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Microwave policy issues for solar space power
Space Policy 16 (2000) 111}115
Microwave policy issues for solar space power John M. Osepchuk Full Spectrum Consulting, 248 Deacon Haynes Road, Concord, MA 01742, USA
Abstract This article reviews the three major policy issues likely to arise from an SSP system: environmental safety, frequency allocation and prevention of interference with other frequency-using activities. Supporters of SSP must make sure that their case is heard clearly at the ITU, but they must also do more to promote public awareness of the technology's potential bene"ts in order to counter inappropriate use of the Precautionary Principle by anti-technology groups. The strengthening of standard-setting groups world-wide will also assist this process. 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction The technological feasibility of solar space power (SSP) has been considered as highly probable based on Earth-bound experience with the elements of such systems. Economic and policy issues, however, may pose a greater obstacle to the realization of such systems. In this paper we review those policy issues that relate speci"cally to the aspect of microwave power transmission in solar space power systems. First, there is the question of whether microwave power transmission can be and will be approved as environmentally safe with regard to possible e!ects of microwave energy on not only humans but all biota on earth. Second, there is the question of whether a suitable microwave frequency allocation will be made by appropriate international and national authorities. Third, there is the question of whether the microwave emissions, both in-band and out-of-band, are acceptable with regard to regulations for prevention of interference. The history of SSP development suggests that early realization of such systems will "rst occur at lower power levels and then later at the highest powers for full-scale systems (e.g. 5 GW or 5;10 W). Clearly, it will be easier to obtain approvals on microwave safety and interference issues at the lower powers. A review of the evolving framework of standards for microwave safety indicates two trends that will eventually ease acceptance of SSP; international harmonization and the development of environmental standards. The obstacles do not derive from the scienti"c database but from misapplication of concepts conceived for potentially catastrophic technologies, i.e. the Precautionary Principle. To overcome such think-
ing there must be increased support of the standardssetting organizations which are based on due process and broad consensus, as well as increased public education. The problem of frequency allocation has increased with time because explosive growth of wireless communications systems has moved up in frequency and into the bands reserved for microwave power applications, the so-called industrial, scienti"c and medical (ISM) bands. The technically most-desirable band of 2.45 GHz is most probably not attainable and this makes the 5.8 GHz ISM band the most desirable. Early action by SSP interests is necessary to ensure such an allocation before the forthcoming conferences of the International Telecommunications Union (ITU). The potential interference from SSP systems remains the most severe technical problem in the microwave portion of such systems. Since this problem intensi"es with the ongoing growth of telecommunications, it is important that technical studies be done early to ensure compliance with likely regulations, both international and national.
2. History After the original proposal for the Solar Power Satellite (SPS) by Glaser [1] and its original full-scale de"nition by NASA [2], the microwave policy issues were focused at the frequency of 2.45 GHz where a substantial band of $50 MHz has been reserved for non-communications applications (ISM). Although some government personnel deny it, the original conception [3] of ISM included power transmission and unlimited radiation.
0265-9646/00/$ - see front matter 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 5 - 9 6 4 6 ( 0 0 ) 0 0 0 1 2 - 6
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J.M. Osepchuk / Space Policy 16 (2000) 111}115
Thus was the thinking during the early studies of the SPS. The optimum frequency for microwave power transmission was considered to be 2.45 GHz, [4] because of the proven feasibility of e$cient microwave power sources of the crossed-"eld type and some indications that the ubiquitous excess noise of such devices could be mitigated [5]. Original attention to environmental aspects of SSP was connected to the NASA reference system, [2] with 5 GW being transmitted from geo-synchronous orbit to a rectenna on earth. The system design resulted in a microwave power density of 25 mW/cm over the rectenna area with power density well below 0.01 mW/cm outside the rectenna area with a theoretical possibility of grating lobes producing the lower value of power density at a few isolated areas several hundreds of kilometers from the rectenna. Research indicated no serious exposure hazards. Some birds, however, may experience some thermal