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Cost effectiveness requirements for space power stations
,a Astronautica Vol. 6, pp. 1745-1752 Pergamon Press Ltd., 1979. Printed in Great Britain
Cost effectiveness requirements for space power stationst G. K. C. P A R D O E General Technology Systems Limited, Brentford, Middlesex, England Abstract--The concept of converting solar energy in orbital space stations and transmitting electrical power to Earth at radio frequency, is receiving increasing attention both in paper studies and experimental and development work. The projects conceived are large in scale and implications and will demand major resources in their development and deployment. In addition to the technological requirements, the problem of reaching international decisions at political levels to fund and operate such systems will be immense. It will therefore be essential to establish as accurately as possible the basic parameters which will lead to a viable project, particularly with regard to economics. This paper, therefore, examines the requirements which together will determine the appropriate levels of cost effectiveness of space power stations and should assist in establishing critical or sensitive areas which will influence the operational validity of the concepts. The r.f. transmission of electric power to and from, or between, spacecraft may itself have wider implications and is another aspect considered in the paper. In summary, the paper does not seek to introduce new design concepts, but appraises the situation and exposes indicators concerning cost effectiveness.
Introduction SINCE 1968 when first seriously proposed, interests have been deepening in the possibility of augmenting the world's electrical p o w e r supplies towards the beginning of the next century, by the conversion of solar energy in orbit and the transmission of the derived electrical p o w e r at radio f r e q u e n c y to earth by microwave beam. The major centre of activity is undoubtedly the United States of America at this time, although the project if it matures, will be on a macro-international scale, and will involve many nations of the world and certainly influence all. Greater attention to the implications of such systems should, I suggest, have been paid already by many countries of the world and in the E u r o p e a n arena particularly, as the developed countries as well as some of the developing countries, will have serious policy and industrial decisions to make in due course when the concepts begin to crystallize into hardwareorientated activity. A bibliographical search on world wide data related to SPS reveals an impressive number of calculations on different facets, (admittedly some work tending to repeat and cross-refer to others) but in total, much ingenuity and expertise has gone already into conceiving the various project types which are emerging within the original c o n c e p t frame. This, as I say, is predominantly within the United States but more recently Europe, via the E u r o p e a n Space tPaper presented at the XXIXth Congress of the International Astronautical Federation, Dubrovnik, Yugoslavia, 1-8 October 1978. 1745
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Agency, has been giving serious thought to this field of activity, and in the last few months General Technology Systems has been asked by the British Government to study certain aspects of this field in more detail. Against this wealth of information and work from both private as well as public funded study and experimental contracts, I do not intend this paper to be a contribution to design aspects of the systems, nor to be a rigorous analysis of the work done so far. In the framework of this particular symposium concerned with cost reductions, I seek basically to consider some of the factors involved which will have a particular bearing on cost requirements and to expose in a descriptive manner, some of the directions which must be pursued in ensuring that project proposals as they emerge will be sufficiently soundly conceived in order to qualify for a positive political decision to proceed, and within the operational phases, to ensure that the projects do indeed work on a cost effective basis for the benefit of mankind.
Range of concepts considered An interesting number of variations on the basic theme have already emerged in recent years, so that now the field covered by general heading of "space power stations" tends to embrace firstly the two subdivisions between thermal conversion of the solar flux and photovoltaic conversion of flux, to a prime electrical output. Either system then depends on the fundamental technique of conversion to radio frequency and the subsequent transmission at this frequency in a microwave beam to receiving antenna on Earth, ready for reconversion back to electric power in form that can meet domestic and industrial requirements. We now consider however, other variations on the theme, such as the use of the r.f. electrical power transmission (in a parallel to a communication satellite) when used as a power relay satellite between a power station location somewhere in the world, up to the satellite and back to the user area. We must also consider suggestions made for the establishment in orbit of a nuclear power station with its output being beamed down to Earth by the r.f. carriers. Yet another application to be considered is the possible value of feeding power in the other direction--namely from Earth up to a satellite which may require considerable power levels more economically provided by an Earth station. In this case of course we are not discussing contributing to the world energy problems but rather using the part of the derived technology for a specific project purpose. Finally we must also consider what implications there are in satellite-to-satellite r.f. power transmission, in the same way that consideration is being given to satellite communications systems at more modest ends of the power spectrum. Clearly a remarkably wide field of technology, economics, resource utilisation and humanitarian considerations are encompassed by such projects and the extension of technologies, e.g. the use of micro waves for transmission of power, which emerge from them. The range in scale is another interesting factor to be given serious thought; perhaps the most popular size of station in orbit which is talked about, is that in the order of 10GW useful d.c. output at the bus bar. It has been pointed out that 20-25 such stations with this output would provide roughly the
