JAE - Journal of Aerospace Engineering, April 2001

By G. Pignolet (CNES) , A. Celeste (U. Réunion),
M. Deckard (Space Frontier Foundation), J.P. Esperet (SREPEN)

Abstract :

Many environmental issues surrounding Space Solar Power (SPS), with impacts and benefits to the environment, must be addressed. The environmental issues surrounding SPS impact factors such as people, the landscape, equipment and pollution, including physical safety for persons and for equipment, social questions connected with aesthetics, politics and economics, as well as the more general issues of global change and sustainability of energy supply.

Wireless Power Transportation (WPT) is a key component of SPS systems, and the Grand Bassin WPT project, currently under development in La Reunion (France), will be a valuable test bed for many environment issues. The facility will allow us to study the environmental integration of the facility, which is the number one priority of the project, and the actual effects of an operational microwave power beam.

 

Introduction

Space Solar Power (SSP) is an idea for collecting sunlight in space and transporting the power in the form of microwaves to collecting sites on the surface of the Earth. This idea could potentially be exploited to help meet a large part of the Earth's growing energy needs in the 21st century. However, in the last two decades, the nations of the World have begun to appreciate the impact of humans on the global environment. At the same time, the Earth's population continues to grow, along with human demands on the environment as well as on energy. The U.S. Department of Energy has projected worldwide demand for energy will double in 20 years, and double again in the next 20. Space Solar Power may be an environmentally friendly technology that can help meet the growing demand for energy.

 

Environments

Figure 1. The key environment factors to be considered
for the successful development of SSP

When we speak of "environment", we must realize that this is a powerful word with many meanings, to be considered from the various points of view. To explore environmental questions connected with SSP, we have illustrated the related key factors in Figure 1. Each of these elements, at every point of the star, must be addressed if SSP is to gain acceptability. There are many experts who already have made valuable contributions. In the 1970's and early 1980's, the U.S. Department of Energy conducted preliminary environmental studies on the effects of microwaves at 2.45 GHz frequency, and Japanese Space Power Satellite (SPS) teams have become very active in the field since the beginning of the 90's. These studies have been mostly concerned with the effect of microwaves on biota, but a more general integrated systematic approach to building an environmental impact study is critical to the successful development of SSP as a terrestrial energy source.

 

People

In Japan, they call it the "yakitori effect". In other places in the World, it is referred to as the "fried chicken" syndrome. If some day we have giant satellites beaming huge amounts of power towards the surface of the Earth, and "something goes wrong" and the energy beam goes wandering astray, will entire cities be zapped to ashes and smoke ? If the level of ambient microwave radiation is significantly increased, shall we see an explosion of cancers and other genetic diseases ? If in addition of the natural solar energy captured by the Earth, we divert from space additional energy to the surface of our planet, shall we upset the global balance ?

Public health and safety and public perception of health and safety factors are critical in the development of SSP. While the public health and safety issues with respect to microwave use have been examined extensively, there have been little specific studies of SSP technology or WPT done to date. This research has not been done primarily because the technology and system design are not yet mature enough to conduct the research. For example, recent work done by NASA has led to the proposed use of 5.8 GHz to transport the power instead of 2.45 GHz studied in the 1970's. This gives environmental researchers the powerful opportunity to impact the design of a SSP system from preliminary design to end-of-life termination. The international Grand Bassin Project for operational WPT, which is designed to meet the current safety standards, as presented later in this paper, may soon offer a unique test-bed to measure the actual effects of a microwave beam on surrounding biota.

Figure 2 : The Electromagnetic Spectrum -

Microwaves overlap Radio and Optical Bands Electromagnetic waves form a continuous spectrum (Figure 2) that for practical purposes can be divided into three regions : radio waves which go around obstacles, optical rays that go in a straight line, and ionizing radiation where the energy of photons is large enough to eject electrons from the atoms of an illuminated object. Microwaves, or hyperfrequencies, are on the overlapping area between radio waves and optical rays, very far from the ionizing frequencies, which begin at the wavelengths of the ultra-violet, below one tenth of a micrometer. With a wavelength of 12 cm, microwaves used in WPT/SSP technologies may not have any ionizing effect. There is no danger of cancer or genetic alterations due to microwave radiation.

