RD-191

The RD-191 (Russian: Ракетный Двигатель-191, romanized: Raketnyy Dvigatel-191, lit. 'Rocket Engine 191') is a high-performance single-combustion chamber rocket engine, developed in Russia and sold by Roscosmos. It is derived from the RD-180 dual-combustion chamber engine, which itself was derived in turn from the four-chamber RD-170 originally used in the Energia launcher.

The RD-191 is fueled by a kerosene / LOX mixture and uses an oxygen-rich staged combustion cycle. In the future the engine is expected to become a workhorse in the Russian space sector, as older launch vehicles are phased out of production and service.

Burn ignition is provided chemically, by feeding a starter fluid into the combustion chamber and gas generator, which is self-igniting on contact with liquid oxygen. The engine is capable of throttling down to 30% of nominal thrust; the design also allows for a short-duration enhanced thrust (up to 105% of nominal level) in emergency situations. A Cardan suspension provides for yaw and pitch controls by gimballed thrust deflection up to 8 degrees.

A modern design, the engine incorporates sensors monitoring burn conditions. The measurements are used for telemetry and an emergency protection system.

The engine's powerhead fulfills two additional functions, heating helium gas for pressurization of propellant tanks and generating hydraulic power for hydraulic actuators to deflect the nozzle and aerodynamic rudders.

On 5 September 2008, the creator of the engine, NPO Energomash, stated that the engine had completed the full cycle of development and burn tests and is ready for manufacturing and delivery. The primary launch vehicle utilizing this engine is the Angara carrier rocket family, first flown in 2014.

By 2010, the engine had passed all development phases, and its nine prototypes had accumulated over 23,000 seconds in 105 firing tests, with one of them reaching the maximum running time of 3,635 seconds in 12 tests. In July 2014, the engine made its maiden flight, propelling the Angara 1.2pp test vehicle on a suborbital flight. In December 2014, the engine flew again, powering the Angara A5 heavy carrier rocket. In the same month, Orbital Sciences announced it would purchase RD-181 engines, a variant of the RD-191, for use on the Antares rocket.

A version of the RD-191 with thrust reduced to 170 tonnes, called RD-151, was fire-tested on 30 July 2009. The first flight test of this engine was conducted on 25 August 2009 as part of the first launch of South Korean Naro-1 rocket.