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equivalent electrical demand to that of the total United States at this time. Clearly to make a contribution to the worlds power requirements we must be talking in these orders. This then is the scene to consider. Discussion on cost requirements and implications The two essential macro-questions regarding cost are (I) how much will it cost to develop it, build it, launch it and operate it, and (2) will it be an economic proposition at that time, or in due course and at what cost will SPS power be socially and politically acceptable? We are talking in this project of considerable sums of money with capital outlay on research and development as non-recurring costs measured in billions or tens of billions of dollars and capital costs for units of each SPS, also in orders of tens of billions of dollars. Before getting into the technical discussion, it might be appropriate to spend a few minutes on more general, perhaps even philosophical aspects; I think most people employed in the business of medium or advanced technology would agree that one of the greatest problems with projects of large size is assembling the facts in such a manner that a decision can be taken to commit those sums at the commencement of the project. This is particularly true of a project of a new type (such as the supersonic Concorde, Apollo programme, etc.) where not only is a straight-forward business decision required, but a complex decision by politicians, based on advice from permanent civil servants as well as the business community. The problem of this level of decision-making becomes even more complex where international activities are involved, as indeed they will be on the SPS type projects we are discussing. A sure formula for delay and frustration will be the preparation of a proposal for a single vast commitment of several tens of billions of dollars at the outset of the project. Recognising the lead times involved in implementing the project to the point of gaining return on the investment, politicians have regrettably remarkably short forward vision or interests as it frequently bears more relationship to the timescale of the current government they are serving, and we are faced with the fact that the realization time of such expenditure is indeed several generations of the life of the governments in question and therefore the case must indeed be irrefutable to gain the sort of total support necessary at that level. In the many papers already produced on the SPS subject, it emerges in so many ways that to make forward projections of accuracy in some of the areas concerning costs and performance will be very difficult and therefore the lead time of 15 or 20 years even more difficult to produce the convincing argument which I postulate above will be necessary. The principle of what I am saying is obviously not n e w - - I seek mainly to emphasise the implication of presenting too large a bite of finance and commitment at the outset. I believed it is important to consider how one many minimise this commitment and advance in a phased manner to assist both the protagonists and the deciders to move positively together through a long and difficult programme of work. A phased approach is advocated by various people already for various reasons. On examining the literature however, the motiviation tends to be more
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on establishing the performance as well as cost criteria at each stage in advocating for example a pilot station of 150 kW followed by a more advanced pilot station of say 2mW. I think some wider and deeper thought and consideration should be given to the motivation for the steps and the criteria used to evaluate them prior to moving ahead. To do this I think also one should start earlier in the sequence of the development process. We have several main divisions of technological activity of which two are: (1) the conversion of solar energy into electrical power, and (2) the transmission of electrical power - - S P S to Earth - - E a r t h to Satellites - - E a r t h to space receive/transmission to Earth - - S P S to satellite. It might be useful to consider possible sequences of events in these two divisions. Taking the solar conversion activity first of all, we have of course, at the present time, a current capability in orbit with reasonably high cost and moderate efficiency solar cells of producing several kilowatts of d.c. power. Specifically as a forerunner to later massive SPS systems, work is going ahead in various countries on pilot developments of extensible arrays of considerable size which can be accommodated in a shuttle and carried out into a low orbit. The arrays can then be extended and levels of electrical power in the order of hundreds of kilowatts generated from these. In the first instance these arrays will have the ability to augment the power available from the shuttle itself or the Spacelab experiment module attached within the shuttle, as well to test certain functioning of the array itself. A second aspect of this would be to carry such an array into orbit and leave it there parked ready for later shuttle flights to ascend and plug into the array, thus capitalising on an in-orbit level of power of some sizeable amount without the necessity to carry expensive batteries both in cost and weight into our orbit and back to Earth. Indeed this concept can be extended by carrying a further array up in subsequent shuttles and building up in modular form an even larger array. These arrays can now service more power demanding experiments in the shuttle or the shuttles themselves or could power separating experiments carried up and left in orbit by the shuttle. Let us now consider the implications of such a simple early step; first while the work will be of benefit to SPS development in the years to come, the activity is justified in its own right, in performing a useful function in supplying electrical power to operational craft, but it also is providing the opportunity to test the improved arrays, cells, power conditioning equipment, etc. or even the fabrication of arrays in orbit. This satisfies the first objective I would postulate, namely that the phases of the development work should be worked out as far as possible in such a way that the equipment that is produced and the transportation into orbit and the subsequent use of that equipment is not offset totally against R & D but can appear on the credit side of the total SPS balance sheet in earning its own money by providing useable electrical power, albeit not for
