Space Power Resources, Manufacturing and Development Volume 11 Number 1 1992
SPACE POWER Published under the auspices of the Council for Social and Economic Studies EDITOR Andrew Hall Cutler, NASA Space Engineering Center, The University of Arizona ASSOCIATE EDITORS Roger A. Binot, European Space Agency, The Netherlands Eleanor A. Blakely, Lawrence Berkeley Laboratory, USA Richard Boudreault, Consultant, Montreal, Canada Lars Broman, SERC, Sweden Gay Canough, Extraterrestrial Materials, Inc., USA Lucien Deschamps, Paris, France Ben Finney, University of Hawaii, USA Josef Gitelson, Academy of Sciences, USSR Peter Glaser, Arthur D. Little, Inc., USA Owen Gwynn, Mars Center for Exploration, Moffet Field CA. Praveen K. Jain, Northern Telecomm, Ottawa, Ont., Canada Dieter Kassing, ESTEC, The Netherlands Mikhail Ya. Marov, Academy of Sciences, Moscow, Russia Gregg Maryniak, Space Studies Institute, USA Michael Mautner, University of Canterbury, New Zealand Makoto Nagatomo, ISAS, Japan Mark Nelson, Institute of Ecotechnics, USA John R. Page, University of New South Wales, Australia Geoffrey Pardoe, Brunel Science Park, UK Gillian Pierce, Oxford University, UK Vladimir Prisnyakov, Dniepropetrovsk State University Tanya Sienko, NASDA, Tsukuba, Japan Ray A. Williamson, OTA/US Congress, USA Space Power: Resources, Manufacturing and Development is a quarterly, international journal for the presentation, discussion and analysis of advanced concepts, initial treatments and groundbreaking basic research on the technical, economic and societal aspects of: large-scale spaced- based solar power, space resource utilization, space manufacturing, space colonization, and other areas related to the development and use of space for the benefit of humanity. Papers should be of general and lasting interest and should be written so as to make them accessible to technically educated professionals who may not have worked in the specific area discussed in the paper. Editorial and opinion pieces of approximately one journal page in length will occasionally be considered if they are well argued and pertinent to the content of the journal. Submissions should represent the original work of the authors and should not have appeared elsewhere in substantially the same form. Proposals for review papers are encouraged and will be considered by the Editor on an individual basis. Editorial Correspondence: Dr. Andrew Hall Cutler can be reached by telephone at (602) 322- 2997, by Facsimile at (602) 326-0938 and by mail at 4717 East Fort Lowell, Tucson, AZ 85712, USA. Dr. Cutler should be consulted to discuss the appropriateness of a given paper or topic for publication in the journal, or to submit papers to it. Questions and suggestions about editorial policy, scope and criteria should initially be directed to him, although they may be passed on to an Associate Editor. Details concerning the preparation and submission of manuscripts can be found on the inside back cover of each issue. Business correspondence including orders and remittances for subscriptions, advertisements, back numbers and offprints, should be addressed to the publisher: The Council for Social and Economic Studies, 6861 Elm Street, Suite 4H. McLean, Virginia 22101. The journal is published in four issues which constitute one volume. An annual index and title-page is bound in the December issue. ISSN 0883-6272 © 1992, SUNSAT Energy Council
SPACE POWER Volume 11, Number 1, 1992 Stephen L. Gillett & David L. Kuck. Extraterrestrial Resources: Implications From Terrestrial Experience 3 Raymond S. Leonard. The Environmental Benefits of Solar Power Satellites^ 17 William C. Brown. Experimental Radiation Cooled Magnetrons for Space Uset 27 Roger H. Bezdek & Robert M. Wendling. Impact of the Space Program on the U.S. Economy: National and State Analyses 43 V.A. Vanke, A.A. Zaporozhets & A. V. Rachnikov. Antenna Synthesis for the SPS Microwave Power Transmission System! 67 A.A. Zaporozhets. Illumination Tapers Synthesis for Adaptive Microwave Power Transmission Systems with Variable Distance Between the Antennas 81 Erratum to table of contents of Vol. 10 (3/4). All papers in the previous issue save those by Landis and by Potter & Kadiramangalam were presented at Power from Space ’91 in Gif-Sur-Yvette in August 1991. t Also presented at Power from Space ‘91, held in Gif-Sur-Yvette, France, August 1991.
