Space Settlement Basics
DISCLAIMER: This web site is not a policy statement. It is intended
to be an accessible introduction to the ideas developed in the
Ames space settlement studies of the 1970s and follow on's to support the
annual NASA Ames
Student Space Settlement Contest.
You. Or at least people a lot like you. Space settlements will
be a place for ordinary people.
Presently, with few exceptions, only highly trained and
carefully selected astronauts go to space. Space settlement needs
inexpensive, safe launch systems to deliver thousands, perhaps
millions, of people to orbit. If this seems unrealistic, note
that a hundred and fifty years ago nobody had ever flown in an
airplane, but today nearly 500 million people fly each year.
Some special groups might find space settlement particularly
attractive: The handicapped could keep a settlement at zero-g to
make wheelchairs and walkers unnecessary. Penal colonies might be
created in orbit as they should be fairly escape proof. People who
wish to experiment with very different social and political forms
could get away from restrictive norms.
Although some settlements may follow this model, it's reasonable to
expect that the vast majority of space settlers will be ordinary
people. Indeed, eventually most people in space settlements may be
born there, and some day they may vastly exceed Earth's population.
A space settlement is a home in orbit.
Pictures of space settlements.
- Rather than live on the outside of a planet, settlers will live
inside of large spacecraft. Free-space settlement
designs range from 100 meters to a few kilometers across. A few
designs are much larger.
- Settlements must be air tight to hold a breathable atmosphere,
and may rotate to provide psuedo-gravity. Thus, people stand on
the inside of the hull.
- Settlements close to Earth and near the equator are protected from most space radiation by the Earth itself and the Earth's magnetic field. Further from Earth enormous amounts of matter, probably lunar regolith and asteroidal materials, must
cover the settlements to protect inhabitants from radiation.
- Each settlement must be an independent biosphere. All oxygen,
water, wastes, and other materials must be recycled endlessly.
Pictures of Kalpana
Lewis One space settlement
In orbit, not on a planet or moon. Why should
we live in orbit rather than on a planet or moon? Because orbit is
far superior to the Moon and Mars for early and long term settlement, and other
planets and moons are too hot, too far away, and/or have no solid
For an alternate view, see Robert Zubrin's powerful case for
Mars exploration and settlement. Mars' biggest advantage is
that all the materials necessary for life may be found on Mars, although it will take a long time before Mars settlers can build everything they need.
While materials for free-space settlements must be imported from Earth, the Moon
or Near Earth Objects (NEO's -- asteroids and comets), there are
many advantages to free-space settlements including:
- Proximity to Earth. Early settlements in Low Earth Orbit, say 500 km up, are 760 times closer than the Moon and 100,000 times closer than Mars at closest approach. The Moon is a few
days away from Earth, and trips to Mars take many months. Early
settlements in Earth orbit will be only hours away. This is a massive logistical advantage.
- Earth-normal 'gravity'. The Moon and Mars have
a surface gravity much less than Earth normal (which called 1g -
the g stands for 'gravity'). The lunar surface is at roughly 1/6g
and Mars is a 1/3g planet. Children raised in low-g cannot be
expected to develop bones and muscles strong enough to visit Earth
except in desperation -- it will be too painful and exhausting. For
example, this author weighs 73kg (160 pounds). If I went to a 3g
planet, the equivalent of moving from Mars to Earth, I would weigh
225 kg (almost 500 pounds) and would have great difficulty getting
out of bed. For children raised on the Moon or Mars, attending
college on Earth will be out of the question.
By contrast, free-space settlements can rotate to provide any g level
desired, although it's not true gravity. Spinning the settlement
creates a force called pseudo-gravity, that feels a lot like
gravity. Pseudo-gravity is much like what you feel when a car takes
a sharp turn at high speed. Your body is pressed up against the
door. Similarly, as a free-space settlement turns, the inside of
the hull pushes on the inhabitants forcing them to go around. The
amount of this force can be controlled and for reasonable settlement
sizes and rotation rates the force can be about 1g. For example, a
settlement with an 895 meter (a bit less than 1000 yards) radius
rotating at one rpm (rotations per minute) provides 1g at the hull. At four rpm the necessary radius is 56 m (about half the length of a football field including end zones).
Children raised on free-space settlements should have no trouble tolerating
Earth gravity for extended periods.
- Continuous, ample, reliable solar energy. In
high orbit there is little or no night. Solar power is available nearly 24/7. In low orbit night is only about 45 minutes out of each 90. Most places
on the Moon or Mars are in darkness half of the time (the only
exception is the lunar poles). Mars, in addition, is much farther
from the Sun and so receives about half the solar power available
at Earth orbit. Mars also has dust storms which interfere with
- Great views of Earth (and eventually other
planets). Space settlement is, at its core, a real
estate business. The value of real estate is determined by many
things, including "the view." Any space settlement will have a
magnificent view of the stars at night. Any settlement on the Moon
or Mars will also have a view of unchanging, starkly beautiful,
dead-as-a-doornail, rock strewn surface. However, settlements in
Earth orbit will have one of the most stunning views in our solar
system - the living, ever-changing Earth.
