Hubble is the one telescope everyone knows, and its spectacular images are downloaded daily. Hubble is the comeback kid of telescopes. Launched in 1990 -- over budget and behind schedule -- to great fanfare, it immediately became a late night joke when it turned out the telescope's mirror had problems which caused blurred images.
Hubble, 19 years old now, overcame its early problems, and the rest is history - history that has changed what we know about the universe, and history that won't end soon, thanks to a long-overdue house call to repair and upgrade the venerable orbiting observatory.
Preston Burch, Hubble's project manager, says his team has been working around the clock to get ready for this. "This is the last chance to make Hubble the best it can be, we will almost have completely rebuilt Hubble since it was launched. We will also install a soft capture mechanism to deorbit Hubble in the future."
A space shuttle mission to Hubble is considered risky because there is no safe haven - if something goes wrong on a mission to the international space station, the crew can hang out at the space station until a rescue vehicle comes to get them.
A shuttle at the Hubble has no place to find refuge - so NASA came up with a plan to have a second shuttle standing by ready to go if something breaks on Atlantis that can't be repaired in orbit.
The fifth mission to service the Hubble was scrapped after the 2003 accident that doomed the crew of the space shuttle Columbia. Then NASA Administrator Sean O'Keefe said it was much too dangerous.
"Could we do this and take the risk? Sure, but somebody else would have to make that decision not me, because I'm not doing it,'' O'Keefe said.
That someone was the next NASA Administrator, Mike Griffin.
"We studied it for 18 months and decided we could do this with no more risk than we ask of our astronauts on a space station flight – it was not a trivial undertaking. It wasn't that I snapped my fingers and reversed my predecessors' decision; we studied it for 18 months. But we did find a way. That at the end of the day - that's what is key; we found a way to do it safely."
It's been seven years since Hubble has been serviced, and it is in sad shape. It needs new batteries, its gyroscopes are failing, its main camera isn't working at full capacity, and several other instruments are broken.
Astronauts, on five grueling back-to-back spacewalks, will perform very delicate repairs on electronics, some that were never meant to be replaced on orbit.
Three months after the mission ends the astronauts will know if their work paid off when the first pictures will be seen from the newly refurbished telescope.
Is Hubble worth it? You bet, says astronomer Dr. Sandra Faber: "Hubble has made a number of groundbreaking discoveries that changed our view of the universe. First and foremost for me as student of galaxy formation, Hubble was the first telescope to look back in time and show us infant galaxies, in the process of being born.
That's a first. To use a telescope as a time machine looking back billions of years – that is a terrific legacy"