PLV. Flight time from liftoff to docking at the LEO base is one to several hours, depending primarily on the orbital inclination chosen for the LEO base. The return flight duration would be comparable. Orbit-to-Orbit and Sortie Vehicles. Cargo is transported between LEO and GEO by solar-electric-propelled Cargo Orbital Transfer Vehicles (COTV) using photovoltaic cells (either silicon or gallium aluminum arsenide) as the primary power source and argon as a propellant. The vehicles are 1140 x 1140 x 164 meters and 2250 x 1300 x 1300 meters in dimension for the silicon and gallium options, respectively. Personnel are transported between LEO and GEO by two-stage Personnel Orbital Transfer Vehicles (POTV), the first stage propelled by four high-pressure oxygen- hydrogen engines (vacuum thrust - 0.47 x 10 newtons each) and the second stage by two of the same engines. The POTV is 81 meters long and carries 160 passengers. Flight time from LEO base to GEO base (or vice versa) is about 10.6 hours, assuming Hohmann transfer. If the LEO base is in an equatorial orbit, launch windows occur about every 100 minutes. If the LEO base is in an inclined orbit, launch windows occur only twice a day. In space, small sortie vehicles (SV) or "tugs'* are used to conduct construction, maintenance, and miscellaneous transfer operations. Characteristics of SV are estimated here as extensions from the NASA Reference System Report, in which SV is mentioned only qualitatively. The SVs are assumed to weigh 10 T (20 T carrying maintenance and repair equipment) and to carry four passengers in addition to a crew of two. It is assumed that the LEO base has four SVs (including two for RIO); the GEO base has ten (including two for RIO); each operational power satellite has two; and RIO has six other operating around GEO for RIO crew rotations and spot checks. Transfer time (with minimum fuel consumption) between GEO base and any given power satellite could be as long as 24 hours. 2.2 Low Earth Orbit Base No real design yet exists for the low Earth orbit (LEO) base of operations necessary during SPS construction and operations. Some initial construction and
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