

"Water vapor is one of our top targets,” Dr. Mather said. “We'd like to know if a planet out there has enough water to have an ocean. We think we can do that."

After Webb launches in 2018, it will take another six months before it finishes unfolding and begins sending back pictures – an agonizing wait, after years of planning.

"You never stop holding your breath,” Bolden said. “We never stop holding our breath."

The Hubble Space Telescope is expected to last into the 2020s, but at some point, it will fall out of orbit and burn up on re-entry into Earth's atmosphere. NASA hopes that, for a few years at least, both Hubble and Webb will be able to work together to give us different views of space.