Cost effectiveness requirements for space power stations
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terrestrial domestic consumption! I am suggesting that the broadest possible market research, if that is the word, should be conducted in relation to each possible phase and all possible uses made of the end product emerging from the phase as a subdivision of the main thrust of the development programme towards the SPS achievement later. Continuing this theme therefore, the size of the array may be extended it may be provided with electrical propulsion units carried up by subsequent shuttles and could be then injected slowly into a higher orbit, ultimately to a geostationary orbit where again it is parked and provides a plug-in facility of electrical power for various spacecraft needing it in that location. Each of these stages is also relevant to the power transmission aspects but this will be discussed in the subsequent section. I took as an example, an extensible array of solar cells, but depending on the rate of development of the basic technology, electrical power could be provided for precisely the same end purpose at this stage, by a thermal conversion system if the developers of this system would find it useful, as I believe they would, to have a very small pilot plant available for such purpose. One recalls the "sunflower" project of many years ago which moved even then to quite a successful stage of development and something similar or larger could well emerge from the thermal conversion protagonists. Whether thermal or photovoltaic therefore, we now have several stages each either paying for itself or certainly providing an end use. The next step would then certainly be in terms of generating the power, to extend either the array size or the thermal conversion system to levels of say, 150 kW to repeat that example, and we now have a situation where possibly the power levels available in orbit would exceed the useful levels that could be "sold" but would be now associated with the pilot demonstrations related to the SPS project. Now that may appear to be the position at this time, But this is still several years away and I would strongly recommend in order to minimise the outgoing costs and to put something on the credit side of the balance sheets as I have said above, a major attempt is made ot explore in what other ways electrical power generated by such an activity might be useful. The next step could then be the increase of size to a 2 MW array or thermal conversion system and still at this time some studies to date suggest the insertion of the appropriate equipment is commensurate with the currently conceived shuttle operation--even with an up-dated shuttle--but without the further vast capital commitment by that time of a larger payload logistic support vehicle. It would be an attractive thought to explore whether the 2 MW unit in orbit (with an r.f. output after conversion at ground level something in excess of 1 MW) could be put to good use by feeding local requirement in some remote part of the Earth. However, from the considerable amount of study work which has been conducted already, one factor which emerges clearly is that in order to achieve economic operations, it is absolutely necessary to work on a massive scale and minimum cost on launching and fabricating the stations. The 2 MW station, useful as its output would be, would appear to be way below the threshold of an economic operation and therefore unless careful consideration and ingenuity in
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the coming years proves otherwise, it may be that it will not prove possible to multiply this size of unit for the supply of power to remote locations on Earth. By the time therefore, the 2 MW pilot, if that is indeed what is chosen, has done its task, the economics become more visible, the logistics and operational methods more clear cut, and the numbers a little more certain. It is at this point that a major step-function in expenditure and commitment clearly will emerge since to go beyond this point, not only will the full research and development costs be incurred for a multi-gagawatt output station, but also will the commitment arise for development of the larger space transport vehicle with the payload capability currently postulated in the order of 500 tons per shot. In my opinion this represents the most critical and most sensitive point in the whole operation, which we will come back to after considering the parallel activities regarding electrical power transmission. Going back in time to the early steps suggested above in the development of the power conversion and generation work, the idea of a small unfurlable array or thermal system for augmenting the power of the shuttle and Spacelab, appears to find no parallel when we address outselves to the question of the r.f. power transmission technology. It is of interest that the modular design of the MW transmission-receiving system does not require a step-by-step R & D approach in terms of power transmitted. The step-by-step programme will, presumable, be based on the needs of developing the technology. A 10GW station then simply uses N such developed modules where N is a very large number. Certainly, the technology can and must be examined on an experimental and development basis at an early time, just as early terrestrial work has taken place already, and it could be that in Spacelab the large arrays which will produce several kilowatts of power will have this converted into radio frequency and transmitted to an appropriately experimental but still nevertheless small receiver on Earth. It would be reasonable to expect also that experiments would be conducted in transmitting the power from that array in low orbit to other satellites, perhaps to geostationary orbit or beyond. It is an interesting thought, might it