In recent years the 10 MW, low equatorial orbit SPS pilot plant system design project known as "SPS 2000" has reached a sticking-point: the planned 100% automatic rendezvous and docking of 10 separate payloads and their deployment in orbit to a size of several hectares is impossible to test realistically in the gravitational environment at the Earth's surface. Consequently the system reliability is not sufficiently close to 100% to be considered an acceptable risk. In this context the 2003 decision by ESA and RSA to start operating Soyuz rockets from Kourou in 2007 creates the possibility of a definitive solution to this otherwise intractable problem. Crewed Soyuz flights from Kourou could provide the backup of crewed intervention for trouble-shooting and repairs in the event of problems. This project thus creates a unique need for crewed flight operations from Kourou - a capability which might otherwise remain unused.

The extent to which solar-generated electric power delivered from space will contribute to the future energy economy of the Earth is not known; it will depend on the relative progress made in coming years towards realising the different options for supplying the environmentally benign energy that humans will require during the 21st century. On current understanding of climatic processes, it seems that several tens of Terawatts of electricity supply capacity is required which emits no CO2, as discussed by Hoffert and colleagues [1]. The options for achieving this are quite limited, as reviewed by Hoffert and colleagues in a follow-up paper which is notable as a rare case in which space-based power supply systems are considered alongside terrestrial systems [2]. Which options appear most attractive in a few decades will therefore depend primarily on the results of research in these fields in the coming years. Solar power delivered from space is identified as one important possibility [2], since it is essentially unlimited and available on an almost continuous basis - although it is recognised that in order for its cost to be competitive a major reduction in launch cost is required.

However, delivery of solar-generated power from space to Earth is not an option today. In order to create this option a number of steps need to be taken. One such step is to reduce the cost of launch. The successful sub-orbital flight of "SpaceShipOne" on June 21, at a cost about 1/1,000 that of Alan Shepard's 1961 sub-orbital flight using an expendable rocket, has demonstrated the great potential for launch cost reduction using piloted, reusable vehicles. A second essential step is the development of an orbital pilot plant to act as an operational demonstrator, which is a standard procedure in taking a technology developed in the laboratory towards commercialisation. (Although pilot plants are not normally commercially profitable, participation in such a project can be of considerable commercial value through generating detailed information on many aspects of the system under test, which can enable companies to assess related business opportunities. Companies thereby have an economic incentive to participate in some way.)

The degree of urgency with which the level of CO2 emissions need to be reduced in order to avoid severe climatic changes is still uncertain. However, it is a basic principle of risk management to make timely preparations for possible contingencies; it is therefore desirable to start operating a pilot plant as soon as possible. This would enable electricity industry researchers to perform a wide range of experiments necessary for evaluating space-based solar power systems as a new energy source [3]. Until such a pilot plant is developed and operating experience is accumulated, delivery of power from space will remain at least 20 years in the future, however low launch costs might fall.

Many different ways have been proposed in which space-based solar power might be realised - low orbit systems for local power supply, large-scale geo-stationary satellites generating 10 GW or more, satellite systems constructed partly from non-terrestrial resources, systems sited on the lunar surface, and others. In addition various means of power transmission have been investigated, including different wavelengths of microwave power beaming, laser transmission, and orbiting optical and microwave reflector systems.

All of these alternatives have a common requirement for a pilot plant. However, despite 35 years of research on space solar power, no pilot plant has yet been built, although there has been extensive experimentation on many aspects of the system, including particularly microwave power transmission. Moreover, the failure to build a pilot plant is not for lack of agreement on what form it should take. For example, the largest study over the past few decades, Nasa's "Fresh Look" study published in 1997, stated

"..the non-recurring costs for all of the SPS concepts would be based on flight testing a 10 MW demo version of the particular concept in LEO" [4].

This is very close to the thinking of what came to be known as the "SPS 2000" project, a 10MW pilot plant system which was first announced internationally at the international conference, SPS 91, when a paper introducing the project won the $3,000 "SPS91 Prize" as the best proposal for advancing SPS work [5, 6].

Since then, engineering studies have been performed on all aspects of the system, following the system design guidelines. An equatorial orbit was judged the best candidate for a cost-effective pilot-plant demonstrator in low Earth orbit which is to be used to actually supply power to consumers, since it overflies all the same places on every orbit. The selected altitude of 1100 km is at a local minimum in the orbital debris density. The system is designed to use existing launch systems; to have minimum costs; and to facilitate further evolution through the later addition of new capabilities. The deployment of the satellite structure and solar panels which cover several hectares is to be 100% automated.

