ANALYSIS In an effort to formulate a directed study to investigate viable candidate launch vehicles for the SPSS program, several concepts have been studied. The EDIN Design Center under the direction of Mr. R. Abel, Engineering Analysis Division/EX42, undertook a study to size one of these concepts: two-stage winged reuseable HLLV's. For the initial investigation, six candidate vehicles were sized for a range of stage mass fractions typical of winged launch vehicles. The payload for these vehicles was chosen as 226.795 metric tons (500,000 pounds), and the payload was delivered to a 92.6 x 500 kilometer (50 x 270 nautical mile) elliptical orbit. Two booster engines were used in this study: 1. High chamber pressure, staged combustion cycle engines using LOX/RP-1 propellant, and 2. High chamber pressure, staged combustion cycle engines using L0X/LH2 propellant. Performance characteristics of these booster stage engines, provided by Mr. M. Lausten of the Power and Propulsion Division, are given in Table 1. The data represent the performance characteristics expected achievable for these engine types by 1995. The mass fractions used in this preliminary sizing are given in Table 2 which shows a matrix of the six vehicles initially investigated. The upper stages of all the vehicles used uprated Space Shuttle Main Engines (SSME's). The performance characteristics of these engines were also estimated for the 1995 time period, and their specifications are included in Table 1. Three degree of freedom trajectory computer programs were used to simulate launch vehicle flight and performance. The trajectories were optimized for initial tilt rate and exo-atmospheric pitch profile. Weight estimating routines (WER's) were used to determine subsystem weights and resulting stage mass fractions. The WER's were developed and equation coefficients chosen to provide system weights expected to be achieved in the target 1995 time frame. Subsequent to the initial sizing of the 226.795 metric tons (500,000 pounds) payload class vehicles, ground rules were established which pointed the study toward developing launch vehicles capable of injecting greater payloads into the reouired orbit. Consequently, the candidate vehicles were sized for payloads of 453.59 metric tons (1,000,000 pounds). The groundrules for this study are given in table 3; evaluation criteria used for baseline selection are listed in Table 4. A propulsion system was sized to circularize the payload at 500 kilometers (270 nautical miles). A vacuum specific impulse of 2942 newtons - second per kilogram (300 seconds) and a mass fraction of 0.8 was assumed for this system. The velocity change required at apogee for this maneuver
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