Updated: Cape Canaveral (FL) - Space Shuttle Atlantis has successfully reached parking orbit after launching from the Kennedy Space Center.
The space shuttle Endeavour is sitting on its launch pad, ready for a rescue mission NASA hopes won't be needed.
The shuttle's sister craft, Atlantis, launched earlier today on a flight to repair and upgrade the Hubble Space Telescope.
While there are but a handful of remaining STS missions remaining before the Ares replacement - its own future in some doubt as the Obama administration looks at possible alternatives - NASA cannot afford to run the risk of losing a third shuttle, let alone its crew, in the event of an accident. The Hubble mission will take Atlantis beyond reach of the International Space Station should a serious problem occur.
After Atlantis launches today, Endeavour could follow in less than a week, should engineers discover that Atlantis sustained damage during liftoff, as happened with the ill-fated 2003 Columbia mission.
Endeavour has been equipped with seven extra seats and three spacewalks would be required to bring the Atlantis crew safely home in the event of any problems.