RD-0146 hydrogen engine
The RD-0146 engine was developed by KBKhA design bureau in Voronezh, Russia, in a little-publicized cooperation with the American firm Pratt & Whitney. In 2009, this powerplant, burning liquid oxygen and liquid hydrogen, came into prominence, as Russian space agency chose it for the second-stage of the Rus-M launch vehicle designed to carry future manned spacecraft. The decision marked the return of the Russian rocketry to the use of liquid hydrogen for the first time since this most efficient but hard to control rocket fuel powered the Energia heavy-lifting vehicle in the 1980s.
The RD-0146D1 engine fires during test at KB Khimavtomatiki, KBKhA, design bureau in Voronezh on Dec. 29, 2021.
The ultimate rocket fuel
Hydrogen - the lightest and most abundant chemical element in the universe, had powered the Sun and stars from the beginning of time. The idea of using this highly flammable chemical as liquid rocket propellant was expressed at the dawn of the space era. The father of modern astronautics, Konstantin Tsiolkovsky, had already fueled his theoretical rockets with liquid hydrogen at the beginning of the 20th century, only few years after James Dewar succeeded in turning hydrogen gas into liquid. Yet, the practical introduction of hydrogen into rocket technology took a back stage, as less efficient, but easier to tame propellants, such as kerosene had emerged. Sometimes during 1930s, at the German army's rocket research facility in Kummersdorf, propulsion expert Walter Thiel did test a small hydrogen engine. The project was apparently plagued by leaks and constant danger of explosion, leaving Wernher von Braun with great aversion toward hydrogen, which he expressed years later in the US with his resistance to the development of the Centaur upper stage powered by the RL-10 hydrogen engine. (336)
Yet, the most ambitious projects in the US space program were achieved thanks to rocket engines burning super-cold liquid hydrogen. The Saturn V moon rocket and the Space Shuttle both utilized hydrogen to carry heaviest payloads in the history of space exploration. The Centaur became an irreplaceable part of the US deep-space and other high-energy missions.
History of the project
In the meantime in USSR, despite a number of projects aimed to put hydrogen to work on upper stages of launch vehicles, the practical application of the cryogenic technology in space remained elusive.
In the feverish pace of the Moon Race of the 1960s, the father of the Soviet space program, Sergei Korolev had to rely on tried kerosene engines for its N1 Moon rocket. However a hydrogen-powered upper stages were still planned for follow-on versions of the rocket. To fulfill these hopes, Aleksei Isaev's design bureau, now known as KBKhM, developed the RD-56 engine with thrust of 7.5 tons. It was followed by the RD-57 engine developed by the collective led by Arkhip Lyulka and delivering around 40 tons of thrust. Neither of the engines made it to the launch pad, as the Soviet government terminated ill-fated lunar program, yet, an already completed work had left a rich heritage for the Soviet space industry.
During the 1970s, KBKhA design bureau in the city of Voronezh developed a powerful RD-0120 hydrogen engine for the core stage of the giant Energia booster. The engine could develop up to 200 tons of thrust and rivaled the SSME powerplant on the US Space Shuttle. Cluster of four RD-0120 engines performed flawlessly during two launches of the Energia rocket in 1987 and 1988. However the program was also abandoned, this time due to economic collapse of the 1990s. However, at the same time, the Russian government did manage to secure a contract with India to supply a modified version of the RD-56 engine for the upper stage of the nation's GSLV launch vehicle. Renamed KVD-1, a hydrogen-powered engine made a successful debut on the Indian rocket, simultaneously preserving Russia's potential in development of such technology.
All these engines employed so-called "staged combustion cycle," while the American RL-10 engine remained the only upper stage engine using so-called expander cycle. In this design, the super-cold liquid fuel, upon passing through the cooling loop of the combustion chamber, turns into gas before entering the combustion chamber, where it burns along with oxidizer.
In 1988, RKK Energia became the first Soviet organization to request KBKhA to develop a new hydrogen engine without a gas generator for the prospective Buran-T and Vulcan rockets. Designated RO-95, the engine would be able to generate 10 tons of thrust and a specific impulse of 475 seconds. At the time of the development start in 1989, test firings of the engine were expected in 1991-1992 period, however the work did not go beyond the preliminary design. (332) The Soviet government apparently decided not to fund the project, seeing it as a duplication of KBKhM's RD-56. (335) Further models designated RD-0131 and RD-0132 were also studied and also never developed. Finally, in 1995, KBKhA made another, so far stillborn attempt to develop an exotic RD-0126 engine equipped with an exotic "ring-shaped" nozzle. (331)
In 1997, Khrunichev enterprise, the manufacturer of the Proton rocket, assigned KBKhA to develop an engine with the thrust of 10 tons and equipped with a nozzle extension for best performance at high altitude. The engine would be intended for Kislorodno-Vodorniy Racketniy Block, KVRB, or Oxygen-Hydrogen Rocket Stage in English. The vehicle was conceived as the most powerful upper stage of the upgraded Proton rocket and the next-generation Angara family of launch vehicles.
