EARTH ORBIT: NASA scientists are working to determine what caused a 12-mile experimental cord attached to a small satellite to break loose from the Space Shuttle. Astronauts Monday reeled in the 33 feet of cable that remained after the cord suddenly snapped Sunday. The astronauts had nearly finished deploying the cable, which was part of an experiment to generated by dragging it through the Earth's magnetic field. The experiment had initially been a success: the satellite and cord were generating about 3,500 volts of electricity when the cable snapped. NASA officials says they don't yet know what caused the cable, which appeared to be melted, frayed and stripped, to snap. A full explanation is not expected until sometime after the shuttle's March 7 return.