be cheaper to inject and assemble a large array in low orbit and transmit electric power to a high orbit satellite which demands considerable levels, rather than go to the cost of taking the array up to the higher orbit? If electrical propulsion is used and time is not at a premium, then it would seem a slow spiralling transfer orbit would undoubtedly be a cheaper way of doing it. The thought remains however, that there could be special uses, perhaps in the military field, for having a major source of transmitable electrical power in low orbit if various satellites in the higher orbits could have their batteries charged or use, in real time, power transmitted from the lower positions. Similarly, in the next stage of the postulated sequence of steps for the solar power generation in orbit, when a large modular array is assembled in geostationary orbit the time will come, perhaps before the 150kW pilot plan for conducting experiments over this transmission range with stations on Earth. However, the point remains that these are part of the evolution programme and it does appear that unlike the use of arrays or thermal conversion systems, the r.f. transmission has a dedicated purpose in life, namely to transmit very high
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levels of electrical power from orbit to Earth as and when the SPS concept is validated. Prior to that time, it is difficult to see how to gain revenue from a system in operational u s e - - e x c e p t possible special purpose use as outlined on a satellite-to-satellite basis in the paragraph above. Of course, much will depend on how the technique of r.f. transmission of electrical power evolves; if the concept stays as at the present time, with large modular array of transmitting and receiving antennae, then the logistics escalate as the size and output of the system escalates. There is, however, a considerable amount of time in the programme to go through the essential early steps and with the acceleration at the moment in the pace of technology, may well by that other more research orientated methods of electrical power transmission may emerge in time for these to be incorporated in spacecraft with lower size of transmitting and receiving antennae. If in fact it proves possible to transmit electric power in a manner analogous to a laser beam at the present time, then the range possibility opens up and in the same manner that a beam of laser light can be located on the Moon, a laser beam of transmitted power could possibly be locked on to a spacecraft for close Earth missions or even deeper planetary missions. This of course must be speculative at this time, but until or unless such developments happened, it would seem more difficult to obtain a revenue entry in the accounts from the r.f. transmission side until the major stations were brought into operation. We come back once more to scale; in recent years, value engineering--the technique of designing a component or product in such a way that it can be made in production at the lowest possible cost--meets a formidable challenge in the solar power station. Huge structures and arrays and activities are involved and the need to develop novel engineering methods of low cost, light weight, rapid fabrication of beams and associated structures extensively by automatic processes and on an unprecedented scale for space. Already exciting advances are being made in the use of plastics in this field and while the opportunity exists in space, it would seem highly likely that many of the new design concepts emerging from this cost requirement could find their way into the terrestrial fields, as so many other space products have done previously. It is not appropriate in this paper to go into the details of technology, no doubt other papers given in this Symposium will expose some of the developments taking place. It is certainly appropriate however, in this paper dealing with cost requirements and exploring the reduction of cost, to re-emphasise once more the utmost importance of attacking this problem with ingenuity and the most modern tools of research. General comments
No one expects in the complexities of modern industrial life to wave a wand and achieve immediate cost reduction. The achievement will depend on the most professional approach to determining the requirements of systems and their cost implications. It is also to be noted that the SPS projects will be international in scale, and there will undoubtedly be an international industrial involvement in the development and manufacture--as well as final operations. Experience suggests that achievement of minimum cost and maximum efficiency on a shared
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international activity demands even more rigorous planning and control of the most detailed parts of the work. Bearing in mind the mass production of structures in space on an unprecedented scale, the integration of participants must be total. This paper has sought to discuss in very general terms some of these problems, but in particular to emphasise the massive decision making problems which will emerge, commensurate in size with the problem of resources which will need to be assembled to achieve the project in question. The step by step phased expansion approach is fully supported and the need to consider each step as a total system in itself is emphasised in order to identify possible, and indeed to plan, the maximum early benefits and associated revenue from the creation of the thermal or photovoltaic conversion systems, as well as the maximum benefit from the r.f. transmission systems. I have not gone into detailed consideration of other more mundane and terrestrial applications of electrical power transmission of radio frequency, but this is achievable and clearly many opportunities will emerge for this, even though in more orthodox field of transmission it would seem this technique cannot at the present time compare with contemporary power lines, be they above or below ground. Again, however, technology accelerates, and if in fact wider applications on earth could emerge for the r.f. transmission feature, then some of the early decision making processes in the sequence I have postulated above might be easier to make. Whatever the outcome, a total systems analysis is advocated in good time at each step.