stress at 25 mW/cm. This was not assessed as a serious problem, however, since birds may adapt and avoid such stress, if it occurs. Interference could be a problem with crossed-"eld devices if mitigation techniques did not evolve as expected. Thus the original NASA reference system was designed to use klystrons, which, though more expensive and larger, present minimum noise problems. The NASA evaluation believed the employment of available "lters would reduce harmonic signals to acceptable levels. During this period SPS proponents openly discussed the choice of 2.45 GHz with regulatory authorities in the US. In 1986 an environmental assessment [6] by the author found the environmental levels of microwaves for the reference SPS system to comply with the exposure standards of all countries in the world. Despite this, it was pointed out that common perception, as gleaned from studies under NASA, was that the microwave safety problem was the number one obstacle for governmental and public acceptance. In this assessment the complexity of the potential interference (RFI) problem was emphasized. Work to make the e$cient crossed-"eld tubes acceptable for SPS was recommended as achievable. Over the years other large microwave systems have been deployed with varying degrees of public acceptance. The importance of public education and marketing of the positive aspects of SPS was recognized as a key to future acceptance of microwave power transmission systems [7]. In 1996 after reviewing the large amount of bioe!ect research done since the early NASA program [8], again no serious exposure hazard was seen for the SPS prototype and the proposed reference system was still compliant with all new exposure standards in the world. In the 1990s NASA resumed studies of many options for SSP * not only the classical full-scale reference system, but many other scaled-down versions with power levels as low as megawatts [9]. NASA now prefers the choice of
5.8 GHz and solid-state devices as the power sources. The reason for the new preferred frequency was the recognition that telecommunications interests had invaded the 2.45 GHz band, rendering it impractical, though not illegal, for the pursuit of rights to develop SSP systems for operation in that popular band (where over 200 million microwave ovens in the world operate). It is important to note that many independent studies of SSP are now being conducted around the world as noted by NASA [9]. Key work is being done in Japan, France, Germany and Russia to name a few. In a recent extensive review [10] of the microwave problems for SSP, the author reinforced the above conclusions with attention to one new aspect * that of proposals by anti-technology groups for the application of various principles of caution to assessment of any microwave system, such as the Precautionary Principle (see references in [10]). Although originally conceived for addressing potentially catastrophic environmental hazards, like global warming, it was being misapplied to even low-power transmitting towers for wireless communication. Such thinking is sure to be brought to the forefront of any serious governmental and public review of a proposed SSP system. The remedy for this new obstacle is the strengthening of the standards-setting groups world-wide that operate by due process and broad consensus. Such a group is the Institute of Electrical and Electronic Engineers (IEEE) which sponsors two committees that develop standards for the safe use of electromagnetic energy. One Standards Coordinating Committee 28 (SCC-28) develops exposure standards [11] that state a safe limit for the exposure of people. This Committee is increasingly international with broad consensus. The other Committee is SCC-34 which develops product performance standards for products that assure compliance with the standards of SCC-28. At present SCC-34 is in the intense development of certi"cation procedures for cell phones, with a large international consensus. In the Fall of 1999, an international conference was held to broaden the assessment of all electromagnetic energy systems from power lines to radar with a view on the environmental e!ects on all biota * plants and animals. A review of SSP concepts was presented [12]. There was an increasing recognition that development of new environmental standards may help ease confusion in assessment of new high-power systems employing EM energy. These standards would simply proscribe environmental levels of EM energy as distinct from exposure limits that apply only to people with some degree of voluntary acceptance of exposure. For environmental limits, considerations other than just human safety apply, and include e!ects on all biota, interference and sidee!ects caused by EM energy, as well as elements of social policy, e.g. the involuntary nature of exposure, etc. In an open forum, however, no pressing environmental
J.M. Osepchuk / Space Policy 16 (2000) 111}115
problem was perceived except for the possible e!ects on birds of high-power systems, because of the mobility of birds. Relevant research at 5.8 GHz on e!ects on birds would be of importance for future SSP systems as presently conceived by NASA.
