Space settlement


A space settlement is a settlement in outer space, sustaining more extensively habitation facilities in space than a general space station or spacecraft. Possibly including closed ecological systems, its particular purpose is permanent habitation.
No space settlement has been constructed yet, but many design concepts, with varying degrees of realism, have been introduced in science-fiction or proposed for actual realization.
Space settlements include orbital settlements around the Earth or any other celestial body, as well as cyclers and interstellar arks, as generation ships or world ships.
Space settlements are a form of extraterrestrial settlements, which more broadly includes habitats built on or within a body other than Earth, such as a settlement developed from a moonbase, a Mars habitat or an asteroid.

Definition

A space settlement is any large-scale habitation facility in outer space, or more particularly in an orbit.
The International Astronautical Federation has differentiated space settlements to space habitats and space infrastructure the following way:
While not automatically constituting a colonial entity, a space settlement can be an element of a space colony. The term "space colony" has been viewed critically, prompting Carl Sagan to propose the term ''space city.''

History

The idea of space settlements either in fact or fiction goes back to the second half of the 19th century. "The Brick Moon", a fictional story written in 1869 by Edward Everett Hale, is perhaps the first treatment of this idea in writing.
In 1903, space pioneer Konstantin Tsiolkovsky speculated about rotating cylindrical space settlements in Beyond Planet Earth. In 1929 John Desmond Bernal speculated about giant space settlements. Dandridge M. Cole in the late 1950s and 1960s speculated about hollowing out asteroids and then rotating the to use as settlements in various magazine articles and books, notably Islands In Space: The Challenge Of The Planetoids.

O'Neill – The High Frontier

Around 1970, near the end of Project Apollo, Gerard K. O'Neill, an experimental physicist at Princeton University, was looking for a topic to tempt his physics students, most of them freshmen in engineering. He hit upon the idea of assigning them feasibility calculations for large space-settlements. To his surprise, the habitats seemed feasible even in very large sizes: cylinders in diameter and long, even if made from ordinary materials such as steel and glass. Also, the students solved problems such as radiation protection from cosmic rays, getting naturalistic Sun angles, provision of power, realistic pest-free farming and orbital attitude control without reaction motors. O'Neill published an article about these colony concepts in Physics Today in 1974. He expanded the article in his 1976 book The High Frontier: Human Colonies in Space.

NASA Ames/Stanford 1975 Summer Study

The result motivated NASA to sponsor a couple of summer workshops led by O'Neill. Several concepts were studied, with sizes ranging from 1,000 to 10,000,000 people, including versions of the Stanford torus. Three concepts were presented to NASA: the Bernal Sphere, the Toroidal Colony and the Cylindrical Colony.
Image:External view of a Bernal sphere.jpg|thumb|Exterior of a 1970s Stanford adaptation of the Bernal sphere
O'Neill's concepts had an example of a payback scheme: construction of solar power satellites from lunar materials. O'Neill did not emphasize the building of solar power satellites as such, but rather offered proof that orbital manufacturing from lunar materials could generate profits. He and other participants presumed that once such manufacturing facilities had started production, many profitable uses for them would be found, and the colony would become self-supporting and begin to build other colonies as well.
The concept studies generated a notable groundswell of public interest. One effect of this expansion was the founding of the L5 Society in the U.S., a group of enthusiasts that desired to build and live in such colonies. The group was named after the space-colony orbit which was then believed to be the most profitable, a kidney-shaped orbit around either of Earth's lunar Lagrange points 5 or 4.

Space Studies Institute

In 1977 O'Neill founded the Space Studies Institute, which initially funded and constructed some prototypes of the new hardware needed for a space colonization effort, as well as producing a number of feasibility studies. One of the early projects, for instance, involved a series of functional prototypes of a mass driver, the essential technology for moving ores efficiently from the Moon to space colony orbits.

Motivation

There are a range of arguments for space settlements, including:
A number of arguments are made for space settlements having a number of advantages:

Access to solar energy

Space has an abundance of light produced from the Sun. In Earth orbit, this amounts to 1400 watts of power per square meter. This energy can be used to produce electricity from solar cells or heat engine based power stations, process ores, provide light for plants to grow and to warm space settlements.

Outside gravity well

Earth-to-space settlement trade would be easier than Earth-to-planetary habitat trade, as habitats orbiting Earth will not have a gravity well to overcome to export to Earth, and a smaller gravity well to overcome to import from Earth.

In-situ resource utilization

Space settlements may be supplied with resources from extraterrestrial places like Mars, asteroids, or the Moon. One could produce breathing oxygen, drinking water, and rocket fuel with the help of ISRU. It may become possible to manufacture solar panels from lunar materials.

Asteroids and other small bodies

Most asteroids have a mixture of materials, that could be mined, and because these bodies do not have substantial gravity wells, it would require low delta-V to draw materials from them and haul them to a construction site.
There is estimated to be enough material in the main asteroid belt alone to build enough space settlements to equal the habitable surface area of 3,000 Earths.

Population

A 1974 estimate assumed that collection of all the material in the main asteroid belt would allow habitats to be constructed to give an immense total population capacity. Using the free-floating resources of the Solar System, this estimate extended into the trillions.

Zero g recreation

If a large area at the rotation axis is enclosed, various zero-g sports are possible, including swimming, hang gliding and the use of human-powered aircraft.

Passenger compartment

A space settlement can be the passenger compartment of a large spacecraft for colonizing asteroids, moons, and planets. It can also function as one for a generation ship for travel to other planets or distant stars

Requirements

The requirements for a space settlement are many. They would have to provide all the material needs for hundreds or thousands of humans, in an environment out in space that is very hostile to human life.

Regulation

The governance or regulation of space settlements is crucial for responsible habitation conditions. The physical as well as socio-political architecture of a space settlement, if poorly established, can lead to tyrannical and precarious conditions.

Initial capital outlay

Even the smallest of the settlement designs mentioned below are more massive than the total mass of all items that humans have ever launched into Earth orbit combined. Prerequisites to building settlements are either cheaper launch costs or a mining and manufacturing base on the Moon or other body having low delta-v from the desired habitat location.

Location

The optimal settlement orbits are still debated, and so orbital stationkeeping is probably a commercial issue. The lunar and orbits are now thought to be too far away from the Moon and Earth. A more modern proposal is to use a two-to-one resonance orbit that alternately has a close, low-energy approach to the Moon, and then to the Earth. This provides quick, inexpensive access to both raw materials and the major market. Most settlement designs plan to use electromagnetic tether propulsion, or mass drivers used instead of rocket motors. The advantage of these is that they either use no reaction mass at all, or use cheap reaction mass.

Protection from radiation

If a space settlement is located at or, then its orbit will take it outside of the protection of the Earth's magnetosphere for approximately two-thirds of the time, putting residents at risk of proton exposure from the solar wind.
Protection can be attained through passive or active shielding. Passive shielding through the use of materials has been the method to shield current spacecrafts.
Water walls or ice walls can provide protection from solar and cosmic radiation, as 7 cm of water depth blocks approximately half of incident radiation. Alternatively, rock could be used as shielding; 4 metric tons per square meter of surface area could reduce radiation dosage to several mSv or less annually, below the rate of some populated high natural background areas on Earth.
Alternative concepts based on active shielding are untested yet and more complex than such passive mass shielding, but usage of magnetic and/or electric fields, like through spacecraft encapsulating wires, to deflect particles could potentially greatly reduce mass requirements.