SpaceX has concluded its investigation into what caused a Falcon 9 rocket to explode on a Cape Canaveral launch pad last year, the company announced Monday.

Nearly four months after the Sept. 1 explosion, the Hawthorne, Calif. company says it has determined the cause.

The SpaceX investigation team concluded that one of the composite overwrapped pressure vessel (COPV) used to store liquid helium failed. The failure was likely caused by a buildup of oxygen between the vessel’s lining and overwrap, the report stated. Investigators also concluded that loading temperatures of the helium was cold enough to create oxygen, increasing the chances of oxygen becoming trapped.

SpaceX plans to implement short-term and long-term fixes to address the issue. One of the fixes will be to load helium at a warmer temperature.

The explosion occurred Sept. 1 at Cape Canaveral Air Force Station.

A $200 million AMOS-6 communications satellite was destroyed.

With the investigation completed, SpaceX plans to return to flight Jan. 8 with a launch from Vandenberg Air Force Base in California.