3. Policy issues on microwave safety of SSP technology In the United States there is a long history [13] of development by consensus of voluntary standards for the safe use of EM energy [13]. Not only has this led to safe exposure standards but these standards have also been applied as environmental standards [14] to limit EM energy levels in uncontrolled areas to which the general public has access. Thus some states in the USA, as well as some localities (towns, cities and counties), have adopted environmental limits, usually based on IEEE C95.1 [11]. In the 1990s, as thousands of wireless base stations were constructed, the US government acted to minimize obstacles to this buildout by preempting local governments from assessing the siting of base stations on the basis of potential environmental health e!ects resulting from microwave energy. Instead the Federal Communications Commission (FCC) issued rules for both occupational exposure and environmental levels [15], based on IEEE C95.1 [11] and those of NCRP [16]. Meanwhile, in Europe and elsewhere in the world similar standards were being developed. Surveys [17] have shown that in the microwave range most of these standards are not that far apart [17], e.g. they present limits in the range of 1}10 mW/cm. More recently, there has been a trend in European countries towards harmonization. Recently, the European Parliament recommended the adoption of safety limits for EM energy that would be based on the Guidelines recently issued by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) [18]. Again, in the microwave range these, limits would be about 1 mW/cm, not too far from limits in the USA. Only a few communist and former communist countries persist in specifying safe exposure limits (time-dependent) for the general public that go as low as 0.01 mW/cm for a 24 h duration and are interpreted as environmental limits. In recent international meetings [19], however, there are signs that in the future these limits will in e!ect be raised. There is a world-wide movement towards international harmonization of standards. Meetings on this subject have been organized by the World Health Organisation [20] as part of its International EMF Project in cooperation with ICNIRP. The IEEE standards community, which forms a far broader consensus than the ICNIRP process, is extending its activities worldwide [21]. There is every expectation therefore that in a few years there will be international harmonization on environ-
113
mental standards for microwave energy and that national regulatory authorities will approve SSP systems on the question of microwave safety as being compliant with science-based safety standards. The vestigial issue on microwave safety of SSP would then be the threat from emerging anti-technology groups advocating the imposition of the Precautionary Principle. As pointed out earlier, this was really meant for potentially catastrophic technologies and we believe it is misapplied when drawn into the reviews of microwave systems like SSP systems and even local wireless systems. Professional groups have prepared papers exposing the unwise nature of such proposals, which amount to the `abandonment of sciencea [22]. In addition, of course, it remains to address the problem of public perception emphasized in all assessments of SSP projects. Under the auspices of the IEEE there is a Committee on Man and Radiation (COMAR) that issues Technical Information Statements and other publications which aim at educating the general public and reducing the in#uence of a pervasive &electrophobia' [23]. Clearly, the future of public and governmental acceptance of SSP projects will be enhanced by international consensus standards and a well educated public. Supporters of SSP should participate and support the IEEE with its ongoing activities in both areas.
4. Frequency-allocation issues It is the author's contention that the historical record supports the use of ISM band allocations for microwave-power transmission as one type of ISM application [3]. Nevertheless, authorities have in recent years begun addressing the question of frequency allocation for microwave power transmission [24]. It is not clear to what extent the wishes of the SSP community are being heard in this process. In the United States it is the National Telecommunications and Information Administration (NTIA) which is developing a US position on this matter. The issue will be deliberated at a forthcoming meeting of the International Telecommunication Union (ITU). Since the output of such meetings is tantamount to international treaty, it is important that the best thinking on this issue be brought to bear. As pointed out above, early thinking favored 2.45 GHz for SSP. This choice is still attractive for technical reasons but is becoming increasingly improbable from a political viewpoint. The ISM frequency at 5.8 GHz is being supported by NASA, and other groups throughout the world have proposed other higher frequencies. There are advantages of antenna size and gain at higher frequencies but there are penalties of lower e$ciency of the microwave generators. Furthermore, these higher frequencies would entail higher power densities in the beam and thus exacerbate the issue of microwave safety and
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perception. It would seem that 5.8 GHz is the best bet for support of SSP at this time. It is important to remember the allied issues. Besides the choice of frequency there is the question of bandwidth and policies regarding the co-use (sharing) of the band with telecommunications interests. It is important to preserve the presently broad band at 5.8 GHz (150 MHz) because it may be that optimum operation of SSP systems will eventually require some type of modulation scheme to enhance performance as well as mitigate problems such as RFI, both in-band and out of band. Finally it is important to support the program [25] to preserve the rights of ISM applications currently being conducted by the International Microwave Power Institute (IMPI). If there is to be any co-use of ISM bands then co-users for communications must accept any interference from ISM sources, including SSP, as has been the understood rule for decades [3].
