NASA has finally completed the construction of the world's largest and most powerful space telescope.

On Nov. 2, NASA announced the completion of the James Webb Space Telescope (JWST), a next-generation telescope and successor to the iconic Hubble Space Telescope, which has been under construction for more than 20 years. The announcement was made at a news conference at the agency's Goddard Space Flight Center in Maryland.

"Today, we're celebrating the fact that our telescope is finished, and we're about to prove that it works," John Mather, an astrophysicist and senior project scientist for the James Webb Space Telescope, said during the announcement as reported by Space.com. "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."

The JWST is a collaboration between NASA, the European Space Agency (ESA) and the Canadian Space Agency. The telescope is twice the size of Hubble--about the size of a tennis court--and is also more powerful with seven times the collecting area of Hubble, which gives it the ability to peer at the first stars in the universe born just after the Big Bang.

"NASA has always sought to unravel the mysteries of our universe; to find out where we come from, where we are going, and whether we are alone in the universe," Charles Bolden, NASA Administrator, said in a blog. "We are building the James Webb Space Telescope to answer these age-old questions and to bring us to new heights in discovery, understanding and human progress."

The JWST is made of 18 highly sensitive gold-coated hexagonal mirrors made of lightweight beryllium, which will detect infrared from even the farthest object in the universe. The infrared sensors will operate at close to absolute zero temperatures from the Lagrange Point 2, point in space directly behind the Earth from the sun's perspective.

The telescope has started completing a series of tests, the first of which is a rocket launch test to ensure that it could withstand the rough conditions during a launch. The mirrors and instruments had also undergone cryogenic testing to check the telescope's capability to thrive in frigid conditions in space. Also recently, engineers have installed the sunshield layers, which will protect the telescope's instruments from the sun.

The JWST will be ready to launch from French Guiana in October 2018 on top of an Ariane 5 rocket and will start doing scientific observations six months after.