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with conventional power plants. Land use for transmission lines could be reduced if receiving antennas were located near major users. Offshore locations should be considered as alternative receiving antenna sites.

Materials for construction will be largely those in plentiful supply, such as silicon and aluminum, although increased capacity will be required for argon, oxygen, and silicon or gallium production for some components. The energy required to produce the materials for SPS construction as well as the propellants to place it into orbit will be generated again in less than three years of SPS operation, depending on the power delivered at the receiving antenna.


The SPS concept was first proposed in 1968 as a baseload power generation option, and since then has been investigated by an increasing number of industrial organizations, academic institutions, and government agencies in the United States and abroad. Early studies identified efficient, long-range microwave power transmission as a pacing technology. In 1975, tests demonstrated that conversion of microwaves directly to electricity can be achieved with an efficiency of about 83. Space transportation systems studies indicate that the transportation costs to geosynchronous orbit could be reduced from present levels to as low as $20/kg, if large and reusable transportation vehicles are used.

Ongoing systems studies are defining SPS technology development requirements. These studies are also leading to an understanding of SPS systems and adding confidence to technology and cost projections. Economic studies are defining the cost uncertainties and risks of SPS development. There is a convergence of cost projections of the SPS that indicates capital costs in the range of $1600 to $3000 per kW, leading to electricity costs based on a 30-year lifetime and a 15% return on investments as low as 30 mills per kWh, a nominal 60 mills per kWh and an upper bound of 120 mills per kWh. These costs lie within the competitive range of the costs of future terrestrial power generation methods.

The SPS development program costs for the satellite, transportation, and receiving antenna systems - spread over 112 units to be placed into operation between 1996 and 2025 are projected to be about 1.3% of the capital cost. Risk analyses have provided an economic justification for proceeding with the initial phases of an SPS development program to obtain the information on which future decisions can be based.

The SPS development and evaluation program initiated by the Department of Energy and NASA is to assess by 1980 technical, economic, and environmental issues so that, if appropriate, SPS systems and space experiments may be selected for future development. The accelerated pace of space operations that will be possible in the 1980's with the advent of the space shuttle will be essential to the performance of these space experiments to resolve any potential obstacles to the widespread introduction of the SPS after 1995.

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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. The major technological and economic uncertainties are in the following areas:

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⚫ The constraints imposed by such environmental effects as microwave
heating of the ionosphere, space vehicle emissions in the upper atmos-
phere, microwave biological effects, and radio frequency interference.

Although the SPS has not yet been demonstrated even on a small scale, many of its institutional impacts are being evaluated, for example, the potential for accidental damage to and by an SPS, the rights to and use of space according to existing space law, the ownership of SPS, and the responsibility of owners in case of accidents from whatever causes, and the sources of the investment capital required during the various phases of SPS development and operation. Potential space law developments are being assessed to establish the need for international agreements to meet the objectives of the SPS. Appropriate international institutions could ensure that the peaceful benefits of the SPS will be available world-wide, lead to increased international cooperation in space and reduce the possibility of deliberate interference with SPS operations. The SPS represents an undertaking that could benefit many nations because of its magnitude, world-wide implications on energy availability, and potential for expanded space activities. It should be in the common interest to obtain agreements on such aspects as frequency assignments, microwave beam power densities and frequency distributions, geosynchronous orbit positions, favorable launch sites for the space transportation system, and sites for the receiving antenna.


The projected scale of SPS development and operation, the financial and material requirements, the economic and social consequences, the international and political significance, and the magnitude of potential benefits on a national and international level place the SPS in the highest rank of socially sensitive technology programs. The potential magnitude of the total development effort and the financial commitment that would be required rivals nuclear fission and fusion, satellite communications, and intercontinental aviation in significance; its development will require a similar scale of effort and time before SPS operations have any substantial effect on other energy resources. Therefore, it is essential to divide the SPS development program into well-defined phases, in order that limited objectives, in proportion to allocated funds, will have been reached at the conclusion of each phase. Decisions can then be made on the development objectives and procedures for the next and succeeding phases.

The greatest need now is to obtain information on which to base future decisions. At this point in the development cycle, the SPS is most vulnerable to criticism, since answers to many questions have not yet been obtained in sufficient detail.

The stage is set to embark on a more intensive evaluation of the SPS option, including key terrestrial tests required to support ongoing system studies, to define the SPS development and operational phases, and to initiate supporting space experiments that will provide crucial information on which to base decisions concerning required technology and its impacts. The objectives of the near-term SPS development program are to:

(1) Identify and assess issues that could constrain successful SPS devel-
opment, and

(2) Seek ways to resolve these issues with a combination of analyses,
system studies and experiments on Earth and in space.

