The Space Settlement FAQ

A space habitat would be a pressurized sphere, cylinder, or torus (donut shape), rotating on its axis so that centrifugal force serves as an artificial gravity. The interior is landscaped with soil, water, and vegetation. Sunlight would be gathered by mirrors and reflected into the interior of the habitat through windows. The goal is to create as Earth-like an environment as possible.

How is space settlement different from any of the other space colonization proposals?

Most thinking regarding human expansion into space has focused on the settling of the surfaces of other planets, sometimes after modifying their environments to make them more Earth-like (called terraforming). The space settlement concept maintains that planets are not the most ideal location for human colonies beyond the Earth.

Aren't we going to terraform Mars or Venus?

Terraforming is a long-term project requiring technology significantly advanced over what we have today. Even terraforming advocates admit it would take a minimum of 200 years to modify Mars to the stage where even simple anaerobic microorganisms and algae can survive. [Ref: Terraforming: Engineering Planetary Environments, Martyn J. Fogg, SAE Press 1995.] Space habitats, on the other hand, can be built with today's technology, and would be homes in space which people initiating the program could move into within their lifetimes.

Interstellar travel may someday become possible, but we have no guarantee that Earth-like planets will be as plentiful in the Milky Way galaxy as in Hollywood, CA.

What advantages would orbital settlements have over a colony built on another planet?

Access to 24-hour-a-day sunlight. This makes solar power a consistent, economical energy source. Photovoltaic panels can convert sunlight into electrical current, and solar mirrors can concentrate it for process heat in industrial operations (such as the smelting of ore). A space-based solar concentrator the size of a football field (which could still weigh less than a car) could provide process heat equivalent to the burning of 1 million barrels of oil over 30 years.

Sunlight also drives the life-support system of the habitat, so the day/night cycle can be set to whatever is convenient. Compare this to the moon, where there is 14 days of continuous daylight, and then a 14-day-long night. Here, some alternate energy source would probably have to be used half the time.
Access to zero gravity. This may have a number of industrial and entertainment possibilities. Structures (such as the above-mentioned solar mirrors) could be built many times larger and flimsier in space than on a planet.

Zero G would be a liability if there were no alternative to it. Astronauts experience loss of bone mass and muscle tone after prolonged exposure to weightlessness. But most of a space habitat would be under Earth-normal gravity, although there would be easy access to regions of reduced gravity and zero G (perhaps for personal flight). With planets, on the other hand, you have to take the gravity that's there, and it's often the wrong kind of gravity to keep us healthy. Lunarians or Martians would probably not be able to visit the Earth (nor accelerate at 1 G).
Long-term expansion of the land area available to the human race. Let's be optimistic and assume that Mars could be made totally Earth-like in the near-term. This would basically double the land area available to humanity, meaning problem solved...until the population doubles again. Right now, that is happening roughly every 40 years. It can be argued that it would take longer than 40 years just to re-settle that many people. By contrast, if we were to conservatively limit ourselves to using only the resources of the asteroid belt, we could build, in the form of space habitats, 3,000 times the livable surface area of the Earth. This makes space settlement a long-term solution.
Location near the top of Earth's gravity well. We here on Earth are the "gravitationally disadvantaged". We are at the bottom of a pit 6,400 km (4,000 miles) deep. This is what makes space launches from the surface so difficult and expensive. Settlers near the top of the gravity well would be ideally situated for departures to points beyond.
Control of the environment. The weather and other aspects of the surroundings would be those of the inhabitants' choosing. Agriculture in space will benefit from weather control (fresh fruits and vegetables year-round!) and the absence of pests.

Who developed the space settlement concept?

Principally, Gerard K. O'Neill (1927-1992), who was a physicist with Princeton University's Institute for Advanced Study. Prior to popularizing space development, O'Neill was well-known as a researcher in high-energy physics, and as the inventor of the colliding beam storage ring, an innovation now standard on most particle accelerators.

Compelled by the logic of space settlement, O'Neill wondered if someone else hadn't thought along these same lines before. A colleague, Freeman Dyson, directed him to the writings of Konstantin Tsiolkovsky, J. D. Bernal, and Dandridge Cole.

Tsiolkovsky was the Robert Goddard of the soviet space effort. As early as the 1920's he wrote about "orbital mansion/greenhouses" which spun for gravity, and realized full well the advantages of continuous sunlight and asteroidal resources. Bernal and Cole had proposed hollowing out asteroids to make orbital habitats. Dyson himself had published a paper speculating that any highly-advanced civilization would have almost completely surrounded its sun with habitats and solar energy collectors (a "Dyson Sphere").

