With great difficulty. Fortunately, although building space colonies will be very difficult, it's not impossible. Building cities in space will require materials, energy, transportation, communications, life support, and radiation protection.
- Materials. Launching materials from Earth is very expensive, so bulk materials should come from the Moon or Near-Earth Objects (NEOs - asteroids and comets with orbits near Earth) where gravitational forces are much less, there is no atmosphere, and there is no biosphere to damage. Our Moon has large amounts of oxygen, silicon and metals, but little hydrogen, carbon, or nitrogen. NEOs contain substantial amounts of metals, oxygen, hydrogen and carbon. NEOs also contain some nitrogen, but not necessarily enough to avoid major supplies from Earth.
- Energy. Solar energy is abundant, reliable and is commonly used to power satellites today. Massive structures will be needed to convert sunlight into large amounts of electrical power for settlement use. Energy may be an export item for space settlements, using microwave beams to send power to Earth.
- Transportation. This is the key to any space endeavor. Present launch costs are very high, $2,000 to $ 14,000 per pound from Earth to Low Earth Orbit (LEO). To settle space we need much better launch vehicles and must avoid serious damage to the atmosphere from the thousands, perhaps millions, of launches required. One possibility is airbreathing hypersonic air/spacecraft under development by NASA and others. Transportation for milllions of tons of materials from the Moon and asteroids to settlement construction sites is also necessary. One well studied possibility is to build electronic catapults on the Moon to launch bulk materials to waiting settlements.
- Communication. Compared to the other requirements, communication is relatively easy. Much of the current terrestrial communications already pass through satellites.
- Life support. People need air, water, food and reasonable temperatures to survive. On Earth a large complex biosphere provides these. In space settlements, a relatively small, closed system must recycle all the nutrients without "crashing." The Biosphere II project in Arizona has shown that a complex, small, enclosed, man-made biosphere can support eight people for at least a year, although there were many problems. A year or so into the two year mission oxygen had to be replenished, which strongly suggests that they achieved atmospheric closure. For the first try, one major oxygen replenishment and perhaps a little stored food isn't too bad. Although Biosphere II has been correctly criticized on scientific grounds, it was a remarkable engineering achievement and provides some confidence that self sustaining biospheres can be built for space settlements.
- Radiation protection. Cosmic rays and solar flares create a lethal radiation environment in space. To protect life, settlements must be surrounded by sufficient mass to absorb most incoming radiation. This can be achieved with left over from processing lunar soil and asteroids into oxygen, metals, and other useful materials.
Space settlement feasibility was addressed in a series of summer studies at NASA Ames Research Center in the 1970s. These studies concluded that space settlement is feasible, but very difficult and expensive. For additional information see the bibliography.
Although we know generally how to build space colonies, we have yet to find an economic path from where we are now to construction of the first colony. One approach is to develop a series of profitable, private industries. For example:
Each of these steps is potentially profitable on its own merits. Once they are completed, we will be able to put people in orbit inexpoensively, generate large amounts of power, and supply ample materials from NEOs and perhaps the Moon -- all the elements needed to build the first space colony.
- Sub-orbital tourism. The key to space colonization is transportation from the Earth's surface to LEO. The key to inexpensive, economic transportation is the same as learning a musical instrument: practice, practice, practice. To date, there have been only a few thousand space launches and only a few hundred people have been to space. Traditional uses of space, such as communication, Earth resources, military, exploration and science won't require a whole lot more in the next few decades. However, hundreds of thousands of people say they would travel to space if the price was right. Tourism is a market that may provide the necessary practice.
- Orbital Tourism. SpaceShipOne went almost straight up 100km to get into space, and then came nearly straight down again. This sub-orbital flight is much easier than orbital flight, which requires the spacecraft to go nearly 30,000 km/hr horizontally to avoid crashing back to Earth. Surprisingly, the first paying orbital tourists have already flown. The Russians have taken Dennis Tito and Mark Shuttleworth to the International Space Station (ISS) developed by the U.S., Russia, Canada, Europe, Japan and other partners. However, even at $20 million a trip, this business only makes economic sense because the international partners spent tens of billions of dollars developing the ISS for other reasons. Nonetheless, if Rutan's prediction is correct we will see affordable orbital tourism within the lifetime of most people reading this. Successful orbital mass tourism will mean not only people, but solar power satellites can be launched from the ground to orbit affordably.
- Solar Power Satellites. Electrical power is a multi-hundred billion dollar per year business today. We know how to generate electricity in space using solar cells. For example, the ISS provides about 80 kilowatts continuously from an acre of solar arrays. By building much larger satellites out of hundreds of solar arrys, it is possible to generate a great deal of electrical power. This can be converted to microwaves and beamed to Earth to provide electricity with absolutely no greenhouse gas emissions or toxic waste of any kind. If transportation to orbit is inexpensive following development of the tourist industry, much of Earth's power could be provided from space, simultaneously providing a large profitable business and dramatically reducing pollution on Earth.
- Asteroidal Metals. John Lewis in Mining the Sky: Untold Riches from Asteroids, Comets, and Planets estimates that the current market value of the metals in 3554 Amun, one small nearby asteroid, is about $20 Trillion. There's $8 trillion worth of iron and nickel, $6 trillion worth of cobalt, and about $6 trillion in platinum-group metals. Once we can easily launch thousands of people into orbit, and build giant solar power satellites, it shouldn't be too difficult to retrieve 3554 Amun and other asteroids to supply Earth with all the metals we will ever need.