BOSTON — The ongoing investigation into the June 28 Falcon 9 launch failure has yet to find a cause for the accident based on the available data, SpaceX Chief Executive Elon Musk said July 7.

Musk, speaking at the International Space Station Research and Development Conference here, said that the destruction of the vehicle nearly two and a half minutes after liftoff from Cape Canaveral did not appear to have a straightforward cause, and that the data the company had was difficult to interpret.

“Whatever happened is clearly not a sort of simple, straightforward thing,” he said in his most extensive public comments to date on the launch failure. “There’s still no clear theory that fits with all the data.”

Musk reiterated earlier statements he made on Twitter that linked the failure to an “overpressure event” in the liquid oxygen tank in the upper stage of the Falcon 9. Video of the launch appeared to show a cloud expanding from the upper stage about ten seconds before the rocket disintegrated. What caused that overpressure event, though, remains uncertain.

One issue engineers are examining, he said, is the possibility that some of the data might be corrupted or otherwise in error. “We’re determining if some of the data is measurement error of some kind, or whether there’s actually a theory that matches” the data they have on hand, he said.

“Everyone who can engage in the investigation at SpaceX is very, very focused on that,” he said. That includes constructing a “super-detailed” timeline, accurate to the millisecond, of the events leading up to the loss of the vehicle that correlates vehicle telemetry and video from the ground. “We want to spend as much time as possible just reviewing the data,” he said, including reviewing it with NASA and others.

Musk, speaking at the conference in an on-stage interview with NASA ISS program manager Michael Suffredini, said that NASA has provided support for the investigation. “The interaction with NASA has been great so far,” he said. “The biggest challenge is that there are a lot of inquiries coming in simultaneously, so it’s hard to keep responding to everyone right away.”

Despite the current difficulty in determining the cause of the failure, Musk believed that SpaceX would be able to soon better identify what took place. “I think we’ll be able to say something more definitive towards the end of the week,” he said.

He added he declined to go into more details now because “I don’t want to say something that subsequently turns out to be a misunderstanding of the situation.”

The results of the investigation could also lead to changes to the vehicle beyond anything directly linked to the cause of the failure. The company, Musk said, would “look at both what most likely happened and then anything that’s a close call and try to address all of those things and maximize the probability of success for future missions.”

Musk didn’t give a timetable for when the vehicle might return to flight, but indirectly indicated he expected launches to resume later this year.

Asked later in the interview about SpaceX’s attempts to make the first stage of the Falcon 9 reusable, he noted the company has tried to land the stage on a ship on several launches, including the previous successful launch in April, without success.

“Hopefully later this year we’ll be able to do that,” he said.

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...