The recent Future European Space Transportation Investigation Program (FESTIP)system study has included onetwo-stage-to-orbit (TSTO)conceptwithanairbreathinge rststageandarocket-propelledsecondstage.Because ofthepureaccelerationmission from Kourou/CSGandthelimitedtechnologylevelthatshouldbeapplied,turbojet engines for staging at Mach 4 were assumed in the e rst stage. Two different TSTO cone gurations were studied in parallel: the fully integrated delta-wing cone guration and the less integrated trapezoidal-wing cone guration. The predesign activities were completed in July 1998, and a better data basis is now available for comparing the two design options in terms of launcher size, performance, complexity, operations, and cost. In spite of the high aerodynamic integration of the delta-wing cone guration, its overall performance is rather limited because of weak turbojet performance at high Mach numbers and altitudes. Inclusion of a ramjet for operation beyond Mach 3 would increase the optimum staging Mach number and overall complexity of this TSTO concept. The trapezoidal-wing cone guration makesbest useofa boost to beyond Mach 1.3 by rocketenginesof the second stage, which are fueled during the combined ascent by cross feeding from the e rst stage. The limited analyses performed on the double-wing aerodynamic interaction between the mated stages has not revealed any severe objections. This TSTO concept has exceeded the current FESTIP performance requirements, delivering 9 Mg into equatorial 250-km-reference orbit and 3 Mg into polar 250-km-reference orbit. With respect to cost, this launcher could be optimized by avoiding any stage integration. Then the internal tank arrangement of the e rst stage is not penalized by additional geometric constraints, and stage separation becomes simpler. Takeoff mass of the trapezoidal-wing cone guration is 470 Mg compared to 430 Mg for the delta-wing cone guration. Nevertheless, the vehicle dry mass, which drives development cost, is 40 Mg heavier for the delta-wing cone guration. The absolute cost e gures of both TSTO options are signie cantly higher than those of the single-stage-to-orbit vehicles investigated in the FESTIP program.