Russian design flaw sent Galileo satellites awry

A production flaw caused the failure of the August launch of two Galileo satellites, the satellite launch company Arianespace said on Wednesday.

Revealing the findings of an inquiry panel that studied why the satellites were put into the wrong orbit after launch from French Guiana, Arianespace said Russian firm NPO Lavochkin would now correct a production flaw identified by investigators and that launches could resume from December.

“The anomaly occurred during the flight of the launcher’s fourth stage, Fregat, designed and produced by NPO Lavochkin. It occurred about 35 minutes after lift-off, at the beginning of the ballistic phase preceding the second ignition of this stage,” said Arianespace.

The independent inquiry into the causes of the anomaly said it was drawing on data supplied by Russian partners in the programme, and that is findings are consistent with the final conclusions of the inquiry board appointed by Russian space agency Roscosmos.

It said the first part of the mission proceeded nominally, which means that the three-stage Soyuz launcher was not at fault. It also eliminated the hypothesis that the anomaly could have been caused by the abnormal behaviour of the Galileo satellites.

The scenario that led to an anomaly in the orbital injection of the satellites was precisely reconstructed, as follows:

  • The orbital error resulted from an error in the thrust orientation of the main engine on the Fregat stage during its second powered phase.
  • This orientation error was the result of the loss of inertial reference for the stage.
  • This loss occurred when the stage’s inertial system operated outside its authorized operating envelope, an excursion that was caused by the failure of two of Fregat’s attitude control thrusters during the preceeding ballistic phase.
  • This failure was due to a temporary interruption of the joint hydrazine propellant supply to these thrusters.
  • The interruption in the flow was caused by freezing of the hydrazine.
  • 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.

The root cause of the anomaly on flight VS09 is therefore a shortcoming in the system thermal analysis performed during stage design, and not an operator error during stage assembly.

The system thermal analyses have been reexamined in depth to identify all areas concerned by this issue.

Given this identified and perfectly understood design fault, the inquiry has chosen the following corrective actions for the return to flight.

  • Revamp of the system thermal analysis.
  • Associated corrections in the design documents.
  • Modification of the documents for the manufacture, assembly, integration and inspection procedures of the supply lines.

These measures can easily and immediately be applied by NPO Lavochkin to the stages already produced, meaning that the Soyuz launcher could be available for its next mission from the Guiana Space Centre from December 2014.

 

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