The cause of the failure which stranded two ESA/EU Galileo navigation satellites in a faulty Soyuz ST-B (Fregat MT) launch from Sinnamary, near Kourou, French Guiana, on 22 August 2014 has been found. The satellites were left in a wrong orbit after a frozen hydrazine fuel line caused an attitude thruster failure in the Fregat upper stage. This failure subsequently confused the stage’s inertial reference system which then failed itself, causing an orientation error during the injection manoeuvres. While many of the recent Russian launch failures, including a Proton failure earlier this year, have been blamed on poor workmanship/quality control, in this case a design error has been cited as the underlying cause.
A board of enquiry has found that the hydrazine fuel lines feeding two of the upper stage thrusters had frozen due to being in conductive contact with very cold helium pressurant lines. Subsequent inspections at the factory disclosed that the two lines were being clamped in position using aluminium clamp, allowing the warmth of the hydrazine line to be “conducted” across the aluminium with the helium line’s “cold” going the other way (metals are good thermal conductors) during the Fregat’s coast phase.
To fix this fault for future Soyuz-Fregat flights, new clamps will be fitted which will be made out of a non-thermally conducting material.
Apart from the sadness of the failure, there was also embarrassment at Arianespace, the launch provider of the flight, after it initially announced that the launch was successful. No more premature congratulations will be allowed. A one hour time delay has now been introduced between the launch success announcement and confirmation of correct orbit. The stranded satellites, GALILEO FOC FM01 and GALILEO FOC FM02, will never reach a full operational use as they are unable to reach the constellation orbit. Nevertheless, the spacecraft are being raised using their own on-board fuel to at least an orbit where they could find a secondary/engineering use.
