Yesterday, SpaceX founder and CEO Elon Musk announced the preliminary results ove the investigation on the mishap to the Falcon 9 rocket which led to its destruction just over two minutes after its June 28, 2015 launch. The culprit appears to be a component of the hardware rocket, one of the support struts of the rocket’s second stage’s liquid oxygen tank that handled a pressure much lower than that it was certified for.
The investigation into the failure of the mission CRS-7 with the destruction of the Dragon spacecraft and the supplies it was supposed to carry to the International Space Station started immediately after the Falcon 9 rocket mishap. The telemetry data were carefully analyzed showing that immediately after launch everything worked regularly until the event that caused the mishap.
On June 28, Elon Musk published a tweet that mentioned an overpressure event in the upper stage liquid oxygen tank. This suggested that the problem wasn’t in the first stage, which actually kept on working. SpaceX investigation, in collaboration with NASA and the US Air Force and the FAA (Federal Aviation Administration) supervision ended up finding what looks like a flawed strut.
Several hundred struts are part of the structure of each Falcon 9 rocket. They’re certified to withstand forces of up to 4,530 kg (10,000 lbs) but the investigation showed that one of them 60 cm (almost 2 feet) long and 2.5 cm (one inch) thick failed at a much lower pressure, about 900 kg (2,000 lbs). The consequence was that a tank that contains the helium used for pressurization broke up releasing the gas into the liquid oxygen tank. This seems to be the overpressure event mentioned by Elon Musk shortly after the mishap.
This overpressure in the second stage of the Falcon 9 rocket caused a loss of its structural integrity. To test that hypothesis, SpaceX performed checks on many struts similar to the suspect with the result that several of them snapped at pressures much lower than those they’re certified for.
A thorough analysis of the struts materials revealed problems with the grain structure of the steel. Basically, there was likely a problem in their production with the result that they seemed normal but in fact they were defective. These struts were produced by an external supplier and SpaceX stated that it won’t use them anymore. Moreover, Elon Musk stated that in future tests on specific components will be carried out to verify that they aren’t flawed.
These are the results of a preliminary investigation but it seems that the “smoking gun” was actually found. If they are confirmed, the addition of component test will be enough to prevent another mishap of this kind.
Elon Musk spoke of the problem caused by the fact that the staff of SpaceX has become a bit complacent after more than 20 successful launches. When the company had to handle the initial failures, seven years ago, it had far fewer employees. Most of the staff who work there today never had the experience of a mishap and the June 28 one will constitute a harsh lesson.
Even in the best case, no launch of the Falcon 9 rocket will happen before September 2015. Elon Musk intends to focus efforts to resume launches as soon as possible, of course after the conclusion of the investigation. Work on the Falcon Heavy, the rocket’s most powerful version, will be postponed.
Another improvement will be made with the implementation of the rescue system on the spaceship Dragon. If on June 28 the spacecraft had been able to open its parachute perhaps the cargo would have been saved. That kind of system was developed for the Dragon V2, the manned version, which requires it to save the crew in case of an accident.
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