Safe delivery of optical power from space

More than a billion gigawatts of sunlight pass through the area extending f rom Earth out to geostationary orbit. A small fraction of this clean renewa ble power appears more than adequate to satisfy the projected needs of Eart h, and of human exploration and development of space far into the future. R ecent studies suggest safe and efficient access to this power can be achiev ed within 10 to 40 years. Light, enhanced in spatial and temporal coherence , as compared to natural sunlight, offers a means, and probably the only pr actical means, of usefully transmitting this power to Earth. We describe sa fety standards for satellite constellations and Earth based sites designed, respectively, to transmit, and receive this power. The spectral properties , number of satellites, and angle subtended at Earth that are required for safe delivery are identified and discussed. (C) 2001 Optical Society of Ame rica.