RD-0124 engines use a multi-stage turbopump powered by pre-combustion of the engine propellants in the preburner. The kerosene fuel is used for regenerative cooling of the engine. Vehicle attitude control during ascent is provided by gimbaling the engine in two planes. The propellant tanks are helium-pressurized. Four combustion chambers are fed by a single turbopump system. The engine operates at a high chamber pressure and, for the type of propellants used, achieves a very high specific impulse.
The inaugural flight of a launch vehicle using an RD-0124 engine took place on December 27, 2006.Orbital Sciences considered using the RD-0124 in the High Energy Second Stage (HESS) for their Antares rocket. It would have replaced the Castor 30B second stage.
This upper stage engine has been adapted to two different launch vehicles, the Soyuz-2-1b/v and the Angara family. As such, there are different versions:
RD-0124 (GRAU Index 14D23). It is the version for the Soyuz-2-1b and Soyuz-2-1v Blok-I. It is the first liquid rocket engine designed in Russia after the Soviet period.
RD-0124A. It is the version that powers the Angara URM-2, both the 1.2 and the bigger 5 versions. It differs on the base model in having an extender burn time of 424 seconds and, at 548 kg (1,208 lb), being 24 kg (53 lb) lighter.
RD-0124DR. Version developed between 2008 and 2013 for the Soyuz-2-3 project. It would differ from the base version in the implementation of a throttled point of 176.6 kN (39,700 lbf) with a reduced chamber pressure of 9.5 MPa (1,380 psi) and a specific impulse of 347s. The throttling capability meant a redesign of the preburner and the combustion chamber.
RD-0125A. Single nozzle version of the RD-0124A, it is planned as an upgrade for the Angara URM-2. It would enable the use of dual engines, which would enhance performance and reduce launch cost. Probably only planned for the Angara-5 URM-2, which is bigger than the Angara-1.2's.