Cluster Ⅱ batteries in-orbit performance

摘要

The four Cluster-Ⅱ scientific spacecraft were launched from the Baikonur Cosmodrome in Kazakhstan on 2 Soyuz rockets in July and August 2000, after a launcher failure (A501) caused the loss of the original set of S/C in June 1996. Each spacecraft carries 5 silver oxide -cadmium (AgCd) batteries on board. The selection of battery type was driven by the high magnetic cleanliness requirements of the satellite payloads, although it was understood by the Cluster Project team that these batteries have rather short shelve and cycle life. On top of that, the batteries require careful charge and discharge treatment compared with other alkaline battery systems used in space applications, because they are very sensitive to cell mismatch. To improve battery performance, all Cluster batteries are equipped with a battery re-alignment facility (BRF). The BRF enables individual cell discharge, keeping the voltage spread within a battery small and thus increasing the battery's lifetime. The battery lifetime is expected to be at least 2.5 years with a worst-case capacity degradation down to 10 Ah/cell. The extension of the mission duration is under discussion.