SpaceX still doesn’t know exactly what caused its Falcon 9 rocket to explode in September, but the company says it has narrowed down the problem to one of three helium pressure vessels in the upper portion of the rocket. It further confirms what SpaceX suspected late last month — that the accident was caused by a breach in the cryogenic helium system in the vehicle’s upper oxygen tank. This helium system is used to pressurize the rocket during flight.

SpaceX has narrowed down the problem to one of three helium pressure vessels

SpaceX has been conducting numerous tests at its facility in McGregor, Texas, in order to recreate the same scenario that led to last month’s failure. The Falcon 9 rocket didn’t explode during flight, but on a launch pad at Cape Canaveral, Florida, as it was being fueled for an upcoming engine test. The accident resulted in the loss of both the vehicle and the satellite it was supposed to carry into space — an Israeli communication satellite called Amos-6.

Though SpaceX has yet to pinpoint the root cause of that explosion, the company’s tests have revealed something concerning about the helium system. The tests showed that the Falcon 9’s helium pressure vessels can fail just from conditions created during helium loading. Both the temperature and the pressure of the helium can be problematic, according to SpaceX. After figuring this out, SpaceX says it’s going to focus on making its helium loading process more reliable, as well as keep searching for answers about the explosion.

The company is still optimistic about returning to flight later this year

Meanwhile, the company is going to start testing rocket stages at its McGregor facility again, with the hope of returning to flight later this year. SpaceX president Gwynne Shotwell said last month that the company was targeting a return-to-flight in November. While the explosion badly damaged the company's Florida launch pad, SpaceX will have the option of flying from two additional sites when it gets back to spaceflight: one at Vandenberg Air Force Base in California, and another launch pad at Cape Canaveral that the company leases from NASA. The Florida pad has been undergoing renovations and is supposed to be operational some time next month.

However, many of SpaceX’s bigger projects that were supposed to occur this year are getting pushed back. The first flight of the Falcon Heavy — a super heavy lift version of the Falcon 9 — will happen some time in the first quarter of next year, according to Shotwell. And SpaceX indicated this week that the first launch of one of its previously flown rockets will occur in early 2017, according to Space News reporter Peter B. de Selding. That flight was originally slated for this fall.