Extraterrestrial Resources: Implications From Terrestrial Experience STEPHEN L. GILLETT & DAVID L. KUCK SUMMARY Terrestrial mining experience indicates that the overwhelming criterion for a potentially economic deposit is its recoverable concentration of the desired mineral or element. Recovery can be based on contrast in physical and/or chemical properties, but processes based on physical properties are typically less expensive. As several of these processes are usually used in sequence, they have a profound effect on extraction costs. These criteria will also apply to extraterrestrial resources. Although the extreme cost of access to space makes even ordinary materials extremely valuable, this inaccessibility also makes capital and maintenance coSts extremely high. The following four development stages will apply, especially with the additional unknowns of an extraterrestrial environment: (1) Exploration for the highest grade of the mineral or element desired. Because the extraction plant must be simple, cheap, and rugged to minimize capital and maintenance costs, high grade is extremely important. (2) Laboratory testing of various physical and/or chemical separation techniques on the possible ore to determine if the material can indeed be recovered economically. (3) A pilot plant test, in which a large sample is dug from the deposit to determine excavation rates, power requirements, and equipment wear, and then run through a pilot mill. Pilot plant testing must be carried out at increasing scales, but several trials are generally necessary at each scale before the size of operations can be increased. Moreover, pilot testing is necessary for each new mineral deposit. (4) Last is the full-scale mine and plant start-up. New problems invariably occur at this point, but they can be kept to a minimum if the pilot plant tests were realistic. If such a development plan is followed rigorously, major cost overruns, with their potentially disastrous effects on resource development, may be avoided. Introduction The overwhelming criterion of a potentially economic deposit is its economically recoverable concentration of the desired mineral or element (e.g., Gillett, 1991). This criterion stems from the difficulty of separating elements, due to the compositional complexity and heterogeneity of natural materials, which seems Department of Geology, Mackay Schools of Mines, University of Nevada, Reno, NV 89557. Geological & Mining Consultant, P.O. Box 369, Oracle, AZ 85623.
largely underappreciated in many extraterrestrial resource scenarios. Although it has been stated that the extreme cost of access to space makes even ordinary materials in space "as valuable as gold," this inaccessibility is a two-edged sword: it also makes capital and maintenance costs extremely high - and such costs - for a mine are high even in the best of circumstances. In the authors’ opinion, many of the scenarios advanced for the development of extraterrestrial resources do not give proper regard to mining experience on Earth. Taking into account the experience of handling natural materials on the Earth, although it will not guarantee the success of extraterrestrial resource extraction, should at least increase its chances of success greatly. In this paper, we will first sketch out the vagaries of natural materials, which make them difficult to deal with, and then describe briefly the approaches that have been found to work in mine development on the Earth. The Complexity of Natural Materials Compositional complexity. Virtually all natural materials, including rocks and the debris derived from them, are compositionally complex. High-purity material is exceedingly unusual even after the early stages of concentrating or smelting an ore mineral. Rocks and rock debris are furthermore not just mechanical mixtures, but chemically complex as well. Rocks are made of minerals, which are chemically distinct phases that nonetheless typically vary - sometimes substantially - in composition. Most minerals are based on oxygen as the anion, with cations of metallic elements fitted in the interstices between the oxygen atoms. (Anions are much larger than cations, of course, due to the smaller effective electric charge of their nuclei.) A great many minerals are silicates, which are based on a tetrahedron of four O'2 anions tightly bound to a small Si+4 cation; in turn, these tetrahedra can occur in isolation, or share vertices to form complex ring, chain, and sheet structures, or even form three-dimensional networks. To maintain charge balance, other cations fit into interstices between the oxygens in the silicate framework. Other minerals are true oxides, in which the cations fit among close-packed oxygen atoms without clear association into radicals such as the SiO4 4 tetrahedron. Finally, although sulfide minerals are insignificant volumetrically in the crust of both the Earth and Moon, they are extremely significant economically, because their physical properties make them easily separable from silicates and oxides, and are as compositionally varied as silicates and oxides. Sulfides are usually non-polar compounds whereas silicates and oxides are polar compounds. Compositional variation in minerals comes about because the cation site is typically not sensitive to anything but the size and charge of the contained cation. Thus, if two cations have similar size and charge, they can substitute for each other. Mg++ and Fe++, for example, are nearly the same size and thus replace one another freely in most minerals, as in olivine, a silicate mineral whose composition is
(Mg, Fe)2, SiO4. Mn++, Ni++, Co++ and others can also substitute for these elements in olivine, at least to some degree. In a given mineral, the exact distribution of the elements it contains depends on the composition of the melt or solution from which it crystallized, the oxygen fugacity, the sulfur fugacity, the temperature, the pressure, and so on. From the above, it can be seen that separating elements from natural materials falls into two parts: first, separating the minerals in the rock from each other (physical separation), and second, separating the desired element(s) from the ore mineral (chemical separation). It is difficult to underestimate the difficulty of both physical and chemical separations. Physical separation, although comparatively cheap, is generally inefficient because different minerals cannot be broken apart exactly at their mutual grain boundaries. Minerals are commonly intimately intergrown in the rock simply by virtue of the way they crystallized, and crushing the rock invariably generates particles in which pieces of one mineral grain are attached to another. This has been encountered, for example, in crushing and grinding eucritic meteorite simulants of lunar materials, which resulted in low grade ilmenite concentrates. To some degree such separations can be improved by finer grinding. However, if the crushed grain size is too small, surface effects begin to dominate the physical properties of the particle so that simple physical separations may no longer work. For example, large grains of gold can be separated from silicate grains by extremely primitive means (e.g., panning), because of their much greater density. Such density separations do not work, however, with micron-sized gold. On the Moon, an example of such a problem is in separating native (metallic) iron from raw lunar regolith. As pointed out by many people, the properties of iron and the background silicates differ greatly, and it should be possibly by relatively simple means to separate