The international Sea Launch group expects to resume commercial satellite deployment missions by year's end now that investigators have concluded their inquiry into a troubled June flight.

The Zenit rocket lifts off with Telstar 18. Credit: Sea Launch

During the June 29 launch of the Zenit 3SL rocket from a floating platform in the Pacific Ocean, the Russian-made Block DM-SL upper stage suffered an early cutoff of its main engine. The premature shutdown resulted in a lower-than-planned orbit for the Telstar 18 communications satellite payload.

Ground controllers were able to maneuver Telstar 18 into geostationary orbit and salvage the craft's entire 13-year life expectancy. But the incident forced Sea Launch to suspend missions until the upper stage problem could be identified and fixed.

On Thursday, Sea Launch announced that a wiring problem on the Block DM-SL triggered a short that disrupted the transmission of data from fuel sensors during the mission and caused the stage to run out of propellant during the launch.

"Immediately following the mission, Sea Launch partner RSC Energia appointed a commission in Moscow to investigate a premature shutdown of the Block DM-SL upper stage. RSC Energia was able to recreate the anomaly on the ground in full scope, matching the flight telemetry data from the Telstar 18 mission," Sea Launch said in a press statement.

"The commission identified the most probable cause as a short in the onboard cable network. This short introduced electrical interference in the circuits that transmit liquid oxygen and fuel flow rate data to the main engine control system.

"The main engine control system performed nominally, given the distorted data it received from the flow rate sensors. As a result of the main engine control system acting upon the distorted data, the Block DM-SL consumed more fuel than planned and prematurely shut down due to fuel depletion."

Sea Launch's own Independent Review Board has unanimously approved the commission's findings and recommended corrective actions, officials said Thursday.

The Independent Review Board was chaired by Kirk Pysher, vice president and chief systems engineer for Sea Launch, and included the Sea Launch partners, independent reviewers, subject matter experts and customer representatives, the press statement said.

Sea Launch indicated that corrective actions to prevent a re-occurrence of the wiring short have been developed and verified through testing.

"The (Independent Review Board) has confirmed the corrective actions are appropriate and will increase the overall Block DM-SL reliability through increased fault tolerance during flight and pre-launch screening for defects. It also confirmed the Block DM-SL is ready for return to flight," Sea Launch said.

The next launch is targeted for early December when the Intelsat Americas 8 communications satellite is hauled into space to serve North and South America. Originally known as Telstar 8, this Loral Space and Communications craft and four others already in orbit were acquired by Intelsat earlier this year.

Sea Launch has conducted 14 missions beginning with a demonstration flight in 1999. The group has experienced one outright launch failure -- in 2000 -- when the second stage malfunctioned, causing the rocket and its ICO mobile communications satellite to fall into the Pacific.