On feasibility of launch vehicle designs

The above limiting values refer to multistage configurations designed with uniform structural factor. Higher payloads and higher limiting values for the last stage structural factor are possible for configurations designed with nonuniform structural factor, that is, with a last-stage structural factor much higher than the structural factors of the previous stages. For example, a double-stage configuration with ε1 = 0.10, ε2 = 0.25 can deliver to orbit a payload mass equal to 4.7% at the takeoff mass; a triple-stage configuration with ε1 = ε2 = 0.10, ε3 = 0.25 can deliver to orbit a payload mass equal to 6.8% of the takeoff mass.