the iron, even though it makes up only about 0.5% of the regolith. However, much of this iron is present as extremely fine grains dispersed in glass generated by meteorite impact and separating such grains from the glass will be extremely difficult. Chemical separations are nearly always more expensive than physical separations. First, they are typically more energy intensive, because they commonly involve heating or (in the case of electrolysis) electricity. Second, they also nearly always involve a physical separation step, too. Chemical separation is based on the differential partitioning of an element into two (or more) separate phases. Examples include the reduction of iron oxide by carbon, in which a solid (Fe metal) separates from a gas phase (CO), or copper smelting, in which a Cu-rich metal phase and a silicate phase (slag) form immiscible melts. Commonly the new phases created by the chemical extraction procedure must then be separated. Moreover, side reactions are ubiquitous in chemical processes. Commonly the original concentrate to be treated is itself impure, because it was made by a physical process that does not yield very clean separations. Additionally, the ore mineral itself may be compositionally variable; e.g., sphalerite, the major ore of zinc, has
the formula (Zn, Fe)S and thus always contains iron. Commonly both are true: for example, copper is generally smelted from a mixture of sulfides physically concentrated by flotation. These include copper-only sulfides, copper-iron sulfides, iron-only sulfides, copper-iron arseno-sulfides, and selenides. Again, therefore, iron is always present and sometimes cobalt and nickel must also be dealt with. Side reactions are nearly always undesirable. They cause reagent loss and/or the creation of undesirable by-products and contaminants. Such by-products can have deleterious effects on the extraction procedure, or even on the very processing equipment itself, as when corrosive compounds are made. Such chemical tangles are why it is so cost-effective to let nature do as much of the separation as possible first; i.e., why "ores," anomalous concentrations of desired elements in easily separable forms, are worth seeking out in the first place. Examples of side reactions include cyanide loss in heap leaching of low-grade gold ore. To extract the extremely fine grains of native gold, which can amount to as little as about 0.6 ppm, broken rock is stacked into flatheaps about 10m high and a cyanide solution sprinkled over them. Gold and silver readily form stable cyanide complexes, which can then be extracted from the solution exiting below. However, cyanide losses, through adsorption by organic matter or reactions with other metals, such as copper, can make such leaching uneconomic, so that the gold content alone may not determine whether a given deposit is economic (cf. Bray, 1941). On the Moon, an important side reaction that has been little noticed is the formation of sulfuric acid if hydrogen is extracted or used as a reactant. Regolith contains a little troilite (FeS), which at moderate temperature will be oxidized by water vapor to yield H2SO4. A casual perusal of any extractive metallurgy text (e.g., Roscnqvist, 1983) will also demonstrate the degree to which side reactions greatly complicate the extraction of metals. Multiple steps of extraction and refining are nearly always necessary to purify a metal before it is usable. Another complication of separation processes, especially chemical processes, is their tendency to oscillate uncontrollably, as is typical of an unstable system. Processing control is made much easier by using a series of simple separations, rather than a single or a few complicated processes. Each such simple step is much less likely to oscillate, because it has a longer time constant and its state can be sensed adequately in real time. Small process steps are easier to sense and control, and any oscillations can be confined to single steps rather than the whole process. As will be discussed below, the heterogeneity of natural materials guarantees that the feedstock to any process will vary, and such variation must be dealt with in real time. This phenomenon is another motivation for using multiple steps in an extraction procedure. Heterogeneity Natural materials are also heterogeneous, both in composition and in physical
properties. Thus, any characterization of such propertiesis an average, and a range of values and area where they are valid must both be determined. The recognition, much less the significance, of this heterogeneity seems profoundly underestimated in many extraterrestrial resource scenarios. Rock types, for example, represent a range of compositions and textures, and a rock name also commonly implies a mode of origin. "Basalt" is a typical example. The name refers to a volcanic rock, or a class of volcanic rocks, relatively poor in silica and relatively rich in iron and magnesium (e.g., Carmichael et al., 1974). Basalts nonetheless have a wide range of compositions, some of which themselves have specialized names (e.g., "tholeiite"). Composition even varies within a single flow, depending on how the lava cooled. The term "basalt" also says very little about the rock itself. The texture could be massive or vesicular, the rock could be broken up or intact; the nature of any fracturing is unspecified; and chemical alteration, by weathering or volcanic fluids, might be present. Lunar mare basalts are no exception. As can be seen, there is also great variation in the nature of heterogeneities in rocks, including: the size and distribution of mineral or sedimentary grains; the nature and distribution of material between the grains; the presence of any layering (and the nature of the variation by which such layering is defined); the nature and degree of any fracturing or veining; the presence of any chemical alteration by weathering, hydrothermal fluids, or sedimentary brines. Such alteration in particular is commonly sporadic, following subtle vagaries in rock permeability, or reflecting the proximity of altering fluid; and such alteration is also an extremely common source of economic mineralization. The values of a potential ore depends greatly on the nature of such heterogeneities with respect to the distribution of the desired element. Is the element dispersed throughout the rock? If so, what is its grain size? Alternatively, is the element concentrated in veins or fracture fillings? Is it then related to later chemical alteration? In any case, what is - or are - the mineral(s) the desired element is contained in? Such heterogeneities, at many levels and of many types, are also the reason that human beings are still so deeply "in the loop" in mineral extraction. Even the seemingly simple process of digging out ore-bearing rock requires real-time judgment calls based on extremely subtle pattern recognition that also must occur in real time. Breaking up rock and digging it out is expensive, so only the rock that absolutely must be dug can be dug, if the mine is to be economic. Such tasks are done well by human beings, but they are so far impossible (not merely difficult) for machines. Hence, the consequences for mineral extraction of natural heterogeneity are profound. Machinery and techniques must be flexible, and processes must be robust. One example of the necessary flexibility comes from a copper plant in the senior author’s experience: if the crushed ore sent to the flotation mill was too high-grade, the flotation vat would overflow. Hence high-grade material had to be diluted first.
