Electrochemical Storage Technology Major advances have been made in improving the number of cycles and the depth of discharge of space qualified rechargeable batteries over the years. The specific weights have been substantially decreased as well. As is the case with solar cell technology, this trend is expected to continue (see Table V). Nickel Cadmium (NiCd) cells have been the most commonly used spacecraft batteries. Today, typical NiCd cells are supplied with specific weights of 17.5 Whr/Kg (8 Whr/lb) for GEO and about 8.8 Whr/Kg (4 Whr/lb) for LEO at an 80% depth of discharge for GEO missions and about 40% depth of discharge for LEO missions. New developments of the Super NiCd cells provide increased cycling capability so that 15-year missions can be accommodated. Within the past 15 years, nickel hydrogen (NiH2) cells have been developed and many new spacecraft batteries utilize this cell design. The major advantage of this cell is that the specific weights are about 33 Whr/Kg (15 Whr/lb) GEO and about 22 Whr/Kg (10 Whr/lb) LEO and the depth of discharge can be increased to at least 90%. A more advanced cell being developed today is the sodium-sulfur cell. This cell should be able to provide over 153 Whr/Kg (70 Whr/lb) initially and eventually
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