What are the origins of the space settlement concept?

In 1969, O'Neill was teaching a physics course at Princeton. America was engaged in the Apollo effort, so O'Neill was working space travel into many of the physics problems assigned. He was concerned about the persistent talk among academics regarding overpopulation and "limits to growth", and was dismayed by many young people's resigned acceptance of the concepts of future totalitarian control over the use of resources, and an inevitable decline in the standard of living. One day he asked his students the following question: Is the surface of the Earth really the best place for an expanding, technological civilization? After some calculation, the answer seemed to be "no" (see advantages above).

They turned to the design of an Earth-like space habitat. When they calculated the maximum size possible, given present strengths of steel cable, aluminum plates, and glass panels, the answer took them by suprise. Later studies funded by NASA defined several highly-detailed habitat designs.

A low-end design is Island One, also known as a Bernal Sphere. Sunlight is reflected in through two ring-shaped rows of windows at either end. Agriculture takes place in external tori. The Bernal Sphere is 1 km (0.6 mi.) in circumference, and could support a population of 10,000.

Island Two is shaped like a cold capsule, with sunlight entering through 3 windows running the length of the cylinder. 1.8 km (>1 mi.) in diameter, it would house 140,000.

A scaled-up version, Island Three, would be a cylinder 6.4 km (4 mi.) in diameter and 32 km (20 mi.) long. Four miles of atmosphere is enough to produce a blue sky overhead, and cloud banks would form at the same level they do here on Earth (approx. 900 m or 3,000 ft). Natural rainstorms would occur (Bernal spheres would probably have a sprinkler system). Island Three would have over 400 square km (250 square mi.) of living space, and be home to 10,000,000 individuals.

There are other designs as well. Stanford University did a study which produced the Stanford Torus, although it is not as efficient of building materials as is a sphere or cylinder.

Island Three was considered the limit of what was economically viable, not what was physically possible. The maximum theoretical size for a space habitat, assuming materials no stronger than those currently used, is a staggering 19 km (12 mi.) in diameter, providing hundreds of square miles of usable land.

With space travel so expensive, how can we afford to build such massive structures in space?

Make no mistake, lifting the materials from the Earth for even a Bernal Sphere would bankrupt the global economy. That's why we will use space resources. Most studies have looked at mining the moon, although Earth-approaching asteroids are another option. A pound of ore can be lifted from the moon to a high Earth orbit for only 1/20th the energy as from Earth to that same orbit. In addition to having low gravity, the moon is also airless, so we wouldn't necessarily have to lift the ore with rockets. Instead, a mass-driver could catapult lunar resources to a location in space where they could be captured and transported to an orbital refinery.

What's a mass-driver?

A mass-driver is a kind of stretched-out linear motor, an electromagnetic accelerator with recirculating "buckets". O'Neill built successively more sophisticated demonstration models of this device, advancing from tens of G's acceleration to over 1,800 G's. A mass-driver of this power 160 meters (530 feet) long could launch softball-sized spheres of sintered soil to lunar escape velocity in 1/10th of a second. If one is interested in bringing in asteroids, it would make a reaction engine requiring nothing more than solar energy and dirt, with an exhaust velocity 2X that of current chemical rockets.

What is there to mine on the moon?

From Apollo, we know lunar ores to be:

40%	Oxygen
20%	Silicon
12%	Aluminum
4-10%	Iron
6%	Titanium
3-6%	Magnesium

Oxygen (obviously useful for breathing) is also 86% the weight of both water and rocket fuel. The silicon will go into glass and solar cells. The metals are useful for structural materials. Aluminum and Titanium are valued by the aerospace industry for their combination of strength and light weight. Titanium, additionally, is a good high-temperature metal. Research has also been conducted toward creating ceramics and cement from lunar materials.

Unless there turn out to be volatiles frozen in permanently-shadowed craters at the poles of the moon, we will have to import Hydrogen, Nitrogen, and Carbon from Earth, at least until we get into asteroid mining. Once retrieval of asteroidal material has begun, every element needed will be available.

Where do you get off calling lunar soils "ores"? It's dirt!

This is a valid point; lunar soils are little different from what's in your backyard. The economic value of extraterrestrial resources lies not in their concentration, but in their location outside of Earth's gravity well. A bucket of dirt in a high Earth orbit is worth its weight in gold. Why? Because that's how much money you'd have to spend to lift it there! Admittedly, this argument proceeds from the assumption that you want to build something in high Earth orbit.

