A Proton-M rocket crashed headlong into the ground shortly after take off on July 2. According to independent website Russian Space Web, which has been monitoring Russian media since the crash, reports that crash investigators examining the wreckage had found the angular velocity sensors had been installed the wrong way up.
According to the website, the sensors are marked with an arrow which is supposed to point upwards. However, several sensors were found among the wreckage were found to be pointing the other way. It's thought that the signals picked up by the wrongly installed sensors threw the rocket's flight control system into disarray, causing the rocket to turn upside down shortly after take off, and crash roughly a kilometer from the launchpad. (A video of the ill-fated flight can be seen on YouTube).
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Though it appears that the error can be traced back to a young technician, if reports that no visual checks were made are accurate, it would seem unfair to lay the blame there.
The crash, which reportedly caused a crater up to 200 m (650 ft) across, posed a significant risk as it failed to clear the launch complex at Baikonur in Kazakhstan. However, no one was hurt as a result of the crash.
See Russian Space Web's account for fuller details of the accident itself, the investigation timeline, and a fuller explanation of the actual cause.