CRS-7 Failure Latest:
SpaceX had enjoyed a string of successes since fighting back from the early days of its history.
After suffering three Falcon 1 failures in succession, the fourth flight provided the company with its first completed mission – prior to achieving a huge amount of success with its Falcon 9 rocket in 2008.
However, an overpressure event in the Second Stage 139 seconds after liftoff resulted in the loss of Dragon and the disintegration of the Falcon 9 launch vehicle.
“There was an overpressure event in the Second Stage liquid oxygen tank. Data suggests a counterintuitive cause. That’s all we can say with confidence right now. Will have more to say following a thorough fault tree analysis.”
That note placed an immediate focus on the helium pressurization system’s bottles in the Second Stage of the Falcon 9.
Both missions were launched without issue.
During the blackout of the initial investigation period, SpaceX worked to recover any remaining items of the destroyed Falcon 9 to aid its knowledge base. It is understood that most publicly recognizable pieces of debris that have been found recently were both solar arrays with covers and one landing leg.
There were also notes (L2) about interest in the rods that support the helium bottles inside the LOX tank in the second stage.
(Image left of a COPV support in the First Stage – which Mr. Musk noted is the same design as those in the Second Stage).
It was suggested that one of these rods – or struts – may have failed during ascent.
Such a scenario would have resulted in a loose bottle – which are classed as “buoyant” – impacting with the surrounding inners of the tank.
Mr. Musk confirmed that the failure of a support strut for a helium bottle is the leading theory, aided by ground-based stress testing that resulted in one of the struts failing, leading to metallurgy evaluations showing a weakness in the material.
“The preliminary conclusion is that the failure arose from a strut in the Second Stage LOX tank – that was holding down one of the COPVs, ” noted Mr. Musk during Monday’s media call.
“It appears that one of those struts broke free during flight.”
The struts – which were supplied to SpaceX by a contractor – are typically used for tank mounting applications and are made up of a shaft with a rod end (containing a spherical bearing) screwed on at one end, and either another rod end or a bracket screwed or welded on at the other end.
The rod end would fit into a bracket on the tank wall, with a nut/bolt combination running through the bracket and rod end, anchoring the assembly. There appears to be a focus on a bolt in the strut assembly.
Mr. Musk explained that ground testing of such hardware isn’t fully sufficient to mirror the stresses such a strut undergoes during flight.
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