|Country of origin||USSR/Russia|
|Designer||NPO Energomash, V.K.Chvanov, V.P. Radovsky|
|Propellant||LOX / RG-1|
|Cycle||Staged combustion cycle (rocket)|
Standard: 834 kN (187,000 lbf)
Standard: [note 1]
Standard: 162.8 bar (16,280 kPa)
|Burn time||315 seconds|
|Length||3.87 metres (12.7 ft)|
|Diameter||1.95 metres (6.4 ft)|
|Dry weight||1,125 kilograms (2,480 lb)|
The RD-120 (GRAU Index 11D123) is a liquid upper stage rocket engine burning RG-1 and LOX in an oxidizer rich staged combustion cycle with an O/F ratio of 2.6. It is used in the second stage of the Zenit family of launch vehicles. It has a single, fixed combustion chamber and thus on the Zenit it is paired with the RD-8 vernier engine. The engine has been developed from 1976 to 1985 by NPO Energomash with V.P. Radovskogo leading the development. It is manufactured by Yuzhmash in Ukraine along most of the rocket.
During the Buran programme initial development of the 11D77 —the launch vehicle later known as Zenit—, KBKhA had been assigned the development of the second stage engine, as they had done for the Proton and Soyuz vehicles. But given the difficulties for NPO Energomash in developing the RD-123 (which would later be known as the RD-170), they ceded the hydrogen / oxygen sustainer engine development to KBKhA. This project, the analog of the SSME, was project RD-130 within NPO Energomash. But when KBKhA tackled the development, named it RD-0120, a name that is always a source of confusion with the engine of the current article. In exchange for them tackling the difficult development of the cryogenic propellant engine, Energomash assumed the responsibility of developing the second stage engine of the 11D77, which would eventually be known as the RD-120. The fact that the RD-120 and the RD-0120 had this intertwined conception, within the same program, and with a swap of designer bureaus, does not help to avoid the confusion.
On March 16, 1976 the Government passed a resolution Resolution for the development of Zenit, the RD-171 and RD-120. By April 1976, Yuzhnoye supplied NPO Energomash with the final requirements for the 11D77 first and second stage propulsion. One of the desirable effects of consolidating the first and second stage propulsion on the same designer, was that they could learn their lessons on staged combustion engines on the smaller and simpler upper stage engine, and then apply them to the bigger and more innovative first stage RD-170. NPO Energomash, had already worked on a prototype kerosene / oxygen staged combustion engine in that range, based on the RD-268 hypergolic engine, which was already under serial production with Yuzhmash.  On February, 1977, the preliminary design of the RD-120 was finished. And on January 31, 1979 the first fire test of the RD-120 was performed.
The RD-120 had a complicated debut, with the seconds stage failing on its first (April 13, 1985), second (June 21, 1985) and fourth (December 28, 1985) flights. While only the first failure could be attributed to the RD-120 —the propellant flow regulator had a leak and the stage ran out of propellant before being orbital—, the program initial performance was quite troubling. Eventually it proved its worth, and by December 1987 the RD-120 (and the Zenit) were considered commissioned. But in the years of the Soviet dissolution, the second stage failed twice in a row on August 30, 1991 and February 5, 1992. Zenit had other second stage failures, but only the first one has ever been attributed directly to the RD-120 itself.
During 1990, the NPO Energomash Head of the Propulsion Department, and leading designer, V.K.Chvanov, was awarded the State Prize for the creation of RD-120.
In October 1992, Pratt & Whitney signed an agreement with NPO Energomash to sale and represent their line of engine in the USA. During the initial version of the X-34 program, the one trying to develop a reusable launch vehicle for small payloads through a public/private association, the was RD-120 seriously considered for the 747 air-launched first stage. The RD-120 offered the best price and performance, and was the preferred choice of Orbital Sciences. In fact, in October 11, 1995, the RD-120 was fired on the U.S. and thus became the first Russian rocket engine actively in production to be fired in American soil. This version of the engine, would mainly differ from the Zenit in the addition of a gimbal mount that would enable it to offer TVC. This version would be known as the RD-120M. The second private partner in the X-34 program, Rockwell International, wanted to use their own engine, the RS-27. And given the constrained schedule and budget of the program, the engine selection was not able to be resolved and the program cancelled and reimplemented as the pure NASA research program that the X-34 was later known for.
