The cause of the SpaceX Falcon 9 explosion has been found

    SpaceX finally solved the mystery behind why its Falcon 9 rocket exploded in September right before flight. And now that they have that answer, they plan to restart missions as early as mid-December.

    The rocket in question was set to launch from Cape Canaveral on September 1 but exploded without warning during a routine pre-flight fueling. The cause of the explosion wasn’t immediately clear and a high-profile investigation ensued with speculation flying about possible sabotage. SpaceX CEO Elon Musk called the explosion the ‘most difficult’ problem the fledgling space transportation company has faced to date.

    Now in an interview with CNBC, Musk shared what he says is the likely culprit of the accident.

    “It basically involves liquid helium, advanced carbon fiber composites, and solid oxygen,” Musk said. “Oxygen so cold that it actually enters solid phase.”

    Supercooled oxygen is the main propellant used on SpaceX’s rockets but should never enter a solid state. Musk wouldn’t divulge more details but it’s possible the solid oxygen that formed in Falcon 9 could have reacted with other materials in the rocket to create the fireball. For instance, helium pressure vessels sat above the oxygen tank and liquid helium has a colder sitting temperature than oxygen. The colder liquid helium could have chilled the oxygen enough to form it into a solid. It’s also possible a carbon fiber composite material wrapped around the tank could have reacted with the solid oxygen to spark the ignition.

    It’s a problem Musk said has never occurred in the history of rocketry. Hence, it took a while for them to figure out what happened. As a result, SpaceX plans to improve the helium loading process on future flights.

    But there’s a lingering problem with fueling that still has NASA worried. Because the oxygen propellant is so cold, the rocket needs to take off pretty quickly after being fueled. And in the event the rocket will carry astronauts – something NASA and SpaceX hope to start doing in  late 2017 – crew members would need to enter the rocket first. That order of events runs counter to NASA’s safety policy and puts crew members at potential risk.

    Long before the explosion, an advisory committee at NASA wrote a letter raising concerns over SpaceX’s fueling process, according to the Wall Street Journal. Last week, the committee reconvened to reiterate that concern once more.

    For their part, SpaceX has been working with NASA closely to make sure they meet the agency’s safety requirements. But they’ll need to make a pretty strong argument for their rockets’ safety if they want NASA to approve sending their astronauts inside. We’ve already seen what could happen in the worst case.

    Kelly Paik
    Kelly Paik writes about science and technology for Fanvive. When she's not catching up on the latest innovations, she uses her free-time painting and roaming to places with languages she can't speak. Because she rather enjoys fumbling through cities and picking things on the menu through a process of eeny meeny miny moe.