AIAA 94-4339 System Sensitivity Analysis Applied to the Conceptual Design of a Dual-Fuel Rocket SSTO

This paper reports the results of initial efforts to apply the System Sensitivity Analysis (SSA) optimization method to the conceptual design of a single-stage-to-orbit (SSTO) launch vehicle. SSA is an efficient, calculus-based MDO technique for generating sensitivity derivatives in a highly multidisciplinary design environment. The method has been successfully applied to conceptual aircraft design and has been proven to have advantages over traditional direct optimization methods. The method is applied to the optimization of an advanced, piloted SSTO design similar to vehicles currently being analyzed by NASA as possible replacements for the Space Shuttle. Powered by a derivative of the Russian RD-701 rocket engine, the vehicle employs a combination of hydrocarbon, hydrogen, and oxygen propellants. Three primary disciplines are included in the design — propulsion, performance, and weights & sizing. A complete, converged vehicle analysis depends on the use of three standalone conceptual analysis computer codes. Efforts to minimize vehicle dry (empty) weight are reported in this paper. The problem consists of six system-level design variables and one systemlevel constraint. Using SSA in a “manual” fashion to generate gradient information, six system-level iterations were performed from each of two different starting points. The results showed a good pattern of convergence for both starting points. A discussion of the advantages and disadvantages of the method, possible areas of improvement, and future work is included. NOMENCLATURE Ae nozzle exit area AR area ratio of engine nozzle C vector of weights and sizing outputs CONSIZ configuration sizing and weights program E1 vector of engine outputs 1 E2 vector of engine outputs 2 GSE global sensitivity equation Isp specific impulse LH2 liquid hydrogen LH2%1 LH2 propellant % in modes 1A and 1B LOX liquid oxygen LSM local sensitivity matrix LSV local sensitivity vector Mtr transition Mach number MDO multidisciplinary design optimization MR mass ratio (gross weight/burnout weight) P vector of trajectory outputs POST program to optimize simulate trajectories RP1 hydrocarbon rocket propellant (kerosene) Sref aerodynamic reference area (wing area) SDV sensitivity derivative vector SSA system sensitivity analysis SSTO single-stage-to-orbit Tvac engine vacuum thrust (T/W)eng engine thrust-to-weight ratio TPS thermal protection system ẇ2 total propellant flow rate in mode 2 W vehicle dry (empty) weight X vector of design variables ∆V velocity change