Russian Space Web - By July 9, investigators sifting through the wreckage of the doomed rocket found that the critical angular velocity sensors, DUS, were installed upside down. Each of those sensors had an arrow that was suppose to point toward the top of the vehicle, however multiple sensors on the failed rocket were pointing downward instead. As a result, the flight control system was receiving wrong information about the position of the rocket and tried to "correct" it, causing the vehicle to swing wildly and, ultimately, crash. The paper trail led to a young technician responsible for the wrong assembly of the hardware, but also raised serious issues of quality control at the Proton's manufacturing plant, at the rocket's testing facility and at the assembly building in Baikonur. It appeared that no visual control of the faulty installation had been conducted, while electrical checks had not detected the problem since all circuits had been working correctly.
A similar problem caused a rocket failure from the same manufacturing plant many years ago. Although the sensor has a this way up marking on it. Clearly they needed to design with three screws position so that they would only install the correct way. The kind of design setup that goes into Ikea furniture.
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