Tripropellant motors use high-density kerosene for the boost phase, then low-density, high-performance liquid hydrogen for the later stages of ascent. However the propellants are stored in separate tanks. The fuel density indicated is the average for the MAKS design, which burned 17,850 kg LH2 and 18,698 Kerosene to reach orbit using 175,758 kg of liquid oxygen oxidizer.