The International Launch Services (ILS) Failure Review Oversight Board (FROB) concluded its work, concurring with the most probable cause and the associated corrective action plan which were identified by the Russian Interagency Commission (IAC) as a result of the May 16 Proton launch vehicle failure carrying the Centenario spacecraft.

The members of the FROB reviewed the findings and conclusions from the IAC along with results from testing and investigations that the IAC directed to be performed by Khrunichev and their subsidiaries.

Based on the data presented by KhSC, the FROB agreed that the most probable cause of the failure was a result of a higher than expected vibration environment most likely caused by the combination of a marginal mechanical joint used to mount the Stage III steering engine turbo pump and a steering engine turbopump rotor material that had marginal strength under maximum operating environments.

This led to a premature shutdown of the turbopump and loss of Stage III control authority and subsequently to the failure of the mission during 3rd stage operation approximately 497 seconds after liftoff.

"The participating customers, insurance underwriters and independent subject matter experts are to be commended for their valuable contributions during the extensive FROB review process. We thank our customers for their support as we prepare for the safe return to flight of ILS Proton," said ILS Vice President and Chief Technical Officer, John Palme.