SpaceX is aiming to return to flight on January 8th, as the company has officially determined what caused one of its Falcon 9 rockets to explode on a Florida launch pad this past September. In an online update this morning, SpaceX detailed the source of the rocket failure — a complex process that involved broken carbon fibers causing super cold oxygen to ignite. The company says it has identified all of the “credible causes” that may have been responsible for this combustible interplay of materials, and corrective actions have been taken to make sure the same accident doesn’t happen again.
SpaceX was forced to ground all of its vehicles after the accident
SpaceX was forced to ground all of its vehicles after the accident, which happened in Cape Canaveral, Florida on the morning of September 1st. The failure occurred as the Falcon 9 was being being fueled for an upcoming static fire test — a routine procedure SpaceX does before launch to see if the rocket’s engines are working properly. During fueling, the Falcon 9 exploded in a huge fireball, leading to the destruction of the rocket and the communications satellite it was supposed to carry into space.
Video of the event revealed that the explosion began toward the top of the rocket, and SpaceX later narrowed down the source of the problem to the vehicle’s upper oxygen tank. That’s the tank that stores the super cold liquid oxygen propellant needed for the engine in the second stage, or the top portion of the vehicle. Along with liquid oxygen, the tank also houses three smaller vessels that store really cold helium. They’re called COPVs, for composite overwrapped pressure vessels, and they’re responsible for pressurizing the tank during flight; the helium from these vessels fills the empty space left behind by the oxygen when it leaves the tank. It seems that the materials used for these helium pressure vessels may have had a bad reaction with the oxygen in the tank.
The vessels are made up of an aluminum liner surrounded by a carbon fiber composite material. SpaceX was able to recover some of the debris from the accident, and the company found something strange about the COPVs. Something had caused the vessels’ aluminum liners to scrunch up, creating buckles in the material. The most likely scenario, according to SpaceX, is that some of the liquid oxygen in the tank pooled into these buckles and got trapped there. Then, some of the carbon fibers wrapping the helium vessel may have snapped, causing friction that ignited the trapped oxygen. Additionally, the helium in these vessels is incredibly cold too — so cold that it may have caused the pooled liquid oxygen to turn into a solid. And solid oxygen has an even greater chance of combusting due to friction.