Russian investigators probing the November launch failure that doomed a massive communications satellite to a worthless orbit say excess fuel in the Proton rocket's upper stage main engine is to blame.

"The commission exonerated the three-stage Proton K vehicle in the incident and focused on the Block DM upper stage," International Launch Services, the marketer of Proton, announced Tuesday. "It stated that the engine of the Block DM experienced excessive temperatures and was destroyed during its second ignition, resulting in the separation of the spacecraft into the wrong orbit.

"Indications are that there was excessive fuel in the main engine at the time of the second burn, leading to the burn-through."

Liftoff occurred November 25 from the Baikonur Cosmodrome in Kazakhstan to deliver the Astra 1K satellite into geosynchronous transfer orbit. The powerful spacecraft, called the largest commercial communications satellite ever built, was designed to transmit digital TV and multimedia programming across Europe for operator SES-ASTRA.

The three stages of the Khrunichev-built Proton "core vehicle" all fired and released the Block DM and Astra 1K spacecraft on a suborbital trajectory. The upper stage, built by RSC Energia, performed its first burn as planned and reached a circular parking orbit of 109 miles.

But after coasting for about an hour, the stage was supposed to re-ignite to raise one side of the orbit to about 22,237 miles. The rocket would then travel to the apogee and perform its third and final firing to raise the orbit's low end and reduce inclination from the equator.

The second burn suffered the malfunction, leaving Astra 1K stranded into the useless 109-mile orbit. Ground controllers were able to maneuver the satellite into a more stable orbit. But officials ultimately commanded the craft to reenter the Earth's atmosphere over the Pacific Ocean to burn up harmlessly.

The failure commission is continuing its investigation into the probable cause of the launch accident, including the indication of excessive fuel, ILS said.

"The commission is expected to release its final report and recommended corrective actions next month. ILS' Failure Review Oversight Board will then commence a review of the final report and issue its findings at the appropriate time."

ILS successfully launched the Canadian Nimiq 2 direct broadcasting satellite Sunday night aboard the upgraded Proton M rocket and its new Breeze M upper stage.