The plant also must be as simple as possible, and must focus on specific elements to the exclusion of others. Finally, a totally automated facility seems unattainable at this point, at least without major breakthroughs in sensors and artificial intelligence. The cases described below result from unforeseen consequences of underappreciated complexities in the material on which processing was attempted. They have salutary lessons for the extension of resource extraction to other worlds. Concentrating the Ore Mineral Even the most valuable mineral deposit is rarely sufficiency high grade to be processed directly without first forming a high-grade mineral concentrate from it by mineral dressing. Terrestrial mineral dressing ordinarily concentrates a single mineral or element, with the bulk of the rock mined (the "gangue") discarded. The gangue may even contain grains of the desired ore mineral that were too small or too dispersed to be economic. Only the relatively pure ore mineral is included in the mineral concentrate. Ore mineral recovery can be based on contrast in physical and/or chemical properties between the desired mineral or element and the host rock, but physical processes are generally cheaper. Since several mineral separation processes are usually used together or in sequence, they have a profound economic effect on the cost of the mineral or element. Physical properties of interest are (e.g., Richards - Locke, 1940; Taggart, 1954): Hardness or softness Tenacity, brittleness or friability. Structure and fracture. Friction. Aggregation. Color and Luster. Density. Electroconductivity. Magnetic susceptibility. Decrepitation by heat Surface properties: Greasiness. Adhesion. Wettability. Contact angle. Polarity. Surface tension. Chemical processes that affect physical properties are (e.g., Richards - Locke, 1940):
Change in mechanical condition by heat from dense to porous. Change in magnetic properties by heat. Change in surface properties by reagents due to adsorption or chemical reactions. Mine Development Stages We now turn to the procedures evolved by experience to cope with the these problems of complexity and heterogeneity in natural materials, and the implementation of the complex chemical and physical processes necessary to separate elements from ores. Stages in mine development will be described and illustrated by examples. The following four development stages apply in developing a mine, and following them conscientiously will be especially important with the additional unknowns of an extraterrestrial environment if financial - and other - disasters are to be avoided. Exploration This is the search for the highest recoverable concentration of the mineral or element available. For extraterrestrial resources, high grade is especially important because the extraction plant must be simple, cheap, and rugged to minimize capital and maintenance costs. It is highly unlikely that ordinary rock will be separated into all its components; indeed, this is impractical even in the much more favorable environment of Earth. Because of the high cost of element separation, it is always cost-effective to let nature carry out as much of it as possible. Laboratory testing Samples of the possible ore are tested by various techniques of physical separation and/or chemical separation to determine if the mineral or element can indeed be recovered. A high concentration of the mineral or element in the sample can only make the rock an ore if it can be recovered in a relatively pure form. This must be done on rock from the deposit under consideration; simulantswill not do. Only when the best site is found should a bulk sample be taken for a pilot plant test. Pilot Plant Test To estimate the mining cost, a large sample is dug from the mineral deposit to test the difficulty, excavation rate, equipment wear and power requirements. This sample is run through a pilot mill designed from the results of the laboratory testing. This step usually has to be repeated several times in order to balance the several steps and the equipment components so that they work together to give a clean uniform product. For large mines and plants, the pilot plant tests might be repeated in steps of about 100, 10,000 or 100,000 to 1,000,000 tonnes, depending on the
difficulty encountered in scaling up the process. The pilot plant test stage needs to be made for each new mineral deposit. Full Scale Mine and Plant Start Up. Invariably, problems develop at this stage. If the pilot plant tests are conducted properly, modifications of the mine and plant can be kept to a minimum. Later modifications to the plant will be made after the plant is in operation to improve its efficiency and product quality. The above four steps are essential for developing a terrestrial mining and mineral processing plant. These steps must be rigorously followed for the additional unknowns that will be encountered in extraterrestrial environments. Exploration It was noted above that the most important criterion of a potential ore is its concentration of the desired material. This stems from the difficulty, already emphasized and to be illustrated, of separating elements. It is thus highly cost-effective to find places where nature has done as much of the separation as possible. This is exploration. In terrestrial minerals exploration, samples are collected widely, almost all of which could not possibly be ore. Such sampling is carried out to establish a geologic context to find where ore might be. Seeking out such concentrated deposits of desired materials is critical before committing to the enormous risk and capital expenditure of a extraterrestrial mine. On the Moon, we have just begun to establish an economic-geology context. Basing mining and extraction scenarios on the ordinary country rock sampled at the handful of sites directly sampled in the Apollo and Luna missions, and indirectly sampled by the lunar meteorites, compromises the value of lunar fractionation. Despite the conventional wisdom in some quarters that the Moon is a dull, homogeneous rock, concentrations of common elements must certainly occur locally on the Moon, and anomalous deposits of rare elements are probable as well (e.g., Haskin et al., 1991), as the Moon is a large, complex body that underwent extensive igneous differentiation over a significant fraction of geologic time. Further telescopic exploration of the Moon is a first step, as with the current multispectral imaging of the near side of the Moon. Stereographic techniques can provide topographic information. In addition to compositional and topographic data, the surface maturity and percentage of agglutinates can be measured (e.g., Johnson, 1990). Orbital observations, however, will be needed to improve on the Earthbased data and to extend them into the near ultraviolet and infrared parts of the spectrum (e.g., Johnson, 1990). Landers and roving teleoperated or automated mappers will be needed to map, sample and analyze favorable areas found from orbit. From these sites, the best will be selected for further sampling. Samples can
