Friction is a possible reason for SpaceX Falcon 9 explosion

September 1 of 2016 at Cape Canaveral SpaceX lost is Falcon 9 rocket on a launch pad due to dramatic explosion. During a routine preflight fueling test, the  rocket and the $200 million Israeli Earth communication satellite Amos-6 were lost. No one was injured.

A four month intensive investigation together with NASA resulted in a determination of the possible reason for the encountered anomaly.  According to the investigation team, the failure of one of the three liquid oxygen tanks (LOX tank, see figure below) leaded to the explosion. Oxygen is used in many spacecrafts as a liquid oxidizing propellant. The failure of the tank leaded to accumulation of the oxygen in a space between the tank and its composite overwrap. Accumulated oxygen further exploded. Interestingly, friction was named as the likely source of the oxygen ignition.

Friction may cause ignition in a number of ways [1]. Sparks can be produced due to high speed grinding or impact during the rubbing. On the other hand, frictional heating around a repeated contact may increase the local temperature and create so called hot-spots. Once the auto ignition temperature is reached, the ignition occurs. It is also pointed in [1], that the latter mechanism is more likely in case of gas or vapor of explosive atmospheres. This may indicate that a repetitive fretting-type of contact occurred between the liner and the composite overwrap prior the explosion of Falcon 9.

Further details can be found on the SpaceX website.

[1]. IGNITION OF DUST CLOUDS AND DUST DEPOSITS BY FRICTION SPARKS AND HOTSPOTS,

R. L. Rogers, S. Hawksworth, M. Beyer, C. Proust, D. Lakic, J. Gummer and D. Raveau.

 

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