"SPS 2000" is an energy system being designed to use a satellite in Earth orbit to supply electricity for use by people living at the Earth's surface. The satellite will collect solar energy using solar cells, and will transmit a microwave beam to a number of receivers (called "rectennas") on the ground, which will convert the beam back to electricity for delivery to users. The concept of SPS ("solar power satellites") was proposed in 1968 by Peter Glaser as a potentially large-scale new energy source for the Earth. Studies funded by the US Department of Energy in the 1970s concluded that such a system would probably be technically feasible and environmentally clean, but that it would be too expensive using existing space technology. Consequently most SPS work in the USA stopped. Thus, although other new energy sources continue to be researched, SPS has still never been demonstrated.

"SPS 2000" was started in Japan as a project to answer a question which engineers from the electricity industry sometimes ask space engineers: "What is SPS?". The only answer today is to describe something that might be possible far in the future - something like a dream for the practical engineers of the electricity industry.

"SPS 2000" is being designed to start assembly in orbit in the year 2000 (though assembly may take several years). So SPS 2000 may become the first SPS - a "pilot plant" to demonstrate that SPS can be a practical energy source. In order to limit the cost, the SPS 2000 satellite will not be in "stationary" orbit, but in low Earth orbit (LEO) at about 1100 km altitude. So it will transmit 10MW for about 200 seconds as it passes over each rectenna, where it will be stored. By orbiting above the equator it can deliver to each rectenna every orbit. Consequently SPS 2000 has to be an international project, and the ground segment an equatorial project.

An essential part of any energy project are the users, who decide whether the system is acceptable or not. In the case of SPS 2000 the rectennas will be spread literally around the world, and will involve more people than the satellite system, each rectenna being used by a local electricity company to supply the local neighbourhood. The rectenna systems together constitute the SPS 2000 "ground segment".

"Equatorial Times" is concerned primarily with the SPS 2000 ground segment in the equatorial countries, in all its aspects - commercial, technical, political, environmental, legal. It is also intended to provide a means of communication between those working on different aspects of the ground segment in the equatorial countries, Japan and elsewhere, and to encourage the exchange of information between different groups around the equator. We will also try to keep readers up-to-date on recent news relevant to the overall SPS 2000 project (as far as space permits).

We warmly invite all readers to submit material for publication in "Equatorial Times" - articles, letters, photos, reports, comments, cartoons - concerning any aspect of the SPS 2000 project. We are keen to express the views of the potential user-community of microwave energy from space. As work on the SPS ground segment progresses and expands expect to publish more frequently.

In 1994 the Japanese Ministry of Education, Science and Culture awarded a grant for field research in a number of equatorial countries in order to study the feasibility of siting SPS 2000 rectennas there. The objectives of this research are to make contact with colleagues in these countries; to have initial discussions with government representatives; to identify candidate rectenna sites; to develop some preliminary ideas about appropriate rectenna designs for each site; and to consider how each rectenna might best be utilised.

For potential users of the power produced by the SPS 2000 system, the most important issues are different from those of satellite design. In the design of the ground segment the major issues include selecting a rectenna site and deciding the size of the rectenna; selecting the most appropriate designs for the microwave reception sub-system and the rectenna structure; calculating the actual amount of energy that will be received; estimating the most attractive 24-hour pattern of electricity supply for potential users in the neighbouring district; calculating the appropriate size for the electricity storage system and the amount of electric energy that will be available for use; planning the electricity distribution network and its operation; and estimating the overall cost of the ground segment. In the mechanical design of the rectenna, practical engineering problems such as birds nesting on the rectenna, cattle rubbing against the support structure, or heavy rain causing electrical short-circuits are also important.

The first field visits have been to Tanzania, Papua New Guinea and Brazil. In each of these countries contacts have been made with researchers in universities and government research centers, and with appropriate government staff and business people. In each of these countries also, one or more potentially attractive sites have been identified for rectennas. In all the countries there is enthusiasm to participate in the SPS 2000 project, and collaboration between staff in these countries and in Japan will continue in order to make more concrete designs for the rectenna systems. Until it is decided that the SPS 2000 project will go ahead, only limited resources can be used. However, even at the present stage preparatory research is needed to plan rectennas, since in the absence of clear prospects of successfully installing, using and maintaining sufficient rectennas, it will not be possible to be confident of the value of the overall SPS 2000 project. In each country visited, as well as visiting relevant government offices and research centers, visits were also made to regions close to the equator, since the SPS 2000 satellite is being designed to deliver to sites within about 3 degrees latitude of the equator.