- Weightless recreation. Although space settlements
will have 1g at the hull, in the center you will experience
weightlessness. If you've ever jumped off a diving board, you've
been weightless. It's the feeling you have after jumping and before
you hit the water. The difference in a space settlement is that the
feeling will last for as long as you like. If you've ever seen
astronauts playing in 0g you know weightlessness is fun.
Acrobatics, sports and dance go to a new level when constraints of
gravity are removed. It's not going to be easy to keep the kids in
1g areas enough to satisfy Mom and Dad that their bones will be
strong enough for a visit to Disneyland.
- Zero-g construction means bigger settlements.
Space settlers will spend almost all of their time indoors. It is
impossible for an unprotected human to survive outside for more
than few seconds. In this situation, obviously bigger settlements are
better. Settlements on the Moon or Mars won't be much bigger than
buildings on Earth, especially at first. However, in orbit
astronauts can move spacecraft weighing many tons by hand.
Everything is weightless and this makes large scale construction
much easier. Settlements can be made so large that, even though you
are really inside, it feels like the out-of-doors.
- Much greater growth potential. The Moon and
Mars together have a surface area roughly the size of Earth. But if
the single largest asteroid (Ceres) were to be used to build
free-space settlements, the total living area created would be
hundreds of times the surface area of the Earth. Since much
of the Earth is ocean or sparsely inhabited, settlements built from
Ceres alone could provide uncrowded homes for more than a trillion
- Economics. Near-Earth free-space settlements can
service Earth's tourist, energy, materials and other markets more easily
than the Moon. Mars is too far away to easily trade with Earth.
Space settlements, wherever they are built, will be very expensive.
Supplying Earth with valuable goods and services will be critical
to paying the bills.
Mars and the Moon have one big advantage over most orbits:
there's plenty of materials. However, this advantage is eliminated
by simply building orbital settlements next to asteroids. Fortunately, there are tens of
thousands of suitable asteroids in Near Earth orbits alone,
and far more in the asteroid belt.
Early settlements can be
expected to orbit the Earth where all the products of Earth's industrial might are available if transportation is sufficient for settlement in the first place.
Later settlements can spread out across the solar system one step at a time eventually taking
advantage of the water in Jupiter's moons or other icy bodies in the far reaches of the solar system.
Eventually the solar
system will become too crowded for some, and groups of settlements will head for
Interstellar travel seems impractical due to long travel times.
But what if you lived in space settlements for fifty generations?
Do you really care if your settlement is near our Sun or in transit
to Alpha Proxima? So what if the trip takes a few generations? If
energy and make up materials for the trip can be stored, a stable
population can migrate to nearby stars. At the new star, local
materials and energy can be used to build new settlements and
resume population growth.
To survive and thrive.
Why build space settlements? Why do weeds grow through cracks in
sidewalks? Why did life crawl out of the oceans and colonize land?
Because living things want to grow and expand, to thrive, not simply exist. We have the ability
to live in space (see the bibliography), therefore we will -- but
not this fiscal year
A key advantage of space settlements is the ability to
build new land, rather than take it from someone
else. This allows a thriving, expansive civilization without war or
destruction of Earth's biosphere. The asteroids alone provide
enough material to make new orbital land hundreds of times greater
than the surface of the Earth, divided into millions of settlements.
This land can easily support trillions of people.
Someday the Earth will become uninhabitable. Before then humanity
must move off the planet or become extinct. One potential near term
disaster is collision with a large comet or asteroid. We don't know where the next killer comet is and although we know where most of the potential killer asteroids are, some have not yet been found. Such a
collision could kill billions of people. Large collisions have
occurred in the past, destroying many species. Without intervention, future collisions are
inevitable, although we don't know when. Note that in July 1994,
the cometShoemaker-Levy 9 (1993e) hit Jupiter
If there were a major collision today, not only would billions
of people die, but recovery would be difficult since everyone would
be affected. If an extensive branch of our civilization is in space before the next
collision, the unaffected space settlements can provide aid, much
as we offer help when disaster strikes another part of the
Building space settlements will require a great deal of
material. If NEOs are used, then any asteroids heading for Earth
can simply be torn apart to supply materials for building settlements
and saving Earth at the same time.
Power and Wealth
Those that settle space will control vast lands, enormous amounts
of electrical power, and nearly unlimited materials. The
societies that develop these resources will create wealth beyond
our wildest imagination and wield power -- hopefully for good
rather than for ill.
In the past, societies which have grown by colonization have
gained wealth and power at the expense of those who were
subjugated. Unlike previous settlement programs, space
settlement will build new land, not steal it from the locals as there simply are no locals.
Thus, the power and wealth born of space settlement will not come
at the expense of others, but rather represent the fruits of great
A Nice Place to Live
There will be little enthusiasm for moving into space unless people want to live there. In that vein, a few features of orbital real estate are worth mentioning:
- Great Views. Many astronauts have returned singing the
praises of their view of Earth from orbit. Low earth orbit
settlements, and eventually settlements near Jupiter and Saturn,
will have some of the most spectacular views in the solar system.
