It looks large when we see the school-bus sized telescope next to the floating astronauts. But NASA scientists say it's actually not that big for a telescope.
Hubble's primary mirror is about 8 feet in diameter, much smaller than the 34-foot mirror in the world's largest telescope, the Great Canary Telescope on the island of La Palma, part of the Canary Islands. The mirror for the Keck telescope in Mauna Kea, Hawaii, is about 25 feet.
"It's very average," said Malcolm Niedner, the Hubble deputy senior project scientist. "I'd love to have it in my backyard but it's not a large telescope."
But Hubble makes up for its size with incredible optics and design. Most importantly, Niedner said, its placement outside Earth's atmosphere enables it to see greater distances with greater clarity than any other telescope.
The massive Hubble makeover is expected to give the space telescope about five more years. If all goes according to plan, it should retire just as astronauts launch the heir to NASA's space telescope throne: The James Webb Space Telescope.
Slated for launch in 2014, the replacement telescope will have a mirror 21.3 feet in diameter and a sunshield the size of a tennis court.
As opposed to Hubble's humble 350 mile orbit, the Webb telescope will orbit 1 million miles from Earth, which means that the days of risky servicing missions, for better or for worse, will end with Hubble.
But the telescope, named for James E. Webb, NASA's second administrator, will be able to explore the most distant galaxies and give scientists even more information about the earliest moments of the universe.