Cost effectiveness requirements for space power stationst G. K. C. P A R D O E General Technology Systems Limited, Brentford, Middlesex, England Abstract--The concept of converting solar energy in orbital space stations and transmitting electrical power to Earth at radio frequency, is receiving increasing attention both in paper studies and experimental and development work. The projects conceived are large in scale and implications and will demand major resources in their development and deployment. In addition to the technological requirements, the problem of reaching international decisions at political levels to fund and operate such systems will be immense. It will therefore be essential to establish as accurately as possible the basic parameters which will lead to a viable project, particularly with regard to economics. This paper, therefore, examines the requirements which together will determine the appropriate levels of cost effectiveness of space power stations and should assist in establishing critical or sensitive areas which will influence the operational validity of the concepts. The r.f. transmission of electric power to and from, or between, spacecraft may itself have wider implications and is another aspect considered in the paper. In summary, the paper does not seek to introduce new design concepts, but appraises the situation and exposes indicators concerning cost effectiveness.
Introduction SINCE 1968 when first seriously proposed, interests have been deepening in the possibility of augmenting the world's electrical p o w e r supplies towards the beginning of the next century, by the conversion of solar energy in orbit and the transmission of the derived electrical p o w e r at radio f r e q u e n c y to earth by microwave beam. The major centre of activity is undoubtedly the United States of America at this time, although the project if it matures, will be on a macro-international scale, and will involve many nations of the world and certainly influence all. Greater attention to the implications of such systems should, I suggest, have been paid already by many countries of the world and in the E u r o p e a n arena particularly, as the developed countries as well as some of the developing countries, will have serious policy and industrial decisions to make in due course when the concepts begin to crystallize into hardwareorientated activity. A bibliographical search on world wide data related to SPS reveals an impressive number of calculations on different facets, (admittedly some work tending to repeat and cross-refer to others) but in total, much ingenuity and expertise has gone already into conceiving the various project types which are emerging within the original c o n c e p t frame. This, as I say, is predominantly within the United States but more recently Europe, via the E u r o p e a n Space tPaper presented at the XXIXth Congress of the International Astronautical Federation, Dubrovnik, Yugoslavia, 1-8 October 1978. 1745
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Agency, has been giving serious thought to this field of activity, and in the last few months General Technology Systems has been asked by the British Government to study certain aspects of this field in more detail. Against this wealth of information and work from both private as well as public funded study and experimental contracts, I do not intend this paper to be a contribution to design aspects of the systems, nor to be a rigorous analysis of the work done so far. In the framework of this particular symposium concerned with cost reductions, I seek basically to consider some of the factors involved which will have a particular bearing on cost requirements and to expose in a descriptive manner, some of the directions which must be pursued in ensuring that project proposals as they emerge will be sufficiently soundly conceived in order to qualify for a positive political decision to proceed, and within the operational phases, to ensure that the projects do indeed work on a cost effective basis for the benefit of mankind.
Range of concepts considered An interesting number of variations on the basic theme have already emerged in recent years, so that now the field covered by general heading of "space power stations" tends to embrace firstly the two subdivisions between thermal conversion of the solar flux and photovoltaic conversion of flux, to a prime electrical output. Either system then depends on the fundamental technique of conversion to radio frequency and the subsequent transmission at this frequency in a microwave beam to receiving antenna on Earth, ready for reconversion back to electric power in form that can meet domestic and industrial requirements. We now consider however, other variations on the theme, such as the use of the r.f. electrical power transmission (in a parallel to a communication satellite) when used as a power relay satellite between a power station location somewhere in the world, up to the satellite and back to the user area. We must also consider suggestions made for the establishment in orbit of a nuclear power station with its output being beamed down to Earth by the r.f. carriers. Yet another application to be considered is the possible value of feeding power in the other direction--namely from Earth up to a satellite which may require considerable power levels more economically provided by an Earth station. In this case of course we are not discussing contributing to the world energy problems but rather using the part of the derived technology for a specific project purpose. Finally we must also consider what implications there are in satellite-to-satellite r.f. power transmission, in the same way that consideration is being given to satellite communications systems at more modest ends of the power spectrum. Clearly a remarkably wide field of technology, economics, resource utilisation and humanitarian considerations are encompassed by such projects and the extension of technologies, e.g. the use of micro waves for transmission of power, which emerge from them. The range in scale is another interesting factor to be given serious thought; perhaps the most popular size of station in orbit which is talked about, is that in the order of 10GW useful d.c. output at the bus bar. It has been pointed out that 20-25 such stations with this output would provide roughly the
