U.S. officials are continuing to track the orbit of a nuclear reactor which once powered a Soviet spy satellite but say there no longer is a danger of radioactive debris falling to Earth. The reactor earlier had been ejected from the satellite, Kosmos 1900, and sent into a higher orbit where it does not pose a threat to Earth, officials said. Maj. Alex Mondragon, a spokesman for the U.S. Space Command's Space Surveillance Center in Cheyenne Mountain, Colo., said Sunday that the rest of the Soviet satellite has disintegrated and poses no danger. Two pieces fell to Earth along the eastern coast of Africa on Saturday, he said.