5. Interference issues The problem of interference (RFI) may turn out to be the most severe environmental problem for SSP systems. The policy issues for interference are less clouded than for microwave safety or frequency allocation. The most recent speci"cation on out-of-band limits of emissions from ISM equipment is that of CISPR 11 [26], which is expected to be approved very soon by the International Electrotechnical Commission (IEC). These new limits above 1 GHz are designed around the dominant emissions at 2.45 GHz, the microwave oven. Thus, the limits make some allowance for the characteristic emissions from magnetrons in microwave ovens. Limits in the sideband regions 2.2}2.4 and 2.5}2.7 GHz are much higher than at frequencies far from 2.45 GHz. Of course, this relaxation is of no bene"t to SSP if SSP systems are developed for a di!erent frequency, e.g. 5.8 GHz. For quiet sources, like klystrons and solid-state sources, the main problem of emissions is simply the suppression of harmonic energy. Crossed"eld devices, on the other hand, will require some suppression at all frequencies, especially in the sideband regions. The CISPR limits and the associated test speci"cations are designed with the microwave oven in mind. It is quite possible that this might work to the detriment of SSP systems and any system with very stable frequency. The unstable frequency and noise of microwave ovens appear easier to work around than stable frequency sources, with regard to interference issues. To mitigate the potential RFI threat of SSP systems, therefore, it is wise to reserve su$cient bandwidth around an SSP frequency for suitable modulation if deemed desirable to mitigate RFI at some frequency emitted by the SSP source.
6. Conclusions Systems developed for space solar power will involve microwave power transmission and microwave environmental policy issues relative to microwave safety, frequency allocation and interference. In order to ensure the most rational environmental limits imposed on SSP, it is desirable to support the strengthening of the standardssetting community which develops the broadest scienti"c consensus. This is the IEEE SCC-28 community that operates under the due process oversight of the IEEE. Frequency allocation policy will be dictated in large part by the actions of the ITU. Since that subject is shortly to be heard before the ITU, it is important to present the best thinking on SSP frequency allocation to the ITU now. Interference issues involve a straightforward approach to reducing out of band emissions. In-band emissions, however, for the SSP systems cannot in principle be reduced. Therefore, SSP proponents should support the program of IMPI to minimize or eliminate the co-use of ISM bands by communications interests. This appears di$cult, if not impossible, for 2.45 GHz but there is still hope that the higher frequency bands, like 5.8 GHz, can be preserved for ISM, including SSP.
References [1] Glaser P. Power from the sun: its future. Science 1968;162:857}66. [2] NASA: The Final Proceedings of the Solar Satellite Program Review, DoE/NASA Conference 800491, 1980. p. 107}8. [3] Allen Jr EW, Garlan H. Evolution of regulatory standards of interference. Proceedings of IRE 1962;50(5):1306}11. [4] Brown, WC. A history of microwave power transmission. IEEE Trans. 1984;MTT-32:1230}44. [5] Osepchuk, JM. The cooker magnetron as a standard in crossed"eld research, Proceedings of the First International Workshop on Crossed-Field Devices, University of Michigan, August 15}16, 1955. p. 159}77. [6] Osepchuk JM. Environmental issues for the solar power satellite. Space Power 1986;6:165}73. [7] Osepchuk, JM. Overcoming perceived microwave radiation hazards relative to microwave power transmission. Proceedings of the 29th Microwave Power Symposium (IMPI), 1994. p. 132}34. [8] Osepchuk JM. Health and safety issues for microwave power transmission. Solar Energy 1996;56(1):53}60. [9] Mankins J, et al. Space solar power: a fresh look. Washington, DC: NASA/HQ Advanced Concepts O$ce, July 1996. [10] Osepchuk JM. Health and safety issues of microwave power transmission. In: Glaser PE, Davidson FP, Csigi KI, editors. Solar power satellites. New York: Wiley, 1998. p. 471}500. [11] IEEE Standard for safety levels with respect to human exposure to radiofrequency electromagnetic "elds, 3 kHz to 300 GHz. IEEE C95.1-1991, 1999 ed. Adopted by ANSI in 1992. Piscataway, NJ: IEEE, 1999 [see Ref. [21] for web site]. [12] Osepchuk JM. Solar power satellites. Proceedings of the International Seminar on E!ects of Electromagnetic Fields on the Living Environment, October 4}6, 1999; WHO/ICNIRP; Geneva. In press.