The first field visit was made to Tanzania in September and October 1994. One of the largest countries in east Africa, Tanzania has an area of almost 1 million square kilometers (sq km), and a population of about 25 million people. Visits were made in the capital Dar es Salaam to the Ministry of Water, Energy and Minerals, the Directorate of Meteorology, Tanzania Electricity Supply Company, Tanzania Communications Commission, the Commission for Science & Technology, the University of Dar es Salaam and other organisations. In all cases there was interest in Tanzania participating in the SPS 2000 project.

A visit was then made to a region north of Kilimanjaro and Mount Mern, where a wide plain extends over some 300 square kilometers up to the border with Kenya. An attractive site for a rectenna was found between Mount Longido and the small border town of Namanga. The land is semi-arid with thin tree cover, and is used mainly for grazing of nomadic herds of cattle. A design in which the rectenna surface is raised perhaps 2-3 meters above the ground would allow cattle to pass firely underneath. Visits were also made to the Musha office of the National Land Use Planning Commission, and the nearby National Radiation Commission. Collaboration on the SPS 2000 project in Tanzania will be led by Professor P N Materu, Dean of the Faculty of Engineering at the University of Dar es Salaam.

A country comprising both continent and pacific islands, Papua New Guinea (PNG) has an area of almost 0.5 million sq km, and a population of some 4 million people. Independent of Australia for some 20 years, PNG has substantial mineral resources, and fertile land.

In February and March 1995 visits were made to a number of government offices in the capital, Port Moresby, including the Department of Village Services and Provincial Affairs, the Prime Minister's Office, the Department of Energy Development, and the Spectrum Management Department of the Post and Telecommunication Corporation. A number of issues were discussed and the staff were all interested in PNG participating in the SPS 2000 project

Visits were then made to potential rectenna sites in four different northern provinces within a few degrees of the equator - New Ireland, Manus, East Sepik and Sandaun. The conditions of a rectenna sited in PNG would be interestingly different from Longido Plain, since the climate would be maritime, and the rectenna might be sited over trees or short crops. In addition there is periodic torrential rain which may affect the microwave power transmission. Finally a visit was made to the University of Technology (Unitech) in the city of Lae, where staff in the Depaitnent of Electrical and Communications Engineering agreed to collaborate in further study of a PNG rectenna. This collaboration will be led by the Head of the Department, Dr Lason Watae.

The largest country in south America, Brazil has an area of 8.5 trillion sq km and a population of some 150 million people. The northern part of the country stretches for more than two thousand kilometers along the equator. Being a much larger country than Tanzania and Papua New Guinea, with a longer history of economic development, Brazil has a long established space research center (INPE), a civilian space agency (AEB), and an equatorial launch site (CLA) for which it is developing a satellite launch vehicle, due to fly for the first time in 1996.

Visits were made in September and October 1995 to several INPE sites, to the headquailers of AEB, and to the launch center at Alcantara near Sao Luis in the state of Maranhao. During all of these there was considerable interest in the SPS 2000 project. The Director-General of AEB offered to co-ordinate Brazilian participation in SPS 2000, and to collaborate with the Ministries of Energy and Telecommunications and other appropriate organisations to study the possibilities. Thus, although details remain to be decided, there is a possibility that Brazil may paitcipate in the SPS 2000 project by hosting a rectenna; by doing research on the ionospheric impact of the SPS 2000 microwave power beam; and also by utilising the launch center at Alcantara.

There are good prospects for a rectenna site within the 600 sq km Alcantara launch center. Another rectenna might be sited 1200 km to the west in the state of Amazonas. Dr Ajax Melo, Director General of AEB will be responsible for Brazils participation.

A number of issues that require further study were identified during the field visits to date, and others are expected to arise in future. First, although the frequency range between 2.4 and 2.5 GHz is defined by the International Telecommunications Union (ITU) as the Industrial Scientific & Medical (ISM) band, it is also used for communications in countries including Tanzania and Papua New Guinea. Thus there is a need to solve any such interference problems that SPS 2000 might cause for telecommunication systems in equatorial countries.

Second, in districts where there is currently no electric power the first priority is often for electric lighting in the evenings. Consequently, the output of SPS 2000 rectennas may be used primarily in the evenings. In this case the energy storage system would need to be several times larger than for supplying power evenly thiough the day.

