SDS Power Generation Design Solar Concentrator The concentrator is needed to provide a solar flux density of 1.7 MW/m2 on the collecting area of the generator. The solar flux of 1.3 kW/m2 is focused using a parabolic shape concentrator. The architecture of this component uses 24 petals, each 8.5 meters high, covering an area of 282 m2. Calculations have been performed using formulas presented in [Hedgepeth, 1978]. This system is coupled with a smaller concentrator in a cassegrain configuration to direct the solar flux back to the spacecraft. An additional reflector is needed to reflect the flux directly onto the collecting area. This design is presented in Figure 10.3.12. Figure 10.3.12 Solar Dynamic Concepts Using a Gyroreactor Currently, the reflecting surfaces have an efficiency of 0.9. This type of configuration using three reflectors imposes a mass penalty of -200 kg compared to having only one concentrator which reflects the energy directly onto the collecting area. However for structural reasons during launch, it is important to minimize the weight of equipment's that are located on the tower, ie.,„ the receivers are heavier than a secondary mirror. This approach also minimizes the vibration on the spacecraft, due to the high rotation speed of the engine. To estimate the mass of this subsystem we have considered a unit mass of the collector of 2.5 kg/m2. This weight is equivalent to 375 pm thick sheet of aluminum. It seems very low but it is a very conservative number. Some ultra lightweight concentrators are designed with a unit weight of only 0.1 kg/m2. So, this concentrator has a total mass of 700 kg to which has been added 50 kg due to additional support structures. Gyroreactor Engine The gyroreactor briefly presented in the section 7.1.4 New Technologies and described in [Baillly du Bois, 1991] has been chosen as the power generator to be used in this concept. This engine is a new technology which has not yet been demonstrated. We are fully aware of the risk taken by using this technology but it is so promising that additional investigation is necessary. As mentioned earlier this reactor offers an 45% thermal efficiency which directly lowers the radiator and the concentrator mass. The proposed gyroreactor prototype weighs 50 kg and could generate 50 kW with an energy density of 136 kW/m2 on the collecting area. The temperature on this surface is 850 K. In order to produce
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