A system called Over-the-Horizon Wireless Power Transmission, OTH-WPT, is proposed as a low-cost precursor for Space Solar Power, SSP. The proposed system would use high-power lasers and high altitude aerostats to beam 100s of kWs of electric power over distances of 10s of km from one point on the Earth to another. The demo system will present technical challenges similar to those of an operational SSP system. It will also include many of the major components required by an operational SSP system. But it will not require the extreme cost of transportation to and assembly of components and subsystems in geosynchronous orbit in space. It is the great cost of getting to space that has been a major obstacle to progress in SSP development. It is expected that the proposed demonstration will help overcome this obstacle. The OTH-WPT system proposed will test techniques for (i) atmospheric turbulence compensation, (ii) platform jitter control, (iii) incoherent beam combining, (iv) aerostat maintenance and durability and (v) employing a low-loss aerostat electric power cable/tether. The successful demonstration of these techniques will be an important milestone in establishing the feasibility of SSP. Various configurations are presented to meet a variety of range, power, weather and tactical needs. In addition to being a low cost demo of SSP, the proposed OTH-WPT system has important civil, commercial, and military applications for the supply of power as an alternative source or on an emergency basis to remote areas, and to rapidly changing theaters of operation.

This paper begins with an introduction to the concept of space solar power (SSP) and summarizes selected prior studies of proposed solar power satellite (SPS) systems. The functional components of a generic SPS are delineated, and various approaches and promising concepts from prior and current development efforts are elucidated. The fundamentals of wireless power transfer for the SPS application are reviewed, including a discussion of retrodirective beam control approaches. A survey of related technology research and development campaigns for energy conversion and transmission modules for recently proposed modular architectures is outlined. Advances in solid state amplifier technology with relevance to SSP are reviewed, with areas of particular criticality highlighted. Performance metrics for proposed SPS systems and their components are enumerated, and efforts to design, fabricate, and test a prototype conversion module operating at 2.45 GHz in a space-like environment are described.