then be obtained for laboratory testing. Asteroidal materials, another commonly proposed source for extraterrestrial resources, are even less well characterized. Although the compositions of certain meteorites recovered on Earth are encouraging for possible resource value, ambiguities remain in the relation of meteoritic and asteroid compositions (e.g., Lipschuk et al., 1989). More importantly, we still have no idea of the in-situ heterogeneity of the meteorite parent bodies, including their degree of fracturing or consolidation, the lateral continuity of rock types, the grain size distribution, the presence and/or degree of alteration and vein filling, and most critically, the distribution of the desired element(s) with respect to these small-scale textures. This is the sort of information, as emphasized elsewhere in this paper, that is critical to reasonable extraction scenarios. Much further exploration is required before asteroids can be considered seriously for resource extraction. As for the Moon, some of this exploration can be done remotely, by space-probe missions, to map and sample in-situ material at small scales, and will be needed before any processing scenarios can be constructed. Laboratory Testing Initial laboratory tests will be on samples collected during exploration. The laboratory location may be on the lunar surface, in orbit or on Earth. Although an orbital location may be the most convenient since numerous samples from a large number of locationswill probably need to be tested on an ongoing basis, many tests will require gravity, and simulating gravity on the scale required may be too expensive. These tests may include assaying, crushing, grinding, trying various mineral separation methods; grading of various mineral concentrates, middlings, and tailings; and recovery testing. The goal will be to maximize concentrate grade yet still recover a significant percentage of the ore mineral from the ore. In order to make a sufficiency high-grade mineral concentrate, however, total recovery may be less than 50%. High grade alone, moreover, may not be enough to make a particular rock an ore, because of inability to make a high-grade mineral concentrate from it. In early 1965, for example, Kennecott’s Ray, Arizona open-pit copper mine had to abandon a million-ton block of ore-grade sulfide mineralization because the chalcocite (CuS) was so fine-grained that grinding could not liberate it from the silicate gangue. Hence, flotation would not work for concentration. Similarly, it was mentioned above that extremely fine-grained, Carlin-type gold cannot be recovered by density separations; cyanide leaching must be used, and in some cases the leaching does not work because of cyanide scavenging by other minerals in the rock. Once a mineral concentrate is made, chemical separation tests can be made to determine the quality and recovery of the desired element or elements. Even a high-grade concentrate may be unusable if it contains too many of the wrong impurities, such that undesirable side reactions occur during chemical processing. For example, some lunar ilmenites contain micron-sized grains of troilite (FeS).
Such troilite must be separated from the ilmenite before reduction with hydrogen to produce oxygen, or else the plant must be designed to withstand and separate the sulfuric acid by-product. Thus, a very high grade ilmenite concentrate might be less desirable than a poorer grade concentrate that contains less troilite. Laboratory testing should search for contrasts in physical properties between mineral grains of the rock or soil that can facilitate separation of the desired mineral from the gangue. On Earth, an extreme case of the utility of large contrasts in physical properties is in placer gold mining, where enormous tonnages of gravel are washed and discarded to recover a tiny quantity of gold. The high density of the gold, and the availability of water to carry out easy density separations, makes this practical. More commonly, surface properties of the mineral grains are taken advantage of, as in froth flotation, where relative polarity of the mineral grains forms the basis of separation. Pilot Plant Test Once the laboratory testing has determined that a site has rock from which a mineral concentrate can be made, and that the concentrate can be treated chemically, a pilot plant test must be made. This test will include: (a) mining a large sample for a preliminary test, which will determine mining difficulty such as equipment wear, power costs, equipment sizes and operating costs. (b) Comminution tests, which will determine the types and sizes of equipment, and the required sizing of the product so that minerals can be separated from the gangue. (c) Mineral separation tests, which will determine the types of equipment, the modifications that must be made to the equipment, and the recovery, concentrate grade, middling grade and tailings losses. (d) Finally, once a satisfactory concentrate is produced, chemical separation of the desired element from the residue must be determined. All these steps must successfully completed to produce the desired product. The dangers of skimping on the pilot plant test are illustrated by the following case. A mining company was developing a mineral property south of Tucson, Arizona in the 1970s. The company chose not to sink a shaft, excavate a drift out to the mineralized area, and take a large mill test sample. Instead, they drilled some large holes from the surface into the mineralized area to make up a composite mill test sample. They then designed the mine and mill based on the tests on the drill samples. Only then, after building the mill, did they sink a production shaft and excavatea drift out to the mineralized area. They found that the mineralization was so broken up by faulting that it could not be mined. Thus, by skipping the step
