Effects of engine cycle type on payload delivery of the future European launchers

Optimal propulsion parameters were determined for cryogenic stages of the future European launcher (Ariane 5P) on the basis of an engine cycle analysis and an engine mass model. Depending on chamber pressure, the optimal tank mixture ratio of launcher types with cryogenic core stages assisted by large solid booster stages was 5.5-5.6 for open cycle engines like the HM60 and 6-6.5 for closed cycle engines like the LE-7. Optimal chamber pressure will be achieved for an open cycle at 100 bar if the efficiencies in the pump and turbine are low; at higher efficiencies the optimal chamber pressure is 150-200 bar. No optimum was found for a closed cycle. It is shown that the higher the chamber pressure, the greater the payload efficiency that can be obtained. This implies that the highest technologically possible chamber pressure of the SSME engine will not necessarily be a limit to payload transport from earth to orbit.