Russia's Proton rocket could fly again in the last week of December after investigators exonerated the vehicle's core stages in an embarrassing mishap that doomed three Glonass navigation satellites Sunday.

The Proton rocket lifts off from the Baikonur Cosmodrome Sunday. Credit: Roscosmos

A preliminary report from the official commission investigating Sunday's launch failure has traced the anomaly to a blunder during fueling of the rocket's Block DM upper stage, which was supposed to inject three Russian navigation satellites into orbit 12,000 miles above Earth.

Sunday's launch was the first flight of a new version of the Block DM, called the Block DM-03, featuring larger propellant tanks. Operating on outdated procedures, Russian fueling technicians filled the Block DM oxidizer tank to a level prescribed for earlier Block DM stages, according to the state commission update.

The fueling team unknowingly loaded more propellant than necessary into the Block DM, making the rocket stage heavier than anticipated. The Proton's third stage was unable to place the more massive Block DM on the proper trajectory, causing it to crash back to Earth in the Pacific Ocean.

"When you fill your gas tank in your car to three-quarters of a tank, if you have a 20-gallon tank that means you have 15 gallons," said James Bonner, vice president and chief technical officer of International Launch Services, the U.S. firm managing commercial Proton sales. "If you have a 24-gallon tank that means you have 18 gallons in there."

The report found no fault with the Proton rocket's three stages or its flight computer, tentatively clearing the way for the booster to launch a massive European Ka-band communications satellite for Eutelsat in the last week of December.

Commercial ILS Proton missions use a different upper stage, the Breeze M, to inject payloads into orbit.

The state commission's final report is expected some time next week, and ILS and Eutelast officials will travel to Moscow next week for their own review of Proton telemetry before deciding on a launch date for the KA-SAT spacecraft.

An ILS press release Friday said the processing team at the Baikonur Cosmodrome in Kazakhstan will halt preparations for about one week.

"We will meet with the Khrunichev team, and we'll do our due diligence and review the post-flight data from the Proton portion of the flight," Bonner said. "We will do our own verification that there were, in fact, no anomalies on the Proton vehicle that contributed to or caused the failure."

Liftoff of the KA-SAT mission was scheduled for Dec. 19.

"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 ILS statement said.

Khrunichev is the manufacturer of the Proton rocket and the lead investor in ILS.

The preliminary state commission report found "no issues with the functioning of (launch vehicle) systems and assemblies that have been detected. The trajectory parameters calculated by the (launch vehicle) motion control system conform to the trajectory measurements obtained from external sources."

"Command generation times of the flight timeline correspond to estimated values. The (launch vehicle) motion control system was found to have been functioning nominally, in line with the preset algorithms," the report said.

Photo of KA-SAT undergoing testing and assembly. Credit: EADS Astrium

The 13,558-pound KA-SAT satellite, built by EADS Astrium, will serve Europe and the Mediterranean region with broadband connectivity. With a throughput of more than 70 gigabits per second, the satellite can serve more than a million users at a time, according to Eutelsat.

The KA-SAT project is aimed at customers beyond traditional broadband Internet lines.

Roscosmos, the Russian space agency, had overall responsibility for the Glonass launch. Khrunichev and Energia were subcontractors for the Proton and Block DM components, respectively.

"I have full confidence in the Khrunichev team and full confidence in the mission assurance and quality assurance we have in place for our commercial missions," Bonner said.

After the KA-SAT mission, Proton teams will prepare for a dual-payload launch of Kazakhstan's Kazsat 2 and the commercial SES 3 communications satellites. That flight is scheduled for March and is currently the first Proton launch in 2011, according to Bonner.