The motivations for the construction of space colonies are varied, among others: survival, security, energy, extraction of raw materials and monetary.

Space habitats are immune to most of the natural disasters that Earth suffers, such as earthquakes, volcanic activity, hurricanes, floods and tornadoes. A space habitat can be the passenger compartment of a large spacecraft destined to colonize asteroids, moons, distant stars, or other planets (see also: Space and Survival). Dispersing our population into multiple self-sustaining space habitats throughout the Solar System will increase our chances of survival as a species in the event of a global disaster on Earth.[4]​.

Space is literally filled with light produced by the Sun. In Earth's orbit, it reaches 1400 watts of energy per square meter. This can be used to produce electricity using photovoltaic cells or heat engines installed in power generating stations, and providing light for plants to grow and to heat space colonies, or to heat colder planets (such as Mars "Mars (planet)").

Most asteroids are a mixture of the materials mentioned above, virtually all the stable elements of the periodic table can be found in asteroids and comets and more importantly, because these bodies do not have substantial gravity wells, it is very easy to remove the materials obtained from them and transport them to the construction site.[3]​.

It is estimated that there is enough material in the main asteroid belt to build space habitats equal to the habitable surface area of ​​3,000 planets on Earth.[5]​.

The colonies would have constant access to solar energy up to very great distances from the Sun. The lack of weight allows the construction of large flimsy structures such as mirrors to concentrate sunlight.

Space habitats can be supplied with resources from extraterrestrial locations such as Mars, asteroids, or the Moon (In-Situ Resource Utilization, ISRU;[4] See also asteroid mining.) One could produce oxygen for breathing, drinking water, and rocket fuel with the help of ISRU.[4] It may even be possible to build solar panels from lunar materials.[4]

Habitats can be built to have immense population capacity. Using free-floating resources in the solar system, current estimates range into the trillions.[6]​.

Trade between Earth and space habitats would be easier than trade between Earth and a planetary colony, since colonies orbiting Earth do not have to overcome a "gravity well" to export to it, and a smaller gravity well to overcome to import from Earth.

Even the smallest of the habitat designs mentioned is more massive than the total mass of everything launched by Humanity into Earth orbit. The prerequisites for building habitats are cheaper launch costs or a mining and manufacturing base on the Moon or another body that has a low delta-v from the desired habitat location.[3]​.

Air pressure, with normal partial pressures of oxygen, carbon dioxide and nitrogen, is a basic requirement of any space habitat. Basically most colony designs propose large thin-walled pressure vessels. The required oxygen could be obtained from lunar rocks. Nitrogen is easier to obtain from Earth, but it is also almost perfectly recyclable. Nitrogen is also the form of ammonium that can be obtained from comets and moons of the outer planets. Nitrogen can also be obtained in unknown quantities in certain other bodies in the outer solar system. The air in a colony could be recycled in several ways. The most obvious method is to use photosynthetic gardens, possibly via hydroponics or forests. However, this does not remove certain industrial contaminants, such as volatile oils and excess simple molecular gases. The standard method used on nuclear submarines, a similar form of closed environment, is to use a catalytic burner, which effectively removes most of the organic contaminants. Additional protection could be provided by a small cryogenic distillation system that would gradually remove impurities such as mercury vapor. (element)") and noble gases that can be burned catalytically.

Organic materials for food production also need to be provided. At first, most would have to be imported from the Moon, asteroids or Earth. After that, recycling should reduce the need for imports. One proposed recycling method would begin by burning cryogenic distillate, plants, trash and wastewater with air and an electric arc, and then distilling the result. The resulting carbon dioxide and water could be directly used by agriculture. The nitrates and salts in the ash could be dissolved in water and separated into pure minerals. Most of the nitrates, potassium and sodium salts would be effectively recycled as fertilizers. Other minerals containing iron, nickel and silicon could be chemically purified in batches and reused industrially. The small fraction of remaining materials, well below 0.01% by weight, could be processed into pure elements with zero-gravity mass spectrometry and added in appropriate amounts to fertilizers and industrial supplies. This method currently only exists as a proof of concept being considered in NASA studies. Most likely, this method would be greatly refined when people begin to actually live in space habitats.

Long-term orbital studies have proven that zero gravity weakens bones and muscles and disrupts calcium metabolism and the immune system. Most people have suffered from problems with congested airways and sinusitis, and a few others have been affected by dramatic and incurable dizziness. Most space colony designs would rotate to use the resulting inertial force to simulate gravity. NASA studies with chickens and plants have proven this to be an effective physiological substitute for gravity. Rapidly turning your head in such an environment causes a tilt to be felt because the inner ear moves at a different rate of rotation. Studies carried out in centrifuges show that people suffer from motion sickness in habitats with a rotation radius of less than 100 meters, or with a rotation rate of over 3 rotations per minute. However, using the same studies and statistics it can be inferred that almost all people should be able to live comfortably in habitats with a rotation radius of more than 500 meters and with a rotation less than 1 rotation per minute. The more experienced people were not only more resistant to motion sickness, but they could determine the "spinward" and "antispinward" directions in the centrifuges.

