Effects of the rocket engine on the single-stage-to-orbit vehicle

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For the given flight mission, the effects of the main propulsion system on the dry mass of the single-stage-to-orbit vehicle are calculated, the propulsion system being made up of the existing and new liquid rocket engines. For the SSMEderivative engines powered single-stage-to-orbit vehicle, the effects of the engine expansion ratio on the vehicle dry mass are calculated and it is shown from the calculation results that the optimal expansion ratio is about 51. The effects of the engine specific impulse and engine mass on the vehicle dry mass are also calculated with the payload fixed, and the calculation results indicate that the effect of reducing the engine mass by 88kg on the vehicle dry mass is equivalent to the effect of increasing the engine specific impulse by lOm/s on the vehicle dry mass. Introduction With the development of the vehicle materials and the progress in liquid rocket engine and vehicle design, the rocket powered single-stageto-orbit vehicle is feasible and practical now and * Professor ** Professor, Member AIAA Copyright © 1997 by W. D. Huang. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. the SSTO is widely studied in recent years. For the next generation vehicle, it is economic to develop the fully reusable single-stage-to-orbit vehicle. The launch cost of the single-stage-toorbit vehicle is related to the vehicle dry mass, since the vehicle with less dry mass will lead to less launch cost. So for the rocket engine powered single-stage-to-orbit vehicle, it is important to assess the effects of the liquid rocket engine on the vehicle dry mass. The purpose of this paper is to analyze the effects of the main propulsion system on the dry mass of the single-stage-to-orbit vehicle, the propulsion system being made up of the existing and new liquid rocket engines. For the SSMEderivative engines powered single-stage-to-orbit vehicle, the effects of the engine expansion ratio, specific impulse and mass on the vehicle dry mass are also calculated with the payload fixed. Engines Selected for Calculation The main propulsion system of the singlestage-to-orbit vehicle considered is made up of four types of liquid rocket engines. The engines selected are the Evolutionary SSME, the NK-33 engine, the dual-fuel/dual-expander(DF/DX) engine and the RD-704 engine. The reliability and operability of the Evolutionary SSME are enhanced by using extended-life, high-pressure turbomachinery, electromechanical actuators, etc. The Russia NK-33 engine is a high Copyright© 1997, American Institute of Aeronautics and Astronautics, Inc. performance booster engine, the thrust to weight ratio of the engine being 124. The engine has high reliability and low cost, but it is no longer in production in Russia. The RD-704 Engine is a new tripropellant engine, which is derived from the RD-701 engine. The dual-fuel/dualexpander engine has high performance and high thrust to weight ratio, and it is a strong competitor among the engines used for singlestage-to-orbit vehicle. The performance characteristics of these engines are shown in Table 1. Flight Mission and Vehicle Dry Mass Calculation Method In this paper, the flight mission is assumed to deliver the payload of 10000kg to the circular orbit at a 360km altitude from the launch center located in 28.2 degree north latitude. The transfer orbit is a 100x200km altitude, 28.5 degree inclination one. The vehicle dry mass calculation process is shown in Figure 1. Three main tools are used in the process, i.e. the aerodynamic analysis system, the .ascent trajectory calculation algorithm and the vehicle mass and size calculation package. The vehicle dry mass is calculated by iteration. Results and Analysis Considering the effects of the main propulsion system on the vehicle dry mass, the main propulsion system studied is made up of seven Evolutionary SSME, or seven RD-704 engines, or four dual-fuel/dual-expander engines, or four NK-33 engines and three Evolutionary SSME. In order to compare the effects in the same level, all the vehicle dry masses include 12% design margin and the transition Mach number is six. The calculation results are shown in Table 2. It is shown from the calculation results that the single-stage-to-orbit vehicle with dual-fuel/dual-expander engines has the minimum dry mass. The results also indicate that the dry mass of the tripropellant engine powered single-stage-to-orbit vehicle is less than that of the bipropellant engine powered singlestage-to-orbit vehicle. For the single-stage-to-orbit vehicle powered by SSME or the SSME-derivative engines, the vehicle dry mass is calculated with several expansion ratios. The performance characteristics of the derivative engines are given in Reference 1. The calculation results are shown in Table 3, in which the vehicle dry mass includes 10% design margin and the average specific impulse is defined as: