• Why should we colonise outer space? An insurance for existential risks to mankind (nuclear war, climate change), to create new ecosphere instead of destroying it, to allow human population to expand while not pressing on land and resources – and because it is exciting.
• Yes, it is feasible to build colonies outside the Earth for human habitation, with current knowledge of physics and reasonable assumptions about technology – so no warp drives, and utilising the nearby solar system, no further than Mars.
• The biggest single barrier is the huge cost of getting stuff (people and goods) free of the Earth’s gravity. Some cost reductions are possible by recovering rocket stages for reuse (as Space X have done with first stages) and perhaps in the longer term by imparting energy from a fixed point on Earth or in space (skyhook, launch loop, or space elevator). But if space is to be colonised, the large amount of resources needed will need to be sourced from places with lower gravity. Moving around in space takes much less energy.
• Such resources are plentiful. Major metals (notably iron, and aluminium ores) are available on the Moon, water from Mars, and the lunar dust (regolith) provides soil for crops and building materials. The dense carbon dioxide-rich atmosphere of Venus could provide oxygen, carbon and nitrogen (collector ships could skim through the atmosphere, without incurring a major gravitational penalty).
• However the Moon and planets are not suitable for settlement. Venus and Mercury are too hot. The Moon and Mars are rather small, mountainous, and virtually or actually airless. The main problem with them is the low gravity (20-40% of Earth). Living for any extended period in low gravity has substantial health issues.
•There is an alternative. In the mid 70s academic physicist Gerard O’Neill asked the question: how big could you build free standing structures (cylinder or torus) in space, which you could rotate to provide artificial gravity (through centrifugal force)? The answer, it seems, is surprisingly large; using steel, up to 6kms radius.
• There are two major objections to O’Neill style habitats: exposure to cosmic radiation and meteorites, and that the cost of building them would be prohibitive.
Micrometeorites will continuously bombard a habitat, but experience with the International Space Station suggest that they will do little damage. The risk of being struck by a larger meteorite is very low, and they may be detected and deflected. The problem might be worse in Low Earth Orbit (LEO) with the amount of space junk up there.
The radiation problem is more serious. Surrounding the habitat with a water jacket and a lightweight plastic (such as polythene) would provide sufficient protection in LEO, but the weight of such shielding required in deep space would be prohibitive. A magnetic field mimicking the Van Allen belts which surround the Earth would do it, and research on this is promising.
I have shown some calculations below which estimate construction costs for a large scale habitat, capable of supporting 200,000 people with space for agriculture and recreation. They are very rough and ready, but give an order of magnitude – about 2-3 times the average installed capital costs per head of a developed country, comparable to that of major metropolitan areas on Earth.
• The cost calculations, however, assume an established infrastructure of manufacturing and transport in space. How do we get there? One way forward is suggested by the European Space Agency’s ideas for building a small Moon base. Essentially, get a robot to do it, including using 3D printing techniques. This can be taken further, to the next stage of getting a robot to construct processing equipment to produce metals, silicon for solar panels, and so on , for assembling in space for a small habitat which would then construct the parts for a larger habitat, and so on.
• It would be a long term goal, nevertheless. Some income may be made in the development from solar power from space, from space tourism and technical spin offs, but it is doubtful that any financial return on investment in space colonies for a very long time – so state funding would be needed. Why, however, would states do this? Prestige, military strategy – and environmental pressure. A realisable objective is to campaign for 1% of GDP in developed countries to be spent on space development. It’s a lot less than is spent on defence
It’s the right thing to do