With the current solar array available for space use.the specific mass is about 30 W/kg, and the highest specific mass of solar array is 66 W/kg at the beginning of life. Given the solar array's size by 50 m by 10 m, the mass of two solar arrays are 4000 kg and 2000 kg respectively. The service module is almost the same as the existing 3-axis stabilized satellites except that the sizes of solar arrays and antennae of solar power satellite are larger than the current ones. So the solar power satellite service module will be heavier, larger and more complicated. If we take into account the solar power satellite's high reliability requirement because of the uniqueness of its application, more redundant parts are needed in order to achieve the goal. So the mass of the service module could be 2 or 3 times of the mass of the existing satellites which means that the mass of the service module of the solar power satellite is in the order of 2 or 3 tons. In order to minimize the ground rectenna and keep the ground power output at a given level, the size of the transmitting antennae should be as large as possible but within the constraints of spacecraft structure. Assuming that the phase array transmitting antennae is 10 m by 10 m when deployed, and the materials used to build the antennae has a density which is two times of the density of die solar array (4 kg/m^), we get a mass of 0.8 ton for the service module of the solar power satellite. Since the sun-synchronous orbit of 1000 km is chosen,there will be almost no eclipse during the whole operational period, we do not need batteries to store energies for eclipse usage which saves quite a lot of mass. So the total diy mass of the solar power satellite is about 4+3+0.8=7.8 tons. If we add the mass of propellant which is about 20% of the total mass of the spacecraft, then the mass of the $800 M solar power satellite will in the order of 10 tons. One thing we should remember is that the mass of transmitting antennae is mainly determined by the current technology available and its size which is closely dependent on the ground segment and the frequency selected for beaming the power. Spacecraft Cost Estimation The only cost assumption is that the space solar power program is a $800 M space to ground demonstration project. Now the question is how to spend the amount of money in the three main parts, the launch, the ground segment, and the satellite. With a satellite of 10 tons and a sun-synchronous orbit of 1000 km, the only launcher which is capable to put it into such orbit is the Energia. The cost of one Energia launch is about $80 M. The second part is the ground segment cost of about $120 M which includes the cost for building the huge rectenna, power distribution system and also the cost for operation maintenance. At the early phase of the demonstration within the budget constraint, only one ground rectenna could be built. Hopefully this is enough to demonstrate the technologies we have achieved to beam power from space to ground and to find some true usage of power from space. With the development of the full scale space solar power system, the cost for ground segment will grow at a moderate rate as the case of telecommunication satellite ground receivers which may be far beyond the $800 M budget constraint. So we can only build a ground rectenna with this limited amount of money under the extremely favorable conditions. The most expensive part is the satellite which is estimated to cost $500 M to $600 M for research and development, manufacturing and testing. As for the detailed cost of every part of the satellite, much more data are needed in order to proceed the cost estimation. So now only the analogous method is used here. We feel that the spacecraft can only be built within the given budget by assuming satellites cost will be lowered by 50% of the current cost during the next 10 years. Based on the current satellite cost, 20 to 25% of the cost is for the Control Subsystem, 25% is for Payload Subsystem, 5 to 10% for the Power subsystem. But for the solar power satellite the situation may be a little different because of the unique purpose of the solar power satellite. So the portion for the Payload Subsystem and Power Subsystem will be relatively higher than those for the existing satellites, may be 30 to 35% for the Payload Subsystem and 20% for the Power Subsystem. If GaAs solar cells, which are three times expensive than the silicon cells .must be used in order to reduce the size of solar panel for the same amount of power level, the percentage for the Power Subsystem may be even higher. But with the current budget constraint of $800 M, Silicon cell is the only choice for us. For the two solar panels the cost will be about $200 M which leaves some money to us for the other parts of the spacecraft. Since the phase array is used to beam the microwave to the target on the ground, it will cost much money to develop the technology used in space, so the cost of the phase array transmitting antennae will be in the order of $150 M. We still have about $250 M for the other
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