RD-181 Engines

The Energomash RD-181 rocket motor is an all-new engine based on other successful liquid rocket engines Energomash designed and produced. The engines use an oxygen-rich staged combustion cycle that can be throttled, and has a variable mixture ratio for controlling relative flow rates of oxidizer and fuel. The Antares core tank design and design verification is by KB Yuzhnoye (Zenit-derived heritage). The core tank is produced by Yuzhmash. There are two Energomash RD-181 engines in the first stage.

The company changed the engine in the Antares launch vehicle from the the AJ26 (derived from the Russian NK-33 engine) to the RD-181 Russian engine. The RD-181 was specifically designed as a replacement for the NK-33, which the AJ-26 was based on. So the arrangement of the thrust vector, the piping for the fuel systems, the connections, the size of the engine, and the thrust levels were all very comparable to the NK-33 because it had been in development for almost 10 years now to replace that engine on a couple of different Russian rockets.