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The RD-191 engine

Russia's newest rocket engine will power an American space launcher, the two sides agreed. In January 2015, the Russian rocket industry struck a deal with a US company to supply a modified version of the RD-191 engine for the US Antares rocket. The RD-191 engine was originally developed for Russia's new-generation Angara family of rockets and was already modified under name RD-151 to propel the South-Korean KSLV-1 launcher. The latest US-Russian agreement puts another upgrade of the engine, designated RD-181, on the first stage of the Antares rocket developed by the Orbital Sciences Corporation, OSC


Key components and basic operation of the RD-191 engine.

Technical specifications of the RD-191 engine:

Thrust at sea level
196 tons
Thrust in vacuum
212.6 tons
Specific impulse at the sea level
311.2 seconds
Specific impulse in vacuum
337.5 seconds
3,780 millimeters
2,100 millimeters
Dry mass
2,200 kilograms
Fueled mass
2,430 kilograms
Combustion chamber pressure
262.6 kilograms per square centimeter

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Multitalented RD-191


Integration of the RD-191 engine with an experimental version of the URM-1 booster for the Angara rocket.

Developed at NPO Energomash in Moscow, the RD-191 engine was based on the RD-170 engine family originally intended for the Energia super-heavy rocket and for the Zenit launch vehicle. While the RD-170 used four combustion chambers, the developers essentially split it into four parts to form a one-chamber engine for the URM-1 module of the Angara rocket. The concept of splitting RD-170 into four independent engines was first entertained in the beginning of the 1980s. At the time, designers considered installing four such engines, then known as MD-185, on the first stage of the Energia rocket, apparently, after facing serious technical problems in development of RD-170.

Before the work on RD-191 commenced at the end of 1998, the RD-170 was already "halved" to create the two-chamber RD-180 engine for the US Atlas rocket. All three engines use non-toxic kerosene fuel and liquid oxygen oxidizer. Unlike the original RD-170, Angara's RD-191 sports a single gas generator instead of two and a smaller main turbine responsible for pumping the fuel and oxidizer into the combustion chamber.

Driven by the hot gas from the generator, the main turbine spins a pair of pumps on the oxidizer and fuel supply lines. Both pumps are attached to the vertical shaft of the turbine.

After powering the main turbo-pump of the engine, the oxidized hot gas from the gas generator is directed into the combustion chamber to burn with the rest of the fuel. The fuel is also used to cool the combustion chamber.

The combustion chamber of the RD-191 is designed to swing up to eight degrees along two axis (yaw and pitch) in a special gimbal suspension to enable steering of the rocket in flight. This feature required feeding the hot gas into the combustion chamber through a special flexible hose.

From its predecessor, RD-191 inherited the capability to be reused for more than one burn, which allowed live-firing flight-worthy engines on the ground before sending them into the flight on an expendable rocket. Theoretically, the same capability could enable the reuse of the first stage of the Energia and Zenit rockets for multiple missions, even though it was never achieved. Still, NPO Energomash proposed a future version of the one-chamber engine designated RD-195 for Russia's next-generation reusable launcher MRKS-1. According to the company, the engine could be fired as many as 10 times. In an apparently related development, NPO Energomash also studied a methane-fueled version of the engine, designated RD-192. (145) The switch to methane fuel would eliminate the formation of burn residue in the engine, thus facilitating its servicing between multiple flights.

Another version of the RD-191 engine, with a retractable nozzle extension, was also studied. A telescope-like extension would slide into position during the ascent of the rocket as the engine was firing, in order to boost its performance in the vacuum of space. (727)

Like all members of the RD-170 family, Angara's engine has its critics. First off all, the very high combustion-chamber pressure in all the engines of the family leaves little margin for any deviations from flawless performance before a catastrophic failure. As a result, its use on rockets intended to carry cosmonauts will always be controversial. In addition, it was speculated that metal particles injected into the high-temperature stream of the oxidizer gas generator could cause a burn through in the main turbopump of the engine. (526) Ironically, in the Antares rocket, the RD-191-based engine was intended to replace the NK-33 engine, which operated at lower combustion-chamber pressure.

Development history


The design documentation for RD-191 was completed during 1999 and tests of individual components for the engine started in 2000. Thanks to the use of computer 3D modeling, a great deal of this engine's design was completed before full-scale prototyping. The first full-scale mockup of RD-191 was ready in March 1999. The assembly of the first workable engine was completed on May 22, 2001, clearing the way for the first live firing in July of the same year.

