A Proton rocket. Photo: Roscosmos

[Via Satellite 08-04-2015] International Launch Services’ (ILS) Failure Review Oversight Board (FROB) has concluded its investigation of the May 16 Proton failure, concurring with the most probable cause and the associated corrective action plan identified by the Russian Interagency Commission (IAC).

Based on the data presented by Khrunichev, Proton’s manufacturer and owner of ILS, the FROB agreed that the most probable cause of the failure was a result of a higher than expected vibration environment. The most likely cause of this environment was the combination of a marginal mechanical joint used to mount the Stage 3 steering engine turbo-pump and a steering engine turbo-pump rotor material that had marginal strength under maximum operating environments. This led to a premature shutdown of the turbo-pump, loss of Stage 3 control authority, and subsequently to the failure of the mission during third stage operation approximately 497 seconds after liftoff.
The members of the ILS FROB reviewed the findings and conclusions from the IAC along with results from testing and investigations that the IAC directed Khrunichev and its subsidiaries to perform.