J.M. Osepchuk / Space Policy 16 (2000) 111}115 [13] Osepchuk JM, Petersen RC. Past may help solve electromagnetic issue. Forum 1994;9(2):99}103. [14] Osepchuk JM. Impact of public concerns about low-level EMFRFR database. In: Klauenberg BJ, Grandolfo M, Erwin DN, editors. Radiofrequency radiation standards. New York: Plenum Press, 1995. p. 415}26. [15] FCC. Report and Order FCC 96-326, In the matter of Guidelines for Evaluating the Environmental E!ects of Radiofrequency Radiation. ET Docket No. 93-6, August 1, 1996. [16] NCRP. Biologic e!ects and exposure criteria for radiofrequency electromagnetic "elds. NCRP Report C86, 1986. [17] Petersen RC. Radiofrequency/microwave protection guides. Health Physics 1991;61:59}67. [18] International Commission on Non-Ionizing Radiation Protection. Guidelines on limits of exposure to time-varying electric, magnetic and electromagnetic "elds (1 Hz}300 GHz). Health Physics 1998;74:494}522. [19] NATO. NATO Proceedings of Advanced Research Workshop: Radiofrequency Radiation Dosimetry, October 12}16 1998. In press.
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[20] World Health Organization (WHO). The international EMF project: health and environmental e!ects of exposure to time varying electric and magnetic "elds, WHO, Geneva, as described in Bioelectromagnetics Newsletter 1996;132. [21] IEEE Standards Coordinating Committee 28 (SCC-28). http://grouper.IEEE.org/groups/scc28. [22] Electromagnetic Energy Association (EEA). http://www. elecenergy.com. [23] Osepchuk JM. COMAR after 25 years: still a challenge. IEEE Engineering in Medicine and Biology 1996;15(3):120}5. [24] ITU. Radiocommunication Study Groups, Working Party 1A, Wireless Power Transmission. Draft New Question, ITU-R [Doc.1/11]/1, 25 October 1996. [25] IMPI Spectrum Committee Report. Microwave World 1999;20(1);4}6, 13. [26] CISPR B. Proposal for Emission Limits from 1 to 18 GHz, proposed amendment to CISPR 11, International Special Committee on Radio Interference (CISPR); International Electrotechnical Commission (IEC), 1996.
Microwave policy issues for solar space power John M. Osepchuk Full Spectrum Consulting, 248 Deacon Haynes Road, Concord, MA 01742, USA
Abstract This article reviews the three major policy issues likely to arise from an SSP system: environmental safety, frequency allocation and prevention of interference with other frequency-using activities. Supporters of SSP must make sure that their case is heard clearly at the ITU, but they must also do more to promote public awareness of the technology's potential bene"ts in order to counter inappropriate use of the Precautionary Principle by anti-technology groups. The strengthening of standard-setting groups world-wide will also assist this process. 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction The technological feasibility of solar space power (SSP) has been considered as highly probable based on Earth-bound experience with the elements of such systems. Economic and policy issues, however, may pose a greater obstacle to the realization of such systems. In this paper we review those policy issues that relate speci"cally to the aspect of microwave power transmission in solar space power systems. First, there is the question of whether microwave power transmission can be and will be approved as environmentally safe with regard to possible e!ects of microwave energy on not only humans but all biota on earth. Second, there is the question of whether a suitable microwave frequency allocation will be made by appropriate international and national authorities. Third, there is the question of whether the microwave emissions, both in-band and out-of-band, are acceptable with regard to regulations for prevention of interference. The history of SSP development suggests that early realization of such systems will "rst occur at lower power levels and then later at the highest powers for full-scale systems (e.g. 5 GW or 5;10 W). Clearly, it will be easier to obtain approvals on microwave safety and interference issues at the lower powers. A review of the evolving framework of standards for microwave safety indicates two trends that will eventually ease acceptance of SSP; international harmonization and the development of environmental standards. The obstacles do not derive from the scienti"c database but from misapplication of concepts conceived for potentially catastrophic technologies, i.e. the Precautionary Principle. To overcome such think-
ing there must be increased support of the standardssetting organizations which are based on due process and broad consensus, as well as increased public education. The problem of frequency allocation has increased with time because explosive growth of wireless communications systems has moved up in frequency and into the bands reserved for microwave power applications, the so-called industrial, scienti"c and medical (ISM) bands. The technically most-desirable band of 2.45 GHz is most probably not attainable and this makes the 5.8 GHz ISM band the most desirable. Early action by SSP interests is necessary to ensure such an allocation before the forthcoming conferences of the International Telecommunications Union (ITU). The potential interference from SSP systems remains the most severe technical problem in the microwave portion of such systems. Since this problem intensi"es with the ongoing growth of telecommunications, it is important that technical studies be done early to ensure compliance with likely regulations, both international and national.
