Needed on the Moon
If you tour any construction site or factory on Earth you will see a number of basic industrial mechanisms that are at the foundation of all processes. We must design lunar versions of these mechanisms if we are to build a successful settlement on the Moon. The harsh lunar environment makes many of these very challenging designs.
The factors making machine design difficult in the lunar environment include:
The familiarity of the Earth versions coupled with the harshness of the lunar environment make many of these redesigns excellent student projects. They are also a fertile field for entrepreneurs.
The following list covers basic mechanisms found in Earth industry that we must have for commercial operations on the Moon:
This is the seal on a spinning shaft such as a motor. It keeps dirt out of the bearings and the lubrication in. It must be flexible yet stand up in a long life of riding against a spinning shaft.
On Earth, these seals are made from rubber and plastic compounds and are highly successful in a wide range of environments.
On the Moon, the big challenges include the gritty dust and the lack of an atmosphere. This adaptation should not be too challenging but a great many materials may need to be tested in realistic lunar conditions.
These seals must slide across a polished metal rod as in hydraulic pistons. Look around an Earth construction site and you will see these pistons everywhere. These shafts move in and out exposing their surfaces first to the internal hydraulic oil and then to the local environment. The seals must hold in the significant pressure while withstanding the wear of sliding.
On Earth, these seals are made from rubber and plastic compounds and, again, are highly successful in a wide range of environments. The gas shocks in modern cars are one good example.
On the Moon, this design problem is a project killer that must be solved. The lunar dust is highly abrasive. The film of oil left on the rod will probably hold the fine dust. The seals must push this mix out of the way or withstand this extremely abrasive paste for a very long time. A blow out of the oil would be a major break down and could be life threatening.
Linear seals are one of the design challenges for commercialization of the Moon.
Hydraulic pistons can be lubricated to maintain a linear seal by encasing the entire length of the hydraulic piston in accordion-fold type sleeve that holds a pound per square inch or so of gas pressure around the hydraulic piston so the lubricant does not evaporate. The same can not be done for the rotary bearings of wheels. A thin foil accordion-fold micrometeor shield can in turn protect the pressure retention sleeve. The dual sleeves around the hydraulic pistons would also keep dust away from the polished metal rod. This is the sort of solution that is referred to in Robots in Space Suits.
Wire Rope Systems
Wire rope systems with their wrenches, pulleys, and hooks, are one of the most useful devices in Earth industry. They are very widely used despite their inherent dangers. These systems are notorious for crushing off fingers and delivering slashing wounds when broken cable ends fly.
On the Moon, wire rope systems will have difficulty surviving in the dusty environment, but the chief design challenge is the danger they pose to a person working in a spacesuit.
This problem will be addressed by having all wire rope work in a vacuum environment done by remotely controlled machines.
The conveyor belt is the foundation mechanism of mass production. They move stuff. Typically they contain a large number of moving parts and joints. They are driven at one location and many have many support wheels and rollers along their length.
On the Moon, the primary challenge is wear from the dust.
A conveyor belt designed for lunar vacuum use can be a train of slats supported at their ends by magnetic suspension in tracks and a belt of fiber-glass riding on the slats. Electronic controls are needed for the magnetic suspension, a control unit at both ends of each slat. The tracks can be roughly U shaped channels that are swept clean of dust continuously by fiber-glass brushes. The belt and brushes would be expendable items. The U shaped tracks will have holes at the bottom so dust can be swept out through the bottom.
The production of parts out of solid blocks of different types of steel would require a lathe. This lathe would work the same way as on Earth and will become the first machining tool. It is possible to build complex machines with a lathe. It is the corner stone of the manufacturing establishment it is the tool to build tools and to build the machines that build machines. The lathe, drill press, milling machine and other machine shop tools will be used in a pressurized machine shop and so require no different design considerations than on Earth.
Electrical Discharge Machining
EDM technology has been used on Earth to manufacture small metal parts that cannot be mass produced with lathes or other metal cutting technologies.
Metal, in blocks or sheets, is placed between two electrodes and a current is passed to remove material.
EDM is expensive on Earth, it requires a complex instructions set to be programmed in a CNC language.
Moving around a lunar settlement will not require vehicles with wheels. Wheels must have tires of some sort. The ability to negotiate lunar slopes will be a major factor in lunar transportation. Good tires on wheels can be used for transversing these slopes, but there are other options.
