It can only be started once, and as a high altitude engine it has a thrust of 78.45 kN (17,640 lbf) and aspecific impulse of 342 s (3.35 km/s).[5][6] It is the first ever steering engine to use the staged combustion cycle, and as such is the basis for a family of planned engines for theMayaklaunch vehicle family.[3]
The engine itself is built like a hollow cylinder, with a cylindrical space in the center so the RD-120 nozzle can pass through.[9]
WhilstYuzhnoye's propulsion experience had been mostly onhypergolic propellants engines, likeRD-855 orRD-861, they are considered too toxic for current ecological standards.[7][8] While Yuzhnoye still offer to develop hypergolic propulsion, such asRD-843 for theVega'sAVUM stage or theTsyklon-4 project, Yuzhnoye selected a more environmentally friendlyLOX andkerosene propellant for theMayak launch vehicle family.[3]
Not only had Yuzhnoye mastered the most complex cycle for the propellant (oxidizer rich staged combustion cycle) with the RD-8, but they had worked closely withNPO Energomash during theRD-120 program. The manufacturing is done at its sister company ofYuzhmash in Dnipropetrovsk, and the RD-120 thrust augmentation project of 2001 to 2003 had been a mixed project between the three companies.[3]
On the base of this experience, a family of derivatives engines were proposed. While theRD-801 andRD-810 are really just based on the general technology, the other members of the family are related enough that they reuse many components of the RD-8.[3] One characteristic of this family is the limitation of keeping the preburner output temperature below 500 °C (932 °F).[3]
RD-805 (orRD-802): A proposed upper stage engine of just 19.62 kN (4,410 lbf) of thrust, it would use a single chamber of the RD-8.[10] While many new components would be required, it is considered a low technological risk since it only needs smaller versions of already developed component.[3]
RD-809 (sometimes identified asRD-809M): It is an RD-8 re arranged to minimize its diameter. It would use practically every single component of the RD-8, but arranged without the big hollow section in the middle. It was a proposed engine for a proposed liquid upper stage of theAntares rocket, then named Taurus II.[3] It would be capable of five engine burns in a single mission.[11]
RD-809K: A single nozzle version of the RD-8. It mixes most principal elements of the RD-8 like the turbopumps with a main combustion chamber and nozzle adapted from theRD-861K.[3][12] Initially it was announced that it would be capable of 4 starts in a single mission[12] later reduced to 2.[13] It is expected to be used in a dual engine configuration in theMayak upper stage.[3]
