Updated 11:15 pm EDT Oct. 28

WASHINGTON — An Orbital Sciences Corp. Antares rocket carrying a Cygnus cargo spacecraft on a mission to the international space station exploded seconds after liftoff Oct. 28.

The Antares rocket lifted off on schedule at 6:22 pm EDT from the Mid-Atlantic Regional Spaceport at Wallops Island, Virginia. Approximately ten seconds after liftoff, however, an explosion took place at the base of the rocket’s first stage. The rocket fell back to the ground near the launch pad, triggering a second, larger explosion.

“The ascent stopped. There was some disassembly of the first stage, it looked like, and then it fell to earth,” said Orbital executive vice president Frank Culbertson at a press conference at the NASA Wallops Flight Facility about three hours after the failure. “We don’t have any early indications of what exactly might have failed.”

Culbertson said there was limited access to data from the launch, in accordance with post-accident procedures to lock down and preserve data. He did say that controllers first saw problems 10 to 12 seconds after liftoff, and the range safety officer triggered the rocket’s flight termination system about 20 seconds after lifoff.

No injuries were reported in the launch failure, NASA and Orbital officials said. Damage was contained to an area on the south end of Wallops Island, according to NASA Wallops director Bill Wrobel. The launch pad sustained damage, but Wrobel said it was too early to determine the extent of that damage.

The accident, the first launch failure in five Antares launches, took place after a problem-free countdown. The launch was originally scheduled for Oct. 27 but was scrubbed when a boat entered restricted waters off the coast from the launch site and did not leave before the ten-minute launch window closed.

The mission, designated Orb-3 by NASA, was the third of eight Commercial Resupply Services missions that Orbital Sciences is under contract to perform for the space agency. The Cygnus, named by Orbital the “SS Deke Slayton” after the late astronaut, was carrying 2,290 kilograms of cargo for the station.

NASA officials said that the failure will not have an immediate effect on ISS operations. “We’re in good shape from a consumables and supplies standpoint,” Bill Gerstenmaier, NASA associate administrator for human exploration and operations, said. “There was no cargo that was absolutely critical to us that was lost on this flight. The crew is in no danger.”

ISS program manager Mike Suffredini said there was four to six months of supplies on the ISS. A Progress spacecraft is scheduled for launch Oct. 29 and a Space Exploration Technologies Inc. Dragon spacecraft is planned for launch no earlier than Dec. 9 to transport more supplies to the station.

In addition to supplies for the ISS crew, the Cygnus was carrying experiments for the station and spare parts. Also on board were about 30 small satellites planned for later deployment from the station, 26 of which were from commercial remote sensing company Planet Labs.

“Planet Labs understands the risks of launch. Our approach to mitigate these risks is to deploy our fleets of satellites on multiple launch vehicles, from multiple vendors,” Planet Labs chief executive Will Marshall said in a statement. “The beauty of this approach is the very fact that this event is not catastrophic to our company.”

The failure will likely raise new questions about the AJ-26 engines that currently power the first stage of the vehicle. In May, an AJ-26 engine was destroyed during a ground test at the NASA Stennis Space Center in Mississippi. Aerojet Rocketdyne, which provides the AJ-26 — a refurbished version of the Soviet-era NK-33 engine — took $17.5 million loss in its latest fiscal quarter because of issues with the AJ-26 rocket engine.

The cause of the May failure has not been disclosed by Aerojet or Orbital. An investigation into that failure was wrapping up as of a month ago, Culbertson said at the International Astronautical Congress in Toronto on Sept. 30.

“We have come up with probably two potential root causes, both of which we can screen for,” he said at the conference. Engine tests were slated to resume in October at NASA Stennis.

At the post-failure press conference, Culbertson declined to speculate on any role AJ-26 problems may have played in the launch failure. The engines used on this vehicle had gone through normal acceptance testing both at Stennis and at Wallops prior to the launch. “We didn’t see any anomalies or anything that would indicate there were problems with the engine,” he said.

“We need to go through this investigation and be very thorough before we determine if that’s a factor in this or not, and if it is, whether there’s any relationship to any of our other experiences with the engine.”

Orbital announced in its Oct. 16 conference call with investors that it had selected a new engine for the Antares rocket, but had not disclosed what that engine was.

Culbertson said the overall value of both the Antares rocket and Cygnus spacecraft was more than $200 million. The company has “some” insurance on the launch, he said, but was not more specific.

Asked abut a timetable for a return to flight, Culbertson said it was too soon to make any estimates, expecting it would take a few weeks before the company knew enough to better determine a schedule to resuming launches. “Something went wrong and we will find out what that is,” he said. “We will correct that and we will come back and fly here at Wallops again, hopefully in the very near future.”

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Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...