of sinking an exploration shaft to explore the mineralized zone, they did not find that it could not be mined until after they had spent a fortune on a useless mine, mill and concentrator. The western United States has numerous such monuments to trying to save money by skipping mine development steps. Full Scale Mine Concentrator and Recovery Plant Start Up After rejection of the vast majority of deposits found in the exploration stage, due to their failing the laboratory and pilot plant testing, one or more deposits are selected for development. In spite of all the care taken up to this point, most plants initially fail to operate as designed. Many can be improved and made to operate satisfactorily by subsequent modification. Although mistakes will be made, these mistakes hopefully can be corrected at a reasonable cost without destroying the operation. For example, at the startup of the Copper Cities mine near Miami, Arizona, the water did not separate properly from the tailings; the thickener overflow carried suspended solids that would destroy the clear-water pump seals and erode the impellers. The fact that the upper part of the ore had excessive non-settling clays ("slimes") had been observed in the early laboratory tests but was later overlooked. Thus, a hydroseparator and flocculent feeding equipment were added to the tailings processing stream to save the pumps. The suspended clays also threatened the tailings dams, since the slimes did not separate from the sands at the dam face to form a clean sand dam behind which the slime tailings would be retained. "Cyclones" (centrifugal separators) had to be purchased and installed on the tailings dam to separate the sands from the slimes. In this case, these expensive retrofits worked. Other examples come from the many horror stories stemming from the over-hasty development of the Ambrosia Lake uranium district in New Mexico during the uranium rush of the late 1950s. In the hurry to get mines and mills into production, the ability of the mining, milling and recovery equipment to operate under conditions in the district was not investigated so that nearly disastrous mistakes compelled major equipment redesign, redevelopment and retrofitting. Fortunately the companies involved had the financial resources to withstand this huge financial drain. However, all the costs were not monetary: in one fiscal year there were sixteen separate fatal accidents plus many serious injuries. Disastrous choices of equipment were made. A whole fleet of brand new D-6 Caterpillar front-end loaders had to replaced, after only six months’ use, with new articulated rubber-tired front-end loaders. Electric loaders and blast hole drills had to be scrapped after a few weeks’ use because the electrical systems could not be maintained under the wet conditions in the mines. Electrical connectors exploded when acidic mine water, an electrolyte, seeped in past the seals. The electric-powered loaders and drills were replaced with air-powered equipment, which required purchase, design, and construction of a large compressed-air system for the mines. Moreover, the rubber-tired equipment was found to be unusable more
than 500 feet from the shaft due to its high maintenance costs. A battery-powered electric rail haulage system was overlaid on the truck and loader system; this necessitated building a different tunnel layout around the shaft station and skip loading pockets. The additional excavation weakened the shaft station pillar, causing cave-ins in the shaft area that required shutting the mine down till repairs could be made. Finally, it should be emphasized that the mining equipment initially installed was not experimental; all of it was standard equipment operating successfully in other mining districts in the United States. Extensive thorough exploration, careful laboratory testing, stepwise pilot-plant testing, and careful plant design will all help to reduce the errors in the design of lunar mine, mill, concentrator and chemical recovery plants. If sufficient flexibility and reserve capacity is designed into the components of a lunar mining, milling, concentrating and chemical recovery system, it might be able to operate at partial capacity until modifications can be made to the system. This might avert a complete shutdown of the plant if the initial configuration did not work as planned. The Earth has innumerable monuments to errors in design and construction of mining and mineral recovery systems. The Moon is all too visible a place on which to build similar monuments to errors and miscalculations. Conclusion Terrestrial mining experience has much to offer in guiding the search for economic sources of space materials. Fundamental lessons from this experience include: (1) the recoverable grade of a potential deposit is its most important economic characteristic, and (2) it is seldom cost-effective to commit to a mine without a great deal of exploration first. Of the mineral deposits found, only a few will be suitable for exploitation. These must be selected on the basis of laboratory and pilot plant testing. Although the Moon is smaller and less complex than the Earth, it is by no means simple, and this complexity affords many opportunities for the existence of exploitable mineral concentrations (ore). The country rock of the few limited landing sites is probably not suitable for exploitation. It will be cost effective to invest heavily in exploration, laboratory testing and pilot plant tests before investment in a lunar mineral exploitation system. REFERENCES [1] Bray, J.L., (1941) Non-Ferrous Production Metallurgy. John Wiley & Sons. [2] Carmichael, I.S.E., E.F. Turner & J. Verhoogen. (1974) Igneous Petrology, McGraw-Hill. [3] Gillett, Stephen E, (1991) "Lunar Resources: Thoughts of an Economic Geologist." Space Power: Resources, Manufacturing and Development, Vol. 10, No. 1, pp. 3-17.
