Spaceflight Insider

SpaceX narrows cause of Falcon 9 explosion, targets mid-December launch

Falcon 9 explosion, fairing with Amos-6 satellite falls – 2016-09-01

The Falcon 9 payload fairing containing the Amos-6 satellite falls moments after the explosion on Sept. 1, 2016. Image Credit: Mike Wagner /

Elon Musk, founder and CEO of SpaceX, believes the company has ultimately determined the cause behind the loss of its Falcon 9 rocket, as well as the Amos-6 satellite it was slated to launch, in a spectacular explosion on September 1, 2016.

“I think we’ve gotten to the bottom of the problem – a really surprising problem that’s never been encountered before in the history of rocketry,” stated Musk in an interview on CNBC on November 4, 2016, and classified it as the toughest puzzle the company has ever had to solve.

This announcement aligns with statements Musk gave in a presentation to the National Reconnaissance Office (NRO), more than three weeks prior, when the SpaceX CEO posited that the explosion might have been caused by the formation of solid oxygen within the carbon fibers in the overwrap on the helium pressure bottle.


SpaceX uses composite overwrapped pressure vessels (COPVs) similar to these in order to store helium aboard the Falcon 9. They are located inside the rocket’s fuel tanks, which the helium serves to pressurize. Photo Credit: ESA

Normally in its liquid phase when used in cryogenic rocket engines, oxygen can become a solid when its temperature falls to –361.82 degrees Fahrenheit (–218.79 degrees Celsius).

Most rocket propellant applications don’t require oxygen chilled anywhere close to that level. However, SpaceX’s desire to fit more liquid oxygen (LOX) into the Falcon 9’s tanks – a process called “propellant densification” – the company loads the oxidizer at a chilly –340 degrees Fahrenheit (–207 degrees Celsius). The firm began using this method with their upgraded Falcon 9 in December 2015.

That is significantly colder than the nominal LOX temperatures on Space Shuttle missions, with oxidizer temps on the now-retired spacecraft about 43 degrees Fahrenheit (24 degrees Celsius) warmer than the sub-cooled LOX used on the Falcon 9 v1.2, and much closer to the freezing point of oxygen.

Alone, the sub-cooled LOX would pose little problem, even if loaded near its phase change temperature. However, within the second stage’s LOX tank reside three liquid helium composite overwrapped pressure vessels (COPVs), which are used to pressurize the LOX tank as the propellant is consumed.

With helium becoming a liquid at –452.2 degrees Fahrenheit (–269 degrees Celsius), the temperature difference between the LOX and the COPVs holding the liquid helium might have been enough to chill the LOX and induce the formation of solid oxygen crystals within the carbon fibers of the composite overwrap.

Less clear, though, is what might have caused the solid oxygen and carbon composite amalgam to ignite – and SpaceX has been quiet on that front.

Nevertheless, the company feels they have identified the culprit behind the loss of the vehicle and its payload on September 1, and they are ready to resume launches of the Falcon 9 as soon as mid-December 2016, though with the customer and launch location yet to be disclosed.



Curt Godwin has been a fan of space exploration for as long as he can remember, keeping his eyes to the skies from an early age. Initially majoring in Nuclear Engineering, Curt later decided that computers would be a more interesting - and safer - career field. He's worked in education technology for more than 20 years, and has been published in industry and peer journals, and is a respected authority on wireless network engineering. Throughout this period of his life, he maintained his love for all things space and has written about his experiences at a variety of NASA events, both on his personal blog and as a freelance media representative.

Reader Comments

I hope the changes if any made will ensure the safety of crews and missions

I wouldn’t have thought that the liquid helium could boil off fast enough to pressurize the tank as fast as the oxygen is consumed. I guess that is why they use 3 of them.
It still seems like a stretch to me. I would guess that the tank would have to fail before the carbon would fuel an explosion. Only thing we know is that if their theory is wrong, another one will blow up.

When I was looking into the properties of Liquid oxygenr ecently , Ic ame across this line at WikiPedia: ” Further, if soaked in liquid oxygen, some materials such as coal briquettes, carbon black, etc., can detonate unpredictably from sources of ignition such as flames, sparks or impact from light blows. Petrochemicals, including asphalt, often exhibit this behavior.”

– sounds like a mostly carbon article in the presence of LOX can in fact become an explosive and be detonated by an impact, not a spark. I also came across a reference somewhere that Carbon in contact with LOX transitioning to SOLID oxygen becomes much more explosive than that.

I do know that LOX exhibits some very odd properties , like becoming very magnetic. You can suspend a blue glob of the stuff between poles of a magnet.

Cryogenics is voodoo.

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