Space shuttle Atlantis on pad 39A, left, and space shuttle Endeavour on pad 39B stand ready at Kennedy Space Center in Cape Canaveral, Fla. Atlantis is scheduled for an Oct. 10 launch on mission STS-125 to service the Hubble Space Telescope. Endeavour will be on standby in the unlikely event that a rescue mission for the Atlantis's crew would be necessary.

Cape Canaveral, Fla. ? In an unprecedented step, a space shuttle was moved to the launch pad Friday for a trip NASA hopes it will never make – a rescue mission.

The shuttle Endeavour is on standby in case the seven astronauts who go up on Atlantis next month need a safer ride home.

Atlantis and its crew are headed into space for one last repair job on the 18-year-old Hubble Space Telescope. It’s a venture that was canceled when first proposed a few years ago because it was considered too dangerous.

The risk is this: If Atlantis suffers serious damage during launch or in flight, the astronauts will not be at the international space station, where they could take refuge for weeks while awaiting a ride home. They would be stranded on their spacecraft at the Hubble, where NASA estimates they could stay alive for 25 days. Air would be the first to go.

Endeavour and four more astronauts would need to blast off on a rescue flight as soon as NASA determined Atlantis was too damaged to fly home.

On Friday, Endeavour was parked at its launch pad just a mile from where Atlantis is tentatively set to lift off on Oct. 10.

It is the first time since 2001 – when flights were more closely spaced – that both of NASA’s shuttle pads have been occupied. And it will probably be the last.

The Atlantis astronauts say there’s a slim chance any rescue will be needed, and they say they would fly to Hubble even if there were no such backup plan.

Scott Altman, Atlantis’ commander, said it may seem like overkill, but having a rescue ship on the pad is the right thing to do.

“It’s kind of a belt-and-suspenders approach. But if you need the belt after your suspenders fail, you would be glad you had it,” said Altman, a retired Navy captain and former fighter pilot.

On top of the usual launch and landing dangers, the Atlantis crew faces an estimated 1-in-185 chance that a piece of space junk or a micrometeoroid will cause catastrophic damage to their ship. Those are greater odds than for a typical shuttle flight because of Hubble’s extremely high and debris-littered orbit.

Ever since space shuttles resumed flying following the 2003 Columbia tragedy that killed seven astronauts, NASA has had a rescue plan in case of irreparable damage. But all those missions have been to the space station, where astronauts could camp out for two months.

The Hubble mission offers no such safe haven. That’s why the Hubble repair mission was canceled in 2004; NASA’s boss at the time deemed it too dangerous.

A new NASA regime reversed that decision, once space shuttles were flying safely again and repair methods became available to orbiting astronauts. The caveat was that another shuttle be on the launch pad, all prepped and ready to fly – something never before attempted.