Tomorrow NASA is set for its most dangerous mission in the long and storied history of the agency.  This really is serious business, with NASA having another shuttle, Endeavor, on emergency standby in case the worst happens to Atlantis.  I do not recall this ever happening before.  Two shuttle on the launch pad, one ready to attempt a rescue if necessary:

Nasa is set to dispatch seven astronauts on its most dangerous ever shuttle mission as it attempts to rescue the $7 billion Hubble Space Telescope from meltdown.

Led by former US Navy fighter pilot Scott Altman, 49, a one-time stunt flier for actor Tom Cruise in the film Top Gun, the crew of Atlantis will repair and upgrade the orbiting observatory, risking a potentially deadly space-junk collision that could leave them stranded 350 miles above Earth.

The mission, which is costing Nasa $1.4 billion and is due to blast off from Florida  tomorrow, is considered so perilous that it was once cancelled  by space agency chiefs who feared that it could cost the astronauts their lives.

It was resurrected only after they agreed to place a second shuttle and crew on  emergency standby, ready to blast into space to save their colleagues should a  catastrophe occur. The move is unprecedented in the 28-year history of the shuttle fleet.

'It’s a belt-and-suspenders kind of approach - but when your suspenders fail, you’re glad to have the belt,' said Cdr Altman, who is due to launch with his crew from Kennedy Space Centre at  Cape Canaveral tomorrow evening, returning in 11 days.

'I don’t know if I’ll be breathing comfortably until our wheels stop back  at KSC,' he added.

Like I said, serious business.  I know I'll be watching the launch.  Godspeed Atlantis.