To the uninitiated, this webpage may seem out of place in a website devoted to the classic Railway Series and its author. We temporarily digress to feature a technical literary piece written by the Rev. Awdry's younger sibling, George. George Awdry must have been a very interesting man, with many interests and equally conversant in those subjects. In addition to being a prominent Ricardian, George was also a member of the British_Interplanetary_Society. The article that we are about to present to you was authored by George for the Journal of the British Interplanetary Society, vol.13.No.16, in May, 1954.
DEVELOPMENT OF A LUNAR BASE
Few mining engineers seem to have joined the B.I.S., perhaps understandably. A layman can be forgiven therefore for considering some of the problems which will arise in the field of mining and metallurgy during the development of a lunar base, with a view to making this base as useful as possible, while keeping the cost in supplies brought in down to the minimum. The solutions advanced may or may not be valid, but these are real problems which call for attention.
It is assumed that a small permanent base has been established underground for scientific research, with the obvious laboratory and field equipment, and that plentiful electrical power is available, either from solar heat or nuclear energy. A regular, though infrequent shuttle plies between the Moon and an orbit about the Earth, so that anything worth the energy-cost can be imported. The base uses algae-tanks to replace oxygen consumed, and to grow its food, any wastage being made up by imports. The moon itself is assumed to consist of complex silicates, similar to un weathered igneous rocks on Earth, probably with much uncombined silica, any volatile elements or stable compounds having been dissipated.
I am not competent to discuss mining in detail. But for some time the ores will be a by-product of excavations for additional living and storage space. The expedition must have come prepared to do some tunneling, in order to get underground, so equipment will be available. the aim should be first to use explosives as little as possible. Their transport will be an appreciable item. Meanwhile, a core-drill will be a better choice, say one 6 in. diameter. The cutting-head should be tipped with tungsten carbide, or industrial diamonds, so that only these relatively light items need to be imported as consumed.
Silicates are hard and abrasive, but mostly brittle, and wedges, thermal shock, or even hammers will probably serve to break down the working face once enough holes have been drilled. Later on, liquid oxygen will become available for blasting, and boring may be done with an iron pipe, burning in oxygen fed through it. This method is already in use, and will melt concrete. It should be particularly useful in association with thermal shock produced by injecting a little liquid oxygen afterwards. Tunneling under these conditions will be heavy work, and should be carried out in an atmosphere, if the rock is firm, to avoid physical distress. Dust-respirators, however will be essential, to prevent silicosis. None of the excavation will be wasted, as prudence will demand that the base be subdivided into sections connected by tunnels with emergency air-locks.
The simplest means of transport will be by suspended railway, at first with manual haulage, later electrified. This uses one rail instead of two, and fewer wheels as well - a considerable saving in metal at installation - though wear will be higher. It can be easily suspended from the roof, by something resembling the familiar Rawlplug. It will have a further advantage as the base becomes extensive and speeds rise, for such a system is naturally stable under centrifugal force on curves. The conventional railway depends on gravity, assisted by super-elevation of the outer-rail, to resist this force, and lunar gravity is dangerously weak for the purpose, unless an impracticably broad gauge is adopted. In the reduced gravity, gradients need not be so carefully avoided, but some means will have to be found to increase adhesion at starts. Electrical drive applied to all wheels might suffice, or spring-loaded rollers underneath the rail which could be engaged or disengaged at need. Brakes should be of the electromagnetic sledge-type commonly used on tramways.
Silicates are unpromising ores by their abrasiveness, the large quantities needed for a given yield of metal, the close association of several metals in any one sample, and the great bulk of tailings. These latter present a less immediate problem on the Moon, being silica, which can be used as an insulator, or fused and formed into many useful articles, notably tanks and piping for ore-processing. It would be worth while to subject the tailings to heat treatment in any case, to recover the last traces of reagents and water. The first ore treated will be lunar dust, which will need no grinding. Later on, it will be possible to build an old-fashioned tube-mill, in which the larger lumps of ore will do the actual grinding, thus saving the need for hard-wearing steels at some cost in efficiency and time. But power is plentiful. The dust is leached with acids, and the liquor subjected to a series of selective precipitations, until it contains only sodium and petroleum salts, when it can be concentrated and electrolyzed to yield these metals or their hydroxides, which will be needed to leach out aluminium. Heat treatment, or electrolysis, will recover water or acids still locked up in the precipitates.
The various metals will call for different methods of treatment. Pure iron can be deposited electrolytically from a sulphate solution, if the bath is topped-up with iron oxide from time to time. Calcium, which may be useful as a bearing-metal under airless conditions, can be electrolyzed out of the fused oxide, magnesium from its chloride. Even aluminium can be plated out of a non-aqueous solution with an admixture of lithium hydride. Wherever possible, to save reprocessing, metals should be deposited in moulds1, so that the article needs only finishing. Where powder metallurgy can be used, this also makes a worthwhile saving in time and plant.
