The propulsion options that are currently being evaluated for a liquid booster for shuttle are shown in Figure 12-11. Prime candidates for booster engines are the space shuttle main engine with a shortened skirt (expansion ratio of 35:1 optimized for booster application) and a modified SSME (dubbed SSBE for space shuttle booster engine) that can use LOX/RP-1 propellants with hydrogen being used for engine cooling. The use of the F-l and the HiPc (O2/RP-1) for this application has been deemphasized because of the weight, performance, and thrust levels (or cost to provide deep throttling capability) on the F-l and development costs for the HiPc (O2/RP-1) engine (estimated to be approximately $800 million). Figure 12-11. Liquid rocket booster engine candidates. The shuttle capabilities for delivering a payload to the assembly orbit of 270 km at an inclination of 28. 5° (due east launch from Kennedy Space Center) are from 25 500 kg for the baseline shuttle with one OMS kit to 29 500 kg with a liquid booster replacement for the solid rocket booster and integral OMS. The OMS kit is added to the orbiter and is internal to the payload bay (requires 2.75 m of payload bay length). The use of the orbiter within the SPS program is primarily for personnel transfer to and from LEO and possibly for
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