In parallel, the US firm Pratt & Whitney proposed to adapt its venerable RL-10 engine from the Centaur upper stage for the use on Proton. KBKhA then worked on adapting RL-10 for the Proton's upper stage, along with partial redesign and upgrades of some of the engine's components. However, due to potential proliferation problems, Pratt & Whitney was not able to continue this cooperation, prompting KBKhA to start an independent development of the RD-0146 engine. (331) Pratt & Whitney still partially financed the development of RD-0146, while also taking responsibility for marketing the applications of the engine outside the former Soviet Union. In such case, the company's Rocketdyne division would be responsible for delivery and maintenance of the system. (333)
In 1999, Khrunichev requested KBKhA to develop RD-0146U version of the engine for Proton and Angara rockets, also with the thrust of 10 tons. (332)
The RD-0146 became the first Russian rocket engine without a gas generator, and it was also equipped with extendable nozzle extension without a coooling system and it was capable of multiple firings and thrust control in two planes. According to KBKhA, the lack of generator ensured high reliability of the engine, especially for multiple firings.
Also, for the first time in its development experience, KBKhA decided to employ two separate turbopumps for fuel and oxidizer, in the effort to improve the engine's performance characteristics. The fuel turbopump would spin with a record-breaking 123,000 (130,000 according to 331) rotations per minute. Such high rate enabled to minimize the size and mass, while still guaranteeing high efficiency of the pump. Load-bearing pumps were made of titanium alloys employing granular technology. A nozzle extension of the combustion chamber would be made of heat-resisting carbon-carbon composite. The engine itself would employ latest titanium and aluminum alloys in its design.
By the beginning of 2001, KBKhA produced a complete design documentation for the RD-0146 engine and a number of components of the engine had been manufactured at KBKhA's experimental facilities. For the first time in the Russian practice, ball-shaped valves had been developed with complete leak-proof and minimal resistance. The igniter was also developed and model tests of the injectors completed. Autonomous tests of some engine components were underway. At the time, the development of the section of the nozzle, which does not have cooling system and movable extension was conducted in cooperation with Institute of Thermal Chemistry and Iskra enterprise in the city of Perm.
At the beginning of 2001, a full-scale mockup of the RD-0146 engine had been shipped to Pratt & Whitney per previous agreements. Additionally three experimental components of the engine had been manufactured, including oxidizer and fuel line systems and a combustion chamber with the igniter. At the time, this hardware was scheduled for tests in March-May 2001. (331)
In 2002, RKK Energia returned to KBKhA with the request to develop a 10-ton engine for the prospective Onega booster. The engine was designated RD-0146E. (332)
In 2008, official KBKhA documents said that RD-0146U fired 17 times, including eight firings burning oxygen-hydrogen propellant and six tests using mix of oxygen and methane. At the time, KBKhA had already expected increased funding for the RD-0146 and RD-0163 projects in connection with the development of the prospective launch vehicle for the manned space program based in Vostochny. (334)
According to KBKhA web site accessed in 2009, all components of the RD-0146 engine, including the combustion chamber with the ignition system went through rigorous individual testing under tougher than nominal parameters. Four copies of the engine had been manufactured and used in 30 test firings, reaching 109.5 percent of nominal thrust. Total burn time had reached 1,680 seconds. One engine accumulated 1,604 seconds of performance in 27 test runs. There was no accidents or failures during tests, KBKhA said.
On Nov. 8, 2011, KBKhA announced that a long-duration test of the RD-0146 engine had been conducted at the company's test facility in Voronezh, lasting 300 seconds for the first time. The firing completed the engine's test program in 2011 accumulating a total of 630 seconds during the year, the company said.
By November 2013, various models of RD-0146 engine went through a total of 68 firing tests, including six tests burning methane fuel. At the time, KBKhA started "dovodochnye ispytaniya", DI, (tune-up tests) of the RD-0146D engine developed within the Dvina-KVTK program. The company also said that with the help of experts from NITs RKP, TsIAM, Keldysh center and NPP Molniya, it had developed a new test bench in Voronezh allowing to simulate high-altitude conditions during the firing of the engine. It apparently employed a special gas-dynamics wind tunnel.