More conventional reduction processes call for greater thought. If enough alkali metal is readily available, aluminium can be reduced with this instead of carbon, while a simple cyclic process can be used to reduce iron. Hydrogen passed over heated iron oxide is partly oxidized, reducing the oxide to iron. water vapour is extracted from the gas by metallic sodium, which reaction replaces half of the hydrogen. The rest is recovered by electrolysing the sodium hydroxide formed, and the water evolved in this electrolysis.
It will be easier, however, if we can avoid using so elusive and bulky a gas as hydrogen as a reducing agent. The alternative is carbon, or its monoxide. By hypothesis, we have on the Moon no source of carbon such as coal, but we have in the algae tanks the means of fixing it from its dioxide, and the algae can be distilled to yield a reasonably pure carbon. Briquetted with the pitch that will be another product of this distillation and baked, this will provide usable electrodes for an arc-furnace. It will be necessary in any case to have extra tank capacity available, in case of breakdown at the sudden arrival of additional inhabitants, and it may as well be in constant operation. Possibly, the algae could be left in the dark, or otherwise kept dormant, but this is a waste of capacity when they can be put to good use. To maintain the cycle, the other installation products must be oxidized and recycled, but that should be straightforward enough. On the basis of a recent paper, 1 litre of solution containing 55 grams algae produces a usable surplus of 2·5 grams algae daily. It is reasonable to suppose that 20 per cent. of this yield is readily recoverable as usable carbon,2 so that 2 cubic metres of liquid will yield daily 1 kg. electrodes, enough to reduce, in theory, 3 kg. aluminium or 7 kg. iron (from a mixture of both oxides, quoted as a mean figure).
There are still considerable difficulties. In order to reduce worthwhile quantities of metal, very large tanks will be needed to recycle the carbon. Mining operations will soon provide space for these. Fluorine, or its compounds, are always found in these gases resulting from aluminium reduction, due to the breakdown of the cryolite used as flux. It should not be difficult to separate these off by inducing them to combine with some base or metal relatively inert to carbon dioxide. In case carbon monoxide is present, oxygen ought to be added to these gases while hot, and this may present technical difficulties. There will be an inevitable wastage of reagents used for leeching , and of carbon and water. Perhaps the ores themselves may yield enough of the latter, included as water of crystallization, but the others will have to be replaced. Sulphur may be present. If not, it can be imported, and converted to acid on the Moon. There will be no point in hauling up oxygen. Nitrogen, combined as hydrazine, is a likely rocket fuel, and prudence will indicate building up stocks, from which a little can be spared for conversion into nitric acid. If the chosen oxidant is nitric acid, it will be well worth while making this on the Moon from hydrazine, at least for the return trip. Fluorine is a constituent of some igneous rocks, but will otherwise have to be imported. Carbon is the most important item, for there will be consumption as well as loss, steel containing up to 1-5 per cent. But a little ingenuity can be used here. Activated carbon is an excellent insulator for liquid oxygen tanks, but gelatinous silica - which leaching operations will produce in enormous quantities - is an acceptable substitute, and could replace it for the earthward trip.
Whatever else is scarce on the Moon, oxygen will be abundant. A tonne will be extracted in the reduction of 2·625 tonnes of iron, or of 1·125 tonnes of aluminium, 1000 days' supply for a man, with no recycling. There will be leakage losses, but on nothing like this scale. The Moon will be able, therefore, to supply all space-craft and artificial satellites except those departing from Earth. It seems essential, also, despite the long transit time, to adopt ion-drive, at least for freight shuttles, between the Earth satellite and circumlunar orbit. Spitzer has shown that an acceptable performance can be achieved by a vehicle using nitrogen accelerated to 100 Km./sec. as reaction-mass. Allowing for differences in atomic weight, the same installations would presumably accelerate oxygen to about 80 km./sec. This apparently gives a mass-ratio for oxygen equal to 5/4 power of the "nitrogen" mass ratio, which would be tolerable for a relatively short haul, and oxygen need not be brought up from Earth, as nitrogen would have to be. The ionizing grids might present some difficulty owing to the danger of corrosion. But one cannot imagine the United States promoting an export from the Moon which will only entail further excavations at Fort Knox, so that gold, if it is found, will be merely another metal, to be out to any use for winch it is suited. Being very ductile, and a good conductor of heat and electricity, as well as being immune to oxidation, it should be an excellent material for ionizing-grids, if ut can be adequately supported.
From this, it appears that the necessities of life and development can be made available without excessive cost and the hope of using the resources of the Moon to open the Solar System to exploration is a good one. The main obstacle will be time, for until enough development has been done to support a larger population any progress can only be gradual. But much can be done without massive equipment, and with the import only of essentials. Very few of these need be consumable stores.
(1) Reported in The Engineer, February 13, 1953, p. 258.
Addendum: Space exploration enthusiasts should check out Martin's page about the SKYLON PROJECT. Moon exploration in the 2020s looks like it’ll be a bit different than what George envisaged!