Commercial flights of Russia's Proton rocket will resume next month, officials announced Tuesday, following redesign efforts on the booster's upper stage.

A Proton rocket like the one pictured here will carry the Inmarsat 4-F3 satellite in August. Credit: International Launch Services

The Breeze M motor failed during its last launch on March 14 when an exhaust gas duct in the main engine ruptured. The stage was in the midst of a lengthy engine firing to propel the AMERICOM 14 satellite payload toward geosynchronous transfer orbit, but the mishap left the commercial communications spacecraft well short of its intended destination.

Russian rocket-maker Khrunichev has spent the subsequent months since the failure analyzing what went wrong and testing a corrective fix for the Breeze M upper stage.

The redesign replaces the faulty duct, which led to the main engine's turbopump shutting down, with a thicker-walled conduit. Khrunichev has finished certification testing of a flight engine with the new conduit, and the new design will be used on all future engines.

"The Khrunichev team, including Khimmash, manufacturer of the Breeze M main engine, demonstrated its commitment to mission success at every level. We are confident that the root cause has been determined and that the corrective actions provide more than enough margin to prevent this from happening again," said Jim Bonner, head of the Failure Review Oversight Board and International Launch Services' chief technical officer.

"In addition to making this change in the engine, Khrunichev has moved forward with its overall quality initiative by completing a detailed quality assurance review, including an independent audit, in support of near-term Proton/Breeze M missions."

An older version of the Proton rocket with the Energia-made Block DM upper stage successfully launched a Russian military satellite last week.

The return to flight for Proton and its redesigned Breeze M stage will be targeted for liftoff August 13 at 6:46 p.m. EDT (2246 GMT), commercial marketer International Launch Services and its payload customer announced Tuesday. The Inmarsat 4-F3 mobile communications spacecraft will be carried aloft from the Baikonur Cosmodrome in Kazakhstan.

"Having participated in the Failure Review process in its entirety, I am satisfied that appropriate actions have been taken to deal with recent failures and to reassess the quality of the Proton vehicle," said Gene Jilg, chief technology officer for Inmarsat.

"Inmarsat now expects to transport the satellite to the launch site and complete certain other formalities in sufficient time to target the launch date we have announced."

An artist's concept shows the Inmarsat 4-series satellite in orbit. Credit: EADS Astrium

Built in Europe by EADS Astrium, this third craft in a three-satellite series will provide office-like broadband services such as Internet, email, voice and data-relay using laptop and palm-sized terminals.

The sophisticated Inmarsat 4-series satellites transmit over 200 spot beams to deliver strong signals to the small receivers. Each craft has a giant unfurlable antenna reflector stretching 30 by 39 feet.

The new craft are 60 times more powerful and have 20 times more capacity than their predecessors, the Inmarsat 3-series of satellites.

Inmarsat 4-F1 was flown aboard an Atlas 5 rocket in March 2005; and the F2 satellite was lofted in November 2005 by Sea Launch.

Once the F3 spacecraft becomes operational later this year, the next-generation constellation will provide global coverage for users at sea, in the air and on land.

"We thank Inmarsat for its support and patience," said Frank McKenna, president of International Launch Services. "We know how important this satellite is for the continued success of Inmarsat's growing broadband services, and we look forward to the start of the campaign in the coming days."