The launch of the space shuttle Discovery on its final scheduled mission has been delayed by at least 24 hours until Tuesday because of a leak in a pressurization system, NASA said.
"We have developed two leaks on the pressurization system on the maneuvering system of Discovery on the right side," Kennedy Space Center spokesman Allard Beutel told AFP on Friday.
Fixing the shuttle and getting it ready for take-off would take until "Tuesday at the earliest," the spokesman added.
Discovery and its crew of six astronauts had been scheduled to launch Monday on its last mission to the International Space Station, but that now has been reset for 4:17 pm (2017 GMT) Tuesday, assuming repairs are successful, NASA said.
Managers were discussing plans to repair what the US space agency described as "helium and nitrogen leaks" in Discovery's right-hand orbital maneuvering system (OMS) pod.
Discovery, the oldest orbiter in service and the busiest in history with a record 38 trips into space, had already been moved to launch pad 39A at the Kennedy Space Center in Florida.
The flight will be Discovery's last mission before its scheduled retirement, and the fourth and last shuttle flight of the year.
The three US shuttles -- the other two are Atlantis and Endeavour -- are due to be sent off to become museum pieces after a final shuttle mission to the space station in late February.
That means Russian Soyuz spacecraft, a modernized version of which recently dropped off three fresh crewmembers to the International Space Station, doubling the crew to six, will for several years be the only vehicle for transporting humans into space.
However, NASA's recently approved 2011 budget has left the door open to an additional shuttle flight in June.
The Discovery's all-American crew, including female mission specialist Nicole Stott, will deliver a pressurized logistics module called Leonardo, which will be permanently attached to the space station to give it more storage space.
The shuttle will also bring Robonaut 2, the first human-like robot in space, and a permanent addition to the orbiting space station, as well as spare parts.
Two space walks, for maintenance work and component installation, are scheduled.