If Prometheus fell from the heavens, it would be like an atom bomb going off... On the launch pad, Prometheus weighed 20,000 tons. It was the largest spacecraft ever made - a triumph of US-Soviet cooperation designed to end the Earth's energy shortage once and for all. It was planned to put a huge solar energy converter into orbit 22,300 miles high. All the energy needs of humankind could then be beamed down to Earth.…