Third, since the rectennas will be like a wire mesh, and will permit sunlight to pass through and reach the ground, the approximately 1 sq km of land needed for a rectenna could also be used for agriculture. It will therefore be desirable to plan the use of the land beneath the rectenna in combination with planning the rectenna itself.

Fourth, as more detailed plans for each site are developed, there will be increasing collaboration between researchers in Japan and in the equatorial countries, and also between the equatorial countries, which have common interests and can learn from each other. As the number of participating countries grows and their contribution to the project increases, the influence of the ground segment on the project will grow, and the views of SPS 2000 users, the customers for the power produced, will grow more important.

Fifth, in Brazil there is already considerable expertise in ionospheric research, centered on studying the behaviour of the magnetic equator over Brazil. Using this expertise to study the impact of the SPS 2000 microwave beam on the ionosphere near the equator would be a unique opportunity for advancing SPS research in general.

A report on each visit is available on request. The next visit will be to Indonesia during March 1996.

On July 29, the annual Open Day was held at the Institute for Space and Astronautical Science and a 1/200-scale functional model of the SPS 2000 satellite was displayed. This had a phased-array transmitting antenna that was capable of switching the direction of its beam between three different rectennas. The photograph shows the model transmitting microwave beams to model rectennas in Tanzania, Papua New Guinea and Brazil, where the direct-current electricity produced was used to power miniature lights, refrigerators and water-pumps.

Following the successful WPT 1 conference held in San Antonio, Texas in February 1993, WPT 2 was held at Kobe University in October. Luckily the University was only slightly damaged by the earthquake which devastated the city and killed more than 6000 people in January, and the conference was held as planned. Attendees came from USA, Russia, France and Japan, making this a truly international conference.

Although WPT is a key part of the concept of SPS, the technology of WPT is in itself independent of SPS, and the conference programe included papers on such topics as ground-based micro-wave transmission of electric power to remote sites, and microwave-powered aeroplanes and space transportation systems.

There were some 15 presentations about different aspects of SPS, including a statement about the newly established SPS study in NASA - their first SPS work for 20 years. Four papers were presented on SPS 2000 (copies available on request).

There were also demonstrations of a microwave-powered airship and helicopter, demonstrating the maturity of retro-directively-controlled WPT as a working technology, ready for application today. It was also agreed that WPT 3 would be held in the USA in 1997.

From all of this activity we can see that, despite the very small budgets available, WPT research seems to be thriving - which of course is excellent news for SPS, and for SPS 2000!

In early 1996 an application will be made to the Ministry of Education, Science and Culture for funding of a co-ordinated SPS research plan by members of the SPS Working Group. Applications were also made in 1995 and 1994, both unsuccessfully. There are strong hopes that this time the application will be accepted, enabling many areas of SPS research to move forward faster.

This photograph shows a "mini-rectenna" made in the Space Energy Engineering Laboratory at ISAS. This comprises two 12.5 cm dipoles connected to a suitable diode, and a 1.8 mW LED. When held in front of the closed door of an operating microwave oven, the LED lights up - demonstrating wireless power transmission. That is, the small amount of microwave power leaking through the door is absorbed by the dipoles, rectified by the diode and the DC current drives the LED. This is an excellent, simple way of demonstrating WPT, and of explaining the concept of SPS. It is also very cheap to make! The diode costs 20 yen, the LED costs 100 yen, and the rest is just wire and plastic. Note that this design uses a reflecting panel made of ordinary wire mesh behind the dipoles, which increases the proportion of microwaves that are absorbed.

We will be happy to help SPS 2000 researchers to make their own mini rectennas, by providing information and/or components. We particularly look forward to receiving photographs, or even better, examples, of mini-rectennas made by readers in different countries.

Safety Note: Some people, on seeing this demonstration say: "Oh, now I see that microwave ovens are dangerous, because microwaves are leaking out of them". However, this conclusion is incorrect. Microwaves do leak from ovens, but their intensity is governed by an international safety standard. For exposure of the general public, the intensity of continuous-wave radiation at 2.45 GHz must be less than 10 W/sq m (= 1 mW/sq cm). These mini rectennas can pick up microwave power at less than this intensity, and convert it to DC electric power. So, if an oven is damaged, microwaves above this intensity may leak out, but all ovens leak a certain amount within the safety limit, and this is not dangerous.

The concept of solar power satellites, first put forward in the 1960s, is still not widely known by the general public. For example at many public exhibitions about Energy, SPS is not even mentioned. This is mainly because very little funding has been spent on SPS research to date - about 1/1000 of 1% of the approximately 100 trillion yen (US $1 trillion) that governments have spent subsidizing the development of nuclear power over the past 50 years.

