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Lunar Mining

  • The Moon's crust is about 43 percent oxygen by weight, water is about 89 percent oxygen by weight, and for a LH2/LOX rocket powered craft, about 85 percent of the fuel weight is oxygen. On this basis alone the oxygen in the Moon's crust has a very high potential value. It can be extracted and shipped to Earth Orbit efficiently using solar energy and low thrust propulsion methods. Combined with other useful minerals available in the Moon's crust in significant quantities - such as silicon, iron, calcium, aluminium and magnesium, lunar mining would reduce the cost of running a developing space economy by at least 75 percent.

    However, establishing a mining operation on the Moon that could produce millions of tons of oxygen and other materials per year is no small undertaking. The infrastructure required is considerable and can only be safely developed once a stable industrial base has been established in Earth Orbit. The cost of lunar operations will gradually decrease as they become more automated and self-sustaining, which in turn lowers the cost of bringing any additional materials from the Earth to the Moon.

    A highly developed lunar mining operation will probably use mass accelerators to launch both crushed moon rock and processed elements such as oxygen and metals from the surface of the Moon. They will be directed to either the L1 or L2 Lagrange points before being transferred to Earth or elsewhere using low thrust propulsion - ion drives or magnetic sails or beam propulsion are possibilities. However, rocket powered craft will have to do the bulk of the work in the initial phases of development, which will require the establishment of orbiting space stations around the Moon and reusable shuttle craft between Earth Orbit and Lunar Orbit. Access to the lunar surface will be with a reusable rocket powered craft which can attach a variable payload module to a support frame structure.

    On the lunar surface as much work as possible must be carried out by autonomous vehicles and robotic devices. Astronauts can control such devices either from protected modules on the surface, or increasingly as the mining complex develops, from underground facilities. Excursions by astronauts to the lunar surface wearing only space suits might still be required to fix some problems or perform some tasks, but they will be kept to a minimum and eventually become very rarely needed.

    Operating on the lunar surface is inherently dangerous. In addition to the normal hazards of space, there is lunar dust which is electrostatically charged and sticks to surfaces, and is composed of rock fragments with razor sharp edges as there is no weathering process on the Moon. Long term exposure will certainly cause serious health problems, hence all facilities must enforce strict policies to eliminate dust from the interior environment on moon bases. Operating on or rather under the lunar surface does have some advantages. Oxygen will be in plentiful supply near a mining facility and being on the surface of a planetary object has the advantage that not being in orbit, the base does not have to worry about or adjust its trajectory. Another major advantage is that in an underground facility, even though it is only a few metres below the surface, the moonrock overhead will provide very good radiation protection. Some facilities could be built even deeper, 20 - 30 metres underground, which with some shielding would provide very good protection even against major solar storms. Lunar mining staff who will initially spend most of their time in rotating space stations in Lunar Orbit, could evacuate to shelters below the surface in the event of a solar flare. This would save weight on the space stations and allow staff to carry on working in a fairly normal manner. Basic emergency shielding will still be provided on the stations to cope with the situation where staff cannot move to the surface for some reason.

    In theory an underground moonbase could include a large centrifuge structure that would provide artificial gravity for its inhabitants. It would be similar to a small rotating space station except the outer surface would be at an inclined angle to the main axis to augment the Moon's own gravity. Such facilities could also be built on Mars and other low gravity bodies, but would need heavy industrial capability on the surface of the body in question. About 250 metres is generally needed for an artificial gravity system that avoids Coriolis force problems, but smaller systems could be valuable as habitats for astronauts to use temporarily on the lunar surface, either to extend there safe working shift time there, or in the case of emergencies that see astronauts stranded on the surface for weeks or months.

    In practice the Moon is prone to "moonquakes" every few months that are equivalent to an earthquake of at least 5.5 on the Richter scale. This is severe enough to damage building structures. Those that have complex dynamics in particular, will need to be carefully designed to be moonquake proof. Nonetheless, the idea of a moonbase which is highly self-sufficient and able to maintain astronauts in good health for long periods of time without external resupply is attractive. It is also highly attractive to be able to gain practical experience with the engineering requirements of below surface artificial gravity structures on the Moon before going to Mars. For that reason, the implementation of such a structure will be included in the first moonbase specification. It may not be required to have such a facility operational before astronauts land at the base, however it should be a major goal to get such a facility working as soon as is practically possible.