What work would the people living in space habitats be doing?

There's no shortage of proposals, but right now the one with the most economic promise is the construction of Solar Power Satellites (SPS).

What is SPS?

The SPS concept was invented in 1968 by Peter E. Glaser of Arthur D. Little, Inc. A SPS would be a satellite in Geosynchronous Earth Orbit (GEO). It would consist of a solar array several miles across, and a microwave transmitting antenna. In GEO, a satellite is in sunlight 24 hrs a day 99% of the time. The SPS would covert solar energy to electricity, and transmit the power to Earth in the form of a low-density microwave beam. The beam would be intercepted on Earth by a receiving antenna (rectenna) 7 km (4.2 mi.) across, and converted back into electricity. The goal is to undersell electricity generated by fossil fuels or nuclear energy.

Wouldn't the microwave beam from an SPS be harmful?

There is an unfortunate tendency that when we hear "microwaves" we think of what happens to our cheese-melt in the microwave oven. But the SPS microwave beam was studied extensively by the Department of Energy (DOE); they could find no harmful environmental effects. The actual Watts-per-square-meter are not terribly high: less than 1/2 that of sunlight. However, unlike sunlight, the beam is there 24 hours a day, rain or shine, and is convertible to electricity with an efficiency of around 90%.

Couldn't terrorists use the microwave beam from an SPS as a weapon?

No. It would not make a useful "death-ray". Moving an SPS beam off of its rectenna would simply cause the beam to harmlessly defocus.

Why not build solar power stations on the moon?

We would be building solar power stations in a place which is dark half the time (for 14 days at a time). Near sunrise and sunset, lunar-based solar collectors would not be able to point at the sun optimally. A larger transmitting antenna would be needed to hold the beam spread down over >10x the distance. Also, the Moon is on only one side of the Earth at a time, so any given point on Earth could get power from a lunar power system only half the time.

For a lunar-based solar power station to be competitive, these disadvantages would have to be offset by the advantage of not having to lift resources (or components) off the lunar surface. Mass-driver technology makes the delivery of lunar ores into space a pennies-per-pound proposition.

Why not just build mirrors in space to reflect light to the Earth?

We have no way of predicting what this may do to the heat balance (and hence climate) of the Earth.

Won't SPS alter the heat balance of the Earth?

It is true that SPS involves the beaming of energy from space to the Earth, but since the major inefficiencies are in space, and since the microwave beam is convertible into electricity with 90% efficiency, only a little over 10% of the energy beamed to Earth ends up as waste heat before use. By contrast, a nuclear or coal-fired power plant puts 1½ times as much heat energy into the environment as usable power. For a given amount of electrical capacity, SPS is the more benign energy source from a heat dissipation standpoint. Plus, any fossil-fuel plant retired in favor of SPS energy is another victory in the battle against Greenhouse Warming.

Why not put the solar collectors here on the surface of the Earth?

Large arrays of black solar cells on the surface would lower the albedo of the Earth, contributing to global warming. And we would need lots of arrays. Due to the sun's absence at night, interruptions due to weather, and photovoltaic conversion inefficiencies, you would have to give up 30 times as much land area to solar panels as to rectennas in the SPS concept. Since the solar arrays would be opaque to sunlight, the land underneath would not be very useful. A rectenna, by contrast, would be a fine wire mesh supported well off the ground. It would block the microwaves, but allow sunlight and rainfall through. The land underneath could be used for agriculture, or conceivably even for cattle grazing.

Would SPS mean the end of the oil industry?

No. We will always need petrochemicals for plastics and fertilizers. In fact, it seems foolishness to light a match to it.

If SPS is such a good energy option, then why aren't we pursuing it?

Most of the DOE and NASA studies centered on supporting SPS from the Earth with massive Heavy-Lift Launch Vehicles (HLLV's). The economics of this approach were judged viable, but marginal. The space-resources option is the key to reducing launch costs, but was viewed as somewhat riskier, and hence did not receive full consideration.

After a prolonged period of inactivity, NASA has recently resumed funding for additional studies of the SPS concept.

Do we have to build large space habitats in order to establish an SPS industry?

