Performance Characteristics of the HM7 Rocket Engine for the Ariane Launcher

This paper presents the main performance characteristics of the 60,000 N thrust HM7 rocket engine, designed to power the LOX/LH2 third stage of the European launcher Ariane. The development test phase of the engine has almost been completed, and qualification testing is scheduled before the end of 1979. During development testing under altitude-simulated conditions, a mean specific impulse of 440.8 s was demonstrated compared to a specification value of 430 s. The first vacuum tests resulted in ignition delays of about 0.5 s and produced hard starts. Reducing the helium purge on the oxidizer side of the injector from 34 g/s to 8 g/s and simultaneously increasing the opening rate of the main LOX valve reduced the ignition delay to 0.13 s and eliminated the hard starts. The ability of the engine to meet the mixture ratio accuracy specification of ±1% has been demonstrated.