Of course, all space settlements will have unmatched views of the
stars, unhindered by clouds, air pollution, or (with some care)
bright city lights.
- Low-g recreation. Consider circular swimming pools
around and near the axis of rotation. You should be able to dive
up into the water! Sports and dance at low or
zero-g will be fantastic. For dancers, note that in sufficiently
low gravity, always available near the axis of rotation, anyone can
jump ten times higher than Baryshnikov ever dreamed.
- Environmental Independence. On Earth we all share a
single biosphere. We breathe the same air, drink the same water,
and the misdeeds of some are visited on the bodies of all. Each
space settlement is completely sealed and does not share atmosphere
or water with other settlements or with Earth. Thus if one
settlement pollutes their air, no one else need breathe it.
- Custom living. Since the entire environment is
man-made, you can really get what you want. Like lake front
property? Make lots of lakes. Like sunsets? Program sunset
simulations into weather system every hour. Like to go barefoot?
Make the entire environment foot-friendly.
With great difficulty. Fortunately, although building space
settlements will be very difficult, it's not impossible particularly if we start small and close to Earth.
Studies suggesting that small settlements in Low Earth Orbit directly above the equator are practical mean that the first settlements can be much closer, much simpler, and much easier to build than previously believed. Nonetheless, building
cities anywhere in space will require radiation protection, materials, energy, transportation,
communications, and life support.
Space settlement feasibility was addressed in a series of summer studies at
NASA Ames Research Center in the 1970's. These studies concluded
that space settlement is feasible, but very difficult and
Follow on work has made early settlement construction much easier by taking advantage of
low radiation levels in ELEO (eliminating most or all shielding) and
rotating at up to 4rpm to keep early settlements small. So small that space tourism offers an attractive route from where we are today to the first space settlements. Space tourism has already started. As of 2017 the Russians have flown seven space tourists, one of them twice, using the Russian portion of International Space Station (ISS) as a part time hotel.
- Radiation protection. Cosmic rays and solar flares
create a lethal radiation environment in space but
settlements in Equatorial Low Earth Orbit (ELEO) are protected from most space radiation by the Earth itself and Earth's magnetic field. Further out, beyond Earth's magnetic field,
settlements must be surrounded by sufficient mass to absorb most
incoming radiation, about 7-11 tons per square meter depending on the material.
- Materials. Launching materials from Earth is
expensive, so for far away settlements bulk materials such as radiation shielding 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, carbon, and at least some nitrogen.
- 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. 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. Transportation for millions
of tons of materials from the Moon and asteroids to settlement
construction sites is also necessary once settlements expand beyond Earth's magnetic field. One 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. Early settlements close to Earth can plug into Earth's communication system.
- 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.
The tallest poles in the space settlement development tent are launch, construction, and life support. Launch is expensive today because most vehicles are expendable. After a single flight they are thrown away. The keys to reusability are technology and launch rate. There are multiple efforts in progress to develop reusable rocket technology but today's flight rate, less than 100 per year, is completely insufficient. A single reusable vehicle that can fly twice a week can meet that demand. Somewhere above 10,000 flights per year is probably needed, and tourism -- at the right price -- can generate use that kind of flight rate. No other application, with the exception of space solar power, again at the right price, has the potential to require so many flights.
Space tourists will need hotels to stay in. A primitive space hotel is very similar to today's space stations, but does not need expensive scientific equipment. Should early space hotels be successful bigger and better hotels will be built. These hotels will need to provide life support, including recycling the air and water and perhaps even some agriculture. At some point the largest hotels will be the size of a small settlement (~100 m diameter). At that point building the first space settlement is not much more difficult than building yet another hotel.
Space solar power is the other source of high launch demand, although it cannot develop space hotels. 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 space energy systems, it is possible to generate a great deal of electrical
power. This can be converted to microwaves or infra-red 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 creating a
large profitable business and dramatically reducing pollution.
How long did it take to build New York? California? France?
Even given ample funds the first settlement will take decades to
construct. No one is building a space settlement today, and there
are no immediate prospects for large amounts of money, so the first
settlement will be awhile.
However, a few commercial firms are developing space stations which could double as space hotels. These may well be deployed in the next decade or perhaps even less. After that we are may need at least two or three decades of hotel development to get to the size of a small settlement. Construction of the first settlement could easily take most of a decade. Thus, somewhere in the neighborhood of 30-50 years from now people may be moving in to the first settlement.
We cannot say when the first space settlement will be build but, with a little luck, the right unit of measurement is decades, not years or centuries. In the meantime, there's a lot to do. Better get started!
To the space settlement home page.
DISCLAIMER: This web site is not a policy statement. It is
intended to be an accessible introduction to the ideas developed in
Ames space settlement studies of the 1970s to support the
annual Student Space Settlement Design Contest.
This site was hosted by the NASA Ames Research Center from 1994-2018 and is now hosted by: