The RD-8 four-chamber pump-fed single-run engine operated in a staged combustion scheme with afterburning of the generator gas. Development began in 1976, and it was designed from the beginning for high reliability (no less than 0.995%) long service life (more than 4000 seconds); and for installation in the upper stage after a factory firing test without the need for post -test refurbishment. A safe shutdown was commanded upon depletion of any propellant component. The propellants were ignited in the gas generator and chambers by use of a starting fuel. The control units were fed with helium through electropneumatic valves. The engine could stay ready on the pad, filled with propellants, for 24 hours before a launch would need to be scrubbed and the engine purged and recycled. The engine design of the engine allowed for multiple bench firing tests.