Laying the Foundation for Space Solar Power: An Assessment of NASA's Space Solar Power Investment Strategy (2001)

Throughout history, human progress has been fueled by energy. In early ages, wood to cook food, provide heat, and later to smelt metals provided the primary source of energy. By the seventeenth century, coal to heat homes and factories, make iron and steel, and produce steam for the engines of industrial production was a primary energy source. The twentieth century saw the advent of oil, natural gas, nuclear energy, and various renewable forms of energy, as well as the continuing use of coal to fuel humanity’s energy needs. The availability of inexpensive energy that can be converted to usable forms has provided the people of the industrialized nations of the world a standard of living that would have been envied by kings of only a few centuries ago. A nation’s economic development and standard of living go hand in hand with readily available, useful forms of energy.

Electricity is one such useful form that can be made from readily available energy sources and is used worldwide. Global demand for electricity has risen tremendously in recent years. In 1990, the world used approximately 11 trillion kW-hr of electricity per year—a figure that is projected to be 22 trillion kW-hr by 2020 (EIA, 2000). However, as this global market grows, other issues have come to the public consciousness. Concerns have arisen about the deterioration of Earth’s biosphere and potential long-term changes in climate that may result from pollutants such as carbon dioxide exhausted into the air as a result of fossil fuel combustion.

Using sunlight to generate electricity has been discussed for many years as an alternative source and perhaps a way to relieve some of these concerns. In 1968, in a paper published in Science, Peter Glaser proposed that solar energy could be collected by earth-orbiting satellites and then beamed to power stations on Earth’s surface (Glaser, 1968). The energy collected would be converted to electricity and introduced into the commercial power grid for use by terrestrial customers. Both the Department of Energy (DOE) and the National Aeronautics and Space Administration (NASA) examined the concept in the late 1970s and early 1980s.

NASA found that generating electric power for terrestrial consumer use was not the only potential application for space solar power. Other uses have been postulated, including power transmission to other space vehicles, power generation for lunar and Martian exploration, power for commercial space development such as communications satellites, and as a source of additional power to enhance the capabilities of such on-orbit facilities as the International Space Station (Grey, 2000). Making some or all of these uses of space solar power a reality requires developing, fielding, and making effective use of a number of complex technologies within a constrained budget. The next section provides a brief history leading up to NASA’s current

Space Solar Power (SSP) Exploratory Research and Technology (SERT) program.

From 1979 to 1981, the Committee on Solar Power Systems, Environmental Studies Board, of the National Research Council (NRC) evaluated DOE’s and NASA’s work on SSP from the 1970s (NRC, 1981). The committee was tasked to perform a critical appraisal of this work, including identifying gaps in the DOE/NASA program and examining the results that the DOE/NASA study obtained. The study’s conclusions were not favorable for development of a satellite solar power system. The 1981 NRC report concluded that cost was a major prohibitive factor and the necessary technologies were not of the proper maturity. Estimates of the energy outlook at the time did not indicate that SSP would be a cost-competitive source of electrical energy for the next 20 years. The size and complexity of financing and managing the infrastructure that would be necessary would strain the abilities of the United States. International legal, political, and social acceptability caused by such issues as fear of possible health hazards could make SSP difficult or impossible for the United States to achieve. That earlier report concluded that no funds should be committed specifically to development of a satellite solar power system during the next decade. Realizing, however, that circumstances could change that would make more advanced satellite solar power systems an option in the more distant future, the 1981 NRC report also recommended vigorous investigation of technologies relevant to satellite solar power systems that were synergistic with the goals of other programs.

In August 1981, the U.S. Office of Technology Assessment (OTA) also published a report on the DOE/ NASA efforts that was unfavorable to continued work in SSP (OTA, 1981). According to the OTA report, too little was known about the technical, environmental, or economic aspects to make a sound decision on whether to continue further development and deployment of SSP. Under the circumstances prevailing at the time, OTA concluded that further research would be necessary before any decisions could be made. When the unfavorable assessments, high initial costs, and need for more research, development, and testing were combined with the drop in oil prices that began in 1984, the urgency that drove development of an SSP system largely evaporated, and work essentially stopped. There was little official interest until the mid-1990s.

In 1995, NASA took a fresh look at the feasibility, technologies, costs, markets, and international public attitudes regarding SSP. The Fresh Look study, published in 1997, found that much had changed (Feingold et al., 1997). Several promising concepts were identified as alternatives to the original 1979 reference concept. The study showed that great cost savings, for example, could be achieved over the 1979 reference concept by making use of modular, self-deploying units and on-orbit robotic assembly as opposed to the original concept, involving human-occupied, in-space construction bases. Modularization would also permit the use of smaller launch vehicles in place of a two-stage-to-orbit, reusable, heavy-lift launch vehicle that would require unique ground launch infrastructure. The study noted the critical importance of low-cost transportation to orbit and noted further that, although costs were still too high, the technology to lower launch cost to orbit was separately under development in other NASA programs (although it is uncertain if or when those programs will result in a new generation of launch vehicles or what improvements might be provided in terms of performance or cost). The study asserted that technologies and concepts involved in SSP could become more feasible if both government and commercial non-SSP applications were considered. Finally, the study noted that the market for SSP, though global in nature, might be uncertain for some time to come depending on how various nations’ policies treated SSP in comparison with other means of generating electricity (Feingold et al., 1997).

