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 Main Page > Colonising Space > Space habitats
 A pair of O'Neill cylinder habitats  Inside a large landscaped cylindrical habitat (credit: Eric Bruneton) Space is a very harsh environment and it may be hard to imagine wanting to live in such a seemingly bleak place, but taming it is only a matter of some (admittedly fairly serious) engineering and is entirely within our current technical capability.
There are many challenges to enable building these towns and cities off-Earth. Two prominent ones are raw materials and gravity. A colony of any size will have to be self-sufficient in materials as it will not be practical to ship them up from the surface of the Earth due to the enormous energy required to climb against its pull. Escaping this pull long-term also causes major problems for the human body. Muscles get very weak, including the heart, and bones de-mineralise. The only real solution is to generate artificial gravity by rotation – even for Moon-bases if people are going to stay for any length of time.
To balance these difficulties, living in space brings many advantages. One is reliable, abundant solar energy, not blocked by the atmosphere or subject to weather or time of day. Another is control of gravity; a rotating space colony would have normal Earthlike gravity at the periphery and zero gravity at the center. Large-scale construction and other industrial activities could be done at the center, reducing the energy they need to almost zero. A space habitat offers an opportunity to construct an artificial ecosystem, which could be optimized for agriculture and for human culture. A space colony could be kept at any desired temperature, have any desired weather conditions and any desired seasonal and diurnal cycles. Careful controls could keep pests from being introduced to the ecosystem, allowing significantly higher agricultural yields. Moreover, infectious diseases could be excluded from space habitats.
There have been many studies over the past thirty years to understand what kind of habitats could be built and what size constraints there are based on current engineering knowledge. Surprisingly in the 1970s the answer was that using bridge and ship-building techniques it would possible to build cylindrical mega-structures up to 30 kilometres long and 6 kilometres in diameter, with a single one able to comfortably house several million people. Materials like carbon fiber have since allowed us to imagine safer, stronger, more efficient habitats. A more recent design for a space habitat is described here.
Being mega-scale engineering projects, it is not hard to see that similar techniques used in the habitat's construction could be used to make the interiors of these habitats be like beautiful places on Earth, such as rolling green English countryside. Some designs even have enough atmosphere inside them to make the sky appear blue.
Material
 Lunar mass driver which could be used to launch mined material from the moon into lunar orbit using solar power. The moon is rich in titanium and aluminium, which could be used to build space colonies. It would be far too inefficient to build these huge structures from material brought up from the surface of the Earth, so for orbiting colonies near Earth it has been proposed to use material mined from the moon or near-Earth objects  (particular asteroids and comets) and transported to where it needs to be using solar powered mass-drivers .
Life support
To survive in space, a person needs a minimum of 1kg of oxygen, 0.5kg of dehydrated food and 3.5kg of water per day [1]. Shuttle flights simply bring all the food they need, and bring their waste back with them, but for permanent space habitats, it is necessary to find a way to produce food in space.
 Biosphere 2 was an attempt to make a closed ecological system on Earth. Mastering this is an important step towards building permanent space habitats. There have been several attempts on Earth to construct a closed ecological system and we have learned a lot from these. If we can build a fully closed ecological system on Earth, there is no reason why we cannot do so in space.
Space settlements will not have the easy access to the large store of resources we have on Earth. For this reason, they will have to be models of sustainable communities without pollution, waste or unsustainable harvesting of materials. The technologies of sustainable communities on Earth and sustainable communities in space must be considered together; they both require non-polluting industry, circular resource-chains and sophisticated recycling.
Areca palm, Snake plant and money plant are exceptional for their ability to create clean, fresh air for people [2]. A human can survive in a sealed environment with just four plants like these. The application of this to space habitats is obvious.
Aeroponics, as discussed here, can be used to grow plants in space. An aeroponic greenhouse could easily provide all the air and food space-dwelling humans need. Conservatively, this would require 20m2 per person, perhaps as little as 5 m2.
