CAPE CANAVERAL, Fla. -- A SpaceX Falcon 9 rocket lifted off successfully Friday but thruster problems on the Dragon spacecraft threatened to jeopardize its mission to resupply the International Space Station.
In a statement shortly after noon, SpaceX said Dragon experienced a problem with a propellant valve after reaching orbit, and that only one of four Draco thruster pods was functioning.
The thrusters are used to propel the rocket to the space station.
"We are trying to bring up the remaining three," the statement said. "We did go ahead and get the solar arrays deployed. Once we get at least two pods running, we will begin a series of burns to get to station."
The Dragon had been scheduled to dock at the station Saturday morning, however, NASA said three of the four sets of thrusters must be working for Dragon to be allowed to approach the station.
Nor was it clear whether the Dragon could safely return to Earth if SpaceX is unable to activate more thrusters.
SpaceX presumably would continue working to bring a third pod online while it got on its way with two.
The mission began with a successful launch of a Falcon 9 rocket from Cape Canaveral Air Force Station at 10:10 a.m. EST Friday.
After separating from the rocket, the Dragon's two solar array wings were supposed to unfold about 11 minutes into the flight.
That's when SpaceX first reported a problem from its mission control center in Hawthorne, Calif.
Although the Dragon could have flown for many hours under battery power, the arrays provide power needed to complete a mission.
SpaceX CEO Elon Musk reported via Twitter around 11:45 a.m. that the arrays had been deployed, a development that likely bought engineers more time to work on the thruster issues.
The spacecraft is carrying about 1,200 pounds of supplies and science equipment for the space station, plus another 600 pounds of hardware in its unpressurized "trunk." The resupply mission is SpaceX's second of 12 planned under a $1.6 billion NASA contract.
The launch, capping a five-month turnaround from a successful mission, was a dramatic demonstration of the vehicle's ability to survive an engine failure in flight.
Standing 157 feet tall, the powerful Falcon 9 blasted off from Cape Canaveral Air Force Station at 10:10 a.m. EST with a Dragon space freighter. It's the company's second cargo-delivery mission to the International Space Station.
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Musk is well known for proclaiming that the Falcon 9 is the first rocket designed with "engine-out" capability since NASA's Saturn V moon rocket.
Many at heritage aerospace industry companies scoffed. Nine Merlin 1C engines are linked together in a square at the base of the Falcon 9's first stage. Surely, an engine failure would result in collateral damage, leading to a catastrophic loss of mission.
But one-minute and 19 seconds into a brilliant night launch last October, a defect in a Nomex-and-Kevlar flak jacket around one of the rocket's engines triggered a depressurization within its combustion chamber.
The rocket's prime flight computer detected the problem and commanded an engine shutdown. The engine's protective fairing broke apart. Pieces of it were violently consumed in the fire-orange stream that trailed the rocket.
It looked as if the engine had exploded. But it didn't. It was shut down automatically, as intended under the circumstances. Nonetheless, the Falcon 9 delivered the Dragon spacecraft to orbit and it arrived at the International Space Station 30 minutes ahead of schedule. The first of 12 SpaceX cargo delivery missions under a NASA contract valued at $1.6 billion ended up a success.
"As a matter of fact, I have to tell you that I think the industry and the public was dramatically impressed by the fact that we had an engine issue, an engine shutdown, and still made mission," SpaceX president Gwynne Shotwell said Thursday.
"I want to point out that this vehicle has been designed to accommodate an engine out, and though you never necessarily want to see it happen, it's nice that we've demonstrated the vehicle (operates) as it was designed."
Over the past four months and 22 days, SpaceX engineers have been busy with an investigation into the engine failure - one focused on finding the root cause, fixing the problem, and flying again.
That's considered fairly fast in the U.S. aerospace industry.
"We did extensive analysis, obviously, to understand the problem, extensive assessment and testing on these particular engines," Shotwell said.
Investigations into engine failures typically involve what aerospace engineers call "Non-Destructive Testing." For example, ultrasonic examinations, radiography or thermography might be used to detect flaws on Nomex or Kevlar without destroying the material being tested.
NASA International Space Station Program Manager Mike Suffredini said the agency lent SpaceX a hand during its investigation into the October 2012 engine failure. But the company still is clearly looking for help in this discipline.
"It's as much an art as a science, and we certainly are getting much better at it as we mature here," Shotwell said. "But I am going to make a shameless call for any extraordinary NDE experts that want to come and change the state of science, or the state of the art, we're hiring you at SpaceX."