PARIS and MOSCOW — Incorrectly installed angular rate sensors on the first stage of a Russian Proton M/Block DM-03 rocket most likely caused the vehicle to crash seconds after its July 2 launch, according to a government investigation published by Russian space agency Roscosmos July 18.

The launch vehicle—with three Glonass-M navigation satellites on board—crashed 32 sec. after liftoff from Baikonur Cosmodrome in Kazakhstan due to loss of stability in its yaw axis. The investigation revealed that at least “three of six angular rate sensors were installed incorrectly,” Roscosmos spokeswoman Anna Vedishcheva said July 19, though electric connectors between the sensors and the first stage were properly aligned.

As a result of improper installation, the sensors failed to send the correct signal to the Proton’s engine control system to maneuver the vehicle back to its intended flight path when it started to yaw. Investigators discovered traces of forced installation of the upside-down sensors and later verified the incorrect installation through experiments.

A Russian space industry source explained to Aviation Week that the faulty installation was not detected during assembly-line testing at the Khrunichev State Research and Production Space Center in Moscow, where the Proton M is built.

Vedishcheva said the investigation is ongoing, and that the commission also is probing the liftoff of the Proton M from its Baikonur launch pad 0.4 sec. earlier than planned.

The industry source said that the loss of Glonass-M satellites should not affect the accuracy of Russia’s satellite navigation system, as these spacecraft were intended for orbital reserve.

Russia’s quality-control issues have so far not affected launch vehicles serving the International Space Station (ISS), but could have implications for Reston, Va.-based International Launch Services (ILS), which annually launches half of the world’s largest commercial telecommunications satellites atop Proton.

ILS and its majority shareholder Khrunichev have launched 81 commercial Proton missions since 1996, six of which were failures. But the majority of Proton mishaps have occurred on Russian federal missions, including the July 2 failure. A total of five mishaps in the past 30 months include two caused by human error on Russian missions, a December 2010 loss of three Glonass spacecraft due to over-fueling of the rocket’s DM-03 upper stage, and the August 2011 loss of Express-AM4, a telecom satellite left in a too-low orbit due to a faulty parameter entered into its flight software system.

Two subsequent Proton failures—one federal, the other managed by ILS—took place within six months of each other, and were attributed to technical issues associated with the Breeze M upper stage.

A manufacturing defect in the Breeze M helium pressurization system led to the loss of Russia’s Express-MD2 and the Indonesian Telkom-3 satellites in August 2012, while an early Breeze M shutdown following the December 2012 launch of the Gazprom Space Systems Yamal 402 commercial telecom satellite left the spacecraft in a useless orbit.

A failure review attributed the shortfall to a combination of worst-case factors—including temperature and pressure—that led to damage in an upper-stage turbopump bearing.

Satellite manufacturer Thales Alenia Space was able to maneuver Yamal 402 into its intended orbit, though it cost the customer—Gazprom Space Systems of Moscow—four of the spacecraft’s intended 15 years of service life.