James Webb Space Telescope - the world's largest - ready for October liftoff Sci-Tech Wed, May 12, 2021 WASHINGTON: The world´s largest and most powerful space telescope unfolded its giant golden mirror for the last time on Earth on Tuesday, a key milestone before the $10 billion observatory is launched 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.