On Earth, tires are universally made from synthetic rubber and inflated with air. This design is completely unsatisfactory for the lunar environment.
On the Moon, the Apollo rover tires were made from metal mesh and worked reasonably well. They did however throw up a lot of dust and were never pushed onto steep slopes. Wheels designed for lunar vacuum use have so far been of rather limited design lifetime. The challenge of producing wheeled vehicles for ten years of industrial use might be successfully accomplished but legged vehicles could serve. Vehicles on the moon that walk on legs do not need rotary seals and the linear seals that they need can be satisfactorily produced (see above).
The Caterpillar or tank tread is used extensively in construction and mining on Earth to allow heavy equipment to move across open ground. They are massive and contain a very large number of joints and bearings.
Treads can be a difficult maintenance problem in dusty environments. One of Field Marshal Romel's great innovations in the WWII North Africa campaign was to load his tanks onto trucks for long hauls. This greatly reduced the break down rate of the treads.
On the Moon, the dust will be a severe challenge for treads. It will simply wear them out. The mass of most tread designs is also a problem as long as that mass has to be shipped from Earth.
One solution is to not use tank treads on Luna but to use legged vehicles in their place. Legged vehicles do not need a rotary seal which has been a problem on the moon but use linear seals in hydraulic pistons in their legs. A method of designing such seals is available (see above). Computerized means of controling legged vehicles have also been developed in recent years.
Power Distribution Cable
Lunar power generation stations, solar or nuclear, will need to be separated from both living areas and commercial operations. Distance is needed both for safety and to avoid the dust kicked up by human activity. Also the optimal site location for one activity is rarely the optimum location for another.
We will need a way to efficiently send electrical power over at least a few kilometers. This must be done safely and with a minimum of mass shipped from Earth.
Cooling for a power distribution cable is often not a problem on Earth where convective cooling from the ambient air is readily available. On Luna, if a cable were buried in regolith, resistive heating could build up in the distribution cable. A cooling system with radiators is possible but overhead cable may be the most economic solution.
See also Structural Engineering
How can we build a settlement without good cement? Both in the form of concrete and as mortar, it is the universal construction material on Earth.
Cement is a good example of a process we depend on on Earth that must be modified for the Moon. On Earth we heat limestone driving off the water to make slaked lime. We add a stabilizing mineral. The Romans used volcanic ash; we use gypsum. We mix this cement with washed sand to make mortar or with sand and crushed rock to make concrete.
The cement has the amazing property when mixed with water, it sticks to rock or brick and becomes stone hard. The water does not evaporate or dry. The water reacts chemically with the lime and remains. Every drop put in the wet mix is present in the finished product. This cannot happen in a vacuum.
The finished product has great compressive strength but little tensile strength. Fortunately when iron bars, which have great tensile strength, are placed inside concrete, the cement coating both bonds strongly and protects the iron from rust.
On Earth, most of the minerals used to make cement are associated with water in some way. Limestone is laid down by living organisms at the bottom of shallow seas. Gypsum forms when an inland sea dries up. There is no water on the Moon and there never has been. No minerals of this type can be expected.
The Moon is covered with ground up rock and we will produce a number of interesting by-products when we harvest volatiles from it. We need to find a way to convert some of that particulate mater and some of those chemicals into a solid construction material. We need to do this with as little mass shipped from Earth as possible.
Steel rebar will be hard to manufacture on the Moon. On Earth it is made by recycling old cars. It should be possible to make rebar from meteoric iron on the moon but fiberglass may be cheaper for many purposes.
With a decent mortar, rough stone masonry could become the defining architectural element of our lunar settlement (see Architecture in Field Stone). There is certainly no shortage of rocks.
Glue & Sealants
Outside on the Moon, we need to be able to glue things together and to seal leaky enclosures. This ability is life-or-death. Welding metal containers is possible. Organic polymers for sealing structures needing repair will be necessary in some cases.
Color in Architecture
The Moon is gray, asphalt parking lot gray, monotonous, boring gray. We need to add color. We need bright colored paint. The bulk of the paint must come from lunar materials. Titanium is available on Luna. Titanium dioxide is used as a white pigment. Various elements on Luna can be mixed into glass to change its color. Iron(II) oxide gives glass a blue-green color. Cobalt can give a blue color. Cadmium sulfide produces yellow or when used along with selenium can produce red. Tiny colored glass beads can be used to color paint.