Actually, no. All that's required is a Space Manufacturing Facility capable of taking in the lunar (or asteroidal) soils, smelting them into silicon, metals, and other pure elements, and fabricating the needed components. Workforce living quarters are apt to be spartan at first, but past a certain point (after SPS has begun to turn a profit) it's likely that some portion of the industrial output will be turned to the task of building better homes for the workers in order to reduce employee turnover. In the long term, the construction of additional settlements may become a chief occupation of the space settlers. Industrial productivity, in the form of additional living space, is calculated to exceed population increase, so an industry can exist for the building of habitats for immigrants from Earth.

Is space settlement a solution to the overpopulation problem?

Probably not. No space transportation system we can imagine (although that might be a significant qualifier) could keep up with the number of babies being born. But space settlement provides options. You can decide to stay on Earth, and live with the inevitable population control laws, or choose to immigrate to space, where there would be no such restrictions.

Another point is that there is a direct, inverse relationship between living standard and population growth. There is additionally a direct relationship between living standard and energy use. Perhaps a cheap, clean, plentiful supply of energy (like SPS) would go a long way toward helping to improve the standard of living in many poorer nations, thus slowing their population growth rates.

If space habitats are spinning around, won't the inhabitants get dizzy?

Studies have indicated that the average person can tolerate 2-3 Revolutions Per Minute (RPM's). Only the rare individual has a problem with 1 RPM, the rotation rate of an Island Three model. The bigger a habitat, the lower the rotation rate which creates 1 G of centrifugal force.

What if a meteor hits the habitat?

Space is not as densely populated with large meteors as "Lost In Space" has led us to believe. Even the largest model, Island Three, might have to wait a million years for a one-ton meteor to impact, and even that may not completely destroy the habitat. The odds of dying in this way would be 1/60th those of dying in an automobile accident. Island Three could expect to be hit by a meteor the size of a tennis ball roughly every three years. Even if the hull were punctured, it would still take several years for the air to leak out; plenty of time to implement repairs.

What about cosmic radiation?

This is a more serious concern. Anything beyond Earth's magnetic field will get bombarded by such radiation. There are a couple of solutions, but the simplest is probably the best: a shield consisting of around 2 meters (>6 ft) thickness of the slag left over from the ore-smelting operation. This would reduce radiation levels to those considered safe for everyone, including infants and pregnant women.

What if a terrorist tries to blow up the habitat?

The kind of bomb most terrorists are capable of making would probably not be powerful enough to penetrate the metal hull, even if over-laying soil were dug up. If a terrorist could get to the windows, he could certainly blow out several panes. But like the meteor scenario, this would mean a routine repair, not a life-threatening emergency.

A terrorist armed with a nuclear weapon could no doubt completely destroy a space community, but consider that he could completely destroy an Earthly community just the same.

Still, will many people be willing to face the dangers of living in space?

We tend to think of space as a dangerous place because rocket travel from the surface of the Earth into orbit is undeniably hazardous. But imagine a space settler watching the Evening News and seeing reports from Earth of hurricanes, earthquakes, floods, and tornadoes (all absent from the space habitats). He would certainly conclude that a planet is a very dangerous place to live!

Wouldn't space settlers eventually choke on their own waste products, or pollute space?

When energy is very cheap, and resources are comparatively more expensive (the opposite of the situation here on Earth), it pays to break every waste product down to its constituent elements for re-use.

Will we emigrate to space after pollution has destroyed the ecology of the Earth?

This has been called a "disposable Earth" policy, and certainly wouldn't be supported by any individual of good conscience. Ideally, we should try to remove as much of the burden humanity has placed on our planet into space before catastrophic damage is done, not afterwards. Plus, space habitats may make ideal refuges for endangered species.

If we eventually reach the point where more people are living in space than on Earth, the Earth's primary industry may then become tourism. In such a situation, there would be an economic incentive to restore much of the planet to a natural state.

Where would a space habitat be located?

In the near term: Some Earth orbit above the Van Allen radiation belts, but probably no further away than the moon. After initial consideration of the 5th Lagrange point (L-5), the most recent thinking was a circular, 2-week orbit about half-way to the moon.

In the long term: Anywhere you like, as long as you're not frequently eclipsed by a planet. You can go farther from the sun simply by making your mirrors bigger, and curving them to concentrate the sunlight to make up the difference. How far out can you go? Let's assume no one would want to build a habitat where the mirrors weighed more than the rest of the habitat (a totally arbitrary cut-off point). Earth-like conditions could still be sustained approximately 4 light-days from the sun. That's 10x the distance of Pluto!

What are the implications for interstellar travel?

