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A just released independent investigation by Arianespace of the Soyuz rocket launch failure that put two European Galileo GPS satellites in the wrong orbits has concluded that the design of the Fregat upper stage, not an assembly error, was at fault for the failure.
The upper stage was not oriented correctly because fuel lines to thrusters had become frozen.
The freezing resulted from the proximity of hydrazine and cold helium feed lines, these lines being connected by the same support structure, which acted as a thermal bridge. Ambiguities in the design documents allowed the installation of this type of thermal “bridge” between the two lines. In fact, such bridges have also been seen on other Fregat stages now under production at NPO Lavochkin. The design ambiguity is the result of not taking into account the relevant thermal transfers during the thermal analyses of the stage system design.
That the Russian investigation found that this arrangement of feed lines happened once in every four stages that were assembled still suggests sloppiness, if not in assembly then in design. The Arianespace investigation, though thorough, thus appears to me to be trying to provide cover for thier Russian partners here.