Cost e~ectiveness requirements for space power stations
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equivalent electrical demand to that of the total United States at this time. Clearly to make a contribution to the worlds power requirements we must be talking in these orders. This then is the scene to consider. Discussion on cost requirements and implications The two essential macro-questions regarding cost are (I) how much will it cost to develop it, build it, launch it and operate it, and (2) will it be an economic proposition at that time, or in due course and at what cost will SPS power be socially and politically acceptable? We are talking in this project of considerable sums of money with capital outlay on research and development as non-recurring costs measured in billions or tens of billions of dollars and capital costs for units of each SPS, also in orders of tens of billions of dollars. Before getting into the technical discussion, it might be appropriate to spend a few minutes on more general, perhaps even philosophical aspects; I think most people employed in the business of medium or advanced technology would agree that one of the greatest problems with projects of large size is assembling the facts in such a manner that a decision can be taken to commit those sums at the commencement of the project. This is particularly true of a project of a new type (such as the supersonic Concorde, Apollo programme, etc.) where not only is a straight-forward business decision required, but a complex decision by politicians, based on advice from permanent civil servants as well as the business community. The problem of this level of decision-making becomes even more complex where international activities are involved, as indeed they will be on the SPS type projects we are discussing. A sure formula for delay and frustration will be the preparation of a proposal for a single vast commitment of several tens of billions of dollars at the outset of the project. Recognising the lead times involved in implementing the project to the point of gaining return on the investment, politicians have regrettably remarkably short forward vision or interests as it frequently bears more relationship to the timescale of the current government they are serving, and we are faced with the fact that the realization time of such expenditure is indeed several generations of the life of the governments in question and therefore the case must indeed be irrefutable to gain the sort of total support necessary at that level. In the many papers already produced on the SPS subject, it emerges in so many ways that to make forward projections of accuracy in some of the areas concerning costs and performance will be very difficult and therefore the lead time of 15 or 20 years even more difficult to produce the convincing argument which I postulate above will be necessary. The principle of what I am saying is obviously not n e w - - I seek mainly to emphasise the implication of presenting too large a bite of finance and commitment at the outset. I believed it is important to consider how one many minimise this commitment and advance in a phased manner to assist both the protagonists and the deciders to move positively together through a long and difficult programme of work. A phased approach is advocated by various people already for various reasons. On examining the literature however, the motiviation tends to be more
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on establishing the performance as well as cost criteria at each stage in advocating for example a pilot station of 150 kW followed by a more advanced pilot station of say 2mW. I think some wider and deeper thought and consideration should be given to the motivation for the steps and the criteria used to evaluate them prior to moving ahead. To do this I think also one should start earlier in the sequence of the development process. We have several main divisions of technological activity of which two are: (1) the conversion of solar energy into electrical power, and (2) the transmission of electrical power - - S P S to Earth - - E a r t h to Satellites - - E a r t h to space receive/transmission to Earth - - S P S to satellite. It might be useful to consider possible sequences of events in these two divisions. Taking the solar conversion activity first of all, we have of course, at the present time, a current capability in orbit with reasonably high cost and moderate efficiency solar cells of producing several kilowatts of d.c. power. Specifically as a forerunner to later massive SPS systems, work is going ahead in various countries on pilot developments of extensible arrays of considerable size which can be accommodated in a shuttle and carried out into a low orbit. The arrays can then be extended and levels of electrical power in the order of hundreds of kilowatts generated from these. In the first instance these arrays will have the ability to augment the power available from the shuttle itself or the Spacelab experiment module attached within the shuttle, as well to test certain functioning of the array itself. A second aspect of this would be to carry such an array into orbit and leave it there parked ready for later shuttle flights to ascend and plug into the array, thus capitalising on an in-orbit level of power of some sizeable amount without the necessity to carry expensive batteries both in cost and weight into our orbit and back to Earth. Indeed this concept can be extended by carrying a further array up in subsequent shuttles and building up in modular form an even larger array. These arrays can now service more power demanding experiments in the shuttle or the shuttles themselves or could power separating experiments carried up and left in orbit by the shuttle. Let us now consider the implications of such a simple early step; first while the work will be of benefit to SPS development in the years to come, the activity is justified in its own right, in performing a useful function in supplying electrical power to operational craft, but it also is providing the opportunity to test the improved arrays, cells, power conditioning equipment, etc. or even the fabrication of arrays in orbit. This satisfies the first objective I would postulate, namely that the phases of the development work should be worked out as far as possible in such a way that the equipment that is produced and the transportation into orbit and the subsequent use of that equipment is not offset totally against R & D but can appear on the credit side of the total SPS balance sheet in earning its own money by providing useable electrical power, albeit not for
