CAPE CANAVERAL, Fla. - A massive fireball and explosion erupted Thursday at SpaceX's main launch pad, destroying a rocket as well as a satellite that Facebook was counting on to spread internet service in Africa.
There were no injuries. The pad had been cleared of workers before what was supposed to be a routine pre-launch rocket test.
SpaceX chief Elon Musk said the accident occurred during the fueling of the rocket and originated around the upper-stage oxygen tank.
"Cause still unknown," Musk said via Twitter. "More soon."
The explosion -- heard and felt for miles around -- dealt a severe blow to SpaceX, still scrambling to catch up with satellite deliveries following a launch accident last year. It's also a setback for NASA, which has been relying on the private company to keep the International Space Station stocked with supplies and, ultimately, astronauts.
SpaceX was preparing for the test firing of its unmanned Falcon rocket when the blast occurred shortly after 9 a.m. at Cape Canaveral Air Force Station. The test was in advance of Saturday's planned launch of an Israeli-made communications satellite that was supposed to provide home internet for parts of sub-Saharan Africa and the Middle East.
A video of the explosion shows a fireball enveloping the top of the rocket. Moments later, the payload fairing plunged to the ground, followed by more explosions.
Buildings four miles away shook from the blast, and a series of explosions continued for several minutes. Dark smoke filled the overcast sky. A half-hour later, a black cloud hung low across the eastern horizon.
TV cameras showed smoke coming from the launch pad five hours later. Most of the rocket was still standing, although the top third or so was clearly bent over.
The explosion occurred at Launch Complex 40 at the Air Force station, right next door to Kennedy Space Center, where emergency staff was on standby following the accident. At the same time, personnel were monitoring the air for any toxic fumes. The Air Force stressed there was no threat to public safety in the surrounding communities.
The initial blast sent next-door NASA employees rushing frantically outside to see what happened.
Because the pad was still burning, it remained off-limits to everyone as the afternoon wore on. "We want to make sure we isolate any potential problem," said Shawn Walleck, a spokesman for the Air Force's 45th Space Wing, "because at this point, we've had no casualties, we've had no injuries, and we want to keep it that way."
Facebook spokesman Chris Norton said his company was "disappointed by the loss, but remain committed to our mission of connecting people to the internet around the world." Founder Mark Zuckerberg was in Kenya on Thursday, discussing internet access with government officials.
The satellite's Israeli-based operator, Spacecom, said the loss will have "a significant impact" on the company. Just last November, ground controllers lost contact with the previous satellite in this so-called Amos series. Spacecom said the new satellite was supposed to provide services to television and internet operators.
The Falcon rocket destroyed Thursday is the same kind used to launch space station supplies for NASA. The last such flight took place in July. SpaceX is one of two companies making deliveries. The company also is working on a crew capsule to ferry station U.S. astronauts.
Two NASA astronauts were conducting a spacewalk 250 miles up, outside the International Space Station, when the explosion occurred. Mission Control did not notify them of the accident, saying all communication was focused on the spacewalk.
The California-based SpaceX had been ramping up with frequent launches to make up for a backlog created by a launch accident in June 2015. In that mishap, a support strut evidently snapped in the upper stage; the problem was fixed.
SpaceX is leasing the pad from the Air Force for its Falcon launches. The company is also redoing a former shuttle pad at Kennedy for future manned flights for NASA. The first crewed flight was supposed to take place by the end of next year. Boeing also is working to develop a crew capsule for NASA.
Sen. Bill Nelson, D-Fla., whose single space shuttle flight ended 10 days before the Challenger disaster in 1986, said the SpaceX accident "reminds us all that space flight is an inherently risky business."
"As we continue to push the frontiers of space, there will be both triumphs and setbacks. But at the end of the day, I'm confident that our commercial space industry will be very successful," Nelson said in a statement.
AP writers Rodney Muhumuza in Kampala, Uganda, and Daniel Estrin in Jerusalem contributed to this report.
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