SpaceX CEO Elon Musk said the Falcon 9 "experienced a problem shortly before first stage shutdown."
SpaceX came up empty Monday in its search to figure out why an unmanned Falcon 9 rocket exploded minutes after blasting off from a NASA launchpad with a load of space-bound cargo.
"Cause still unknown after several thousand engineering-hours of review," CEO Elon Musk wrote on Twitter early Monday. He said experts were now focusing on the final milliseconds of the flight in order to determine a cause.
MIAMI - An unmanned SpaceX rocket exploded less than three minutes after liftoff from Cape Canaveral, Fla., on Sunday, in the first major disaster for the fast-charging company headed by Internet tycoon Elon Musk.
The accident was the third in less than a year involving U.S. and Russian supply ships bound for the International Space Station, and raised new concerns about the flow of food and gear to the astronauts living in orbit.
Skies were sunny and clear for the 10:21 a.m. (1421 GMT) launch of the gleaming white Falcon 9 rocket that was meant to propel the Dragon cargo ship on a routine supply mission, the seventh for SpaceX so far.
But two minutes, 19 seconds into the flight, contact was lost. Live television images from SpaceX's webcast and NASA television showed a huge puff of smoke billowing outward for several seconds, then tiny bits of the rocket falling like confetti against a backdrop of blue sky.
"The vehicle has broken up," said NASA commentator George Diller.
There was an overpressure event in the upper stage liquid oxygen tank. Data suggests counterintuitive cause.— Elon Musk (@elonmusk) June 28, 2015
SpaceX's live webcast of the launch went silent as the rocket exploded.
Moments later, a SpaceX commentator said the video link from the vehicle had been lost.
"There was some kind of anomaly during first stage flight," the commentator said, noting that the rocket had ignited its nine Merlin engines and reached supersonic speed.
Later, on Twitter, Musk said the Falcon 9 "experienced a problem shortly before first stage shutdown," referring to the phase of flight before the cargo ship would have been able to separate from the first stage of the rocket and reach orbit.
The problem appeared to be linked to excessive pressure in the liquid oxygen tank, Musk wrote.
"Data suggests counterintuitive cause," said Musk, a lifelong space enthusiast who also heads Tesla Motors.
"That's all we can say with confidence right now."
More details were expected in a NASA press conference scheduled for no earlier than 12:50 pm (1650 GMT).
Our thoughts are with the @SpaceX team. We understand getting to space is hard, but very important work. Wishing you a speedy recovery.— Orbital ATK (@OrbitalATK) June 28, 2015
The loss came as a surprise to many who have followed Musk's California-based company through more than a dozen successful launches, even as competitor Orbital Sciences lost one of its rockets in an explosion in October, and a Russian Progress supply ship was lost after liftoff in April.
"These things do happen, but this was not the best time for this to happen," said Marco Caceres, a rocket industry analyst with the Teal Group.
"The one thing you could count on over the past few years was that the Falcon 9 was going to perform and was going to perform well," he told AFP.
"In the midst of all this other chaos in the launch industry this was like, the one stable point and now we don't have that," he told AFP.
Caceres said the accident forces SpaceX, which has a billion-dollar-plus contract with NASA for supplying the ISS but is also competing with Boeing to send astronauts there by 2017, to launch again quickly.
"The moment they launch again successfully, this accident starts to fade into history really quickly. The longer they wait to launch again, the more people start talking about, 'Maybe we were too overconfident about SpaceX,'" he said.
The Dragon cargo ship was carrying 4,000 pounds of gear to the space station, including a large parking space, known as an International Docking Adaptor, designed to make it easier for an array of commercial crew spacecraft to dock at the orbiting lab in the future.
"Very sorry to see @SpaceX launch failure. Serious ramifications for Space Station resupply. Good thing it's international," wrote Canadian astronaut Chris Hadfield on Twitter.
NASA administrator Charles Bolden said the U.S. space agency was "disappointed" at the loss but that the space station has "sufficient supplies for the next several months."
A Russian Progress supply ship is scheduled to launch July 3, followed in August by a Japanese HTV flight, Bolden said.
"Orbital ATK, our other commercial cargo partner, is moving ahead with plans for its next launch later this year."
Three men are currently living at the space station. Russian cosmonaut Mikhail Kornienko and American astronaut Scott Kelly began their year-long mission in orbit back in March.
"Sadly failed. Space is hard," Kelly said on Twitter, posting a picture of his view of the Florida coast from space.
Earlier Sunday, station commander, Russian cosmonaut Gennady Padalka, 57, set a new world record when he became the person who has officially spent the longest amount of cumulative time in space -- 804 days.
His career includes one trip to the Mir Space Station and four to the ISS.
By Kerry Sheridan
Copyright Agence France-Presse, 2015