The other effect of electromagnetic energy is production of heat : whatever energy is not used in energy conversions is transformed into heat. Microwaves are used for kitchen ovens, and also for healing therapies. More commonly, the energy of absorbed sun rays is turned into heat. Heating from radiation is rarely life threatening. The danger is connected with the lack of capability of bodies to reject the heat produced by the absorbed energy. Specific absorption rates (SAR) or power density measured in amount of energy received per unit of surface are ways the effect of heat can be examined. The nature of the source, Sun, microwaves, artificial light is not important, only the density of energy is to be considered. In the case of the Sun, the average power density on the surface of the Earth is about 100 mW/cm². Exposure to the bare sun is not comfortable (Figure 3), and the danger of sunburns is common, especially if the power density is increased by ground reflection, which is the case on white sand. The safe level for humans and most living beings is limited at about half the power density of the bare sun, about 50 mW/cm². The energy density from a point source decreases with distance as the square of the distance to the source : if you touch or stay too close to an electrical bulb, you will get burned, but if you stay at a distance of half a meter or more, then you may enjoy the light safely.

Figure 3 : Heat from the bare Sun (about 100 mW/cm²)
is not comfortable and calls for umbrella protection

The behavior of microwave radiation is similar. In the confined volume of a microwave oven, the energy density is quite high, several Watts per square centimeter, which is why foods are cooked. If the same amount of energy that is released in a microwave oven were distributed over a large area, there would be no danger of overheating or burns. In fact the amount of energy produced by a domestic microwave oven is quite similar to the amount of energy released by some halogen light fixtures, but these are placed far enough away from where the light is required that heating is not a problem. In most countries, the safety standard level for continuous microwave exposure is set at 5 mW/cm²

The design of SSP systems call for power densities on the collecting sites (rectennas), that may be higher than the standards set for continuous exposure, but would be well below the danger limit, with a design maximum of 25 mW/cm². The Reference System (proposed in NASA studies in the 1970's) design proposed a power density of 23 mW/cm2 at the center of the collecting site and 1 mW/cm2 at the edge (Glaser et al., 1998).

The problem will be quite different near the SSP satellites themselves or in the higher parts of the microwave beam, where the energy density will be as much as one hundred time above the safety level limitations. They will be a definite hazard for space workers and other satellites, for which adequate warning and protection will have to be duly considered and implemented.

 

Perceptions

Public perception of health and safety issues can be just as important as the issues themselves. In their article on public acceptance of SSP, Woodell and Schupp (1996) point out that public acceptance will ultimately determine if there is a market for SSP. In order to gain public acceptance, the communications process between SSP developers and potential customers must be ongoing. The Space Frontier Foundation and NASA Marshall Space Flight Center recently completed a year-long study to assess the environmental community's opinion of SSP (Deckard et al., unpublished). Environmental groups (academics, industry, and activists) across the United States were introduced to the concept of SSP and then asked to comment on what they thought the issues surrounding SSP and the environment would be. The top three concerns identified by participants were (1) the effect of the system on the atmosphere and biosphere (e.g. heat generation and weather), (2) effect of the system on animal and bird migration, and (3) possible adverse health effects due to increased exposure to radiation. Participants also identified possible benefits of the system; the top three benefits identified were (1) no or reduced pollution from burning fossil fuels, which will help with global warming and acid rain, (2) renewable energy supply, and (3) saving fossil fuels for other uses. The environmental community was excited by the discussion of a clean and sustainable energy source, and could clearly see the critical role of environmental impact research of SSP in assessing the conditions for exposure.