2. History After the original proposal for the Solar Power Satellite (SPS) by Glaser [1] and its original full-scale de"nition by NASA [2], the microwave policy issues were focused at the frequency of 2.45 GHz where a substantial band of $50 MHz has been reserved for non-communications applications (ISM). Although some government personnel deny it, the original conception [3] of ISM included power transmission and unlimited radiation.
0265-9646/00/$ - see front matter 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 5 - 9 6 4 6 ( 0 0 ) 0 0 0 1 2 - 6
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J.M. Osepchuk / Space Policy 16 (2000) 111}115
Thus was the thinking during the early studies of the SPS. The optimum frequency for microwave power transmission was considered to be 2.45 GHz, [4] because of the proven feasibility of e$cient microwave power sources of the crossed-"eld type and some indications that the ubiquitous excess noise of such devices could be mitigated [5]. Original attention to environmental aspects of SSP was connected to the NASA reference system, [2] with 5 GW being transmitted from geo-synchronous orbit to a rectenna on earth. The system design resulted in a microwave power density of 25 mW/cm over the rectenna area with power density well below 0.01 mW/cm outside the rectenna area with a theoretical possibility of grating lobes producing the lower value of power density at a few isolated areas several hundreds of kilometers from the rectenna. Research indicated no serious exposure hazards. Some birds, however, may experience some thermal stress at 25 mW/cm. This was not assessed as a serious problem, however, since birds may adapt and avoid such stress, if it occurs. Interference could be a problem with crossed-"eld devices if mitigation techniques did not evolve as expected. Thus the original NASA reference system was designed to use klystrons, which, though more expensive and larger, present minimum noise problems. The NASA evaluation believed the employment of available "lters would reduce harmonic signals to acceptable levels. During this period SPS proponents openly discussed the choice of 2.45 GHz with regulatory authorities in the US. In 1986 an environmental assessment [6] by the author found the environmental levels of microwaves for the reference SPS system to comply with the exposure standards of all countries in the world. Despite this, it was pointed out that common perception, as gleaned from studies under NASA, was that the microwave safety problem was the number one obstacle for governmental and public acceptance. In this assessment the complexity of the potential interference (RFI) problem was emphasized. Work to make the e$cient crossed-"eld tubes acceptable for SPS was recommended as achievable. Over the years other large microwave systems have been deployed with varying degrees of public acceptance. The importance of public education and marketing of the positive aspects of SPS was recognized as a key to future acceptance of microwave power transmission systems [7]. In 1996 after reviewing the large amount of bioe!ect research done since the early NASA program [8], again no serious exposure hazard was seen for the SPS prototype and the proposed reference system was still compliant with all new exposure standards in the world. In the 1990s NASA resumed studies of many options for SSP * not only the classical full-scale reference system, but many other scaled-down versions with power levels as low as megawatts [9]. NASA now prefers the choice of
5.8 GHz and solid-state devices as the power sources. The reason for the new preferred frequency was the recognition that telecommunications interests had invaded the 2.45 GHz band, rendering it impractical, though not illegal, for the pursuit of rights to develop SSP systems for operation in that popular band (where over 200 million microwave ovens in the world operate). It is important to note that many independent studies of SSP are now being conducted around the world as noted by NASA [9]. Key work is being done in Japan, France, Germany and Russia to name a few. In a recent extensive review [10] of the microwave problems for SSP, the author reinforced the above conclusions with attention to one new aspect * that of proposals by anti-technology groups for the application of various principles of caution to assessment of any microwave system, such as the Precautionary Principle (see references in [10]). Although originally conceived for addressing potentially catastrophic environmental hazards, like global warming, it was being misapplied to even low-power transmitting towers for wireless communication. Such thinking is sure to be brought to the forefront of any serious governmental and public review of a proposed SSP system. The remedy for this new obstacle is the strengthening of the standards-setting groups world-wide that operate by due process and broad consensus. Such a group is the Institute of Electrical and Electronic Engineers (IEEE) which sponsors two committees that develop standards for the safe use of electromagnetic energy. One Standards Coordinating Committee 28 (SCC-28) develops exposure standards [11] that state a safe limit for the exposure of people. This Committee is increasingly international with broad consensus. The