By the beginning of 2004, RD-191 logged 10 live firings. Despite being one of the most complex components of the Angara rocket, it ended up far ahead in development of the vehicle it was intended to propel. (424)

However long before Angara had a chance to fly, GKNPTs Khrunichev won a contract to build a launch vehicle for South Korea. Since the rocket's first stage was based on the URM-1 module equipped with RD-191, NPO Energomash also built a version of the engine designated RD-151 for the South Korean rocket.

In 2019, Roskosmos released footage from PO Polyot factory in Omsk apparently showing the assembly of the third Angara-5 rocket. RD-191 engines integrated with the URM-1 boosters of the vehicle had production numbers D028 and D029. The engine numbered D041 was also shown.

Serial production of RD-191 begins (INSIDER CONTENT)

At least some combustion chambers for early RD-191 engines were manufactured at the Voronezh Mechanical Plant, VMZ, south of Moscow, but as early as 2011, the serial production of the overall RD-191 was expected to be organized at the Proton-PM factory in the northern Russian city of Perm. As with other aspects of the Angara project, establishing the new manufacturing process for its engines faced numerous challenges and lengthy delays.

Export of RD-191

Another version of the RD-191 engine, designated RD-193, was intended for the Soyuz-2-1v rocket and a similar modification known as RD-181 was proposed for the US Antares rocket. Unlike its two siblings, RD-193 would not have a gimbal capability, relying instead on the special steering thrusters.

On Jan. 16, 2015, RKK Energia, parent company of NPO Energomash, announced that it had reached an agreement with the American company Orbital Sciences Corporation, OSC, on the export of RD-181 engines for the first stage of the Antares rocket, thus replacing the NK-33 engines previously used on the launcher.

In December 2022, speaking at the expanded session of the Federation Council, Valery Sherin, Deputy Director at Roskosmos, said that the State Corporation was considering supplying around 10 RD-191 engines to India from 2024 to 2029.

RD-191M engine

During the 2010s, NPO Energomash was working on the RD-191M engine, which was intended for the Angara-5M and Angara-5V rockets. The engine was test-fired in 2016, reaching 110 percent above the thrust of the original variant, the company's officials said. In May 2024, Roskosmos said that a full cycle of autonomous tests of components for the RD-191M engine had been completed at NPO Energomash by the end of 2023 and on July 8, 2024, NPO Energomash announced that it had completed tune-up tests of RD-191M. According to the company, the first RD-191M engine for tune-up tests had been manufactured at the end of 2023.


Chronology of the RD-191 engine development:

Beginning of the 1980s: Developers mull splitting the RD-170 engine into four one-chamber MD-185 engines for the installation on the first stage of the Zenit rocket.

1998: Development of the RD-191 engine starts at NPO Energomash in Moscow.

1999 March: The first full-scale prototype of the RD-191 engine is completed.

2001 July 27 or 31: NPO Energomash conducts a test-firing of the RD-191 engine No. D001 for the 1st stage of the Angara rocket.

2002: Two prototypes of the RD-191 engine are manufactured for dynamic testing with a mockup of the URM-1 stage and for cryogenic fueling tests. The engine No. D002 for tune-up tests is also manufactured.

2003: An electric prototype of the RD-191 engine is manufactured.

2003 Jan. 30: The RD-191 engine No. D003 is manufactured. (424)

2006 Aug. 1: According to NPO Energomash, the RD-191 rocket engine accumulated 4,500 seconds of running time in 35 firing tests. The longest firing lasted 400 seconds. The entire test program aimed to accumulate 15,000 seconds of work in 70 test firings on 10 copies of the engine.

2007 Dec. 6: NPO Energomash conducts testing of the RD-191 engine for the first stage of the Angara rocket, along with the operational hydraulic system and the gimbal mechanism of the engine.

2009 Jan. 19: NPO Energomash announced that the last test version of the RD-191 rocket engine was going through final firings after a total of 97 tests with an accumulated firing time of 20,789. The maximum firing time accumulated by a single engine reached 3,635 seconds in 12 tests. At the time, the manufacturer had already supplied an engine for the firing tests of the entire rocket stage and promised to supply first six flight-ready engines in 2010 for actual test launches of the Angara rocket.

