120 kW, two engines are required with slightly improved performances than the actual proposed design. An gyroreactor of 80 kg generating 60 kW, using a solar flux density of 170 kW/m2 is the design selected for this solar dynamic system. The estimate for the mass of each gyroreactor has been increased from 50 to 80 kg to incorporate a mass margin in the development of this equipment. Compare this generator to more classical types such as the solar Brayton cycle the following operating characteristics should be high-lighted. Concerning the rotors speed, the gyroreactor rotates at about 20 000 RPM which is two times less than the Brayton's turbine. The turbine inlet temperature is also two times less in the gyroreactor (476 K vs 1013 K). These numbers suggest that the life time of the gyroreactor will be longer. For the space station freedom design solar dynamic system a 7 to 10 years life was planned. The Space Station Brayton generator has been designed to weigh 145 kg and to generate 40 kW. Compared to the system discussed here it is twice as massive. Radiator A radiator is needed to get rid of the excess heat. A classical heat pipe radiator is used in this system to radiate 73.3 kW. For the radiator's material, we have considered an emissivity factor of 0.8. The radiation temperature will be 400 K. So, the area needed in this case is -126 m2. Using the assumption that the radiator mass is proportional to its area and that the unit mass for such heat pipe radiator is 5 kg/m2 this gives a total radiator's mass of 630 kg. This consists of 3 radiator panels, each one weighs 210 kg Costing The estimation of such system is very hard to evaluate because this is new technology which is yet to be developed. Additional cost margins have been applied. The cost evaluation is based on the mass of each subsystem. Development, production and management costs have been considered. We considered two gyroreactor engine of 80 kg each, 24 petals concentrator and 3 panel radiators. The cost summary is seen in Table 10.3.13. This high cost is mainly due to the development of new technologies and will be reduced for follow on satellites. However this price is competitive with the Si solar array described in the baseline. The total mass of the system is also less at -1.5 tons and so for launchers which are dependent on the mass of the payload, further cost advantages are possible. Table 10.3.13 Cost Summary of the Solar Dynamic Subsystem 10.3.4 Ground Segment The power density on the ground is very low, and some sort of collection scheme must be employed in order to rectify the RF signal. The focusing of the incident power can be performed by connecting individual elements in parallel. The focusing is performed in order to operate the rectifying elements at a reasonable efficiency level. In any case, focusing of the received power will introduce beam focusing in the rectenna system. When the satellite elevation is 35“ the incident power density is estimated to be 0.02 W/m2. Assuming a 100 mW threshold for the rectifying diode, a 5 m^ antenna is required for each diode. A 5 m2 antenna corresponds to a 1.3 m parabolic dish antenna. The beam width of a 1.3 m dish is approximately 0.4”. The footprint of the antenna along the satellite track is roughly 7 km. Since the satellite is moving at 7 km/s, the visibility-time as seen from the ground station will be only one second. Clearly this is not desirable for a power beaming experiment. To able to monitor the incident field for the entire period of visibility, it was decided to use several small tracking dish antennas for the receiver. The configuration is shown in Figure 10.3.13. The central antenna serves as the master station transmitting the pilot beam to the satellite. The slave stations are distributed over an area corresponding to the satellite-beam footprint size. The network of receiving stations will be able to monitor the beam from the satellite and verify the performance of the phased array.
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