To build the large-scale technology of SPS, it must have international public support. Therefore, it is important to integrate the public into the development of this technology from the earliest stages. It will also be important to understand the cultural differences in technology adoption and acceptance. For example, people in the United States are comfortable with impact/benefit trade-offs in setting exposure limits. The Russians, however, have a zero tolerance when it comes to exposure. The recent announcement of the positive effect on reducing global chemical emissions of the 1987 Montreal Protocol, which is the first global-environmental treaty, is also good news for SSP supporters (Fialka, 2000). The international community is learning to work together to solve environmental problems and it is starting to realize the benefits of their work.

Figure 4 : the SPS-2000 "Attaché Case"
Functional Demonstration Models made by ISAS and CNES

To help bring about a better understanding of the systems and realistic views of the global environments in which SSP systems will play their role, portable "Attaché Case" demonstrators (Figure 4) have been conceived jointly by researchers of the French Space Agency CNES and of the Space Power Laboratory at the Institute for Space and Astronautical Science (ISAS) in Japan. The functional demonstrators have proved quite useful in many presentations with governmental and World organizations, and one of the models has been attributed to the World Solar Program of UNESCO, for presentation to institutions and decision makers.

Changes are needed in the perception of our global environment. This has to be done carefully, based on careful thinking, but also based on practical, real developments that are necessary to support a safe evolution. SSP studies will have to respect the legal national and international frames and standards. Conversely, changes in national and international laws and standards may have to be considered in view of the new environment that SSP will bring about.

 

Landscape

Landscape integration of the system and the impact of the system on its local environment are key factors in the design of ground systems. It has been suggested that local temperature of the ambient environment under or near the collecting sites could be raised. This concern raises questions such as will vegetation grow faster, will birds try to nest in the structures and possibly change migration patterns because they will find more comfort, or will birds overheat as they fly within the transmission beam? As part of the environmental studies conducted in the 1970's by NASA, a report on the effects of the reflected light from an SSP system on biological systems was compiled (White, 1981). The report evaluated the effect on eye hazards, the impact of reflected light on animals, and the impact of reflected light on plant growth. The report concluded that there were no major problems within any of these areas. However, the original research was not well organized and lacked a cohesive structure. Critical questions were not prioritized and studied. An environmental impact study is needed, that addresses the issues in an integrated manner; in which the environmental impacts of the space solar power infrastructure on landscape, people and equipment are considered.

During the construction of the systems, as they will cover relatively large areas (each rectenna may be several square kilometers in area), it is important to consider the associated impacts. Rare or endangered wildlife and plant species should be protected in primary natural environments and these habitats should be excluded from consideration as collecting sites. Conversely, careful consideration should be given to the creation of new animal and plant habitats that take advantage of the development at the energy collection site. Marine rectennas, or collecting sites, could support fisheries, while the land under rectennas could still accommodate some types of agriculture.

The fact that WPT and SSP systems will use a 12 cm wavelength may be a great advantage. Because the operating wavelength is not in competition with visible radiation or with the solar spectrum, where the wavelengths are in the order of the micrometer, it will be possible to paint and decorate the rectenna arrays, which is not possible, for example, with photovoltaic arrays. Also, for the same reason of non-interference between wavelengths, it will be possible for sunlight to pass though the rectenna arrays, which allows for dual-use of these sites. This will undoubtedly create new types of structures, and there is here a definite esthetical challenge for landscape architects.

Figure 5 : The village of Grand-Bassin
as seen from the location considered for microwave projectors

Following the recommendations for the implementation of operational ground to ground WPT systems, which were formulated by Peter Glaser and Bill Brown at the SPS-91 Meeting in Paris, France in 1991, several case studies have been conducted, which have resulted in the Grand-Bassin Project ( Figure 5 ) in the French Region of La Réunion, a large volcano island located in the Indian Ocean and similar to the American State of Hawaii in many respects. The project calls for the transportation of 10 kW over a distance of 700 m from the power grid to an isolated village at the bottom of a scenic canyon. Environmental integration is the prime concern for the project, now in the industrial engineering development phase at the University of La Réunion, and every step is taken to minimize the environmental impact. Already, many of the international specialists who contribute to the development of the Grand-Bassin project have visited the site to have first-hand understanding of the environment issues, and more researchers will have assessed the site on the occasion of the WPT'01 international workshop in May 2001. The experience gained from theoretical and laboratory work is strong enough to enable the design of an operational system. In parallel with the implantation of the WPT system itself, a full program of associated environmental studies has to be conceived and implemented to assess the various impacts of the system. The design will have to consider carefully the impact on vegetation and wildlife to avoid catastrophic changes. Conversely environment study programs will have to be conceived to assess the overall impact of the system and when the project is completed, it is expected to provide international researchers with a valuable test bed for the environmental studies design.

