WASHINGTON: The world's largest and most powerful telescope unfolded its giant golden mirror for the last time on Earth on Tuesday, a key milestone before the $10 billion observatory is launched into space later this year.

The James Webb Space Telescope's 21 feet 4 inch (6.5 meter) mirror was commanded to fully expand and lock itself into place, NASA said -- a final test to ensure it will survive its million-mile (1.6 million kilometer) journey and is ready to discover the origins of the Universe.

"It's like building a Swiss watch at 40-feet-tall... and getting it ready for this journey that we take into the vacuum at minus 400 degrees Fahrenheit (-240 Celsius), four times further than the Moon," said Scott Willoughby of lead contractor Northrop Grumman.

He was speaking at the company's spaceport in Redondo Beach, California, from where the telescope will be shipped to French Guiana to be launched on an Ariane 5 rocket, with NASA targeting October 31 for liftoff.

Webb's primary mirror is made of 18 hexagonal segments coated with an ultra-thin layer of gold to improve its reflection of infrared light.

It will fly to space folded like a piece of origami artwork, which allows it to fit inside a 16-foot (5-meter) rocket fairing, and will then use 132 individual actuators and motors to bend each mirror into a specific position.

Together, the mirrors will function as one massive reflector, to enable the telescope to peer deeper into the cosmos than ever before.