Video captures an explosion that destroyed a SpaceX Falcon 9 rocket and its payload in Cape Canaveral, Florida. (Reuters)

Elon Musk’s SpaceX said Monday that it has discovered the cause of a September rocket explosion and plans to return to flight as soon as Sunday.

The conclusions of the company’s investigation have yet to be approved by the Federal Aviation Administration, and the agency has yet to provide it a license to launch. But SpaceX’s statement means that it has confidence that federal agencies will approve its remedies for the problem and that it will soon receive the green light.

SpaceX’s Falcon 9 rocket exploded while being fueled on a launchpad at Cape Canaveral Air Force Station ahead of an engine test firing on Sept. 1. No one was on board the rocket, and there were no injuries. But the blast touched off a massive fireball and caused extensive damage, including the loss of a commercial satellite.

In its statement, SpaceX said it traced the cause to a pressure vessel in the second-stage liquid oxygen tank. The tank buckled, the company said, and supercooled liquid oxygen pooled in the lining. The fuel was ignited by breaking fibers or friction.

The company said that in the short term, it plans to change the way it loads fuel. Eventually, it plans to change the design of the pressure vessels to prevent buckling.

SpaceX led the investigation, which was overseen by the FAA, the Air Force, NASA and the National Transportation Safety Board. Shortly after the explosion, Musk had said it was “turning out to be the most difficult and complex failure we have had in 14 years” and asked the public for help. Over the past four months, the investigation took several bizarre twists and turns. Musk said there was a mysterious “bang sound” that may have come from “the rocket or something else” seconds before the explosion. And at one point, SpaceX officials asked for access to the roof of a nearby facility used by rival United Launch Alliance, implying sabotage.

The explosion was a major setback for SpaceX, which has a significant backlog of commercial satellite launches. The company is also under contract to fly cargo and, eventually, astronauts to the International Space Station. But the accident — the company’s second failure in less than two years — touched off concerns about its ability to fly safely and reliably.

In June 2015, a Falcon 9 flying cargo to the station blew up shortly after liftoff, destroying $118 million worth of equipment and experiments.

If all goes according to plan, SpaceX plans to launch communications satellites for Iridium, a McLean-based company, on Sunday from Vandenberg Air Force Base in California.

In an interview in November, Matt Desch, Iridium’s chief executive, said he wasn’t worried about entrusting its $3 billion worth of satellites to Musk.

“We’ve been privy to the thinking and the analysis and the data involved at a very deep level,” Desch said. “So, yes, we know why he is saying what’s he’s saying and concur that they have found the issue. We’re encouraged, too, that it was procedural … We are back on the path for a first launch and, yes, I feel very confident that the issue that was found won’t be repeated for our launch.”

Still, he said on Twitter that the company would wait to load the satellites onto the rocket until after the prelaunch engine test.