The concept of solar power satellites, or SPS, 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 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; or because microwave beams will set fire to cities; or because it's 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 energy sources already face serious problems. They're limited; they're polluting; they're 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. Terrestrial solar energy is going to become a colossal business. However, sunlight is diffuse and not available continuously at the Earth's surface. So one additional 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 energy storage for supply during the night-time and when it's cloudy, 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 more research should be done on this possibility - and that SPS research should receive funding similar to other potential new energy sources. We support research efforts aimed at increasing the efficiency of energy use. But we also support efforts to demonstrate new, environmentally benign energy sources.

We must remember that humans 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 much more attractive future for human civilization than any ground-based energy source; and one that the public will support; and that young people will find challenging and exciting. Furthermore energy from SPS can be readily used in developing countries, as the SPS 2000 project will demonstrate, thereby aiding economic development world-wide. In addition, 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, as happens in almost all countries to day, 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 of SPS 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 the SPS 2000 system 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 US$1 billion, that would be just a small fraction of government subsidies to nuclear energy research, and the same scale as other government satellite and energy research projects. We believe that this would be a good investment, which would be popular with the public. We believe that the "space-future", the vigorous expansion of human activities into space to which this will lead - is much more attractive than a future in which humans are confined to the surface of the Earth, competing over dwindling energy resources. It's more likely to be peaceful; it's more likely to permit adequate economic growth throughout the world; and it will certainly be more fun.

Can anyone doubt that, given the choice, young people would choose a future involving large-scale space development than one confined to Earth? But they must be given the choice. And despite the concept of SPS being proposed nearly 30 years ago, noone has yet demonstrated it. Since it was proposed, hundreds of $ billions have been spent on space activities, and hundreds of $ billions have been spent on nuclear energy research and development. But apart from $20 million during the 1970s in the USA, the total spending on SPS work throughout the world has been no more than a few $ million, at most - and it's almost zero at present. This does not reflect its potential; it does not reflect a rational balance of its potential relative to nuclear energy: and it does not reflect the preferences of the general public.