• 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), but for the really low launch costs are from from a fixed point on Earth or in space. It is worth investing in a system like Startram. But if space is to be colonised, the large amount of resources needed will need to be sourced from places with lower gravity or none. Moving around in space takes much less energy.
• Such resources are plentiful. They exist on the Moon and Mars, but even with lower gravity than Earth, the cost of transporting mass materials from them is too expensive. Much lower potential costs are from near Earth asteroids, which contain billions of tons of resources. The dense carbon dioxide-rich atmosphere of Venus could provide oxygen, carbon and nitrogen and propellant for space ships (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.
• Two major objections have been made 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 metropolitan areas on Earth.
• The cost calculations, however, assume an established infrastructure of manufacturing and transport in space. That is not realistic at first, so the first habitat will need to have most of its materials transported from Earth. That is why startram or similar, with launch costs as low as $43/kg, needs to be built.
• 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 • Building a low cost launch system, developing asteroid mining, a starter habitat and then a full size one could be done for around $350 billion, less than half the US annual military budget. It could be done in a generation, if any nation had the will to do so.
A Critical Path