Cost effectiveness requirements for space power stations
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terrestrial domestic consumption! I am suggesting that the broadest possible market research, if that is the word, should be conducted in relation to each possible phase and all possible uses made of the end product emerging from the phase as a subdivision of the main thrust of the development programme towards the SPS achievement later. Continuing this theme therefore, the size of the array may be extended it may be provided with electrical propulsion units carried up by subsequent shuttles and could be then injected slowly into a higher orbit, ultimately to a geostationary orbit where again it is parked and provides a plug-in facility of electrical power for various spacecraft needing it in that location. Each of these stages is also relevant to the power transmission aspects but this will be discussed in the subsequent section. I took as an example, an extensible array of solar cells, but depending on the rate of development of the basic technology, electrical power could be provided for precisely the same end purpose at this stage, by a thermal conversion system if the developers of this system would find it useful, as I believe they would, to have a very small pilot plant available for such purpose. One recalls the "sunflower" project of many years ago which moved even then to quite a successful stage of development and something similar or larger could well emerge from the thermal conversion protagonists. Whether thermal or photovoltaic therefore, we now have several stages each either paying for itself or certainly providing an end use. The next step would then certainly be in terms of generating the power, to extend either the array size or the thermal conversion system to levels of say, 150 kW to repeat that example, and we now have a situation where possibly the power levels available in orbit would exceed the useful levels that could be "sold" but would be now associated with the pilot demonstrations related to the SPS project. Now that may appear to be the position at this time, But this is still several years away and I would strongly recommend in order to minimise the outgoing costs and to put something on the credit side of the balance sheets as I have said above, a major attempt is made ot explore in what other ways electrical power generated by such an activity might be useful. The next step could then be the increase of size to a 2 MW array or thermal conversion system and still at this time some studies to date suggest the insertion of the appropriate equipment is commensurate with the currently conceived shuttle operation--even with an up-dated shuttle--but without the further vast capital commitment by that time of a larger payload logistic support vehicle. It would be an attractive thought to explore whether the 2 MW unit in orbit (with an r.f. output after conversion at ground level something in excess of 1 MW) could be put to good use by feeding local requirement in some remote part of the Earth. However, from the considerable amount of study work which has been conducted already, one factor which emerges clearly is that in order to achieve economic operations, it is absolutely necessary to work on a massive scale and minimum cost on launching and fabricating the stations. The 2 MW station, useful as its output would be, would appear to be way below the threshold of an economic operation and therefore unless careful consideration and ingenuity in
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the coming years proves otherwise, it may be that it will not prove possible to multiply this size of unit for the supply of power to remote locations on Earth. By the time therefore, the 2 MW pilot, if that is indeed what is chosen, has done its task, the economics become more visible, the logistics and operational methods more clear cut, and the numbers a little more certain. It is at this point that a major step-function in expenditure and commitment clearly will emerge since to go beyond this point, not only will the full research and development costs be incurred for a multi-gagawatt output station, but also will the commitment arise for development of the larger space transport vehicle with the payload capability currently postulated in the order of 500 tons per shot. In my opinion this represents the most critical and most sensitive point in the whole operation, which we will come back to after considering the parallel activities regarding electrical power transmission. Going back in time to the early steps suggested above in the development of the power conversion and generation work, the idea of a small unfurlable array or thermal system for augmenting the power of the shuttle and Spacelab, appears to find no parallel when we address outselves to the question of the r.f. power transmission technology. It is of interest that the modular design of the MW transmission-receiving system does not require a step-by-step R & D approach in terms of power transmitted. The step-by-step programme will, presumable, be based on the needs of developing the technology. A 10GW station then simply uses N such developed modules where N is a very large number. Certainly, the technology can and must be examined on an experimental and development basis at an early time, just as early terrestrial work has taken place already, and it could be that in Spacelab the large arrays which will produce several kilowatts of power will have this converted into radio frequency and transmitted to an appropriately experimental but still nevertheless small receiver on Earth. It would be reasonable to expect also that experiments would be conducted in transmitting the power from that array in low orbit to other satellites, perhaps to geostationary orbit or beyond. It is an interesting thought, might it be cheaper to inject and assemble a