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Lunar Infrastructure

  • IST takes the view that placing large space colonies supporting millions of inhabitants in cis-lunar space, or even in a solar orbit that is close to that of the Earth, is too dangerous to even consider. The Earth will continue to support billions of human inhabitants on an indefinite basis and the biosphere as whole has to be protected from what would be complete annihilation if a structure weighing millions or even hundreds of millions of tons were to collide with it. IST supports the idea that a weight limit of about 10,000 tons be imposed on any single structure anywhere in the general vicinity of the Earth-Moon system. On that basis, the Moon becomes important, not just for its mining potential, but as a virtual space colony. It would be useful if a certain percentage of the growing cis-lunar population of astronauts, engineers, geologists and so, could be based for long periods of time on the Moon, rather than on rotating space stations in cis-lunar space. If these space stations are limited to 10,000 tons they will be fairly comfortable to live in, but will still have higher radiation risks, higher meteor impact risks and will need to be supplied with more resources than a lunar colony.

    For the Moon to support large numbers of people living on it for long periods of time, it will have to construct underground rotating habitats which will provide an artificial gravity field of standard Earth strength. This will involve excavating large volumes of the Moons crust to a depth of at least 50 metres and a radius of about 250 metres. The techniques involved for such engineering are somewhat different from on Earth. Blasting is possible in space construction, but requires special explosive compounds which will have to be imported from Earth initially. The large types of boring machines used on Earth are too heavy to transport to the Moon, use a lot of power, and would not work well as they rely on gravity for reaction forces. Alternatively, the hydraulic radial-axial type rock splitter is a lighter, low powered boring technology where reaction forces are provided by its anchoring system. Laser or microwave drilling is a possibility but using lasers to bore out large volumes of the hard compact rock of the Moon's crust would require enormous energy. Lasers and microwave beams could be used however to cause rock formations to crack by inducing thermal stress, which would make the job of a mechanical rock splitter much easier. These beams could also be used to melt the surfaces of underground excavations and tunnels just sufficiently to create a layer of fused material which would make the structure airtight.

    Despite the inherent difficulties of excavating, boring, tunnelling etc, on the Moon, it appears that these tasks are possible, and that large scale underground operations can be carried out there. Even mining operations could be done underground to extract higher yield rock that is free from the complex set of impurities found in regolith. Rail links could also be created between moonbases through underground tunnels. This is more expensive than placing the railway on the surface, but would avoid many serious problems with operating a railway safely on the lunar surface.

    Efficient transport to and from the lunar surface is a critical part of the lunar economy. IST is very much inclined towards using craft specifically designed for the particular type of operation they carry out, and in this case that means craft used for transporting goods and persons between the lunar surface and Lunar Orbit should not be used for travelling between Lunar Orbit and Earth Orbit. Lunar space stations either in orbit or at L1 and L2 Lagrange points can operate like container terminals. Bulk carriers from Earth would have their individual containers probably of about 5 or 10 tons normally, taken down to the lunar surface by smaller and lighter craft, which would also lift up containers of goods for export to the lunar space station, to be assembled in the hold of the bulk carrier. In the initial stages of the lunar economy all transport could be done with rockets, which although the rocket engines themselves are expensive, fuel would be fairly cheap on the Moon. It would be a great advantage if ISRU fuels such as aluminium seeded liquid oxygen could be use in highly reusable propulsion systems, as opposed to using imported fuel such as hydrogen or methane. Into the future it would be a priority to develop more advanced propulsion technologies for these operations, to achieve a higher degree of usability for craft carrying out increasing numbers of flights.

    For transfer to and from the lunar surface, a propulsion system would need greater thrust than provided by ion drives or similar very low thrust technologies. Possibilities are beam propulsion, rotovators, or mass drivers. IST is not currently of the view that tether based transfer technology is possible even though it should be easier on the Moon that on Earth. Although complex models of tether dynamics have been developed it is still not known exactly how tethers will behave in practice. Using them to deposit and lift material from the surface of the moon would be extremely demanding from a logistical point of view and dangerous. Mass drivers look very promising, but currently their is no acceptable solution to the problem of launching millions of tons of dumb mass in small containers with a total weight per unit less than 100 Kg. If the containers are just a simple wrapper, then an extremely large "dumb mass catcher" of some sort would be required, for which no acceptable design currently exist. If the containers are miniature space ships with enough delta-v capability to effect a rendezvous with a "smart mass catcher", they might be too expensive to manufacture at the rate required to potentially export millions of tons per year to Earth Orbit.

