RD-8


The RD-8 is a Soviet / Ukrainian liquid propellant rocket engine burning LOX and RG-1 in an oxidizer rich staged combustion cycle. It has four combustion chambers that provide thrust vector control by gimbaling each of the nozzles in a single axis ±33°. It was designed in Dnipropetrovsk by the Yuzhnoye Design Bureau as the vernier thruster of the Zenit second stage. As such, it has always been paired with the RD-120 engine for main propulsion.
It can only be started once, and as a high altitude engine it has a thrust of and a specific impulse of. 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 the Mayak launch vehicle family.
The engine itself is built like a hollow cylinder, with a cylindrical space in the center so the RD-120 nozzle can pass through.

Derivatives

Whilst Yuzhnoye's propulsion experience had been mostly on hypergolic propellants engines, like RD-855 or RD-861, they are considered too toxic for current ecological standards. While Yuzhnoye still offer to develop hypergolic propulsion, such as RD-843 for the Vega's AVUM stage or the Tsyklon-4 project, Yuzhnoye selected a more environmentally friendly LOX and kerosene propellant for the Mayak launch vehicle family.
Not only had Yuzhnoye mastered the most complex cycle for the propellant with the RD-8, but they had worked closely with NPO Energomash during the RD-120 program. The manufacturing is done at its sister company of Yuzhmash in Dnipropetrovsk, and the RD-120 thrust augmentation project of 2001 to 2003 had been a mixed project between the three companies.
On the base of this experience, a family of derivatives engines were proposed. While the RD-801 and RD-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. One characteristic of this family is the limitation of keeping the preburner output temperature below.
  • RD-805 : A proposed upper stage engine of just of thrust, it would use a single chamber of the RD-8. While many new components would be required, it is considered a low technological risk since it only needs smaller versions of already developed component.
  • RD-809 : 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 the Antares rocket, then named Taurus II. It would be capable of five engine burns in a single mission.
  • 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 the RD-861K. Initially it was announced that it would be capable of 4 starts in a single mission later reduced to 2. It is expected to be used in a dual engine configuration in the Mayak upper stage.