    It is worth bearing in mind here that although the delta-v budget for a transfer from the surface of the Moon to a low Lunar Orbit is only 1.6 km/s, this is still a very risky manoeuvre. Any significant malfunction of a shuttle craft could lead to the loss of the craft and its crew. The craft cannot glide to a landing, nor can the crew parachute to safety. A shuttle craft for transferring astronauts to and from the lunar surface, can be designed as a double spacecraft with a separate crew capsule that has an independent propulsion system capable of achieving lunar orbit independently, although that secondary system would be for emergencies only, not for normal operations. The astronauts could be in individual ejectable pods within the main crew capsule, and could eject independently in the event of a double compounded malfunction. The individual pods would have enough power from a small rocket system to either achieve lunar orbit or land safely awaiting rescue. Needless to say, such safety measures would make a shuttle craft at least twice as heavy - and considerably more expensive, than a simple transfer craft with a single propulsion system that could be used for autonomous transfer of goods between the lunar surface and Lunar Orbit. Even though rocket fuel will become cheap early on in the development of a lunar mining operation, it is likely that the cost of safe transfer of astronauts using the type of craft described above will be significant and should be kept to a minimum. The idea of low cycle fatigue rocket engines that are highly reusable, is fine for autonomous craft where the occasional failure even at the rate of one flight in 1000 is acceptable, but this doesn't apply to manned operations. Much stricter regimes on safe engine operation time limits must apply, hence it will be attractive to minimise such operations.

    For a moonbase to achieve a high degree of self-sufficiency, the extraction of volatile elements and their compounds from the lunar regolith is the only way to provide the required raw materials for life support. Hydrogen, nitrogen, carbon, sulphur and so on, all occur in the lunar soil in generally predictable amounts. They can be extracted quite easily and efficiently by applying heat incrementally to the fine particle component of the lunar soil. However, the amount of these substances in lunar soil is measured in parts per million. This means that to extract one ton of hydrogen, twenty thousand tons of lunar soil material would have to be processed. This would yield about 9000 litres of water. Over the course of one year that would give about 30 litres of water per day or about enough for 20 astronauts assuming recycling of at least two thirds efficiency.

    An area about 15 metres by 15 meters would have to excavated to a depth of about 2 metres every day to provide the feedstock for this extraction process. This is a very small scale mining operation, but if all the processes involved can be fully developed in a scalable fashion, lunar soil mining could provide a supply of millions of tons of oxygen and metals per year for thousands of years. The volatiles extracted in such a process would be used mainly to enable the mining operations to be as self-sufficient as possible. The supply of volatiles to space stations in Earth Orbit would be from Earth but fairly cheap once they begin using lunar oxygen as a fuel source. Space stations in Lunar Orbit could be supplied with volatiles either from the Moon or from Earth. Even Earth Orbit stations could be supplied with volatiles from the Moon in an emergency situation, should the supply chain from Earth break down for some reason.

    In the long term, as rocket propulsion is replaced by more advanced propulsion methods at all stages of launch and orbital manoeuvring near Earth, the value of lunar oxygen will be somewhat reduced. However, the number of space stations including large interplanetary craft in the vicinity of Earth could rise steadily till they support about 1 million inhabitants or travellers. These vessels will probably be built and equip ed using a significant amount of lunar metals, and will need constant resupply of oxygen on the scale of millions of tons per year, hence the market for lunar materials could be quite steady for many years to come, although it may prove convenient to uses other sources, either from Earth or from asteroid mining.

    For the first phase of lunar mining, a major target will be to efficiently extract oxygen and other materials from ilmenite and anorthite minerals using fluorine. It will also include the extraction of oxygen from various type of lunar rock using hydrogen. The use of hydrogen as a reagent is much less efficient than using fluorine, but it is a much simpler process and will yield useful amounts of oxygen from all common lunar rock types. Hence it is important as a means for a new lunar base to become quickly self-sufficient in oxygen, if it can be provided with a certain amount of hydrogen and the fairly simple equipment needed for the hydrogen based extraction process.

    Prior to the extraction process, mined regolith will undergo various filtering, crushing and separating processes. In the case of oxygen extraction using hydrogen, this preprocessing can be kept to a minimum, but separation of mineral types will allow the oxygen extraction to be set at an optimum temperature for each mineral and increase the final yield of oxygen. As regards the extraction of various volatiles by simply heating the excavated material, this can be done most efficiently by using the finest lunar soil dust which lies at the top of the lunar surface. If more energy is available then all grades of dust and powdered excavated rock can be used, but will give progressively less of an increase in overall yield.

    For the process of extracting oxygen and other materials from lunar rock using fluorine, only specific minerals are used as feedstock to the reaction. High quality ilmenite or anorthite bearing rock is pulverised and the required specific minerals magnetically separated. The ilmenite or anorthite mineral is then fed into a reaction vessel where fluorine gas is passed over it, which results in the production of oxygen and various fluoride compound by-products. The by-products are separated using electrolysis to recover the fluorine and other useful products, specifically, titanium and iron from ilmenite, and calcium, aluminium and silicon from anorthite.

