Because we are planetary creatures, most people assume the first and most numerous space settlements must be on the Moon or Mars. In fact, we may live in orbit long before settling the Moon or Mars, and there may always be far more space settlers in orbit than on any planet or moon. Orbital settlements are huge spacecraft, big enough for many thousands to live in comfortably, that provide radiation protection, a breathable atmosphere, nearly self-sufficient life support, and that rotate to provide something that feels much like Earth-normal gravity at the rim.

Why do I think orbital settlements will precede and vastly outperform those on planets and moons? Three reasons:

  1. It's easier.
  2. There's more.
  3. The kids will be able to visit Earth

Getting back and forth to orbit is far easier than getting to the Moon or Mars, which is why we've had space stations circling Earth for thirty years and have yet to see the first base on the Moon much less on Mars.

Location is also critical for economic self-sufficiency. Thriving communities beyond Earth can't be an endless drain on Earth's economy, and settlements in Earth Orbit can provide energy, exotic materials, and a tourist destination for earthlings. Nearly unlimited, clean, electrical power can be provided by giant solar arrays in orbit that beam energy to Earth. Asteroids in orbit near Earth have vast quantities of valuable metals -- one small Earth-approaching asteroid has been valued at $20 trillion! Finally, Earth orbit is already a tourist destination, and studies suggest that the space tourist market is around $50 billion/year (five million flights at $10,000 per).

In most orbits there is a continuous supply of solar energy. Even settlements in Low Earth Orbit (LEO) only lack sunlight for 40 minutes at a time and can be supplied by energy beamed from solar power satellites in sunnier orbits. The Moon's night is two weeks long! Mars has reasonable length nights, but features dust storms, an atmosphere, and is much further from the Sun requiring much larger arrays for the same power. Nuclear power is fine for small bases and short stays, but for a civilization of millions, importing nuclear fuel from Earth is completely impractical. Local sources of fuel must be found and mining, separation, transportation, and processing may be more difficult than bringing lunar or asteroidal materials to Earth orbit.

Finally, there is a smooth path from where we are now to orbital settlements. Today we have the International Space Station (ISS) in orbit and Bigelow Aerospace is flying Genesis I, the first privately financed space station. Bigelow has also committed to flying a private station capable of hosting three people within a few years. It's not a big step from these stations to the first space hotels. When space hotels get larger and more elaborate, it may make sense to rotate parts of them to gain pseudo-gravity just to simplify certain aspects of living (think bathroom). From there, it's a short step to low-g facilities for the handicapped -- no wheelchairs needed. Long-term employees of these facilities may decide they'd like to stay in orbit rather than return home. Maids and bell boys may well be the first space settlers!

On planets you live on the outside of a massive, solid sphere. Orbital settlements are hollow: you live on the inside. The single largest asteroid, Ceres, provides enough materials to build orbital space colonies with 1g living area equal to at least a hundred times the surface area of Earth. Orbital space settlement will be the greatest expansion of life ever.

This has tremendous implications. The Earth holds about six and a half billion people at present, and is considered very crowded. However, most of our planet's surface is nearly uninhabited. The oceans, the frozen wastes of Alaska, Canada, and Siberia, and the vast deserts of Africa, the Middle East, central Asia, the western United States, and Australia have extremely small populations. By contrast, all of an orbital settlement's area can be more-or-less any way we want it, from the temperature to the rainfall. Orbital space settlement in this solar system can provide space for ten trillion or more human beings living in excellent conditions.

All of life has evolved under the force of Earth's gravity. The strength of that force plays a major role in the way our bodies work, including the development and maintenance of human bone and muscle. The potential effects of lower Lunar or Martian g levels are unknown, but a large orbital space settlement can be rotated to have nearly any pseudo-gravity desired. Children raised in orbital settlements should have no problem visiting Earth.

We can all look forward to the day when there are thriving communities of human beings living and working on the Moon and Mars. However, it may very well be that, long before then, there are vast numbers of settlements in orbit. Starting in Earth orbit, our solar-system-wide civilization will expand to take advantage of near-Earth asteroids, those closer to the sun, and eventually even the Martian moons for materials. Then it's off the asteroid belt for the richest mine of near-weightless materials in the solar system. After that, who knows, the sky is definitely not the limit!

NOTE: The views of this article are the author's and do not reflect the policies of the National Space Society.

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