The critical issues that need to be resolved in the SPS development program can be grouped according to the following priorities:

(1) Issues that could prevent successful development:

• Interactions of the microwave beam with the ionosphere.
Effects of launch vehicle emissions on the upper atmosphere.

⚫ Microwave biological effects.

• Radio frequency interference.

• International agreements; e.g., frequency assignment, allocation
of synchronous orbit positions, limitations on power generation
levels in satellites.

(2) Issues that must be settled to proceed with SPS system design:

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Microwave transmission parameters; e.g., frequency, beam intensity and distribution.

⚫ Microwave exposure standards.

⚫ Space vehicle emissions.

⚫ Space radiation exposure standards.

• Construction and assembly sites in Earth orbits.

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These issues are closely interrelated and must be addressed in a system context. Furthermore, studies alone cannot resolve the issues without experimental data from terrestrial and space experiments.

I recommend that a five-year SPS development program be undertaken to address the following critical issues:

1. Technology Development

a. Perform system and design studies to guide technology development for
solar energy conversion; power distribution; attitude control and station
keeping; microwave power generation, transmission and rectification;
space transportation; fabrication and assembly in orbit; and operational
control in order to understand the SPS system and to improve perform-
ance, reduce mass, increase reliability, lower costs, meet environmental
criteria, limit use of scarce terrestrial resources, and to integrate SPS
with utility power production and distribution.

b. Perform key terrestrial tests to guide technology and material devel-
opments, including space simulation tests to evaluate appropriateness of

c. Select, design, and perform experiments in the space shuttle to demon-
strate and evaluate key system functions.

d. Identify terrestrial and space-based programs that can benefit from
synergism with SPS; (e.g., large space communication platforms, terres-
trial photovoltaic systems).

e. Develop program plans for subsequent phases.

2. Environmental Effects

a. Identify potential environmental effects pertaining to all phases of SPS
development and operations (including resource use, construction,
launch, space assembly, and operations), on the biosphere, atmosphere,
ionosphere, and on public health and safety. Select those technologies
and implementation scenarios that will reduce the environmental effects
to acceptable levels.

b. Determine the occupational and social conditions that will be encoun-
tered during fabrication, assembly and operations of the SPS and the
effects of prolonged exposure to the space environment on work crews.
c. Select, design and perform terrestrial and space experiments in order to
obtain data on microwave interactions with the ionosphere, effects of
launch vehicle emissions on the upper atmosphere, microwave biological
effects, and radio frequency interference.

3. Economic Factors

a. Establish cost uncertainties and risks for each phase of the projected development program, and provide economic justification for specific technologies and system choices.

b. Determine development funding requirements, level and timing of capi-
tal investments, sources of funds, and economic impacts and benefits of
development program phases and SPS operations on the U.S. economy
for specific SPS implementation scenarios.

c. Assess effects of SPS implementation scenarios on fuel costs and im-
ports, trade balances, and energy economies, and compare with the
effects projected for other energy production options.

4. Institutional Arrangements

a. Identify legal framework for SPS system construction, tests and oper-
ations, including ownership, liability, insurance, and required inter-
national agreements.

b. Assess political implications of SPS development and operations, in-
cluding international cooperation required for frequency assignment,
synchronous orbit positions, inspection to assure peaceful uses, and
protection from interference with operations.

c. Seek participation of appropriate public interest groups on issues per-
taining to environmental effects, microwave safety standards, and re-
ceiving antenna and launch site locations through effective and open
information exchange.

The five-year SPS development program should lead to a resolution of the critical issues and result in a better understanding of the SPS system. Throughout this period new concepts and technology will emerge that should be integrated in the program for the SPS system to evolve and mature. Decisions made on the basis of a specific system at too early a date may foreclose options. Space flight experiments will be required to evolve an optimized system. Keeping system options open will assure that the best available technology can be utilized when the decision to proceed with an expanded SPS development would be made.


There are several funding levels associated with the SPS development program. The Department of Energy-NASA development program has a budget allocation of about $15 million until 1980. This level of funding during the next four years, while permitting assessments of technical, economic, and environmental issues, does not permit significant technology developments to start until after 1980.

I recommend that the budget for the five-year SPS development program outlined previously be allocated as shown in Table 1.

As the development program proceeds and confidence in the SPS option is increased, allocated funds should approach the levels associated with other significant energy-technology development programs.

At the present funding level, which is about 1% of the funding for each of the advanced nuclear energy options, it will be difficult to achieve the necessary momentum and obtain the commitments essential to a successful SPS development program.

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