other Committee is SCC-34 which develops product performance standards for products that assure compliance with the standards of SCC-28. At present SCC-34 is in the intense development of certi"cation procedures for cell phones, with a large international consensus. In the Fall of 1999, an international conference was held to broaden the assessment of all electromagnetic energy systems from power lines to radar with a view on the environmental e!ects on all biota * plants and animals. A review of SSP concepts was presented [12]. There was an increasing recognition that development of new environmental standards may help ease confusion in assessment of new high-power systems employing EM energy. These standards would simply proscribe environmental levels of EM energy as distinct from exposure limits that apply only to people with some degree of voluntary acceptance of exposure. For environmental limits, considerations other than just human safety apply, and include e!ects on all biota, interference and sidee!ects caused by EM energy, as well as elements of social policy, e.g. the involuntary nature of exposure, etc. In an open forum, however, no pressing environmental
J.M. Osepchuk / Space Policy 16 (2000) 111}115
problem was perceived except for the possible e!ects on birds of high-power systems, because of the mobility of birds. Relevant research at 5.8 GHz on e!ects on birds would be of importance for future SSP systems as presently conceived by NASA.
3. Policy issues on microwave safety of SSP technology In the United States there is a long history [13] of development by consensus of voluntary standards for the safe use of EM energy [13]. Not only has this led to safe exposure standards but these standards have also been applied as environmental standards [14] to limit EM energy levels in uncontrolled areas to which the general public has access. Thus some states in the USA, as well as some localities (towns, cities and counties), have adopted environmental limits, usually based on IEEE C95.1 [11]. In the 1990s, as thousands of wireless base stations were constructed, the US government acted to minimize obstacles to this buildout by preempting local governments from assessing the siting of base stations on the basis of potential environmental health e!ects resulting from microwave energy. Instead the Federal Communications Commission (FCC) issued rules for both occupational exposure and environmental levels [15], based on IEEE C95.1 [11] and those of NCRP [16]. Meanwhile, in Europe and elsewhere in the world similar standards were being developed. Surveys [17] have shown that in the microwave range most of these standards are not that far apart [17], e.g. they present limits in the range of 1}10 mW/cm. More recently, there has been a trend in European countries towards harmonization. Recently, the European Parliament recommended the adoption of safety limits for EM energy that would be based on the Guidelines recently issued by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) [18]. Again, in the microwave range these, limits would be about 1 mW/cm, not too far from limits in the USA. Only a few communist and former communist countries persist in specifying safe exposure limits (time-dependent) for the general public that go as low as 0.01 mW/cm for a 24 h duration and are interpreted as environmental limits. In recent international meetings [19], however, there are signs that in the future these limits will in e!ect be raised. There is a world-wide movement towards international harmonization of standards. Meetings on this subject have been organized by the World Health Organisation [20] as part of its International EMF Project in cooperation with ICNIRP. The IEEE standards community, which forms a far broader consensus than the ICNIRP process, is extending its activities worldwide [21]. There is every expectation therefore that in a few years there will be international harmonization on environ-
113
mental standards for microwave energy and that national regulatory authorities will approve SSP systems on the question of microwave safety as being compliant with science-based safety standards. The vestigial issue on microwave safety of SSP would then be the threat from emerging anti-technology groups advocating the imposition of the Precautionary Principle. As pointed out earlier, this was really meant for potentially catastrophic technologies and we believe it is misapplied when drawn into the reviews of microwave systems like SSP systems and even local wireless systems. Professional groups have prepared papers exposing the unwise nature of such proposals, which amount to the `abandonment of sciencea [22]. In addition, of course, it remains to address the problem of public perception emphasized in all assessments of SSP projects. Under the auspices of the IEEE there is a Committee on Man and Radiation (COMAR) that issues Technical Information Statements and other publications which aim at educating the general public and reducing the in#uence of a pervasive &electrophobia' [23]. Clearly, the future of public and governmental acceptance of SSP projects will be enhanced by international consensus standards and a well educated public. Supporters of SSP should participate and support the IEEE with its ongoing activities in both areas.