    Fluorine does not occur in the lunar soil in significant amounts, hence all fluorine used in the extraction process must be imported from Earth. Although elemental fluorine is one of the most hazardous substances to deal with, it can be safely transported in the form of fluoride salts, usually Sodium or Calcium Fluoride. It is essential that nearly all fluorine used in the extraction process be recovered from the fluoride by-products. This precludes the discarding of any by-products which do not contain any other particularly useful materials. All by-products must be processed using electrolysis or other treatments to recover the fluorine for further oxygen extraction. This is simpler if only one mineral is used as feedstock in any given extractor and there are fewer by-products to process.

    Although oxygen production will be the main business of the first IST lunar base, this will change as it produces not just materials but products or components of products for use in cis-lunar space. These products will include orbiting power stations and zero-g manufacturing facilities. Increasingly the Moon will produce components and equipment used for the exploration of Interplanetary Space, particularly Venus, Mars and the Asteroids.

    The composition of the Moon's crust is essentially very simple. It is about 50km thick on average and consists mainly of anorthositic minerals, of which anorthite - a compound of calcium, aluminium, silicon and oxygen, and other similar plagioclase minerals constitutes about 80 percent by weight. The lunar maria consist of basalt rock made largely of silicate minerals like olivine which erupted from the Moon's mantle. Olivine has a specific gravity of at least 3.2, whereas anorthite has a specific gravity of about 2.7. Hence the basalt layer on the Moon's crust in mare regions, inverts the normal layering of the Moon with heavier compounds generally located deeper than lighter ones. One consequence of this is the characteristic "cracking" marks on the surface of the lunar maria, which indicates that they have slowly pushed down the lighter anorthosistic crust beneath them, causing their own surface to break along fault lines. The lunar regolith is a layer at the top of the lunar crust about 5 metres thick and consists of broken and compacted material formed by the combined effect of countless meteor impacts over the ages. It's composition is more complex, containing a great many minerals and elements, some of them in very small amounts deposited by the solar wind and micrometeorites, some more concentrated in certain areas due to being brought by a specific large meteor impact.

    The simple overall structure of the Moon's crust reveals an enormous amount of variety examined in detail. Currently the geological surveying of the Moon has only been carried out by a small number of orbiting craft and small number of expeditions which have returned data and rock samples directly from the lunar surface. Every such surveying activity to date has revealed surprises about aspects of lunar geology. In order to plan mining activity, both at a large scale for bulk oxygen and common metal extraction, and for specialised operations at a smaller scale for other materials which might useful even in fairly small amounts, accurate detailed survey data of the entire Moon is really needed. This would be useful for planning the location of moon bases in general and contribute enormously to the understanding of the Moon's formation which in turn is a valuable insight into the formation of the entire Solar System and of planetary formation in general.

    In addition to orbiting global survey craft and missions to sites of specific interest, what is needed is a comprehensive high resolution survey of the lunar surface by craft flying slowly at low level over each part of it, followed up by ground vehicles which take soil samples and record other geological data. A problem here is that craft cannot "fly" per se over the lunar surface since there is no atmosphere. Such survey craft would have to be rocket powered, which is relatively expensive even if rocket fuel should be very cheap on the Moon. Nonetheless it will be included in the specification for the first phase of lunar development by IST, that a successful design of both flying and ground based automated survey craft be developed. These could be used for an expedition to the lunar polar regions to determine in detail the composition of frozen material which may have accumulated in permanently dark crater interiors there. It is possible that there are millions of tons of valuable materials including hydrogen in such accumulations, however IST does not intend to try and operate a facility at the lunar poles in the first phase of its lunar activities. The reason is that such operations would be extremely difficult and too dangerous for personnel. Operations would have to carried out in permanent darkness and at very low temperatures, and access to the sites from space would have to achieved through polar trajectories which are more difficult and dangerous compared to orbital manoeuvres in equatorial alignments.

    The potential value of materials at the lunar poles is very great, but IST will not attempt operations there without detailed survey data, and not before a comprehensive support network of lunar space stations and ground bases is in place, and significant experience of lunar mining has been gained in more favourable latitudes.

    It may be of concern to some that mining operations on the Moon will cause irreparable damage to the Moon which is essentially in a pristine state that has evolved naturally over billions of years. Whilst it is true that processing large amounts of lunar regolith will cause a permanent change to the lunar surface in places, it is the intention of IST that the original state of all such areas be recorded as accurately as possible before mining operations commence, and that the composition of excavated material be determined and recorded in as much detail as possible. This will not only make it possible to reconstruct the exact original state of the location in a simulation, but will provide a great deal of valuable geological data about the local and general structure and formative process of the lunar crust. This will enable highly plausible simulations of the state of the Moon not only in the present but also in the past and the future. For potential lunar tourists, the reality is that guided tours of the lunar surface with tourists wearing space suits are not very likely to happen, mainly for safety reasons. Most lunar tourists will be virtual tourists, experiencing the Moon via virtual reality, which in the years to come will be of such quality that it will be almost indistinguishable from reality itself. Lunar operations which provide significant information about the Moon's composition and structure will enhance the quality of such experiences for virtual tourists.

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