Propulsion and staging considerations for an orbital sortie vehicle

Severe weight penalties can occur if the sizes of orbital sorties vehicle stages are not near their optimum values. In particular, single-stage rocket configurations with or without 'zero-stage' boosters are necessarily much larger than two-space configurations. Conventional cryogenic propellant combinations provide a reasonable range of vehicle sizes. By comparison, one storable-liquid propellant combination would require vehicle size to be excessive, while two 'exotic' propellant combinations do not appear to provide enough size reduction to warrant their use. Second-stage structural efficiency has a major effect on overall vehicle size. It appears feasible to design a two-stage orbital sortie vehicle whose gross lift-off weight is 50-70 times the payload weight.