What products are to be made, from what source, and how are they to be made?

At first, a simple return mission would demand only basic needs such as fuel (to allow the spaceship to return to Earth) and life support (for missions involving humans). This might be followed by construction materials for building a permanent base. If this base is able to establish itself and mature into a small colony or science station, more sophisticated products such as performance chemicals will begin to be manufactured.

In the discussion below, oxygen is first used as an example to show the factors affecting the choice of sources and processes. This is followed by a list of other likely products.

Example: Oxygen gas (O₂) provides a nice illustration of many of the issues under consideration.

Oxygen gas (O₂) is critical for breathing, and fortunately compounds of oxygen are very abundant in the Solar System. However, planet Earth appears to be the only place with a large supply of natural O₂, and therefore in other locations O₂ will have to be made from common oxygen compounds such as H₂O, CO₂ or Fe₂O₃. The source (and the process) will depend on three main factors:

1. The abundance of particular materials. CO₂ is the commonest gas in the atmosphere of Mars, yet CO₂ is almost unknown on the Moon.
2. The relative ease with which oxygen can be obtained. Silicates such as MgSiO₃ are common in soil and in many places in the Solar System, but MgSiO₃ has a high melting point and it is also extremely stable, such that production of O₂ from MgSiO₃ requires a very large amount of energy. FeO or Fe₂O₃ may be less common, but easier to break down to the elements.
3. The available energy sources will determine which type of process is most feasible in any given location. Locations near the Sun may favor photochemical or solar powered electrochemical processes, but in places where heat is the main source of energy thermal processes may be preferred. This will in turn affect the source mineral.
4. Production of any one chemical should always be considered in conjunction with other important co-products. Thus on the Moon ilmenite (FeTiO₃) is often advocated as a good oxygen source, because iron and titanium metals would be valuable co-products. On Mars, CO₂ and H₂O would almost certainly be used as the basis for O₂ production, because of valuable coproducts such as hydrogen (H₂) and/or methane (CH₄, for rocket fuel), as well as the large array of organic chemicals (including polymers) which might also be made from methane.

Products for human life support:

Any human presence on a planet or moon for any length of time will require materials for life support. These materials should come from local sources, as much as possible. If a base also includes plants and animals, the materials may form part of a complete biosystem.

As well as oxygen (discussed above), water/ice (H₂O) is also an essential material. In most locations this occurs naturally, but in some (such as the Moon) it is a scarce resource (despite being the main "mineral" of hydrogen). In these places the challenge will be to have a viable method for extracting and recycling the water efficiently.

Local supplies of organic materials of some kind are also highly desirable, even though the biosystem is expected to be able to recycle such materials well. These may be in the form of carbon dioxide (CO₂), which can be fixed by imported plant materials to provide food for humans/animals. This would be the case on Mars, which has an atmosphere composed primarily of carbon dioxide. On hydrogen rich moons such as Titan, there are typically large amounts of alkanes such as methane (CH₄) and ethane (C₂H₆). These would probably best be converted to carbon dioxide and then fixed by plants to provide the complex organic materials needed for human foodstuffs.

Other useful materials:

Fuels are likely to be very important both for local travel on the moon/planet and for interplanetary travel. On the Moon (where hydrogen is scarce), it would be necessary to produce oxygen (see above) as a fuel oxidizer, with hydrogen or methane supplied from Earth. On hydrogen rich moons such as Titan, methane occurs naturally, but again oxygen would need to be manufactured. On Mars, both methane (or toluene) and oxygen would need to be made from naturally occurring carbon dioxide and water. For local ground travel hydrogen/oxygen fuel cells will probably prove to be the most effective.

Construction materials will be based on local minerals, ideally involving no chemical manipulation before use. In silicate-rich locations such as the Moon, silicates are likely to be used (as on Earth) for producing bricks/blocks for construction. On ethane-rich Titan, organic polymers such as polyethylene will require some chemical processing. Metals such as iron, aluminum, magnesium and titanium may be important for more demanding applications, with the metal depending on minerals and applications. Iron may be often the cheapest metal to produce, but it is also the densest ("heaviest") by far. Extreme care must be taken to take into account the chemical environment when selecting a construction metal; the last three metals can only be used on Earth because of a protective oxide coating. It may be possible to use anodic oxidation to protect the metal. If this coating is not present (because of the absence of atmospheric O₂), the metals may prove to be dangerously reactive towards common materials such as water^*, particularly when finely divided. On the Moon and some asteroids, small amounts of iron and nickel occur naturally as the free metals, making these attractive if they can be mined easily. Rare metals such as platinum, palladium and rhodium (useful in catalysts) might be obtained from near Earth asteroids (NEAs), and these might even be used to supply Earth.

Performance chemicals are those with specific applications. These will be needed in much smaller amounts, but a greater variety of chemicals are needed. Initially these would best be brought from Earth, but local production would be vital for the long-term viability of the outpost. Many of these materials are carbon-based, so a local equivalent of Earth's petrochemical industry may be needed. Important materials would include oils and greases, most likely based on silicones, hydrocarbons and fluorocarbons. Organic polymers such as polyethylene, poly(isoprene), nylon, polyester and PTFE would provide a useful range of fibers (for clothing, etc.), rubbers, paper, packaging materials and special engineering materials. Special ceramics may be needed. A variety of other organic chemicals would be useful for other uses such as dyes and inks, medicines, solvents, soaps and surfactants. If microprocessors were to be made locally, then a range of chemicals would be needed to support this industry, such as pure silicon, copper and hydrofluoric acid (or whatever chemicals may be used in the future).

Clearly we do not know what new materials may be invented in the future, but this survey does give some flavor of what products need to be considered.

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Last updated February 6th, 2005.