The most critical problems associated with this concept are the new material technology requirements (Thermal Protection System (TPS) and Propulsion System) and very high reliability of the few engines needed. The requirements for Personnel Launch Vehicle (PLV) is to transport SPS construction (600) and maintenance (30) personnel. The Shuttle derivative approach provides a required capability at low investment cost and risk, but advanced PLV concepts were also studied. Boeing proposed a “modified Shuttle SPS Transportation System” (Figure 8.11), using a winged liquid propellant flyback booster powered by 4 L0X/LCH4 engines similar to the Boeing HLLV booster engines, a smaller version of the Shuttle External Tank and the Space Shuttle Orbiter (up to 60 passengers). Figure 8.11 Boeing Configuration. Rockwell proposed a very challenging (for mass and propulsion system performance) SSTO concept (Figure 8.12) using a multi-cycle air breather propulsion system. This vehicle would require major technology developments, in many areas. Figure 8.12 Rockwell Configuration. Orbit Transfer Vehicles. The cargo Electric Orbit Transfer Vehicle (EOTV) concept is shown in Figure 8.13. This electric propulsion vehicle is used to transport satellite components from the LEO staging depot to the GEO construction base. It has a payload capability of 4000 metric tons and is fully reusable. It consists of a solar array (1 km by 1.5 km, portion of a future SPS platform), a payload mounting and docking
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