Proton M launch undershoot: ILS says it was too warm propellants that ultimately doomed Breeze M turbopump15 Feb 2013, 09:14 UTC
Having already noted that the Proton M Breeze M launch undershoot of the Yamal 402 spacececraft on 8 December 2012 had been caused the failure of the Breeze M upper stage’s oxidiser pump bearing during the start of the 3rd burn, the ILS Failure Review Oversight Board (FROB) has explained that the “adverse conditions” that caused this were that the propellants were too warm at launch and that the engine’s warming effect was more than usual.
The result of this thermal anomaly was that a large volume of oxidizer gas (rather than liquid oxidizer) went into the engine inlet, exceeding the Breeze M main engine specifications. The volume of gas was ingested by the Breeze M turbopump at the start of the 3rd burn, leading to over-speed of the oxidizer turbopump bearing without the cooling normally supplied by liquid oxidizer. The over-speed damaged the bearing, which eventually lead to the premature shutdown of the fourth burn. The adverse thermal conditions were due to higher than previously recorded propellant temperatures at liftoff combined with higher than previously recorded thermal soak-back of engine heat to the Breeze M prior to the 3rd burn.
ILS states that ...