The solar dynamic option results in a four times smaller collector for the 370 km Space Station design orbit and a three times smaller collector for an eternal sun orbit, i.e. no storage is required. Consequently the longer the eclipse, the more advantageous the dynamic option becomes. The 370 km represents the Space Station EOL orbit and is used for the power system design instead of the 450 km Beginning-of-Life orbit. As listed in Table 1, the specific mass of the two systems are comparable for the Space Station orbit. Reference Solar Dynamic System As reference a solar dynamic system is considered which consists of: • a parabolic collector • a receiver with an integrated storage using the eutectic mixture LiF-CaF2 (melting point 1040 K.) as PCM • a closed Brayton cycle as heat engine and • a heatpipe radiator Its design orbit is the Space Station design orbit (370 km) and its design power output is 25 kWe. In a detailed design study [4] a set of parameters and engineering factors have been defined (Table 2, left side) which yield the calculated values listed in Table 2, right side. The design principles for the receiver/storage unit are illustrated in Figure 5. The minimum size of the receiver is determined by the number of heat exchanger tubes, their diameter and the amount of storage medium required to feed the PCU with a continuous heat of 95 kW. The PCM surrounds the heat exchanger tubes in such a way that the latent heat of the storage can be extracted continuously by the working fluid passing the heat exchanger tubes. In order to minimize the mass of the receiver/storage unit the minimum receiver size was taken as reference.
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