We have a new exclusive clip from the finale of When We Left Earth: The NASA Missions, which airs on the Discovery Channell on Sunday June 22 at 10 PM ET. Click below to get a special glimpse at this NASA documentary program.

One of the most complex instruments ever built, the Hubble Space Telescope is expected to transform our understanding of the Universe. But once it is in orbit, NASA discovers a serious problem, a defective main mirror that leaves Hubble short-sighted. NASA sends a team of astronauts to fix the problem, but it won't be easy. It is NASA's greatest and highest profile mission since the Apollo era. It gives NASA the confidence to begin construction on the International Space Station. More astronauts are in space simultaneously than ever before. And despite the tragedy of Columbia, NASA's astronauts are pioneering the way back to the moon, Mars and beyond.