The first firing of RD-0146D at the new test bench took place successfully on Nov. 20, 2013. According to KBKhA the test for the first time simulated operational conditions for the ignition of the engine and provided "non-shear-off" exhaust flow in the nozzle thanks to the use of a gas-dynamic tunnel.
Chronology of the RD-0146 project:
1997 April: KBKhA initiates the development of the RD-0146 engine for the upper stage of the Proton-M rocket.
1997 September: Russia's KBKhA design bureau in Voronezh established contacts with the US firm Pratt & Whitney aimed to research the possibility of development of a rocket engine with the thrust of 250 tons and of a propellant supply system with the thrust of 25 tons, as well as upgrades of the combustion chamber head of the US RL-10 engine.
1999: Khrunichev issued a technical assignment to KBKhA to develop a 10-ton thrust RD-0146U engine for Proton and Angara rockets.
2000 March: KBKhA and Pratt & Whitney (USA) signed an agreement and launched a combined project to develop oxygen-hydrogen engine RD-0146 and RD-0148 for prospective launch vehicles.
2000 April: N. E. Titkov appointed a chief designer of the development of RD-0146 and RD-0148 engines.
2000 August: KBKhA demonstrated RD-0146 at the Aerokosmos-2000 exhibit organized by Moscow State University.
2001 Oct. 9: KBKhA conducted the first test firing of the RD-0146 engine.
2002: RKK Energia requests KBKhA to develop RD-0146E version of the engine for the Onega rocket.
2009 March 16: Roskosmos representatives unseal proposals for the development of the PPTS launch vehicle.
2009 March 19: Roskosmos formally names TsSKB Progress a winner of the tender for the development of the launch vehicle for the next-generation spacecraft.
2009 April 10: Roskosmos signs a contract with TsSKB Progress for the preliminary design phase, EP, of the development of the launch vehicle complex, RKK, for the Vostochny cosmodrome.
2012 Aug. 23: An RD-0146D engine intended for the upper stage of the Angara-A5 rocket undergoes first firing test in Voronezh.
2012 Nov. 30: An RD-0146D engine intended for the KVTK upper stage of the Angara-A5 rocket undergoes triple laser ignition test in Voronezh.
2013 Oct. 28: An RD-0146D engine went through the first series of "tune up" firing tests, DI, at the KBKhA design bureau within the Dvina-KVTK program. The test had confirmed operational design of the engine, KBKhA said.
2013 Nov. 22: An RD-0146D engine successfully fired at a KBKhA test facility in Voronezh simulating high-altitude conditions.
Specifications of the RD-0146 engine and its modifications and compared to Pratt & Whitney's RL10A-4-1 engine:
General overview of the RD-0146 engine and its notable features:
Editor's note. Given enormous significance of the RD-0146 engine for the future of space flight, a contributing editor to this site had calculated a number of parameters of the engine not available from the manufacturer, including characteristics of upper stages, which can rely on RD-0146 to propel future vehicles into deep space. All numbers below are unofficial and have not been published in any other source.
Estimated parameters of the RD-0146 engine:
Estimated maximum mass and volume of upper stage propellant limited by flow rate and burn time:
Density of liquid oxygen - 1141 kg/m3; Density of liquid hydrogen - 69.5 kg/m3Note: Maximum value of the propellant mass/volume are provided as reference only and not recommended ones due to the low thrust to weight ratio of upper stage.
Minimum upper stage diameter limited by configuration and gimbal capability (± 4 degree):
During 1980s, KBKhA design bureau gained extensive experience in hydrogen-powered propulsion, during its development of the RD-0120 engine for the Energia rocket. Click to enlarge. Copyright © 2000 Anatoly Zak
Scale model of the KVD-1 engine. Click to enlarge. Copyright © 2008 Anatoly Zak
General view of the RD-0146 engine. Click to enlarge. Credit: Pratt & Whitney
RD-0146's basic architecture. Click to enlarge. Credit: Pratt & Whitney
A mockup of the RD-0146 engine delivered by KBKhA to Pratt & Whitney. Click to enlarge. Credit: KBKhA
A second copy of the engine designed for operation. Click to enlarge. Credit: KBKhA
A scale model of the RD-0146 engine (right) with a nozzle extension next to a KVD-1 engine. Copyright © 2011 Anatoly Zak