Buckles in Falcon 9 helium tank likely cause of September catastrophe.
Elon Musk's SpaceX has concluded its investigation into the September 2016 Falcon 9 rocket explosion that destroyed the $200 million Amos-6 Israeli communications satellite and pushed back SpaceX's entire launch schedule by months.
The cause? One of the rocket's three helium tanks, called 'composite overwrapped pressure vessels' (COPVs), situated in the second stage liquid oxygen tank, failed.
Specifically, SpaceX said in a blog post on its website that the "investigation team concluded the failure was likely due to the accumulation of oxygen between the COPV liner and overwrap in a void or a buckle in the liner, leading to ignition and the subsequent failure of the COPV." The company made no mention to unfounded rumors of sabotage by rival spaceflight firms, which circulated online in the aftermath of the massive explosion.
In layman's terms: COPVs are used to store chilled helium that maintains the tank pressure. The COPVs are lined on the inside with aluminium with a carbon overwrap. The investigation team concluded that buckles in one of the liners led to super chilled liquid oxygen pooling underneath the overwrap. Subsequently, this liquid oxygen became trapped when pressurized, in turn breaking fibers or creating friction that ignited the oxygen.
"In addition, investigators determined that the loading temperature of the helium was cold enough to create solid oxygen (SOX), which exacerbates the possibility of oxygen becoming trapped as well as the likelihood of friction ignition," said SpaceX.
"The investigation team identified several credible causes for the COPV failure, all of which involve accumulation of super chilled LOX or SOX in buckles under the overwrap. The corrective actions address all credible causes and focus on changes which avoid the conditions that led to these credible causes."
SpaceX said it will now be changing the COPV configuration to allow for helium to be loaded at a warmer temperature and returning to a helium loading method used on prior, successful launches. In the long term, SpaceX said it will make design changes to COPVs to prevent buckles from forming altogether.
The investigation conclusion now means SpaceX can resume launch operations after the four-month dry spell. On Sunday January 8, SpaceX will launch with the Iridium NEXT satellite from Vandenberg Space Launch Complex, pending a launch license issued by the FAA. It's good news for Elon Musk. The September 1 explosion and the following hold on SpaceX's launch cycle lost the company the business of European satellite firm Inmarsat, with the company confirming in December it will be moving to launch with Arianespace's Ariane 5 rocket in 2017.
NASA also confirmed last December that the first crewed test flight of SpaceX's Dragon vehicle has been delayed until May 2018. The launch was initially scheduled for August 2017, when the capsule would ferry NASA astronauts to the International Space Station, becoming the first private spacecraft in the world to carry people into orbit. Instead, November 2017 will see an uncrewed test flight for the Dragon capsule that was originally scheduled for May 2017.
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