Spectrolab Inc., a unit of Hughes Electronics Corp. of Los Angeles, has developed a gallium-arsenide solar cell that converts almost twice as much of the sun's energy as traditional silicon cells found on spacecraft solar-array panels. The solar cells were put to the test with the August launch of PanAmSat Corp.'s PAS-5, a commercial communications satellite. The satellite uses nearly 15,000 dual-junction gallium-arsenide cells to convert the sun's rays into 10 kW of energy. From Spectrolab Inc., a unit of Hughes Electronics Corp.