[4] Haskin, L.A., R. O. Colson, D. Vaniman, and S.L. Gillett, (1991) "A geochemical assessment of possible lunar ore formation," submitted to Near-Earth Space Resources, University of Arizona Press. [5] JOHNSON, Jeffrey R., (1990) "Near-Side Ilmenite Distribution in the Lunar Mare regolith," The SERC Newsletter, V.2, #1, Tucson, Dec. [6] LIPSCHUTZ, M.E., M.J. Gaffey, Q P. Pellas, (1989) "Meteoritic parent bodies: matter, number, size and relation to present-day asteroids," in Asteroids II, ed. R.P. Binzel, Gehrels, & M.S. Matthews, pp. 740-777, University of Arizona Press. [7] RICHARDS, R.H. and Locke, C.E., (1940) Textbook of Ore Dressing, McGraw-Hill Book Company, New York. [8] ROSENQVIST, T., (1983) Principles of Extractive Metallurgy, 2nd ed., McGraw-Hill. [9] TAGGART, A.F., (1954) Handbook of Mineral Dressing, John Wiley & Sons, New York.
The Environmental Benefits of Solar Power Satellites RAYMOND S. LEONARD SUMMARY The environmental issues associated with satellite power systems can be placed in two categories. The first is the environmental impact that either the building or operation of satellite power systems will have on the Earth. The second is the degree to which the environmental impact of technical civilization is lessened or attenuated by substituting electric power from space for electric power from coal, oil and nuclear power plants. This paper is a discussion of the environmental credits which can be attributed to using electricity provided by solar power satellites. Introduction Modern man has added the scourge of environmental pollution to the four great biblical plagues which beset mankind. Pollution has become a global problem and the search for solutions an international quest. It is a quest with the moral challenge of creating an infrastructure for sustainable and equitable global economic development. This quest and challenge presents the proponents of satellite power systems (SPS) with unique opportunity. Can we, the proponents of this technology, justify energy from space as a component of sustainable development? If we can and are also able to demonstrate that it is economical then we will have the justification for a program and the opportunity to build power satellites. Using the resources of space to meet the dual challenges of energy and the environment provides us with a way to appeal to the youth of the world who seek nourishment in dreams, as well as in bread (Pollock, 1980). The enthusiasm of our children is not enough. We also need the support of the taxpayers and the politicians. For the taxpayer we must establish the linkage between energy from space, the quality of the environment, and what he wants from life. In order to the win the support of the politician we must demonstrate it is relevant, cost effective and will make public heros out of the politicians who support the concept of energy from space. Emissions such as carbon dioxide, sulphur dioxide and nitrogen oxide from thermal power plants which burn coal, oil and LPG contribute to long term global environmental damage. While the issue of global warming is still being hotly debated there remains little doubt about how acid rain is created and what its effect on the biosphere is. The most obvious solution is a reduction in the use of fossil fuels for power generation. But what then are our options? President, Ad Astra, Ltd., Rt. 1, Box 92 LL, Santa Fe, New Mexico 87501.
Starr and Searl, 1990, stated in an Electric Power Research Institute study that although both nuclear and solar electric power are capital intensive they both share the ability to expand without being natural resource limited. They go on to state the rather obvious fact that terrestrial solar is limited by its diurnal dependence and its need for a storage system if it is to break the chains of this limitation. In addition, they point out that competitive use of land and water for food production may be a major constraint on the use of biomass as fuel as the world’s population grows. This analysis does not address the already well known problems of deforestation and desertification which are caused by the excessive use of biomass for fuel in the developing nations. Starr and Searl advocate nuclear power as the ultimate solution to global energy problems. As a counterpoint to this, Markovic (1990) points out the impossibility of finding a political and socially acceptable solution to the problem of nuclear waste disposal. This single factor might be a sufficient reason to give up on nuclear energy altogether. What then are our options? I propose that energy from space is a viable solution to the environmental problems posed by power generation. It is not an end all solution and given both the historical time constant of a half-century for substantial changes in the mix of large scale energy systems reported by Starr and Searl (1991), and the need for testing and evaluation, it should not be a threatening technological alternative to vested interests. Rather it is the dark horse or technological long shot. Nevertheless, the almost studied way that the satellite power solution is ignored by energy planners is curious. In order to be an environmentally viable solution, the impact of SPS must be mild when compared to the alternatives and the benefits must be large, since SPS is "the new kid on the block." Environmental Impact of Building SPS There are at least two major environmental concerns about energy from space. They are the effect of the exhaust from the vehicles launching construction materials to LEO and the effect of microwaves on the atmosphere. The former is highly dependent upon the acceleration of the launch vehicle, transit times through atmosphere and the type of propellant used. The first concern can be subdivided into three phases. The three phases are: technology validation and demonstration; acceptance of the technology as a viable alternative and competitor to other forms of power generation; and establishment of SPS as a mature source of environmentally benign energy. Currently there is no foreseeable way to avoid environmental impact during the first two phases. The questions to be answered here are: what is the magnitude of that impact, and is the long term benefit to the environment worth the short term cost. A design constraint which should be considered for future launch systems is the type of propellant that will be used at different altitudes.