As a result of the Fresh Look study, both the U.S. Congress and the Office of Management and Budget became interested in SSP once more. NASA conducted a follow-on concept definition study in 1998. The result was funding of $22 million set aside for NASA to conduct the SERT program. In March 2000, the NASA Office of Space Flight (Code M) approached the NRC with a request to evaluate its technology investment strategy in space solar power with a view to determining whether or not the strategy that the agency had adopted would meet the program’s technical and economic objectives.

Although the current NRC committee neither advocates nor discourages SSP, it recognizes that significant changes have occurred since 1979 that might make it worthwhile for the United States to invest in either SSP or its component technologies. Improvements

have been seen in the efficiency of crystalline photovoltaic and thin-film solar cells. Lighter-weight substrates and blankets have been developed and flown. A 65-kW solar array has been installed successfully on the International Space Station, and wireless power transmission has been the subject of several terrestrial tests. Japanese and Canadian experiments, some of which are discussed later in this report, have shown that small aircraft can be kept aloft by power transmitted via microwaves. The area of robotics, essential to SSP on-orbit assembly, has shown substantial improvements in manipulators, machine vision systems, handeye coordination, task planning, and reasoning. Advanced composites are in wider use, and digital control systems are now state of the art.

Although scientific and engineering advances may help make SSP more feasible, the committee noted that public concerns about environmental degradation are, if anything, even more intense than in the days of the Fresh Look study.

The NRC formed a committee of eight experts with experience in space systems design, engineering, and launch; solar power generation, management, and distribution; on-orbit assembly; robotics; space structures; and economics to independently assess the technical investment strategy of NASA’s space solar power program. The full statement of task, found in Appendix A, asked the committee to address areas of the space solar power investment strategy associated with developmental and operational issues, technical feasibility of various aspects of the program, and opportunities for synergy. The committee restricted its efforts to critiquing NASA’s technical investment strategy and neither advocated nor discouraged the concept of space solar power. Assessments of (and comparisons with) other space solar power concepts, such as the Lunar Solar Satellite concept proposed by David Criswell, were not performed by the committee. The committee also did not attempt to predict the role that space solar power might play in the future among the many alternatives for generating electricity. The purpose of this assessment was to evaluate the technology investment strategy of the SERT program and provide guidance as to how the program can be most effective in meeting its long-term goals, not to influence those goals. This assessment evaluates the SERT program and the follow-on SSP R&T efforts through December 15, 2000. Program changes after that date are not included.

The committee approached the study by adopting the SERT program’s definition of the term “investment strategy,” which includes six areas: (1) program division and organization, (2) use of developmental cycles, (3) opportunities for independent review, (4) balance of internal and external investments, (5) use of systems analysis and modeling to define goals, and (6) periodic review of technology roadmaps. This definition then served as an outline for the approach that the committee used during its assessment.

This report focuses on two levels of assessment: (1) an overall evaluation of the technical investment strategy and program organization and (2) evaluation of individual technology subprograms. Chapter 2 examines the overall investment strategy, the investment strategy methodology, program management issues, and opportunities for synergy with other programs. Recommendations and discussion are categorized in three major areas. Chapter 3 provides individual evaluations of 11 of NASA’s 12 technical investment areas (economics is included in the overall assessment in Chapter 2). Recommendations called out in the Executive Summary and listed in Figure ES-1 were considered key by the committee. Other recommendations in Chapter 3 were considered important to managers of individual technology areas.

EIA (Energy Information Administration). 2000. International Energy Outlook 2000. Washington, D.C.: U.S. Department of Energy, p. 114.

Feingold, Harvey, Michael Stancati, Alan Freidlander, Mark Jacobs, Doug Comstock, Carissa Christensen, Gregg Maryniak, Scott Rix, and John Mankins. 1997. Space Solar Power: A Fresh Look at the Feasibility of Generating Solar Power in Space for Use on Earth. Report No. SAIC-97/1005. Chicago, Ill.: Science Applications International Corporation (SAIC).

Glaser, Peter. 1968. “Power From the Sun: Its Future.” Science, Vol. 162, No. 3856, November 22, pp. 857–866.

Grey, Jerry. 2000. “The Technical Feasibility of Space Solar Power.” Statement to Subcommittee on Space and Aeronautics, Committee on Science, U.S. House of Representatives. September 7.

National Research Council (NRC), Environmental Resources Board. 1981. Electric Power from Orbit: A Critique of a Satellite Power System. Washington, D.C.: National Academy Press.

OTA (Office of Technology Assessment). 1981. Solar Power Satellites. NTIS No. PB82–108846. Washington, D.C.: U.S. Government Printing Office, p. 3.