A partial listing of publications on the project identified 300 papers and reports as of 1999 [7]. Work has continued since then, with collaborators in more than a dozen countries, and publications have reached some 400. SPS 2000 is thus by far the largest coordinated piece of space solar power-related work conducted in Japan. The project has also received considerable praise from different quarters. For example, in a 2000 report to Nasa on international cooperation in research on space solar power ( SSP), Grey described the project's approach:

"Research to date on SSP has understandably concentrated mainly on its engineering aspects. However, after more than 30 years, this approach has not succeeded in attracting substantial public support, producing results that are of interest to only a narrow group of experts.

The SPS 2000 project took a fundamentally new approach; i.e. to include consideration of social, economic, political, legal, public relations and other non-engineering aspects from the start. This was done by planning to deliver useful energy to willing users on Earth, thereby also creating interest on the part of the terrestrial electricity industry, whose leaders will ultimately decide whether or not to use SSP.

...The project therefore provides a useful and popular service on Earth (albeit only on a small scale) which will be readily visible to the mass communications media and understandable to the general public. Hence SPS 2000 has the potential to win the wide public support that is necessary to obtain further public investment in realising the SSP option for future commercial power generation.

From the outset, the SPS 2000 system was designed as an open-ended system in the hope that other organisations will build other satellites of various designs to deliver additional power supplies to the same rectennas. To do this, they will have to use a common standard, which will evolve from the initial specification. In this way, following the precedent set by other systems, a global technical standard will evolve incrementally from practical operations experience.

..The prospect of participating in the establishment of what is likely to evolve into the global technical standard for microwave power supply from space to Earth should provide an incentive for governments of leading countries to enable their researchers to participate actively by contributing to realization of the SPS 2000 system" [8].

The project has also been recognised by Hoffert and colleagues as a key step for assessing the feasibility of space-based power generally:

"Potentially important for CO2 emission reduction is a demonstration proposed by Japan's Institute of Space and Astronautical Science to beam solar energy to developing nations a few degrees from the equator from a satellite in low equatorial orbit" [2].

The budget of several billion Euros that is required for a demonstrator with capacity of 10 MW using existing expendable launch vehicles is small by comparison with subsidies both to other energy systems and to space technology development in general. To date, however, total funding of research into the feasibility of power supply from space, at some $50 million over 35 years, has been several orders of magnitude less than funding of other energy systems. For example, it is far lower than the $1 trillion granted to nuclear fission, the hundreds of billions of dollars granted to nuclear fusion and fast-breeder research, and even the more than $10 billion granted to terrestrial solar power research. The main reason for this huge discrepancy in the level of government support seems to be because space-based solar power has suffered by falling between different government activities, specifically between "energy policy" and "space policy".

The "SPS 2000" system specification included that the rectennae (rectifying antennae) must lie within 3 degrees of the equator, due to the design of the satellite's power transmitting antenna and the satellite altitude. As a related part of the project, the authors received a series of grants from 1994 through 2003 from the Japanese Ministry of Education, Science, Culture and Sports to visit countries near the equator to research the feasibility of siting rectennae (rectifying antennae) in their territory and using microwave power from space for local use.

The authors met a number of university researchers, government officials and other experts in each country, and were pleased at their positive responses. In particular, each country's conditions are different, and their reasons for interest in participating were different; however, all were interested in participating in the project, and agreed to make one or more sites available. The government representatives welcomed the proposal, and were keen to see the project realised, offering various forms of collaboration in addition to rectenna siting and operation [9]. In all, visits were made to 12 equatorial countries, during which 15 candidate rectenna sites were identified and agreed in principle. As a result of these visits, it became clear that an equatorial SPS pilot plant project could benefit from genuine international partnership between developed and developing countries. In recent months another possible benefit of wider international participation has become apparent.

Work by the engineers designing the SPS 2000 system has led to the assessment that the project's largest risk is the technical risk arising from relying on 100% automatic deployment of the satellite. Since it is not uncommon even today for satellites to suffer a failure in the deployment of an antenna or solar panel, the probability of a problem arising with the automatic deployment of a 200 ton satellite some 300 metres in dimensions, and comprising several different payloads which are to dock autonomously, must be assessed as much higher. Indeed, unless this risk can be reduced very substantially, it seems unlikely that this project could be selected for funding as such.