Interstellar travel is likely to be done in habitats very similar to what has been described here, and by people who have already been living in space for generations. The major difference is that instead of relying on the sun, they would have to take their power supply with them (probably in the form of antimatter).

Most significantly, space habitats make any solar system a candidate for settlement, not just the ones with Earth-like planets (or indeed any planets at all).

Isn't this just more utopian dreaming?

Most utopian schemes revolve around "improving" humanity. This is usually done with tight control over people in rigid, highly-disciplined communities. Space communities will be too independent and too widely scattered for any authority to prevent everybody from going off and doing their own thing. Space settlement promises only to improve the standard of living, and nothing more.

Why is space settlement not more in the mainstream of thinking regarding our future in space?

This is the best question of all. Even our science-fiction is dominated by concepts involving the settlement of the surfaces of other planets. Isaac Asimov dubbed it "planetary chauvinism". We also tend to visualize extraterrestrial civilizations as living on planets, when a planetary existence may only represent a very early stage in the development of technological cultures. But living on a planet is all we have ever known, so it may be little more than a failure of imagination. This may be best illustrated by an analogy:

Imagine that you can intelligently communicate with a fetus in his eighth month of development. You inform him that besides himself, there are 5 billion other individuals in existence. What does he visualize? You got it: 5 billion fetuses floating in 5 billion watery wombs rhythmically jiggling in darkness, occasionally turning in odd directions for reasons not clearly understood.

It could be that humanity is on the verge of being born out into the universe. And it may not be just more of the same.

Where are some websites which deal with space settlement?

Space Studies Institute: Founded by Gerard O'Neill, this non-profit organization funds research into space manufacturing. Features the SSI slideshow and several good articles.

http://www.astro.nwu.edu/lentz/space/ssi/home-ssi.html

Space Settlement: Web page maintained by Al Globus, features pictures of space habitats.

http://www.nas.nasa.gov/NAS/SpaceSettlement/

The First Millennial Foundation: Founded by Marshall Savage. Dedicated to expanding life into space.

http://www.millennial.org/

Island One Society: Group emphasizing the political freedom which may be possible in space habitats.

http://www.music.qub.ac.uk:80/~amon/IslandOne/

National Space Settlement Design Competition: Academic contest for students to design their own space habitats.

http://space.bsdi.com/index.html

The Artemis Society: Devoted to a return to the moon with an emphasis on commercial development.

http://www.asi.org/

Moon Miners' Manifesto: Required reading for all lunar prospectors.

http://asi.org/mmm/

The Space Frontier Foundation: Pushing for the opening of the high frontier to the average citizen, and Cheap Access To Space.

http://www.space-frontier.org/

Robert Lentz's Space Resources: An indispensable and vast set of links for all types of space subjects.

http://www.astro.nwu.edu/lentz/space/home-space.html

Bibliography:

The High Frontier by Gerard K. O'Neill, 1976, Bantam Books/SSI Press, ISBN: 0-9622379-0-6

Colonies in Space by T. A. Heppenheimer, 1977, Warner Books, ISBN: 0-446-81-581-0

Toward Distant Suns by T. A. Heppenheimer, 1979, Stackpole Books, ISBN: 0-449-90035-5

The Millennial Project by Marshall T. Savage, 1992, Little, Brown & Company, ISBN: 0-316-77163-1 & 0-316-77163-5

Space Colonies edited by Stewart Brand, 1977, Penguin Books, ISBN: 0 14 00.4805 7

2081: A Hopeful View of the Human Future by Gerard K. O'Neill, 1981, Simon & Schuster, ISBN: 0-671-24257-1

Space Trek: The Endless Migration by Jerome Clayon Glenn & George S. Robinson, 1978, Warner Books, ISBN: 0-446-91122-4

The High Road by Ben Bova, 1981, Pocket Books, ISBN: 0-671-45805-1

A Step Further Out by Jerry Pournelle, 1980, Ace Books

The Illustrated Encyclopedia of Space Technology, 2nd ed. by Kenneth Gatland, 1989, Orion Books, ISBN: 0-517-57427-8

To the space settlement home page.

Distributed by: Al Globus

Curator: Al Globus
If you find any errors on this page contact Al Globus.

This site was hosted by the NASA Ames Research Center from 1994-2018 and is now hosted by:

The Space Settlement FAQ

written by Mike Combs [email protected]

Last update: September, 1996

Questions:

Bibliography:

written by Mike Combs
[email protected]

Last update:
September, 1996