    A heat exchanger based beam technology would be easier in some respects to achieve on the Moon compared with the Earth. The power requirements would be a lot less but still considerable for a lunar colony. On Earth, about 1 Gigawatts of power are needed per ton to achieve orbit. About 100 Megawatts per ton would suffice on the Moon and the total energy requirements would be proportionally less again. This is quite achievable. There would have to be some means of powering the craft close to the ground, perhaps with a separate high power beam group that points more or less straight up. It really depends on the reusability of the system as a whole to determine whether it is economically advantageous. That includes cycle fatigue on the electrical power generation and storage system, the beam generators, the craft heat exchanger and nozzle. A crucial factor would be whether the heat exchanger suffers any significant chemical distortion on each cycle. The system would have to use hydrogen as the inert reaction material, which means initially importing it from Earth. This is not necessarily a problem as IST plans for a lunar economy are premised on a pipeline into space from Earth. Using beam power, about half the weight of oxygen exported back to Earth orbit for general use would have to be imported as hydrogen. The system would become particularly useful if polar ice reserves in the millions of tons could be exploited.

    Such a beam power system could be combined with a maglev launch system to give an initial velocity to the craft. A launch track of 1250 Metres would be required to give a launch velocity of about 500 m/s with an acceleration of 10 g. That would save about half the fuel costs. Similarly for the deorbit phase a decelerator could reduce the transport craft velocity by about 500 m/s. This would improve the import/export ratio of the lunar oxygen economy from 1:2 to about 1:5. Conventional rocket powered craft could also benefit from such assistance, but the problems of building such advanced infrastructure are considerable. Even if most of the structure were placed under a covering to avoid micrometeoroid damage and to provide some radiation shielding, it would be prone to solar flare damage. Also, launch direction is limited for a mass driver, and if only a small number of such sites can be built, material and goods to be launched may have to be brought from some distance.

    Phase 1 of IST's lunar development program will not implement tether based mechanisms, power beaming methods or mass-driver technology for transport between the lunar surface and Lunar Orbit. Instead we will focus on rocket technology, mainly LH2/LOX and gelled aluminium seeded LOX systems. A moon base should ideally have an underground hangar facility for such transport craft, located at least 20 Metres underground. Craft are transferred to and from the external launch pad via a lift similar to that found on aircraft carriers. Thus, they spend as little time as possible exposed to the external space environment, and all maintenance and refurbishment work can be done safely in a shirt-sleeves environment. We intend that such a facility support craft with at least a lift-off mass of 50 tons.

    Transfer of material between Earth Orbit and Lunar Orbit can be done using direct trajectory methods and LH2/LOX rockets. Since most of the weight of the fuel for such rockets is oxygen, a surplus of oxygen can be provided in Earth Orbit from the Moon even though all hydrogen is brought to the Moon from Earth. The high ISP of LH2/LOX rockets gives very good payload percentage of total mass and the potential for fast direct transfer between the Earth and the Moon, which is important to reduce risks for transfer of personnel. A major focus of IST research and development will be to make LH2/LOX rocketry as reliable and efficient as possible. In particular reduction of boil-off of cryogenic fuel components and of LH2 in particular will be reduced to 0.01 percent per day if possible. This will be particularly important in the early stages of moonbase development before more complete transport infrastructure with underground actively cooled cryogenic storage facilities are in place.

    Phase 1 of IST's lunar development program, will also implement transfer of goods between Earth and the Moon using solar sail techniques. At this point IST will limit its ambitions to a sail technology capable of transferring 1 ton between Earth Orbit and Lunar Orbit, although this will require a fairly large sail with advanced control systems. A round trip between Geostationary Earth Orbit and Lunar Orbit using a solar sail could take up to 6 months. This may seem like a hopelessly slow form of transport, even though it doesn't use any significant amount of fuel, however IST believes that the potential of solar sails for cis-lunar and more importantly, for inter-planetary transport, is so great that this method should be implemented in a basic working form as soon as possible. Once that has been achieved, it will be possible to experiment with augmenting the basic method with other technologies such as ion thrusters and laser powered sails. These can boost the performance of sail technology which could potentially become much faster than LH2/LOX rockets.

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