4. Frequency-allocation issues It is the author's contention that the historical record supports the use of ISM band allocations for microwave-power transmission as one type of ISM application [3]. Nevertheless, authorities have in recent years begun addressing the question of frequency allocation for microwave power transmission [24]. It is not clear to what extent the wishes of the SSP community are being heard in this process. In the United States it is the National Telecommunications and Information Administration (NTIA) which is developing a US position on this matter. The issue will be deliberated at a forthcoming meeting of the International Telecommunication Union (ITU). Since the output of such meetings is tantamount to international treaty, it is important that the best thinking on this issue be brought to bear. As pointed out above, early thinking favored 2.45 GHz for SSP. This choice is still attractive for technical reasons but is becoming increasingly improbable from a political viewpoint. The ISM frequency at 5.8 GHz is being supported by NASA, and other groups throughout the world have proposed other higher frequencies. There are advantages of antenna size and gain at higher frequencies but there are penalties of lower e$ciency of the microwave generators. Furthermore, these higher frequencies would entail higher power densities in the beam and thus exacerbate the issue of microwave safety and
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perception. It would seem that 5.8 GHz is the best bet for support of SSP at this time. It is important to remember the allied issues. Besides the choice of frequency there is the question of bandwidth and policies regarding the co-use (sharing) of the band with telecommunications interests. It is important to preserve the presently broad band at 5.8 GHz (150 MHz) because it may be that optimum operation of SSP systems will eventually require some type of modulation scheme to enhance performance as well as mitigate problems such as RFI, both in-band and out of band. Finally it is important to support the program [25] to preserve the rights of ISM applications currently being conducted by the International Microwave Power Institute (IMPI). If there is to be any co-use of ISM bands then co-users for communications must accept any interference from ISM sources, including SSP, as has been the understood rule for decades [3].
5. Interference issues The problem of interference (RFI) may turn out to be the most severe environmental problem for SSP systems. The policy issues for interference are less clouded than for microwave safety or frequency allocation. The most recent speci"cation on out-of-band limits of emissions from ISM equipment is that of CISPR 11 [26], which is expected to be approved very soon by the International Electrotechnical Commission (IEC). These new limits above 1 GHz are designed around the dominant emissions at 2.45 GHz, the microwave oven. Thus, the limits make some allowance for the characteristic emissions from magnetrons in microwave ovens. Limits in the sideband regions 2.2}2.4 and 2.5}2.7 GHz are much higher than at frequencies far from 2.45 GHz. Of course, this relaxation is of no bene"t to SSP if SSP systems are developed for a di!erent frequency, e.g. 5.8 GHz. For quiet sources, like klystrons and solid-state sources, the main problem of emissions is simply the suppression of harmonic energy. Crossed"eld devices, on the other hand, will require some suppression at all frequencies, especially in the sideband regions. The CISPR limits and the associated test speci"cations are designed with the microwave oven in mind. It is quite possible that this might work to the detriment of SSP systems and any system with very stable frequency. The unstable frequency and noise of microwave ovens appear easier to work around than stable frequency sources, with regard to interference issues. To mitigate the potential RFI threat of SSP systems, therefore, it is wise to reserve su$cient bandwidth around an SSP frequency for suitable modulation if deemed desirable to mitigate RFI at some frequency emitted by the SSP source.
6. Conclusions Systems developed for space solar power will involve microwave power transmission and microwave environmental policy issues relative to microwave safety, frequency allocation and interference. In order to ensure the most rational environmental limits imposed on SSP, it is desirable to support the strengthening of the standardssetting community which develops the broadest scienti"c consensus. This is the IEEE SCC-28 community that operates under the due process oversight of the IEEE. Frequency allocation policy will be dictated in large part by the actions of the ITU. Since that subject is shortly to be heard before the ITU, it is important to present the best thinking on SSP frequency allocation to the ITU now. Interference issues involve a straightforward approach to reducing out of band emissions. In-band emissions, however, for the SSP systems cannot in principle be reduced. Therefore, SSP proponents should support the program of IMPI to minimize or eliminate the co-use of ISM bands by communications interests. This appears di$cult, if not impossible, for 2.45 GHz but there is still hope that the higher frequency bands, like 5.8 GHz, can be preserved for ISM, including SSP.
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