Roscosmos, the Russian space agency, announced the results of the investigation on the problem that caused the failure of the mission of the Proton-M rocket on May 16, 2015. The fault was detected in the turbopump rotor of the rocket’s third stage engine which resulted in an instability in the engine that caused the emergency shutdown. According to the investigation, it’s a design flaw and recommendations were issued to correct it.
The May 16, 2015 mission was to carry into orbit the MexSat-1/Centenario satellite on behalf of the Mexican government but after just over eight minutes after launch a serious malfunction in the third stage caused its destruction. The launch was managed by International Launch Services (ILS), a joint venture of Lockheed Martin, Khrunichev and Energia. Khrunichev is subordinate to Roscosmos, which as a result handled the investigation.
The study in deep of the telemetry data recorded during the flight revealed that the emergency shutdown was caused by the engine of the Proton-M rocket’s third stage. The data analysis led to the conclusion that a fault was determined by the degradation of interior materials at high temperatures. This resulted in excessive vibration that caused an imbalance on the turbine shaft of the engine turbopump.
This failure was caused by a design flaw and Roscosmos recommended various measures to correct it: the replacement of the material or coating of the turbopump shaft, the improvement of the rotor balance and the revision of the engine structural design.
It’s a flaw that have existed for many years that manifests itself only in certain limit conditions concerning the thermal environment encountered within the turbine. According to Roscosmos, the same flaw could be the cause of the failure of the launch in May 2014 and also another one that happened in 1988.
The flaw was recognized only now because this time there was a set of sensors installed directly on the Proton-M rocket’s third stage’s engine turbopump. In 1988, the rocket had no sensors on the engine so it wasn’t possible to detect any vibrations. Last year, the sensors were installed in a different place and detected only the signature of an already failed turbopump.
Roscosmos announced that a new launch schedule for the Proton-M rocket will be announced in June, after the planning of the modification tasks necessary to eliminate the problem with the third stage engine. Considering the problems experienced by various Proton-M rockets, the problem needs to be solved for good.