Possibly the only means of overcoming this problem is to plan for the possibility of human intervention in the deployment process. In 2001 a US partnership with Japan was proposed, whereby collaborative use of the space shuttle, ISS and astronaut participation in the deployment of the satellite would become possible [10]. Although this approach offers the possibility of overcoming the problem of 100% dependence on automatic deployment, it would require assembly in a low, inclined orbit and subsequent raising of the altitude and altering of the orbital inclination in order to reach equatorial orbit. However, the addition of large ion-thrusters to the satellite and the associated orbital operations would greatly complicate the system which was designed specifically to be as simple and low-cost as possible. Recently a more promising approach to overcoming this problem has arisen.

5. ESA/RSA COOPERATION ON SOYUZ LAUNCHES FROM KOUROU

A decision was made by ESA in 2003 to build a new launch pad for the Russian made Soyuz rocket at the ESA launch site in Kourou, in South Guiana from where the first Soyuz flight is planned for 2007 [11]. Although the first launch will be a cargo flight, the new Soyuz launch infrastructure has been designed to ensure that it can be smoothly adapted for human spaceflight, should this be decided upon [11]. (Soyuz rockets have been used for both crewed and uncrewed flights longer than any other spacecraft.)

The launch sites used to date for crewed flights from Russia, USA and China are all too far from the equator to enable existing crew-carrying space vehicles to reach low equatorial orbits. Consequently, the start of Soyuz flights from Kourou will create the possibility, for the first time in more than 40 years of space flight activities, of launching crews into equatorial orbits.

In principle, crews launched from Kourou could provide back-up trouble-shooting capability for the automatic deployment of an SPS pilot plant satellite in low equatorial orbit. Consequently, the new capability being developed at Kourou could resolve the main outstanding technical risk of the "SPS 2000" demonstrator system.

The nominal altitude of 1100 km, if kept as part of the system specification, would require Soyuz crew vehicles to fly significantly higher than they have hitherto. The implications of this for their operation would need to be the subject of detailed system studies. Among other advantages, launching from near the equator will give Soyuz a substantial payload advantage over launching from Baikonur in Kazakhstan. For example, a Soyuz-2 (a new version of the Soyuz) will be able to place up to 3 tonnes into geostationary transfer orbit, as opposed to the 1.7 tonnes that can be launched from Baikonur using the standard Soyuz [11]. In order to carry more propellant, tools or consumables, Soyuz could also fly with 2-person crews. Modifications to the Soyuz vehicle could also be made if necessary, such as the 6-person module reportedly being developed for passenger use.

The task of providing crewed backup to the deployment of several hectares of solar panels and microwave power transmitting antenna panels can be considered essential in order to realise a multi-MW SPS pilot plant in low orbit. Such a project in equatorial orbit would provide a unique requirement for crewed flights from Kourou, for which there is no substitute. It would therefore seem that more detailed analysis of this possibility is desirable. The staff responsible for the SPS 2000 system design would be pleased to collaborate with staff from ESA and RSA in providing appropriate design data, and working on the redesign that would be necessary in order to make the system compatible with crew-tended deployment. Indeed, the overall satellite design might well change significantly in order to fulfil the more complex requirements of such an international collaborative project.

If this approach was found to be technically feasible, the European and Russian space industries would thereby have the opportunity to play a key role in testing the feasibility of power delivery from space to Earth. It is to be hoped that the European and Russian governments would then make a proposal to the Japanese government to collaborate in realising an equatorial pilot plant as an essential step towards assessing this possible new energy source.

Another possible form of international collaboration which could have important benefits and would require significant system design changes is participation by India and China. To date, the SPS 2000 satellite system design specified a phased-array microwave power transmitting antenna from which the beam could reach terrestrial receivers (rectennae) only within 3 degrees of the equator. This limits the countries that could participate; in particular it prevents the siting of rectennas in India and China, although colleagues from both countries have expressed interest in participating [12].

Both of these countries have advanced space capabilities; both have grown into major electricity producers during the 15 years since the start of the SPS 2000 project; and both are due to grow by several hundred percent in coming decades to become the dominant energy-using nations. Timely experience in using solar-generated electric power delivered from space would be the most effective means of enabling these two countries to evaluate the option of space-based solar power for themselves.

It therefore seems desirable to consider altering the current SPS 2000 system design appropriately in order to raise the maximum permissible latitude of the rectennae so as to enable participation by these two countries. Achieving a greater offset angle of the microwave beam from the satellite's power transmitting antenna and/or using a higher altitude orbit could contribute to this. Even if somewhat difficult technically, from the point of view of world energy and environment policy, participation by India and China is extremely desirable, and so worth considerable effort to achieve. It would be a friendly gesture, demonstrating capability for technical leadership from a global perspective, for the Japanese government to invite their respective governments to perform a joint study of their possible participation.

