Liquid hydrogen
In mode one, both burn kerosene. Liquid hydrogen is combined with kerosene and oxygen rich preburner exhaust in the combustion chamber. In this mode, it produces 4 MN of thrust, with a vacuum specific impulse of 415s, using 73.7 kg/s of kerosene, 29.5 kg/s of hydrogen, and 388.4 kg/s of oxygen.