Russia’s Energomash Research and Production Association (the manufacturer of space rocket engines) has delivered four RD-181 engines to the US Orbital Sciences Corporation, the Energomash press office reported on Monday.

"On December 6, representatives of the US Orbital Sciences Corporation signed certificates for a new batch of four RD-181 commercial engines," the press office said in a statement.

Before their acceptance, the US specialists examined the engines, their spare parts, instruments and tools together with the accompanying documentation.

This batch is the second this year. The engines will be prepared and delivered to the United States shortly, the press office said.

Energomash delivers its RD-181 rocket engines to the United States for Antares launch vehicles. The engine uses the oxygen + kerosene propellant. The Antares carrier rocket has been developed by Orbital Sciences Corporation.