NASA postponed shuttle Discovery's resupply mission to the International Space Station for a third time on Thursday to review tests of a potentially faulty valve in the ship's fuel tank.
Launch of NASA's 128th shuttle mission was rescheduled for 11:59 pm EDT on Friday (0359 GMT on Saturday).
The agency had been hoping to fly at 12:22 am EDT (0422 GMT) on Friday but managers delayed the launch to allow more time to assess information collected during tests of the suspect valve.
Launch times are determined by when the space station flies over the shuttle's launch site at the Kennedy Space Centre in Florida, which happens about once every 24 hours.
"Shuttle teams decided they need more time to evaluate data before pressing toward launch," NASA said on its Twitter text-messaging service.
The suspect valve, which is needed to drain fuel from the shuttle's tank, apparently failed while the shuttle was being fueled for a second launch try earlier this week.
Bad weather stymied NASA's first launch attempt on Tuesday.
NASA halted fueling when a sensor signaled a possible failure, drained the tank and ordered tests to determine if the valve was actually broken or if sensors that monitor the equipment were to blame.
Engineers cycled the valve five times on Wednesday without incident but NASA decided to take another day to study the issue.
The shuttle is stocked with laboratory equipment, food, supplies and spare parts for the station, a $100 billion project of 16 nations that is nearing completion after more than a decade of construction 220 miles (355 km) above Earth.
NASA has until Sunday to get Discovery off the launch pad, or it will likely delay the mission to mid-October.
Discovery's flight is scheduled to last 13 days and includes three spacewalks to install a new ammonia coolant tank and prepare the outpost for its final connecting hub.