Artist's impression of the Solar Satellite Power System (SPS), under construction in low Earth orbit. The shuttle is docked at the satellite's assembly bay & a cargo vessel is approaching with construction materials. The SPS is being developed by NASA & US Department of Energy contractors as a possible future energy source. The satellite would be equipped with large solar cell arrays or reflectors, which would collect the Sun's energy & transmit it back to Earth in the form of a beam of microwaves. The ground receiving anntenna would convert the microwaves into electricity and feed it directly into the national network.