There are critics who claim that SPS is unrealistic - because launch costs are much too high today; because microwave beams will set fire to cities; because it is too futuristic. So why do we believe that it is important to continue to do research on SPS? The reason is very simple.

Humans are going to need enormous amounts of electric power in coming decades. Within 50 years the world population is expected to double, while economic growth will continue around the world, especially in the poorer countries. But existing power sources already face serious problems. They are limited; they are polluting; they are dangerous. So 50 years from now, 100 years from now, where is our power going to come from? Nobody knows. And so we believe that new large-scale possibilities should be studied further.

The solar energy that reaches the Earth is about 10,000 times total human energy production today, and the energy available in near-Earth space is limitless. Research is being done on many different ways of using solar power economically on Earth, and many of these will be successful.

However, sunlight is diffuse and not available continuously at the Earth's surface. So one possibility is to collect solar energy 24 hours per day in space, and transmit it as microwave beams to receivers on Earth.

Compared to solar power collected at the Earth's surface, SPS faces the extra costs of space transportation and microwave power transmission. But in order to supply continuous electric power, solar systems on Earth need much greater area for collection, large scale storage and long distance transmission from desert areas to population centers. Consequently, at the present state of knowledge we do not know that in future solar power from space could not compete with solar power collected on Earth. And so we believe that we should do more research on this - and that SPS research should receive funding similar to other potential new energy sources.

We should also remember that we have some choice concerning our future. To some extent we can choose the direction in which our civilisation develops. And choices that are made in the coming decades - such as the energy sources that we will or will not use - will have major, long-term implications for human life on Earth. We believe that, provided that research continues to show that SPS is environmentally and economically attractive, SPS will open the door to a more attractive future for human civilization than any ground-based energy source; and one that the public will support and that our young people will find challenging and exciting. First, energy from SPS can be readily used in developing countries as SPS 2000 will demonstrate, thereby aiding economic development world-wide. Second, by creating large commercial revenues for space engineering, SPS will open the frontier of space to economic development, thereby creating a limitless new field for growth of the world economy.

For these reasons we believe that for governments to continue to do almost zero research on SPS would be a terrible mistake. To continue to give most energy research funding to nuclear power, and none to SPS, would be a narrow and dangerous policy which could close off the possibility of this attractive future.

And in order to advance SPS work we believe that the SPS 2000 pilot plant project is now a timely step. The basic technologies have been developed and demonstrated. It is time to start to accumulate experience of operating a real SPS, and to show the electricity industry that this technology is ready for use. At the "SPS 91" international SPS conference a paper on SPS 2000 won the prize for the best proposal, and the project has made good progress since then. Building and operating SPS 2000 will be a major step towards SPS, and a major step towards an optimistic and exciting new era of peaceful growth for humans.

Even if the SPS 2000 project cost 100 billion yen (US $1 billion), that would be just a small fraction of government subsidies to nuclear energy research, and of similar scale to other governinent satellite and energy research projects. We believe that this would be a good investment, which would be popular with the public both in Japan and in the equatorial countries. Consequently we want to work together to produce a complete SPS 2000 plan, which will deserve to be put into effect.

AEB

Brazilian Space Agency

CLA

Alcantara Launch Center

GHz

Giga-Hertz (1 billion Hertz)

Hertz

Frequency of 1 cycle I second

INPE

(Brazilian) Institute for Space Research

ISAS

Institute for Space & Astronautical Science of the Ministry of Education, Science & Culture

ITU

International Telecommunications Union

ISM

Industrial Scientific & Medical band (=2.4 - 2.5 GHz)

LED

Light-Emitting Diode

LEO

Low Earth Orbit

PNG

Papua New Guinea

RCAST

Research Center for Advanced Science & Technology (Tokyo University)

Rectenna

Rectifying Antenna

SPS

Solar Power Satellite

sq cm

square centimeter

sq km

square kilometer

sq m

square meter

trillion

thousand billion

• Field research visit to Indonesia
• More mini-rectennas
• Estimating SPS 2000 rectenna energy output
• SPS 2000 Home Page

For correspondence, contributions or further information, please contact Patrick Collins at: Research Center for Advanced Science & Technology, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153, Japan.
Fax no: (81) 3 3481 4587
E-mail: collins@esa-jpn.rcast.u-tokyo.ac.jp