NASA designs

Designs proposed in NASA studies include:

Bubble World

The bubble world or the Interior/Exterior concept originated in 1964 by Dandridge M. Cole") and Donald W. Cox in a book called Islands in Space: The Challenge of the Planetoids (in Spanish: Islas en el Espacio: El Desafío de los Planetoids).[15]​.

The concept is about drilling a tunnel through the long axis of a large asteroid composed of iron or iron-nickel and filling it with a volatile substance ("Volatility (chemistry)"), possibly water. A very large solar reflector would be built nearby, focusing the heat generated by the Sun onto the asteroid, first to weld and seal the ends of the tunnel, then in a more diffuse way to slowly heat the entire surface. As the metal softens, the water inside expands and inflates the asteroid's mass, while rotational forces help form a cylinder with this material. Once expanded it will be allowed to cool, can be rotated to produce artificial gravity, and also filled with soil, air and water. By creating a small bulge in the middle of the cylinder, a ring-shaped lake can be created. The reflectors will allow sunlight to enter and be directed where necessary. Clearly this method would require a significant human and industrial presence in space to make it feasible.

The bubble world concept was popularized by science fiction author Larry Niven in his fictional Known Space stories, which describe such worlds as the primary habitats of the Belters, a civilization that colonized the Asteroid Ring.

Hypothetical designs

In the 1990s, as the potential utility of carbon nanotubes as a structural material became apparent, proposals arose for much larger habitats taking advantage of the use of this material. The technology to produce nanotubes of the required length is not available, so these designs remain speculative.

Bigelow Commercial Space Station

The Next Generation Bigelow Commercial Space Station") was announced in mid-2010.[18]​

Initial construction of the station is expected to begin in 2014/2015, and will consist of two Sundancer modules and one BA-330 module.[19]

Bigelow has publicly shown design configurations of the space station with up to nine BA-300 modules containing 2,831 m³ of habitable space.[20]

Bigelow began publicly referring, in October 2010, to the initial configuration - of two Sundancer modules) and one BA-330 module - as Alpha Space Complex.[21]​.

Bigelow recently announced that it has agreements with six sovereign states to use commercial space station orbital facilities: the United Kingdom, the Netherlands, Australia, Singapore, Japan and Sweden.[20]​.

The motivations for the construction of space colonies are varied, among others: survival, security, energy, extraction of raw materials and monetary.

Space habitats are immune to most of the natural disasters that Earth suffers, such as earthquakes, volcanic activity, hurricanes, floods and tornadoes. A space habitat can be the passenger compartment of a large spacecraft destined to colonize asteroids, moons, distant stars, or other planets (see also: Space and Survival). Dispersing our population into multiple self-sustaining space habitats throughout the Solar System will increase our chances of survival as a species in the event of a global disaster on Earth.[4]​.

Space is literally filled with light produced by the Sun. In Earth's orbit, it reaches 1400 watts of energy per square meter. This can be used to produce electricity using photovoltaic cells or heat engines installed in power generating stations, and providing light for plants to grow and to heat space colonies, or to heat colder planets (such as Mars "Mars (planet)").

Most asteroids are a mixture of the materials mentioned above, virtually all the stable elements of the periodic table can be found in asteroids and comets and more importantly, because these bodies do not have substantial gravity wells, it is very easy to remove the materials obtained from them and transport them to the construction site.[3]​.

It is estimated that there is enough material in the main asteroid belt to build space habitats equal to the habitable surface area of ​​3,000 planets on Earth.[5]​.

The colonies would have constant access to solar energy up to very great distances from the Sun. The lack of weight allows the construction of large flimsy structures such as mirrors to concentrate sunlight.

Space habitats can be supplied with resources from extraterrestrial locations such as Mars, asteroids, or the Moon (In-Situ Resource Utilization, ISRU;[4] See also asteroid mining.) One could produce oxygen for breathing, drinking water, and rocket fuel with the help of ISRU.[4] It may even be possible to build solar panels from lunar materials.[4]

Habitats can be built to have immense population capacity. Using free-floating resources in the solar system, current estimates range into the trillions.[6]​.

Trade between Earth and space habitats would be easier than trade between Earth and a planetary colony, since colonies orbiting Earth do not have to overcome a "gravity well" to export to it, and a smaller gravity well to overcome to import from Earth.

Even the smallest of the habitat designs mentioned is more massive than the total mass of everything launched by Humanity into Earth orbit. The prerequisites for building habitats are cheaper launch costs or a mining and manufacturing base on the Moon or another body that has a low delta-v from the desired habitat location.[3]​.