2009 July 30, 17:15 Moscow Time: Angara's URM-1 rocket booster (Article I1A1S) test fired for the first time at the IS-102 test stand in Peresvet near Moscow at NITs RKP test facility (former NIIKhimmash). During the test known as OSI-1, the engine was burning for 232 seconds, essentially imitating the entire process of the first stage operation during the orbital launch. According to preliminary information, no major problems arose during the firing. At the time, the second firing was expected at the beginning of September 2009. The total of three firings of the same booster were originally expected.

2009 Aug. 19: Roskosmos and GKNPTs Khrunichev signed an agreement for the development of the manufacturing base at the Proton-PM company in the city of Perm for the mass production of the RD-191 engine.

2009 Aug. 25: A South-Korean Naro-1 (KSLV-1) launch vehicle, fails to deliver the STSAT-2 satellite from the Naro space center, South Korea, due to an upper stage failure, despite initial reports about a successful launch. However the Russian-built first stage, which was identical to the Angara's URM-1 booster and powered by an RD-151 engine, reportedly performs well.

2009 Oct. 1: Angara's URM-1 rocket booster test fired for the second time at NITs RKP test facility (former NIIKhimmash) in Peresvet near Moscow. During the test known as OSI-2, the engine was burning for 203.4 seconds under maximum throttle possible, imitating the flight profile of the Angara-5 vehicle.

2010 Aug. 3: Official Russian media quote a source at NPO Energomash as saying that the RD-191 engine "burned down" during one of multiple tests. The statement implied that the engine was destroyed in a some kind of planned endurance test, not as a result of a catastrophic failure.

2011 May 23: NPO Energomash published a press-release declaring the development of the RD-191 engine completed. By that time, the engine went through 120 firings with a total burn time of 26,747.4 seconds, including three ground tests on the full-scale URM-1 stage and two flights on the Korean KSLV rocket.

2012 Jan. 20: NPO Energomash conducted a certification test firing of the RD-191 No. D016 engine featuring a first combustion chamber manufactured at Voronezh Mechanical Plant, VMZ. A total of 18 firings were to be conducted using three copies of the engine for six tests each. NPO Energomash did not provide any details on the results of the tests, however, the announcement about the test was preceded by unofficial sources reported serious quality problems on combustion chambers produced at VMZ.

2012 Nov. 14: NPO Energomash conducts the fourth of six planned live firing tests of the RD-191 engine intended to certify a combustion chamber manufactured at the Voronezh factory. During the test, the engine had successfully completed its planned 330-second firing profile, the company announced on November 16.

2013 Feb. 20: NPO Energomash conducted live firing test of the RD-191 engine at its Facility No. 2, in order to certify the combustion chamber manufactured at Voronezh Mechanical Plant, VMZ. The engine fired for 30 seconds and the combustion chamber met all the specifications, NPO Energomash announced on February 21.

2016 Sept. 26: NPO Energomash conducted a successful live firing of the RD-191D035 engine. According to the company, after the test, this particular engine will be shipped to GKNPTs Khrunichev.

2023 July: NPO Energomash conducts control and technical firing, KTI, of the RD-191 engine to ensure mass production and prepare the development of the RD-191M engine.


The article and photography by Anatoly Zak; Last update: July 9, 2024

Page editor: Alain Chabot; Last edit: January 20, 2015

All rights reserved

insider content



One of the first workable RD-191 engines. Credit: NPO Energomash


Basic layout of the RD-191 engine. Credit: NPO Energomash


These scale models represent a family of rocket engines developed by Moscow-based NPO Energomash. A four-chamber RD-170 engine powering the first stage of the Zenit rocket is on the right. This power plant was "split in half" to create a two-chamber RD-180 engine (center) for the latest version of the US Atlas rocket. The "half" of the latter engine became RD-191 -- a one-chamber power plant developed for the modular stages of the Angara family, including the Baikal stage. Click to enlarge. Copyright © 2001 Claude Mourier


A demo version of the RD-191 engine integrated with the Angara-1 rocket. Credit: GKNPTs Khrunichev


Main turbopump and gas generator of the RD-191 engine. Credit: NPO Energomash





RD-191 during assembly and testing at NPO Energomash in Moscow. Credit: NPO Energomash


A scale model of the RD-191 engine for the first stage of the Angara launcher. Click to enlarge. Copyright © 2001 Anatoly Zak


A later scale model of the RD-191 engine. Copyright © 2009 Anatoly Zak


The first combustion chamber of the RD-191 engine manufactured at the Voronezh Mechanical Plant, VMZ, was demonstrated at MAKS-2009 show. Click to enlarge. Copyright © 2009 Anatoly Zak