Integrated voltage control of S3R and BDR is achieved by a highly redundant mode controller housed within the S3R which also contains the mainbus tank as common output filter. The energy storage function is provided by a 60 cell 50 Ah nickel hydrogen battery which is operated with 50% DOD. Cell voltage and temperature/pressure monitoring is performed by the Battery Control Unit (BCU). Because the nickel-hydrogen technology for LEO applications is presently not fully available, a 40 cell 40 Ah nickel-cadmium battery is considered as back-up solution (due to the BCR, different battery types can be easily adopted). In order to meet the battery's three years lifetime requirement, the NiCd battery is operated with a reduced DOD of approximately 25%. With regard to the size of BCR and BDR, two NiCd batteries will replace one NiH2 battery which, however, will have the output power of the conditioning cell. Taking the below listed battery parameters and regulator efficiencies into account (NiCd values in brackets) Hence, when the considered modularity is maintained, the Primary Power Assembly can grow in increments of 2.7 kW which stipulates that the solar array grows in steps of 5.5 kW. With respect to ORU packaging it is presently planned that the equipment of the power conditioning cell shall be integrated in one standard ORU. The solar array forms a separate non-standard ORU.
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