By November 29, specialists at NPO Lavochkin, which builds Fregat, had already narrowed down the most likely culprit in the failure of the Soyuz launch from
Vostochny spaceport, industry sources close to investigation told RussianSpaceWeb.com
Although the information is still preliminary, it is increasingly clear that all the hardware aboard the
Fregat upper stage performed as planned.
But, almost unbelievably, the flight control system on the Fregat did not have the correct settings for the mission originating from the new launch site in Vostochny, as apposed to routine launches from Baikonur and Plesetsk. As a result, as soon as Fregat and its cargo separated from the
third stage of the launch vehicle, its flight control system began commanding a change of orientation of the stack to compensate for what the computer had perceived as a deviation from the correct attitude, which was considerable. As a result, when the Fregat began its first preprogrammed main engine firing, the vehicle was apparently still changing its attitude, which led to a maneuvering in a wrong direction.
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At the time, ground control was still receiving telemetry from the mission, but the space tug left the communications range around 7o0 seconds after the liftoff and before the completion of the first maneuver. Apparently, it was not immediately possible to predict the exact trajectory of the stage resulting from the wrong attitude,
but it likely led to a suicidal plunge of the stack into the Earth's atmosphere. The available telemetry also allows to establish the exact culprit in the failure, sources said.
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In the Soyuz rocket, the gyro platform normally rotated from 174 degrees back to a zero position, providing the correct guidance. However on the Fregat, the shortest path for its platform to a zero-degree position was to increase its angle from 184 to 360 degrees.
Essentially, the platform came to the same position, but this is not how the software in the main flight control computer on the Fregat interpreted the situation. Instead, the computer decided that the spacecraft had been 360 degrees off target and dutifully commanded its thrusters to fire to turn it around to the required zero-degree position. After a roughly 60-degree turn, the gyroscope system on the Fregat stalled, essentially leaving the vehicle without any ability to orient itself in space.
