SpaceX has zeroed in on what caused one of the private space company's Falcon 9 rockets to explode on the launch pad nearly two months ago.

The Federal Aviation Association, NASA and the U.S. Air Force launched a joint investigation of the malfunction from Launch Complex 40 at Cape Canaveral in Florida.

On Friday, the company announced replicated the failure of a helium tank and plans to return to flight "by the end of the year."

"SpaceX's efforts are now focused on two areas – finding the exact root cause, and developing improved helium loading conditions that allow SpaceX to reliably load Falcon 9," SpaceX said in a statement. "With the advanced state of the investigation, we also plan to resume stage testing in Texas in the coming days, while continuing to focus on completion of the investigation."

The test site is in McGregor in central Texas.

The fiber composite tanks were used to store helium within the liquid oxygen propellant tank.

"The root cause of the breach has not yet been confirmed, but attention has continued to narrow to one of the three composite overwrapped pressure vessels [COPVs] inside the [liquid oxygen] tank," SpaceX said in the statement.

Changes in temperature and pressure of the helium as it is loaded into the tank highly affected the tank.

Lost in the explosion on Sept. 1 was a $200 million satellite Facebook planned to use to bring internet access to remote regions of Africa.

Billionaire technology executive Elon Musk initially called the explosion "the most difficult and complex failure we have ever had in 14 years" in a post on Twitter.

SpaceX is still contracted with NASA for additional cargo deliveries to the International Space Station and plans one day to take American astronauts there.

Musk also hopes to colonize Mars.

Iridium Communications is the next of several companies that have signed up to have SpaceX to launch their satellites.

"Also, I don't know if Iridium Next will be SpaceX's first launch once they return to flight or whether they might schedule a launch from Florida ahead of us," Matt Desch, chief executive of Iridium, said during an conference call Thursday. "Either way, we're comfortable with SpaceX's investigation and the progress they're making and I assure you that we won't proceed to launch if we aren't confident in SpaceX and their investigation outcome."

The company has not disclosed when it would be able to resume launching from Complex 40.

The company plans to launch from Complex 39A at Florida's Kennedy Space Center and has used Vandenberg Air Force Base in California.

In June 2015, a rocket loaded with space station supplies also erupted shortly after liftoff. Company officials said the two incidents were unrelated, although the earlier loss also originated in the upper-stage helium system. A support strut broke in 2015.