Air pressure, with normal partial pressures of oxygen, carbon dioxide and nitrogen, is a basic requirement of any space habitat. Basically most colony designs propose large thin-walled pressure vessels. The required oxygen could be obtained from lunar rocks. Nitrogen is easier to obtain from Earth, but it is also almost perfectly recyclable. Nitrogen is also the form of ammonium that can be obtained from comets and moons of the outer planets. Nitrogen can also be obtained in unknown quantities in certain other bodies in the outer solar system. The air in a colony could be recycled in several ways. The most obvious method is to use photosynthetic gardens, possibly via hydroponics or forests. However, this does not remove certain industrial contaminants, such as volatile oils and excess simple molecular gases. The standard method used on nuclear submarines, a similar form of closed environment, is to use a catalytic burner, which effectively removes most of the organic contaminants. Additional protection could be provided by a small cryogenic distillation system that would gradually remove impurities such as mercury vapor. (element)") and noble gases that can be burned catalytically.

Organic materials for food production also need to be provided. At first, most would have to be imported from the Moon, asteroids or Earth. After that, recycling should reduce the need for imports. One proposed recycling method would begin by burning cryogenic distillate, plants, trash and wastewater with air and an electric arc, and then distilling the result. The resulting carbon dioxide and water could be directly used by agriculture. The nitrates and salts in the ash could be dissolved in water and separated into pure minerals. Most of the nitrates, potassium and sodium salts would be effectively recycled as fertilizers. Other minerals containing iron, nickel and silicon could be chemically purified in batches and reused industrially. The small fraction of remaining materials, well below 0.01% by weight, could be processed into pure elements with zero-gravity mass spectrometry and added in appropriate amounts to fertilizers and industrial supplies. This method currently only exists as a proof of concept being considered in NASA studies. Most likely, this method would be greatly refined when people begin to actually live in space habitats.

Long-term orbital studies have proven that zero gravity weakens bones and muscles and disrupts calcium metabolism and the immune system. Most people have suffered from problems with congested airways and sinusitis, and a few others have been affected by dramatic and incurable dizziness. Most space colony designs would rotate to use the resulting inertial force to simulate gravity. NASA studies with chickens and plants have proven this to be an effective physiological substitute for gravity. Rapidly turning your head in such an environment causes a tilt to be felt because the inner ear moves at a different rate of rotation. Studies carried out in centrifuges show that people suffer from motion sickness in habitats with a rotation radius of less than 100 meters, or with a rotation rate of over 3 rotations per minute. However, using the same studies and statistics it can be inferred that almost all people should be able to live comfortably in habitats with a rotation radius of more than 500 meters and with a rotation less than 1 rotation per minute. The more experienced people were not only more resistant to motion sickness, but they could determine the "spinward" and "antispinward" directions in the centrifuges.

NASA designs

Designs proposed in NASA studies include:

Bubble World

The bubble world or the Interior/Exterior concept originated in 1964 by Dandridge M. Cole") and Donald W. Cox in a book called Islands in Space: The Challenge of the Planetoids (in Spanish: Islas en el Espacio: El Desafío de los Planetoids).[15]​.

The concept is about drilling a tunnel through the long axis of a large asteroid composed of iron or iron-nickel and filling it with a volatile substance ("Volatility (chemistry)"), possibly water. A very large solar reflector would be built nearby, focusing the heat generated by the Sun onto the asteroid, first to weld and seal the ends of the tunnel, then in a more diffuse way to slowly heat the entire surface. As the metal softens, the water inside expands and inflates the asteroid's mass, while rotational forces help form a cylinder with this material. Once expanded it will be allowed to cool, can be rotated to produce artificial gravity, and also filled with soil, air and water. By creating a small bulge in the middle of the cylinder, a ring-shaped lake can be created. The reflectors will allow sunlight to enter and be directed where necessary. Clearly this method would require a significant human and industrial presence in space to make it feasible.

The bubble world concept was popularized by science fiction author Larry Niven in his fictional Known Space stories, which describe such worlds as the primary habitats of the Belters, a civilization that colonized the Asteroid Ring.

Hypothetical designs

In the 1990s, as the potential utility of carbon nanotubes as a structural material became apparent, proposals arose for much larger habitats taking advantage of the use of this material. The technology to produce nanotubes of the required length is not available, so these designs remain speculative.

Bigelow Commercial Space Station

The Next Generation Bigelow Commercial Space Station") was announced in mid-2010.[18]​

Initial construction of the station is expected to begin in 2014/2015, and will consist of two Sundancer modules and one BA-330 module.[19]

Bigelow has publicly shown design configurations of the space station with up to nine BA-300 modules containing 2,831 m³ of habitable space.[20]

Bigelow began publicly referring, in October 2010, to the initial configuration - of two Sundancer modules) and one BA-330 module - as Alpha Space Complex.[21]​.

Bigelow recently announced that it has agreements with six sovereign states to use commercial space station orbital facilities: the United Kingdom, the Netherlands, Australia, Singapore, Japan and Sweden.[20]​.