APPENDIX B SCENARIO FOR SPS CONSTRUCTION (SEE RSR, 1978) The SPS construction rate is assumed to be two 5-GW systems per year, proceeding over a 30-year time period. (Each satellite is designed to have a 30-year operating life.) One 5-GW system consists of an array of photovoltaic cells in geosynchronous orbit, including the microwave transmission link (at 2.45 GHz, i.e., 1 = 12.2 cm) to send the received power down to a rectifying antenna (rectenna) on the ground. A satellite has a size of order 5 km x 10 km, using either Si cells (more reliable) or GaAlAs (lighter in weight). In geostationary orbit the array receives continuous power input from the sun except for periods of up to 40 minutes during several nights at the spring and fall equinox when the array is in the earth's shadow. Thus the scheme provides baseload, i.e., continuous, electric power from the sun, and it is claimed that the effective power per unit area is ten times as large as for an equivalent array on the ground (AIAA, 1979). The rectenna for a 5-GW system has an area of 10 x 13 ly at latitude 35°; the power density of microwaves is designed to be 23 mw/cni at the center of the rectenna and 1 mw/cm at the edge. Construction will be carried out in geostationary orbit (GEO) using a crew of approximately 550 (see Fig. B.l). The principal structural material will be graphite composite. People and freight will be transported first to Low Earth Orbit (LEO, 500 km, nominal), using a "Hohmann transfer elliptical trajectory." That is, rather than burn the main engine all the way from ground to low earth orbit, the second stage main burn goes up to 120 km, and then the vehicle gains speed while losing a little altitude (see Fig. 1). Now the HLLV moves in an elliptical path up to LEO, and there a short circularization burn puts it into a circular orbit. This procedure is more efficient from the standpoint of payload into orbit per unit mass of propellant than is a direct injection such as was used on Skylab I that produced its large "ionospheric hole." Five hundred km is rather high for a parking orbit; presumably it is used because the elements for the construction of the solar power satellite are so large that the drag at a lower altitude, say 200 km, would be significant. Once the HLLV deposits its payload in LEO there is another relatively short deorbit burn as the vehicle starts on its descent and reentry into the atmosphere, and goes down to the surface for another round trip. The SPS concept involves using two types of vehicles for transportation from the ground to LEO, and another two for transportation from LEO to GEO.' The various space vehicles are described briefly in Table B.l. For transportation from the ground to LEO both vehicles use H2-O2 second stage engines, and the larger of the two vehicles, the HLLV, has a very much greater impact on the atmosphere so that no explicit reference is made to the smaller vehicle, the PLV. For transportation from LEO to GEO most of the weight is carried by the electrically powered COTV, which uses argon ion engines as principal propulsion, with solar energy collected in the panels of solar cells being transported into GEO as power source for the ion rockets. However, note that the COTV uses engines for attitude control and auxiliary power. From
RkJQdWJsaXNoZXIy MTU5NjU0Mg==