The Space Solar Power Exploratory Research and Technology program (SERT) program, conducted by NASA, was initiated by John C. Mankins and led by Joe Howell in March 1999 for the following purpose: Perform design studies of selected flight demonstration concepts; Evaluate studies of the general feasibility, design, and requirements. Create conceptual designs of subsystems that make use of advanced SSP technologies to benefit future space or terrestrial applications. Formulate a preliminary plan of action for the U.S. (working with international partners) to undertake an aggressive technology initiative. Construct technology development and demonstration roadmaps for critical Space Solar Power (SSP) elements. It was to develop a solar power satellite (SPS) concept for a future gigawatt space power systems to provide electrical power by converting the Sun’s energy and beaming it to the Earth's surface. It was also to provide a developmental path to solutions for current space power architectures. Subject to studies it proposed an inflatable photovoltaic gossamer structure with concentrator lenses or solar dynamic engines to convert solar flux into electricity. The initial program looked at systems in Sun-synchronous orbit, but by the end of the program, most of the analysis looked at geosynchronousing unimaginably large initial investments in fixed infrastructure before the emplacement of productive power plants can begin. Space solar power systems appear to possess many significant environmental advantages when compared to alternative approaches. The economic viability of space solar power systems depends on many factors and the successful development of various new technologies (not least of which is the availability of exceptionally low cost access to space) however, the same can be said of many other advanced power technologies options. Space solar power may well emerge as a serious candidate among the options for meeting the energy demands of the 21st century.
Program
Model System Categories (MSCs) were defined and ranged from relatively small-scale demonstrations to very large-scale operational SPS systems. In broad terms, each MSC represented an idea of what scale, technology, missions, etc. might be achievable in a particular future timeframe. The technology investment plan uses a time phased methodology to develop hardware and systems starting at 600 volts, followed by 10,000 V, and ending with 100,000 V to spread development and testing infrastructure costs over the life of the program rather than incur them from the beginning. The 600 V technology had immediate application for the NASA Advanced Space Transportation Program (ASTP).
2005: ~100 kW, Free-flyer, demo-scale commercial space
2010: ~100 kW Planetary Surface System, demo-scale, space exploration
2015: ~10 MW Free-flyer, Transportation; Large demo, solar clipper
2020: 1 GW Free-flyer, Full-scale solar power satellite commercial space
Solar power generation
Current solar cells were considered too heavy, expensive and hard to deploy. Flexible thin film cells promised one viable future option for low mass, low cost, and high production capability by depositing special materials in very thin (micrometers) layers. Flexibility promotes deposition on lightweight inflatable structures needed for packaging large arrays in launch vehicles. The materials considered (kapton) did not have the high temperature properties needed to allow cell growth deposition so development of a low temperature growth process for thin film solar cells was pursued. In the year 2000 the production of 5% efficient prototype small-area cells was followed by a 10% efficient prototype on kapton.
Very high efficiency photovoltaics
Two longer range investigations into high efficiency solar cells was undertaken. 1) "Rainbow" cells to be tailored to the wavelengths of specific ranges of sunlight focused through a prism. 2) An ensemble of quantum dots in a size range to capture most of the radiation from the solar energy spectrum. The collection would be equivalent to an array of semiconductors individually size tuned for optimal absorption at their bandgaps throughout the solar energy emission spectrum. Theoretical efficiencies were in the range of 50–70%.