The next space shuttle of the National Aeronautics and Space Administration will have a standby rescue shuttle in case something should go wrong during flight.
The decision follows intense research in the wake of the explosion of space shuttle Columbia, which killed Indian American astronaut Kalpana Chawla and six others.
NASA's next space shuttle Discovery will not lift off unless the rescue shuttle, Atlantis, is ready to fly within a month after Discovery.
It is a self-imposed requirement for the next two shuttle flights and goes beyond the list of recommendations from the panel that investigated the Columbia accident.
In January 2003, a chunk of foam had punched a sizable hole in Columbia's left wing. The shuttle exploded just before it landed after completing a research mission.