The RD-843 is a Ukrainian single nozzle liquid propellant rocket engine. It burns a hypergolic mixture of unsymmetrical dimethylhydrazine (UDMH) fuel with dinitrogen tetroxide (N2O4) oxidizer. It is pressure-fed. It is rated for up to 5 restarts, and can gimbal up to 10 degrees in each direction.
It was developed by Yuzhnoye Design Bureau for Avio and is manufactured by Yuzhmash. It uses the RD-869 thrust chamber, the old Soviet ICBM SS-18 final stage engine from which it is evolved, and which was also designed by Yuzhnoye. The RD-843 ground test campaign included 74 tests, 140 ignitions, reaching a total of 8,201 seconds, which is approximately 12 service lives on 4 engines. As of June 2020 it has been successfully used on 14 orbital launches.
The Vega and Vega C uses it as the main engine on its AVUM (Attitude & Vernier Upper Module) fourth stage which it calls the MEA (short for Main Engine AVUM).[1]