Further in time, if implemented as proposed by Japanese researchers, the intermediate SPS-2000 program may be very useful to learn further lessons about the environmental impact of SPS systems. It would provide useful and necessary inputs for the design of later full-fledge operational systems. SPS-2000 would beam 10 MegaWatts of power from a circular equatorial orbit at 1,100 km. Contacts have been made with the governments of several equatorial countries to evaluate possible rectenna sites with various types of landscape.

 

Equipment

Equipment, or hardware, may be affected by SSP satellites in two ways: heat, already discussed, and main lobe or side-lobe interference from the microwave projection. Due to the large amount of microwave power generated, (several Gigawatts for the projected operational SSP systems) harmonics will be generated that may cause disruption in electronic equipment if not properly considered. The problem is similar to the low frequency 50 Hz or 60 Hz ambient radiation which is exist nowadays in all the inhabited areas, and which is the cause of the humming noise that one can hear in all the unprotected audio equipment. This has not prevented the development of quality Hi-Fi systems, and the problem has been solved by the appropriate use of shields and filters. Many studies are needed in this critical field of electromagnetic compatibility.

 

Pollution

The visual impact of SSP satellites will also change our skies. A SSP program that creates 60 new stations in Geosynchronous orbit will make a new ring of stars around the Earth (perhaps 10-15 might be visible at one time to a person on the surface), and may be visible even in daytime as bright points in the sky. For the average Earth citizen, the change will not be difficult. However, the brightness of the SSP "stars" in the night may pose a problem for professional and amateur astronomers. In addition to the outreach to the environmental community, the Space Frontier Foundation and the NASA study assessed the concerns of amateur astronomers (Deckard et al., unpublished). An amateur astronomer society was asked to list their concerns regarding SSP technology. The top three concerns were (1) light pollution, (2) effect on other scientific fields and technologies such as radio astronomy and cell phones, and (3) aesthetic/ethos. The astronomical community must be involved so that brightness tolerance limits and interference are considered in the preliminary design of any SSP system.

Environmental problems must be addressed throughout the life cycle of the SSP. Ground pollution during construction of the system must be minimized on the Earth; in space, orbital debris must be minimized. Disposal and recycling plans for the huge SSP structures at the end-of-their life will increase upfront cost ; however, these plans are critical to developing SSP with a green engineering mentality and are absolutely necessary to insure that the full environmental benefits of SSP systems are realized. Because the structures will be located in GEO at the edge of the Earth's gravity well, disposal may be accomplished by pushing them farther from Earth.

Two of the main environmental benefits of a SSP system are low generation of CO2 (the system itself does not generate CO2, but production of the construction materials involves the use of energy and potentially the release of CO2) and the absence of the production of waste associated with the production of fuel (as is the case in coal or uranium mining). Carbon dioxide emissions have been estimated to be approximately 20 gm/kW-hr, which is comparable to nuclear power plants (Mankins, 1998). However, system construction may be environmentally costly. Currently, the production of photovoltaic cells requires the use of highly toxic chemicals. Fortunately, this is a well-regulated industry and technology advances aimed at improving the environmental compatibility of photovoltaic cell production are consistently reducing waste.

Most studies show that SSP may help first order environmental issues, such as the reduction of CO2 emissions into the atmosphere, by producing power in an essentially clean and sustainable way. We must be diligent that uncontrolled second order effects, such as pollution from photovoltaic manufacturing, will not spoil the primary benefits.

