NASA on Friday again delayed the launch of the space shuttle Atlantis for 24 hours, citing a troublesome fuel cut-off sensor, a spokesman said.
"The launch is scrubbed, and we'll come back on Saturday and see how the ... sensor behaves," launch director Mike Leinbach said.
It was the latest in a string of launch delays for this Atlantis mission, an 11-day trip to the International Space Station to undertake construction operations.
The new launch time, set for Saturday at 11:15 am (1515 GMT), came after discussions with the Russians over possible conflicts with their planned September 18 Soyuz flight to the ISS.
The National Aeronautics and Space Administration said the faulty fuel sensor on an external fuel tank was detected during fuelling operations early on Friday, and after lengthy examination of the problem and discussions by mission officials, they decided to put off the launch.
Friday's launch scrub came after the team of six astronauts had already climbed aboard the shuttle and about an hour before the scheduled lift-off.
NASA spokesman George Diller had said there were two options: continue the countdown, since the sensor, which measures the tank's hydrogen level, is one of four and only two are needed to operate the shuttle safely; or delay launch for 24 hours, empty the fuel tank and examine the faulty sensor.
"We judged it was more prudent to delay the launch and review the data," Wayne Hale, the shuttle programme manager, said at a news conference.
Engineers emptied the external tank of nearly two million litres (528,350 gallons) of hydrogen and liquid oxygen, worth more than 500,000 dollars, to see how the four gauges function when it is empty and full.