A rupture of the combustion chamber in the second-stage RL-10B-2 engine caused the failure of the second Delta III launcher in May, according to an interim report by Boeing.

The engine, which was being used for the first time, suffered "a 67in² [43,225mm²] diamond-shaped breach of its combustion chamber" during its second burn, says the report. The breach, which resulted in a shutdown and the loss of the $145 million Orion 3 satellite, was caused by poor manufacturing alone or combined with additional, unexpected, structural forces on the engine during launch.

The hourglass-shaped combustion chamber comprises four sections with strengthener strips brazed or soldered over the seams. The rupture occurred near one of these strips. The brazing technique has been found to be faulty because it leaves voids or gaps, making the joints more susceptible to stress.

Source: Flight International