 

Resources

Frequency allocation for technology demonstrations, tests, and full system operations represent a different type of environmental issue, namely the competition of various potential uses for a limited resource. The microwave frequency bands available for transmitting through the Earth's atmosphere are limited; however, there are many other uses for microwave frequencies (e.g. cell phones) that could also use these bands. These allocations are made through an international body, the World Telecommunications Conference. At this time, no allocation for SSP has been made yet.

 

Politics and Sustainable Futures

Consideration needs to be made of our global environment and its evolution over extended periods of time, centuries and millenia. The "one match" diagram (Figure 6) presented by ESA's Peter Creola illustrates the necessity for sustainable systems beyond the current limited era of fossil energy resources. The diagram plots human use of fossil energy on a scale of a few thousand years, suggesting that if a source of renewable and clean energy is not found, that civilization as we know it cannot be maintained.

Figure 6 : Peter Créola's one and only one match
to light up the energy futures of Mankind's…

Space Solar Systems clearly offer sustainability. They also promise to be cleaner than any other energy system in terms of CO² pollution. Clearly also, they will be integrated with many other energy systems that will remain in use. Integrated studies need to be made to understand where and how SSP systems will be most useful in the global natural, technical, political and economic environment of our planet, and in terms of the co-evolution of these natural and human systems, to understand how the current natural, technical, political and economic environments may be impacted by the SSP solution.

 

Conclusions

Many further studies need be conducted in order to assess the various ways in which the SSP projects will impact their environments, and these studies need to be fed back into the SSP projects from the earliest stages of design. Conversely, clear global impact assessments may also help in developing the proper social and political environments that will allow the SSP systems to grow, for the greater benefit of Mankind.

 

Acknowledgements

We are grateful to the Space Studies Institute ( web site : http://www.ssi.org ) and the F.I.N.D.S. Foundation ( web site : http://www.finds-space.org ) for providing financial support through the Bootstrap Award, and thus contributing to the advancement of the Grand Bassin Project, under the leadership of the University of La Réunion.

 

References and Related Readings

Deckard, M, K. Cusick, R. Sattler G. Friedman (2000) "Assessment, Outreach, and Future Research of Environmental and Safety Factors related to Space Solar Power", IAF-00-R.1.07, International Astronautical Federation, Paris.

Fialka, John J. (2000) "Chemical ban is touted, as hopes for ozone rise," The Wall Street Journal, December 4, 2000, ( www. msnbc.com/news/ 498327.asp?cp1=1).

Glaser, P E., F. P. Davidson, and K. Csigi(1998)Solar PowerSatellites: A Space System for Earth, John Wiley & Sons.

Goldman M. (1999), "Space Solar Power - Environmental Issues", Proceedings from the UNISPACE III Conference, Space Energy and Transportation, Vol 4, No 3, 4

Matsuoka H. (1999), "Global Environmental Issues and Space Solar Power Generation : Promoting the SPS-2000 Project in Japan", Technology In Society, Vol 21, No 1, pp 1-17.

Pignolet G., Clavel O., Lan Sun Luk D., Lefèvre F. (1997) "Wireless Power Transportation and SPS : Environment Issues" , IAF-97-R.4.07, International Astronautical Federation, Paris

Pignolet G. (1996), "WPT Safety and Compatibility", SPS-IdR'96, Edition U. La Réunion, Le Tampon, France (in French).

Pignolet G. (1999), "Wireless Power Transportation - Principles of WPT / The Grand Bassin Project / Future SSP Projects", Grand Bassin Permanent Exhibition, Edition Grand-Bassin TESF, France ( 32 p. in English, in French, in Japanese, in Russian)

White, Margaret(1981) Effects on Biological Systems of Reflected Light from a Satellite Power System, U.S. Department of Energy, DOE/ER-0100, April 1981.

Woodell, M. I. and Schupp, B.W.(1996) "The Role of Pilot Projects and Public Acceptance in Developing Wireless Power Transmission as an Enabling Technology for Space Solar Power Systems," Solar Energy, Vol. 56, No. 1, pp. 41-51.