The incorrect installation affected three of six yaw angular velocity sensors on the unmanned rocket, causing in to veer off course and explode during launch, Alexander Lopatin, deputy head of Roscosmos.
The finding was part of a state commission's investigation of the crash, RIA Novosti reported Friday.
The sensors could have been installed incorrectly either as the result of a mistake by the worker who installed the sensors or by the engineer who drew up the construction blueprints, Lopatin said.
"Installing these devices is complicated and awkward work," Lopatin said, noting the recovered sensors showed traces of having been forced into place.
Since there is no procedure in place for spotting such a mistake in current pre-launch checks, Lopatin said, the investigating commission would draft a set of measures to rectify the situation.
The Proton-M, carrying three satellites for the Glonass satellite navigation system -- Russia's equivalent of the U.S. GPS system -- tipped over and rolled before it blew up 12 seconds after takeoff from Baikonur spaceport in Kazakhstan.
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