large array in low orbit and transmit electric power to a high orbit satellite which demands considerable levels, rather than go to the cost of taking the array up to the higher orbit? If electrical propulsion is used and time is not at a premium, then it would seem a slow spiralling transfer orbit would undoubtedly be a cheaper way of doing it. The thought remains however, that there could be special uses, perhaps in the military field, for having a major source of transmitable electrical power in low orbit if various satellites in the higher orbits could have their batteries charged or use, in real time, power transmitted from the lower positions. Similarly, in the next stage of the postulated sequence of steps for the solar power generation in orbit, when a large modular array is assembled in geostationary orbit the time will come, perhaps before the 150kW pilot plan for conducting experiments over this transmission range with stations on Earth. However, the point remains that these are part of the evolution programme and it does appear that unlike the use of arrays or thermal conversion systems, the r.f. transmission has a dedicated purpose in life, namely to transmit very high
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levels of electrical power from orbit to Earth as and when the SPS concept is validated. Prior to that time, it is difficult to see how to gain revenue from a system in operational u s e - - e x c e p t possible special purpose use as outlined on a satellite-to-satellite basis in the paragraph above. Of course, much will depend on how the technique of r.f. transmission of electrical power evolves; if the concept stays as at the present time, with large modular array of transmitting and receiving antennae, then the logistics escalate as the size and output of the system escalates. There is, however, a considerable amount of time in the programme to go through the essential early steps and with the acceleration at the moment in the pace of technology, may well by that other more research orientated methods of electrical power transmission may emerge in time for these to be incorporated in spacecraft with lower size of transmitting and receiving antennae. If in fact it proves possible to transmit electric power in a manner analogous to a laser beam at the present time, then the range possibility opens up and in the same manner that a beam of laser light can be located on the Moon, a laser beam of transmitted power could possibly be locked on to a spacecraft for close Earth missions or even deeper planetary missions. This of course must be speculative at this time, but until or unless such developments happened, it would seem more difficult to obtain a revenue entry in the accounts from the r.f. transmission side until the major stations were brought into operation. We come back once more to scale; in recent years, value engineering--the technique of designing a component or product in such a way that it can be made in production at the lowest possible cost--meets a formidable challenge in the solar power station. Huge structures and arrays and activities are involved and the need to develop novel engineering methods of low cost, light weight, rapid fabrication of beams and associated structures extensively by automatic processes and on an unprecedented scale for space. Already exciting advances are being made in the use of plastics in this field and while the opportunity exists in space, it would seem highly likely that many of the new design concepts emerging from this cost requirement could find their way into the terrestrial fields, as so many other space products have done previously. It is not appropriate in this paper to go into the details of technology, no doubt other papers given in this Symposium will expose some of the developments taking place. It is certainly appropriate however, in this paper dealing with cost requirements and exploring the reduction of cost, to re-emphasise once more the utmost importance of attacking this problem with ingenuity and the most modern tools of research. General comments
No one expects in the complexities of modern industrial life to wave a wand and achieve immediate cost reduction. The achievement will depend on the most professional approach to determining the requirements of systems and their cost implications. It is also to be noted that the SPS projects will be international in scale, and there will undoubtedly be an international industrial involvement in the development and manufacture--as well as final operations. Experience suggests that achievement of minimum cost and maximum efficiency on a shared
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international activity demands even more rigorous planning and control of the most detailed parts of the work. Bearing in mind the mass production of structures in space on an unprecedented scale, the integration of participants must be total. This paper has sought to discuss in very general terms some of these problems, but in particular to emphasise the massive decision making problems which will emerge, commensurate in size with the problem of resources which will need to be assembled to achieve the project in question. The step by step phased expansion approach is fully supported and the need to consider each step as a total system in itself is emphasised in order to identify possible, and indeed to plan, the maximum early benefits and associated revenue from the creation of the thermal or photovoltaic conversion systems, as well as the maximum benefit from the r.f. transmission systems. I have not gone into detailed consideration of other more mundane and terrestrial applications of electrical power transmission of radio frequency, but this is achievable and clearly many opportunities will emerge for this, even though in more orthodox field of transmission it would seem this technique cannot at the present time compare with contemporary power lines, be they above or below ground. Again, however, technology accelerates, and if in fact wider applications on earth could emerge for the r.f. transmission feature, then some of the early decision making processes in the sequence I have postulated above might be easier to make. Whatever the outcome, a total systems analysis is advocated in good time at each step.