CAPE CANAVERAL, Fla. - A scheduled rendezvous between the privately launched SpaceX Dragon cargo capsule and the International Space Station was postponed Friday when thruster pods on the capsule failed for several hours. But NASA and SpaceX officials expressed confidence the resupply mission would be completed.

After a flawless launch of the SpaceX Falcon 9 rocket from Cape Canaveral Air Force Station put the capsule in orbit Friday morning, ground control detected low pressure in oxidizer tanks for three of the Dragon's four thruster pods. The thrusters allow for precision maneuvering, and NASA requires at least three to be operating before the capsule approaches the space station.

But by late afternoon, SpaceX founder Elon Musk tweeted that all four thrusters were working.

"Preparing to raise orbit. All systems green," he wrote.

Still, it was unclear when the Dragon capsule, carrying nearly 1,300 pounds of supplies, would get permission to dock with the $100 billion station. Earlier, Musk said he would be confident after an hour or two of test firings, but NASA officials were noncommittal.

Berthing opportunities with the space station come only about once a day and require a lengthy, careful dance between spacecraft, since both are flying at 17,000 mph. Michael Suffredini, NASA's space station program manager, said a Sunday berthing was possible.

"We'll plan for the next opportunity," Suffredini said. But he added, "It is not our intention to waive safety requirements."

The exact cause of Friday's problem was unclear. Musk said his team's "preliminary guess" was that a blockage, perhaps something frozen, formed in a line from a helium tank used to pressurize all four thruster oxidizing tanks. NASA officials concurred.

Musk praised SpaceX mission control in Haw-thorne, Calif., for diagnosing and apparently fixing the problem.

None of Dragon's cargo is critical to life support on the station, though there are research packages to support 160 experiments.