for the silicon option (480 in GEO and 75 in LEO) and 715 for the GaAlAs option (680 in GEO and 35 in LEO}. The transportation system is made up of four major items. These include: (1) the Heavy Lift Launch Vehicle (HLLV), the Cargo Orbit Transfer Vehicle (COTV), the Personnel Launch Vehicle (PLV), and the Personnel Orbit Transfer Vehicle (POTV). The HLLV is a two-stage, vertical launch, winged, horizontal land-landing, reusable vehicle with 424 metric ton payload to low earth orbit. The earth launch site was chosen as Kennedy Space Center pending further study. The COTV is an independent, reusable electric engine-powered vehicle which transports cargo from the HLLV delivery site in low earth orbit (LEO) to the geosynchronous earth orbit (GEO). For the GaAlAs SPS option, the COTV is powered by GaAlAs solar cells, whereas a silicon solar cell power supply is used for the silicon SPS option. Personnel for the orbital construction and support functions are transported to LEO via the PLV which is a modified space Shuttle Orbiter with a passenger module. The POTV, a two-stage reusable, chemical fuel vehicle is used to transfer personnel from LEO to GEO and return to LEO. The satellite construction scenario for the Reference System is illustrated in figure 6. The HLLV is shown transporting cargo to LEO while the COTV and the POTV are illustrated transporting cargo and personnel, respectively, from LEO to GEO. A LEO operations base is used for temporary storage of supplies and propellant. One satellite is shown in GEO during the construction phase while another satellite is shown in the conventional operational phase transmitting energy to ground rectenna. Figure 7 summarizes the characteristics of the Reference System. C. Solar Cells and Blankets Both GaAlAs and single-crystal silicon solar cells are considered reference energy conversion devices. Figure 8 shows a cross-section of the GaAlAs and Si solar cells and blankets. The basic GaAlAs solar cell consists of a 5 ^m thick GaAs-P-N cell with a 0.03 to 0.05/pi thick GaAlAs front-side window. The solar cell efficiency is 20% at AMO, 28°C. The design operating
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