Analysis of Liquid Fly-Back Booster Performance

This paper describes in its first part a parametrical investigation of different types of liquid fly-back boosters (LFBB). The preliminary design and performance estimation is exclusively restricted to the incorporation of rocket motors already under development or in operation. Staged combustion as well as gas-generator cycle is looked upon. The focus is on the LOX/RP1 RD-170/172, the NK-33 (AJ-26), the cryogenic RD-0120, and the LOX/LH2 Vulcain 2. The attached reference expendable space transportation system is the Ariane 5 ECB with cryogenic upper stage, but skipped SRB. The basic requirement is to reach almost the same commercial GTO payload as for the launcher with solid rocket boosters. The investigation includes trajectory simulations and optimizations for ascent. Return to the launch site by the LFBB is regarded, concerning the propellant requirements and the loads on the vehicle. Different booster geometries are generated by CAD for a preliminary dimensioning and mass estimation. Critical flight stability aspects are preliminary assessed. In a second step an evolutionary parallel staged launcher of the FESTIP system study is regarded. Originally based on a fly-back booster with expendable Ariane 5 core stage, the vehicle is designed to eventually evolve to a fully reusable sytem. Preliminary calculations and lay-out was done within the system concept team of FESTIP. A succeeding study by DLR of this latter configuration is presented. Since it is based on propellant crossfeed between booster and orbiter, the throttling requirements at booster burn-out are also of interest, due to their influence on performance. The paper includes a comparison of size and mass, as well as flight data of the different liquid fly-back booster configurations. The relevant rocket engine figures of performance, mass, reusability, and throttling capability are presented. A sensitivity analysis concerning the growth factor is given for both fly-back booster applications