Biophilia is an important aspect of plant-based life-support systems. It is psychologically difficult to be surrounded by nothing but metal and machines for months or years on end, and psychological stability is a major issue on long-term space missions. Introducing a leafy, green, fresh stimulus to the space-dweller's sensorium is of immense benefit.
Places
Low Earth orbit
The easiest place to get to from Earth is low earth orbit, although due to the Earth's strong gravitational pull it requires enormous amounts of energy to bring material up from the surface and one could not be classed as self-sufficient here, however the views are pretty good. If we develop more efficient means of access to space than we currently have, low Earth orbit habitats become more feasible.
Geosynchronous orbit
In a geosynchronous orbit the habitat would hover the same spot on Earth which would mean that one would have the same day / night cycle as on the surface which is an important consideration with human physiology.
Lunar orbit
In lunar orbit the moon is within easy reach but the habitat will be subject to the moons two-week long day / night cycles which might not be to everyone's taste, although of course the normal light rhythms can be replicated internally with lighting.
Moons and planets
Surface of the moon
The surface of the moon provides a continent-sized area to inhabit and somewhere to 'get outside'. However it is not clear that the one-sixth of Earth's gravity here is enough to stop degredation of the human body over extended periods, but this could be overcome by having large circular habitats that rotate to simulate a 1g environment.
Surface of Mars
Terraforming refers to re-engineering the environment of a planet to make it more like Earth, that is, more friendly to life. To terraform Mars we need three things: heat, oxygen and water.
Ironically, the very scientific knowledge gained by studying the destruction of the Earth's biosphere can be applied to engineering a new biosphere on Mars; releasing enough CFCs or similar greenhouse gases into the atmosphere should create enough global warming to make the planet amenable to human life. There is plenty of water frozen below the surface, which should melt if the temperature is raised enough. Oxygen could be supplied by culturing bacteria that can release it from metallic oxides, or by using advanced automation to build large-scale plants to release the oxygen using industrial processes.
After enough time in zero-gravity environments, astronauts suffer degeneration of the muscular and skeletal systems. All of Man's experience so far has either been at zero-gravity or Earth's gravity; whether Mars' low gravity will pose the same problems remains to be seen. If this turns out to be an insurmountable issue then homes and other living spaces could be built within very large diameter rotating structures on the surface to simulate 'Earth gravity'.
Venus atmosphere
There are formidable obstacles to establishing human life on the surface of Venus: the surface temperature is around 450°C and the pressure is around 90 atmospheres – equivalent to the pressure at around one kilometre under Earth's oceans. However, 50km above the surface of the planet we find Earthlike temperatures and pressures. It has therefore been proposed that the easiest way to establish a colony on Venus would be to fill a gigantic balloon with breathable air. Such a structure would float above the denser air of Venus in the same way that a helium balloon floats above Earth.
The gravity on Venus is 91% of that on Earth, so it is unlikely any special measures would need to be taken to create artificial gravity.
These floating habitats could also be equipped with devices to alter the atmosphere with the aim of eventually terraforming Venus.
Venus surface
Mars orbit
Other moons
Many to choose from.
Enceladus around Saturn has H2O.
Europa around Jupiter has lots of H2O and O2. Underneath the ice are liquid oceans which may harbour life.
Dyson swarm
A Dyson swarm refers to a series of habitats build in space around the Sun. These habitats would be artificial space stations like a Stanford torus , rather than being built on naturally-occuring celestial bodies. The technology to build these has been around for decades, as they require nothing more than industrial manufacture of large metallic structures, similar to what is used to build supertankers on Earth.
The first step to building such habitats would be to set up automated facilities on the moon to mine titantium and iron and launch it into space. A habitat could then be assembled in space, and used to manufacture another habitat, making them self-replicating. Using materials from the moon and asteroid belt alone, we could create artificial habitats with thousands of times the land area of Earth, able to comfortably accomodate tens of trillions of people.
Lagrangian points
Solar orbit
Asteroid Belt
Ceres
(Water ice)
Various types of habitat
- Stanford torus
- O'Neill cylinder
- Crater bubble
- Rotating moonbase for 1g
- Hollowed out asteroid
- Zero-G station
- Rotating dumbell
Further information
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