File photo of a previous Proton rocket launching. Photo: ILS

Russian space officials have postponed the next Proton rocket launch after a problem with found with one of the booster's engines. The Proton fleet suffered two launch failures last year due to poor workmanship that left debris inside engines.

The Proton rocket was slated for liftoff on April 6 to carry into space the Siberian-European Satellite, nicknamed Sesat. The satellite will be used to relay communications to Central and Eastern Europe, Russia, Siberia, North Africa and Saudi Arabia.

But during recent pre-launch preparations, workers discovered that "one of 12 bolts on the cover of an engine turbopump bearing was not safety wired," according to a statement issued by Proton maker Khrunichev State Research and Production Space Center.

This routine inspection was part of the revised and improved quality control procedures ordered by Khrunichev in the wake of last year's mishaps. Investigators determined the two botched launches were both caused by materials and debris left in the rockets' second stage engines by workers when the powerplants were built in 1992 and 1993. The debris created fires inside the engines that ultimately caused the rockets to explode and crash back to Earth.

Khrunichev said all pre-launch checkouts indicated there were "no deviations from the standard requirements" for the engine hardware on the Proton rocket to launch Sesat.

However, since the sealing of the bolt in question cannot be checked while the engine is attached on the rocket, officials decided to simply replace the engine. The Khrunichev statement did not specify which stage of the rocket the engine belonged.

The extra work will delay the Sesat launch until sometime between April 16 and 18.

Sesat was originally scheduled for launch last fall but was grounded after the Proton failed on October 27.

Once in space, the craft will be deployed in geostationary orbit 22,300 miles above the Earth's equator at 36 degrees East. Sesat will be part of Eutelsat's satellite fleet with Intersputnik operating some of the spacecraft's transponders.

The satellite's structure was built by NPO-PM and Alcatel manufactured the communications payload.

Proton has chalked up two successes this year since returning to flight -- one in February and the other last Sunday.