Table 1 lists the amounts of propellant that will injected into the atmosphere per 19,000 kgs of payload to LEO. As can be seen there is a great deal of improvement that can be made in reducing the amount of pollutant per unit mass of payload. In the third phase we can finesse the rocket plume pollution problem by deriving most of the necessary construction materials from the Moon. Those which are not available from this source might be launched with a mass driver located on the equator (placing a small rocket and control unit on it for inserting the payload into orbit). The microwave issue will not be resolved by theoretical or ’paper’ studies. It needs to be researched in depth. This field of research is new enough that the lack of knowledge about the effects of microwave energy leads to great public concern. To collect the necessary data will require a test bed system. Testing must be done at all altitudes. Small scale experiments in a laboratory are necessary - but we will not be able to lay to rest public concern until test bed data are obtained. If the environmental and health impacts of SPS technology are not addressed, it will face the same problems that nuclear energy now faces. Morone and Woodhouse (1989) present an excellent set of lessons about how not to go about implementing a new technology in The Demise of Nuclear Energy? Lessons in the Democratic Control of Technology. The Environment Benefit of SPS The environmental consequences of economic policy decisions are complex and far-ranging. They typically involve conflicting interests. Air pollution produced by
oil and coal combustion travels hundreds of miles to shower down as acid rain. Acidity can build for years with seemingly little harm - until it finally exceeds the natural buffering capacity of the land and water - and suddenly forests, lakes and streams are affected. There are no choices which do not impact the environment in some way. The question is which energy technology has the least impact?
Environmental problems are also inseparable from the problems of development. Those in developing countries faced with limited resources, high rates of population growth and the need for energy for development are often forced to compromise the environment in their quest for growth. Current options each come with a cost. Dams often dislocate people, flood land and may create health hazards through water borne disease. Coal mining disrupts the environment and coal-fired power plants pollute the atmosphere and the land while heating rivers and lakes with the discharge from the plant’s cooling system. Tables 2 and 3 are a qualitative summary of cost elements (many of which are often externalized in determining the cost of power) and environmental and safety risks for various forms of power generation. Table 4 is the beginning of a quantitative statement about the cost of emissions. A great deal more work needs to be done to complete this table in a through and unbiased manner. There are, however, some additional qualitative statements which can be made about the benefits of energy from space (The data on carbon emission was taken from Amagai, 1991 while the cost of six dollars per ton for carbon emissions was taken from a Wall Street Journal article). SPS and the Industrialized Nations The industrialized nations, with 24% of the world’s population, generate about 80% of the world’s electricity (Starr and Searl, 1990). As a result they release the
greatest amount of emissions into the biosphere. They also have the capital needed to finance megaprojects. It is obvious from both an environmental and financial point of view that they are the place where satellite power systems should be first introduced. However, according to Starr and Searl (1990) there is a historical time constant of a half-century for substantial changes in the mix of large scale energy systems. This is in keeping with both the planned life expectancy of generation facilities (30 years) and the rate of capital formation that takes place within a new industry. It also fits with the 17 year cycle required for new ideas to penetrate existing power structures and to start to have an effect on the younger decisionmakers moving into
power positions. Consequently, if we expect the implementation of SPS’s to change the way the industrialized nations affect the environment we will have a long wait. On the other hand, population growth and the desire to achieve the same levels of development as exist in the industrialized nations point to the developing nations as a major source of new atmospheric pollutants unless they are offered an alternative to fossil fuels. China alone is planning to build over 200 coal fired power plants over the next 30 years. Benefits to Developing Countries Making choices in the search for environmentally sound energy sources can be difficult. Countries need energy to develop, to provide alternatives to the use of biomass for fuel, and to improve the quality of life for their people. The struggle to survive has led people to ask too much of their forests. In developing countries seven out of ten people depend on fuelwood to meet their heating and cooking needs. Villagers cut down trees if they do not have access to inexpensive alternative fuels. As supplies of fuelwood dwindle, people stop using dung and crop cuttings for fertilizer and begin using them for fuel. Once this happens the land very quickly loses its fertility. Crop yields drop, the land dries out and erosion sets in. Example: In Mozambique, the burning of fuelwood accounts for 80 percent of all household energy (World Bank, 1989). This demand has led to deforestation and air pollution. As a result, a project has been initiated by the World Bank to develop other sources of energy and connect more houses to the electric power system. This project also includes a program to market new home cooking devices. Unfortunately, energy from space under an energy as foreign aid program was not considered. Example: In Haiti the people are stripping the land for fuelwood with the result that the top soil is then washed into the sea. The fertile land and the forests are disappearing as a consequence of excessive use of biomass as fuel. But given the poverty and lack of other energy resources what choice do they have? While terrestrial photovoltaic systems could provide some of the power they need it cannot meet the total energy needs of a village without some sort of energy storage system (which, according to Starr and Searl (1990) increases the size of the system by a factor of 5). We can see that "perhaps the single greatest contribution that could be made to environmental conservation would be the invention of a satisfactory fuel-wood substitute" (Dregne, 1985). Energy from Space can provide an economical and socially acceptable substitute for fuel-wood. It would allow many nations to implement development programs without the same degree of impact on the environment that the industrialized nations have historically had. Example: Another example of how satellite power can be linked to both environmental issues and economic development is the Carajas iron ore project in Brazil (World Bank, 1989). Pig iron smelting requires large amounts of charcoal derived from the forest. The World Bank is now helping with an energy options study,
RkJQdWJsaXNoZXIy MTU5NjU0Mg==