Outer Space, Colonization of

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Human beings have established settlements in places as varied as the frigid and dry arctic tundra of northern Canada and the hot and wet Amazon rain forest. Clearly, humans are remarkable creatures. But can humans extend the frontier of settlement into an even less hospitable place, the cold vacuum of outer space? More than forty years after the launch of Sputnik, how far off is the colonization of outer space?

Low Earth Orbit

The first human went into space in the early 1960s. From then until the 1990s, a few astronauts–or, to use the even more grandiose Russian label, cosmonauts–episodically "populated" near-Earth space. Groups of such travelers rocketed into space, stayed a few days or months, and then returned to Earth. In the 1990s the space station Mir, assembled by the Soviet Union and operated by Russia, was continuously inhabited for several years by rotating crews of cosmonauts. The station aged and was abandoned in 1998 after Russia, the United States, and many other international partners began work on the International Space Station.

A demographic regime in space may have begun on October 31, 2000, when the three-person crew of Expedition 1 began its four-month stay in orbit on the space station. The U.S. National Aeronautics and Space Administration (NASA) claims that there will always be a crew in the space station. If this turns out to be right, then the dawn of the third millennium will mark the beginning of a permanent space population, a milestone in space similar to that for Antarctica marked by the International Geophysical Year of 1957.

Water–The Liquid of Life

Are Mir and the International Space Station the first steps toward the human colonization of the solar system? Russian space pioneer Konstantin Tsiolkovsky (1857–1935) wrote that "the Earth is the cradle of humanity, but one cannot live in the cradle forever." It is hard for human beings to leave their literal cradles for the Earth beyond them, because the Earth contains what is needed to sustain life: air, food, and water. Outer space is airless, foodless, and most importantly, waterless.

A single human being needs about eight pounds of water per day, including wash water, to live. It takes a ton of water to sustain an eight-person space station for a month if each drop of water is used by a human being only once. On earth, all of this water is recycled, filtered, and purified by the water cycle. In existing space stations, aerospace engineers have made some progress in closing the water loop, by recycling cabin moisture into drinking water. If large-scale, free-floating space colonies–like those proposed by the Princeton physicist Gerard K. O'Neill (1927–1992) in the 1970s–were to become real, 100 percent of the water, including urine, has to be recycled.

In the past few years space enthusiasts have looked more to the planets as possible future homes for humanity. The discoveries of substantial amounts of water on the planet Mars and on Jupiter's satellite Europa have suggested that it might be more feasible to consider colonizing these places, instead of dealing with the tough (though technically solvable) water problem of space stations. Just as settlers in the American West followed great rivers like the Missouri westward, humans may follow the trail of water, which probably would lead to the surface of Mars. And planets like Mars can not only supply space travelers with water to drink; Martian materials can also provide rocket fuel for the trip home. American engineer Robert Zubrin incorporates the use of Martian materials into his revolutionary and important "Mars Direct" plan, proposed in 1996, which cuts the travel time to Mars from nine months to six and permits astronauts to spend much more time on the Martian surface.

Terraforming Mars

Could humans establish a colony on Mars? The Red Planet is far from being Earthlike. Could it be terraformed, or altered in order to make it habitable by humans? Scholars Joseph A. Burns, Martin Harwit, and Carl Sagan were the first to suggest terraforming in a mainstream scientific journal in 1973. In broad terms, to terraform Mars, colonists would need to darken the surface so it absorbs more sunlight, and find a way to release the water and carbon dioxide that exists underground so that the atmosphere will become thicker and will trap solar heat by the greenhouse effect.

Thirty years after its initial suggestion, the idea of terraforming is still intellectually alive. It has been discussed in mainstream scientific reviews by such writers as Martyn J. Fogg (1998), as well as in science fiction novels that occasionally delve quite deeply into scientific issues, such as Kim Stanley Robinson's 1994 novel Green Mars. But the obstacles to terraforming Mars are formidable. Once enough volatile material (like water and dry ice) is found to create a massive atmosphere, there is still a need to get the gas mixture right. Scuba divers occasionally experiment with breathing oxygen-rich or nitrogen-poor air, and have established that humans need something close to the 4:1 mix of nitrogen to oxygen that humans breathe on Earth. So it may be that nitrogen, the "inert" ingredient in Earth's atmosphere, will limit humans' ability to terraform Mars.

Beyond the Solar System

For a species which has just stuck its toes in the oceans of space, humans have a wonderful capacity to dream. A surprisingly large literature deals with interstellar space flight. Interstellar Migration and the Human Experience, a remarkable book edited by Ben R. Finney and Eric M. Jones (1986), provides an inspiring introduction. Perhaps the most visionary of thinkers is the physicist Freeman Dyson, who suggested in 1979 that very advanced civilizations could construct spherical absorbers that would permit them to harness 100 percent of the energy output from an individual star. Can human beings or other intelligent creatures move from one star to another? While the technical challenges are extreme, it is not impossible.

Whether any such dreams will turn into reality is a matter for the future. Some writers like Dyson and Zubrin believe that the allure of the space frontier by itself is enough to propel humanity–in significant numbers–toward the stars. Others, like Harry L. Shipman and many of the authors in Interstellar Migration and the Human Experience, take a more cautious approach, suggesting that some kind of return on investment, whether it be through space industrialization or space tourism, must provide a political and economic push. Whatever the future brings, space colonization is a fun and mind-expanding concept to dream about.

Will space colonization ever reach a scale at which number of colonizers could make a significant difference to demographic trends on Earth? It seems unlikely in the foreseeable future. Even Antarctica, where there is a large supply of water (in the form of ice) and air, can only support a year-round population of a few hundred. The most optimistic visions of space colonies, whether free-floating or Martian, postulate populations of tens of thousands. A significant effect on terrestrial population requires space for at least a few tenths of a billion inhabitants. Although outer space is vast, the environment may not be entirely hospitable.

See also: Extinction, Human; Literature, Population in.


Burns, Joseph A., and Harwit, Martin. 1973. "Towards a More Habitable Mars, or The Coming Martian Spring." Icarus 19: 126.

Dyson, Freeman J. 1979. Disturbing the Universe. New York: Harper and Row.

Finney, Ben R., and Jones, Eric M., eds. 1985. Inter-stellar Migration and the Human Experience. Berkeley: University of California Press.

Fogg, Martyn J. 1998. "Terraforming Mars: A Review of Current Research." Advances in Space Research 22(3): 415–420.

Freeman, Marsha. 2000. Challenges of Human Space Exploration. Berlin: Springer-Praxis.

O'Neill, Gerard K. 1982. The High Frontier: Human Colonies in Space. Garden City, NY: Anchor Books.

Robinson, Kim Stanley. 1994. Green Mars. New York: Bantam.

Sagan, Carl. 1973. "Planetary Engineering on Mars." Icarus 20: 513.

Shipman, Harry L. 1989. Humans in Space: 21st Century Frontiers. New York: Plenum.

Zubrin, Robert, and Wagner, Richard. 1996. The Case for Mars: The Plan to Settle the Red Planet and Why We Must. New York: Simon and Schuster Touchstone.

internet resources.

British Interplanetary Society. 2002. <http://www.bis-spaceflight.com>.

Fogg, Martyn J. 2002. "The Terraforming Information Page." <http://www.users.globalnet.co.uk/~mfogg/index.htm>.

National Aeronautics and Space Administration. 2002. <http://science.ksc.nasa.gov/history/A97>.

Robinson, Kim Stanley. "The Red, Green, and Blue Maps Site." 2002. <http://www.xs4all.nl/~fwb/rgbmars.html>.

Harry L. Shipman