trackers. A slow feedback loop can use the detected downlink pattern on the receiver to null out error between the reflector surface and the on-board attitude reference. Space Transportation and Operations Requirements Space transportation and operations are required to take the reflector as manufactured and delivered to the launch site, and deliver it disassembled to GEO, assemble it there, place it into operation, and maintain it for an estimated operational lifetime of 30 years or more. The reflector is too large to be delivered to GEO in one unit, assuming a launch requirement of 50-100 t. and a volume envelope of 10 m diameter by 30 m length. The 100 t. mass in this volume represents a density of about 40 kg/nA The densest deployable large space structures are somewhat less dense than this, but the available volume is potentially large enough. • Selection of the best launch payload size and mass is a tradeoff among: • Launch vehicle development cost, which increases with increasing mass capability; • Launch delivery cost per ton, which decreases with increasing mass; • Mass per unit area of the delivered reflector structure, which tends to decrease with greater payload mass and volume capability; • Assembly complexity, which also tends to decrease with greater payload mass; • Size of the (assumed) electric propulsion system for delivery from low-Earth orbit to GEO - large and cumbersome arrays are implied at 100 t. payload; and • Complexity of launch operations, which tends to increase with the greater launch rate dictated by a smaller launch vehicle capacity. Figure 2 shows the functional representation of transportation and operations requirements for the space transportation and operations systems. Cost Targets Since the reflector is part of a utility network energy delivery system, rough- order-of-magnitude allowable costs can be derived from historical and projected utility costs. The power to be delivered to the European Grid from renewable resources is assumed to be 20 GW. This can be beamed with five PRS systems so that loss of functions in one PRS would not have an excessive impact. This leads to power beamed with one PRS system of about 4 GW. Each reflector is estimated to cost between $1000 to $2000 per kW. ($4 to 8 billion). Therefore, a target cost of $4 billion for each of five reflectors was adopted. If the target cost is divided evenly between the costs of space transportation and reflector, and if the mass of a reflector is 722 t., the specific costs are $2770/kg each for the reflector and for space transportation cost to GEO.
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