The YF-79 is a liquid cryogenic rocket engine burning liquid hydrogen and liquid oxygen in a closed expander cycle. It is China's fourth generation of upper stage cryogenic propellant engine, after the YF-73, YF-75 and the YF-75D. It can do multiple restarts thanks to an electric spark igniter and a prototype was tested at 60% and 100% (25 tonnes-force (250 kN; 25 LTf; 28 STf)) thrust levels in December 2021.
|Country of origin||People's Republic of China|
|Designer||Beijing Aerospace Propulsion Institute|
|Associated LV||Long March 9|
|Propellant||Liquid oxygen / Liquid hydrogen|
|Cycle||Closed Expander Cycle|
|Thrust, vacuum||243.3 kilonewtons (54,700 lbf)|
|Chamber pressure||8.0 MPa (1,160 psi)|
|Specific impulse, vacuum||460.1 seconds (4.512 km/s)|
|Long March 9|
It will be used on the third stage of the Long March 9.