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submitted for Hearing on


January 24-26, 1978

of the

Committee on Science and Technology
U. S. House of Representatives
Washington, D.C.

Arthur D Little Inc.


At the May 24, 1973 Hearings of the Committee on Science and Astronautics, I proposed that a solar power satellite (SPS) be developed as an option for power generation on Earth. The development of the SPS meets the criteria applicable to future space programs:

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The results of extensive SPS system studies have confirmed that there are no known technical barriers to the design, deployment and operation of the SPS. Economic studies have showed that projected capital and electric power generation costs are within the competitive range of the costs of future terrestrial power generation methods. Risk analyses have provided an economic justification for proceeding with the initial phases of an SPS development program.

In view of the increasing confidence in the technical feasibility and economic promise of the SPS, I recommend that a five-year SPS development program be undertaken which addresses the critical issues pertaining to: Technology Development, Environmental Effects, Economic Factors and Institutional Arrangements.

On the basis of the available evidence, I believe that:

⚫ The SPS is one of the most promising power generation options;

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The decision to develop this option on an expanded scale should be
made now;

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The SPS development program should be a significant component of
our country's future space programs and energy plan.



Dr. Peter E. Glaser, Vice President
Engineering Sciences
Arthur D. Little, Inc.
Cambridge, Mass. 02140

THE CONTEXT FOR THE DEVELOPMENT OF ENERGY OPTIONS The use of energy has been an essential component in improving the quality of life beyond the basic necessities for survival. A striking feature of the history of exploitation of energy resources has been the sustained growth of energy consumption in the industrialized nations during the last century. Meeting this demand for energy has been the primary driving force in the development of technology to mine coal, dam rivers, drill for oil and gas, and extract uranium. Furthermore, conversion of energy resources into useful forms has been and will continue to be an essential component of human activities.

The recognition that no one energy source will, by itself, meet all future energy demands, that the search for new sources of non-renewable fuels can only put off the day of their ultimate exhaustion, and that uncertainties inherent in achieving the potential of known energy conversion methods are large when applied on a global scale, has led to renewed emphasis on the development of solar energy applications. The degree to which these applications can be successfully developed will to a large extent depend on the economic feasibility of solar energy technology and the reduced availability of non-renewable fuels and their future cost escalation. Although solar energy is a widely distributed resource, its low flux density requires conversion technology that is capital intensive. Finding the best method for converting the available energy efficiently and economically on a scale large enough to have significant impact, therefore, presents a challenge. The successful and widespread introduction of solar technology will require considerable development in order to strike the appropriate balance among conflicting requirements presented by economics, the environment, and society's needs. Current solar energy research and development is directed towards a search for new technology and approaches to reduce the cost of conversion and for designs and processes to permit low-cost mass production. Although expectations for significant benefits are high, results on the desired scale are unlikely to be achieved quickly, not because of the lack of appropriate technology but because of limited experience with such technology and, until very recently, lack of appreciation of the potential of solar energy.


The capacity of solar energy to produce heat sufficient to power heat engines and generate electric power or direct conversion of solar radiation to electricity through the photovoltaic process offer promising alternatives to conventional methods for power

generation. Large-scale conversion of solar energy to generate power by these methods is restricted to favorable locations with abundant sunshine where capital-intensive technology can be used to best advantage. Even in these locations, solar radiation will be attenuated and interrupted by unfavorable weather and by the diurnal cycle, placing solar generated power at an economic disadvantage with base load power generated by conventional methods.

Indirect conversion of various forms of stored solar energy such as bioconversion, wind energy conversion and the extraction of power from ocean thermal gradients are also being explored. However, land, water, fertilizer and labor requirements for the plants that would have to be grown for bioconversion, the variations in favorable wind patterns, and the long distances over which power generated by ocean-based energy conversion platforms would have to be transmitted limit the world-wide applicability of these methods.