Also during the 1990s, the Chinese acquired two or three models of the RD-120, and possibly some documentation. This enabled them to bootstrap their indigenous kerosene staged combustion engine program, the YF-100 and YF-115. According to a WikiLeaks cable dated, September 28, 2007, the Ukrainian government denies any involvement of Ukrainian industry in that transfer, and states that no involvement, at least until 2007, had happened with the Chinese 11th nor 4th Academy regarding the transfer of RD-120 technology.
The RD-120 had significant margins built in, which allowed between 2001 and 2003 to develop a modernized 'Uprated' or 'Forced' version of the engine for Sea Launch which increased thrust 10% to 912 kN (205,000 lbf). It also incorporated many improvements, which allowed it to increase chamber pressure and thrust without additional weight gain. It still has a 5% extra margin, extended the design life to 4260 seconds, the number of ignitions to 19 and allows to consider it as a base for a reusable rocket, the engine is still not capable of restarting inflight After a program that used 4 test engines and performed 28 hot fire tests with an accumulated running time of 8,135 seconds, the engine was qualified for flight. Testing started in March 2004 and it had its debut flight on February 15, 2006 where it successfully orbited EchoStar X.
This engine has had two operative versions and some proposed variations:
- RD-120 (GRAU Index 11D123): Original version developed for the Zenit-2 second stage. The main characteristics is that it uses a vertical turbopump, since the fuel tank is a torus and the engine has to fit in the center hole.
- RD-120 (augmented thrust) (GRAU Index 11D123): Thrust augmented version developed for the Zenit-3SL second stage. Some authors identified it as the RD-120M (GRAU Index 11D123M).
- RD-120K: Project of unknown first stage project. Had reduced expansion area and the subsystem arrangements was done to reduce total length. It had enough development done that it actually performed some fire tests.
- RD-120M: Version proposed for the X-34 program. It added a gimbaled mount, and was test fired in the USA.
- RD-120U: Version proposed for the ULV-22.
- RD-182: Methane / LOX version of the RD-120K. Proposed for the Riksha launch vehicle project for the Makeyev Rocket Design Bureau.
- RD-182M: LNG / LOX version of the RD-182. Proposed for the Vozdushnyy Start launch vehicle project.
|Development years||1976 - 1985||2001 - 2003||1986-|
|Engine Type||Oxidizer Rich Stage Combustion upper stage liquid rocket engine|
|Propellant||RG-1/LOX (O/F 2.6)|
|Chamber Pressure||16.28 MPa (2,361 psi)||17.81 MPa (2,583 psi)||17.63 MPa (2,557 psi)|
|Thrust (Vac)||833.6 kN (187,400 lbf)||912 kN (205,000 lbf)||853.2 kN (191,800 lbf)|
|Thrust (SL)||N/A||N/A||784.5 kN (176,400 lbf)|
|Isp (Vac)||350 s (3.4 km/s)||350 s (3.4 km/s)||330 s (3.2 km/s)|
|Isp (SL)||N/A||N/A||304.4 s (2.985 km/s)|
|Burn time||290 seconds||290 seconds||305 seconds|
|Engine life||2200 seconds||2200 seconds||2200 seconds|
|Length||3,872 mm (152.4 in)||3,872 mm (152.4 in)||2,435 mm (95.9 in)|
|Diameter||1,954 mm (76.9 in)||1,954 mm (76.9 in)||1,400 mm (55 in)|
|Weight||1,125 kg (2,480 lb)||1,125 kg (2,480 lb)||1,080 kg (2,380 lb)|
|Used on||Zenit-2 Second Stage||Zenit-3SL Second Stage||Project|
|Status||In Production||In Production||Project|
- NPO Energomash - Engine designer.
- Yuzhmash - Engine manufacturer.
- Zenit - Launch vehicle that used the RD-120 as second stage.
- YF-100 - Chinese engine that supposedly is based on the RD-120 technology.
- SCE-200 - Indian engine supposedly based on RD-120 technology.
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