reduced launch rates. The optimum launch vehicle size is discussed in the following section. Performance and Cost Results The comparison has been made for launch vehicles with the same payload and a launch rate of 100 per year (launch site: Kourou/Guyane). The launch mass (GLOW) of system C is the smallest, i.e., it has the highest performance, however, the total cost is relatively high, thus resulting in only being the second best in terms of specific cost (Table 1). The single-stage version A is relatively poor in performance, however, the cost is by far the lowest, leading to the best cost to payload ratio. Table 2 summarizes the design features and the rationale for the preferred heavy lift cargo vehicle concept for SPS transportation to GEO. LAUNCH VEHICLE SYSTEM AND SIZING Figure 3 illustrates the typical design of a ballistic SSTO vehicle: compact, with a large heat shield and a number of 12 high-pressure LOX/LH2 engines arranged in a circle and integrated into the heat shield. The vehicle base could consist of water- or hydrogen-cooled titanium sheet metal, in order to minimize refurbishment cost. This type of engine arrangement should lead to a certain thrust augmentation at higher altitudes, an effect which will be analysed by the DFVLR Institute at Lam- poldshausen. The final landing phase after aerobraking will be performed with retro thrust using TABLE 1 COMPARISON OF THREE BALLISTIC CARGO VEHICLE CONCEPTS WITH RESPECT TO COST EFFICIENCY (MODEL COST COMPARISON NOT AN OPERATIONAL CASE)
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