As discussed above, operation of a 10 MW pilot plant in low equatorial orbit is on the critical path to evaluating the potential of space-based solar power systems to supply environmentally clean electric power to the Earth. The largest such project to date is "SPS 2000", which currently faces the daunting challenge of 100% automatic assembly in orbit. However, with cooperation by ESA and RSA in providing crewed intervention by using the new capability to launch Soyuz rockets from Kourour, this problem could be overcome. The start of crewed Soyuz operations from Kourou could therefore be the key step in realising a timely equatorial pilot plant.

Another direction in which international collaboration in the project could be usefullly expanded is to include participation by both India and China. The system redesign that would be necessary to make it suitable for crewed intervention would be a good opportunity to combine with the redesign necessary to enable India and China to participate.

During the authors' visits to Malaysia, it was proposed that an international conference be held on the SPS 2000 project in Kuala Lumpur and Johor Baru [13, 14]. Presentations on the subject of using crewed Soyuz flights from Kourou to overcome the outstanding stumbling block of automatic deployment, and discussion of Indian and Chinese participation would be exciting additions to the programme of such a conference.

1. M Hoffert et al, 1998, " Energy Implications of Future Stabilisation of Atmospheric CO2 Content", Nature, Vol 395, pp 881-884.
2. M Hoffert et al, 2002, " Advanced Technology Paths to Global Climate Stability: Energy for a Greenhouse Planet", Science, Vol 298, pp 981-987.
3. P Collins, R Tomkins & M Nagatomo, 1991, "SPS 2000: A Commercial SPS Test-bed for Electric Utilities", Proceedings of 26th Inter-Society Energy Conversion Engineering Conference, American Nuclear Society, Vol 4, pp 99-104; also at www.spacefuture.com/archive/sps_2000_a_commercial_ sps_testbed_for_electric_utilities.shtml
4. H Feingold et al, 1997, " Space Solar Power: A Fresh Look at the Feasibility of Generating Solar Power in Space for Use on Earth", Nasa Contract no NAS3-26565.
5. M Nagatomo & K Itoh, 1991, "An Evolutionary Satellite Power System for International Demonstration in Developing Nations", Proceedings of SPS91, pp 356-363; also at www.spacefuture.com/archive/ an_evolutionary_satellite_power_system_for_international_demonstration_in_developing_nations.shtml
6. M Nagatomo, S Sasaki & Y Naruo, 1994, "Conceptual study of a solar power satellite, SPS 2000", Proc. ISTS, Paper No. ISTS-94-e-04; also at www.spacefuture.com/archive/conceptual_study_ of_a_solar_power_satellite_sps_2000.shtml
7. S Sasaki (ed), 2001, " Report on Research Results of SPS 2000 Project", ISAS Report No 43, 155 p.
8. J Grey (ed), 31 October 2000, " AIAA Assessement of Nasa Studies of Space Solar Power Concepts: 1. International Cooperation, Report to Marshall Space Flight Center", Nasa Grant NAG8-1619.
9. H Matsuoka, M Nagatomo & P Collins, " Field Research for Solar Power Satellite Energy Receiving Stations", Matsuoka Laboratory Working Papers, Nos 1 - 16, (1994 - 2003).
10. T Rogers, 23 April 2001, " Japan and the United States Should Cooperate in the Conduct of a Large-Scale, Global, Space Solar Power (SSP) Demonstration Program", Space Transportation Association/ Sophron Foundation.
11. ESA, 2003, www.esa.int/SPECIALS/Launchers_ Access_to_Space/SEMQ5P57ESD_0.html
12. P Collins, Y Purwanto & X C Ji, 1998, "Future Demand for Microwave Power from Space in China and Indonesia", IAA paper no IAA-98-IAA.1.3.04; available at: www.spacefuture.com/archive/ future_demand_for_microwave_power_from_space_in_china_and_indonesia.shtml
13. H Matsuoka, M Nagatomo & P Collins, 1998, " Field Research for Solar Power Satellite Energy Receiving Stations: Malaysia", Matsuoka Laboratory Working Paper 9, Teikyo Heisei University.
14. H Matsuoka, M Nagatomo & P Collins, 2002, " Field Research for Solar Power Satellite Energy Receiving Stations: Amazon and Borneo", Matsuoka Laboratory Working Paper 15, Teikyo Heisei University.