At present, there is a lack of confidence in the extent to which future energy options will work and how they will affect society. To develop any one of these options to a stage where it would contribute on a significant basis will require major investments, time to demonstrate their performance, and public acceptance.


Recognizing the obstacles to large-scale solar generated power, I presented to the Committee on Science and Astronautics at Hearings on May 24, 1973, a proposal to convert solar energy in a solar power satellite (SPS) in geosynchronous Earth orbit, where solar energy is available 24 hours a day during most of the year.

The SPS development meets criteria applicable to future space programs:

• The acquisition of new knowledge and understanding;

• Advances based on existing technology;

• An enterprise which is significant to future progress;

Enhancement of peaceful uses of space for the benefit of humanity.

Since the inception of the United States Space Program in 1958, one of its major objectives has been the development of technology that would effectively use space to contribute to the improvement of life on Earth. The development of space technology and associated activities has so matured that expanding activities in space are of increasing benefit on Earth, as already demonstrated by the existing network of communications and Earth observation satellites. It is already commonplace to convert solar energy in space into the power needed by satellites orbiting the Earth and exploring the solar system.

The SPS represents an extension of existing technology and could utilize a space transportation system based on the space shuttle already demonstrated in horizontal flight. The SPS will be fabricated and assembled from components delivered to orbit by a space transportation system which will also be used to support the space-based operations required to fabricate, assemble, and maintain the SPS. There is an increas

ing consensus that the SPS has the potential to provide an economically competitive and environmentally and socially acceptable option for continuous power generation on a scale substantial enough to meet a significant portion of future global energy demands.

The SPS concept relies on solar energy conversion to produce electricity either with solar cells, or with solar concentrators to generate high temperatures for use in heat engines. The electricity produced will be fed to microwave generators, forming part of a transmitting antenna. The antenna is designed to direct a microwave beam of very low power to one or more receiving antennas at desired locations on Earth. At the receiving antenna, the microwave energy will be safely and efficiently reconverted to electricity, and transmitted to users. A large number of SPS's can be stationed in geosynchronous orbit, each beaming power to one or more receiving antennas. One 5GW SPS can deliver the power equivalent of about five nuclear power plants.

In geosynchronous orbit, the SPS will be illuminated by the sun more than 99′ of the time, receiving from 4 to 11 times the solar energy available in areas on Earth that receive copious sunshine. The solar energy in this orbit is available continuously except for precisely predictable periods around the equinoxes, at which time the SPS will be eclipsed for up to 72 minutes a day. At the receiving antenna sites, the eclipses will occur near local midnight, a time when demands for power are at their lowest levels. Although the predictable interruptions in energy conversion in the SPS would be short, they will have to be accounted for in the load management of an electric utility system to reduce or eliminate short-term energy storage requirements.

Environmental effects do not appear to be major constraints on SPS construction or operation. The conversion of microwaves to electricity at the receiving antenna can be accomplished with efficiencies approaching 90', which will reduce thermal pollution to less than 1/3 of that from power generation methods based on thermodynamic cycles. The microwave transmission system must be designed to meet agreed-upon guidelines for continuous exposure of microwaves at the outer perimeter of the receiving antenna site, and to assure that the range of frequencies generated will meet international requirements.

The SPS design must incorporate several fail-safe features to assure control of the direction of the microwave beam and instantaneous shut-off of power. The failure of the microwave beam pointing system will not exceed even the Eastern European guidelines for microwave exposure.

The land requirement for the receiving site, from which the public would be excluded, will be about 270 km2. This compares favorably with land areas required for terrestrially-based solar-powered plants of similar output (400 km2 for photovoltaic conversion without energy storage). The land could be developed for other productive uses because only about one-third of it would be covered by the receiving antenna, a lightweight structure 80% transparent to sunlight and unobstructive to rain. Microwave radiation can be excluded from beneath the antenna, maintenance would be minimal, and transportation of supplies to the site would be infrequent, compared

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