The main cause of the loss of Russia's three Glonass-M satellites was due to human error from fueling the booster rocket with an excess of 1.5-2 tons of fuel, the head of the Russian state commission probing the incident said on Friday.

The excessive fuel caused the DM-3 booster rocket to deviate from its course, leading to the subsequent loss of the satellites in the Pacific Ocean earlier in the week.

"According to preliminary information, the problem was not with the fuel service unit at the launching site, but with one of the sensors showing the fuel level," Gennady Raikunov, the head of the Central Scientific Research Institute of Machine Building, who also heads the investigation commission, said.

"We do not rule out the factor of human error," he said adding that the Russian rocket space corporation Energia may be linked to the incident.

The December 5 launch of the Proton-M carrier rocket was supposed to conclude the forming of Russia's navigation system Glonass, similar to the U.S. GPS.

However, the rocket, which blasted off from the Baikonur Space Center in Kazakhstan, deviated from its course by 8 degrees, resulting in the loss of the DM-3 booster with the satellites. According to reports, the spacecraft fell into the Pacific Ocean to the northwest of Hawaii.

related report
Preliminary Report From Russian State Commission Rules Out Proton M As Cause Of Glonass Launch Failure
The preliminary report of the Russian State Commission investigating the cause of the Proton M Block DM-03 GLONASS launch failure on December 5 exonerates the performance of the Proton M, built and operated by Khrunichev State Research and Production Center (Khrunichev) as a cause of the Proton M Block DM-03 GLONASS mission failure.

However, the KA-SAT mission team of ILS, Khrunichev, Eutelsat and Astrium are standing down at the launch site for about a week and will use the additional time to thoroughly review the preliminary report and data issued by the Russian State Commission.

The KA-SAT satellite was originally scheduled to launch on December 20th from the Baikonur Cosmodrome using the Proton Breeze M launch vehicle. The KA-SAT spacecraft is currently in a nominal configuration mated atop the Breeze M upper stage and adaptor awaiting resumption of joint operations for the mission..

The State Commission was convened on December 5th to determine the cause of the Proton M Block DM-03 GLONASS mission failure as well as corrective actions. According to the preliminary State Commission report, dated 10 December, the three lower Proton M stages performed nominally.

It states that there were "no issues with the functioning of LV systems and assemblies that have been detected. The trajectory parameters calculated by the LV motion control system conform to the trajectory measurements obtained from external sources. Command generation times of the flight timeline correspond to estimated values. The LV motion control system was found to have been functioning nominally, in line with the preset algorithms."

The final report, which is anticipated within one week, will include details on the performance of the Block DM-03 upper stage built and operated by RSC Energia (Energia).

Further information will be provided on the status of the upcoming ILS Proton KA-SAT launch and final State Commission report release as soon as it is available.