From Wikipedia, the free encyclopedia
Space colonization (also called
space settlement, or
extraterrestrial colonization) is permanent human habitation off the planet
Earth.
This article is mainly about colonies on bodies apart from Earth. For free space colonies in micro-g see
space habitat.
Many arguments have been made for and against space colonization.
[1] The two most common in favor of colonization are survival of human
civilization and the
biosphere in the event of a
planetary-scale disaster (natural or man-made),
and the availability of additional resources in space that could enable
expansion of human society. The most common objections to colonization
include concerns that the
commodification
of the cosmos may be likely to enhance the interests of the already
powerful, including major economic and military institutions, and to
exacerbate pre-existing detrimental processes such as
wars,
economic inequality, and
environmental degradation.
[2][3][4]
No space colonies have been built so far. Currently, the building of a
space colony would present a set of huge technological and economic
challenges. Space settlements would have to provide for nearly all (or
all) the material needs of hundreds or thousands of humans, in an
environment out in space that is
very hostile to human life. They would involve technologies, such as
controlled ecological life support systems,
that have yet to be developed in any meaningful way. They would also
have to deal with the as-yet unknown issue of how humans would behave
and thrive in such places long-term. Because of the present cost of
sending anything from the surface of the Earth into orbit (around $2,500
per-pound to orbit, expected to further decrease),
[5] a space colony would currently be a massively expensive project.
There are yet no plans for building space colonies by any large-scale
organization, either government or private. However, many proposals,
speculations, and designs for space settlements have been made through
the years, and a considerable number of space colonization
advocates and groups are active. Several famous scientists, such as
Freeman Dyson, have come out in favor of space settlement.
[6]
On the technological front, there is ongoing progress in making access to space cheaper (
reusable launch systems could reach $10 per-pound to orbit),
[7] and in creating
automated manufacturing and construction techniques.
[8]
Reasons
Survival of human civilization
The primary argument calling for space colonization is the long-term
survival of human civilization. By developing alternative locations off
Earth, the planet's species, including humans, could live on in the
event of
natural or man-made disasters on our own planet.
On two occasions, theoretical physicist and cosmologist
Stephen Hawking
has argued for space colonization as a means of saving humanity. In
2001, Hawking predicted that the human race would become extinct within
the next thousand years, unless colonies could be established in space.
[9]
In 2006, he stated that humanity faces two options: either we colonize
space within the next two hundred years and build residential units on
other planets, or we will face the prospect of
long-term extinction.
[10]
In 2005, then
NASA Administrator
Michael Griffin identified space colonization as the ultimate goal of current spaceflight programs, saying:
... the goal isn't just scientific exploration ... it's also about
extending the range of human habitat out from Earth into the solar
system as we go forward in time ... In the long run a single-planet
species will not survive ... If we humans want to survive for hundreds
of thousands or millions of years, we must ultimately populate other
planets. Now, today the technology is such that this is barely
conceivable. We're in the infancy of it. ... I'm talking about that one
day, I don't know when that day is, but there will be more human beings
who live off the Earth than on it. We may well have people living on the
Moon. We may have people living on the moons of Jupiter and other
planets. We may have people making habitats on asteroids ... I know that
humans will colonize the solar system and one day go beyond.[11]
Louis J. Halle, formerly of the
United States Department of State, wrote in
Foreign Affairs (Summer 1980) that the colonization of space will protect humanity in the event of global
nuclear warfare.
[12] The physicist
Paul Davies
also supports the view that if a planetary catastrophe threatens the
survival of the human species on Earth, a self-sufficient colony could
"reverse-colonize" Earth and restore
human civilization. The author and journalist
William E. Burrows and the biochemist
Robert Shapiro proposed a private project, the
Alliance to Rescue Civilization, with the goal of establishing an off-Earth "
backup" of human civilization.
[13]
Based on his
Copernican principle,
J. Richard Gott
has estimated that the human race could survive for another 7.8 million
years, but it is not likely to ever colonize other planets. However, he
expressed a hope to be proven wrong, because "colonizing other worlds
is our best chance to hedge our bets and improve the survival prospects
of our species".
[14]
Vast resources in space
Resources in space, both in materials and energy, are enormous. The
Solar System
alone has, according to different estimates, enough material and energy
to support anywhere from several thousand to over a billion times that
of the current Earth-based human population.
[15][16][17] Outside the Solar System, several hundred billion other stars in the
observable universe
provide opportunities for both colonization and resource collection,
though travel to any of them is impossible on any practical time-scale
without
interstellar travel by use of
generation ships or revolutionary new methods of travel, such as
faster-than-light (FTL).
Asteroid mining will also be a key player in space colonization.
Water and materials to make structures and shielding can be easily found
in asteroids. Instead of resupplying on Earth, mining and fuel stations
need to be established on asteroids to facilitate better space travel.
[18]
Optical mining is the term NASA uses to describe extracting materials
from asteroids. NASA believes by using propellant derived from asteroids
for exploration to the moon, Mars, and beyond will save $100 billion.
If funding and technology come sooner than estimated, asteroid mining
might be possible within a decade.
[19]
All these planets and other bodies offer a virtually endless supply
of resources providing limitless growth potential. Harnessing these
resources can lead to much economic development.
[20]
Expansion with fewer negative consequences
Expansion of humans and technological progress has usually resulted
in some form of environmental devastation, and destruction of
ecosystems and their accompanying
wildlife. In the past, expansion has often come at the expense of displacing many
indigenous peoples,
the resulting treatment of these peoples ranging anywhere from
encroachment to genocide. Because space has no known life, this need not
be a consequence, as some space settlement advocates have pointed out.
[21][22]
Alleviating overpopulation and resource demand
Another argument for space colonization is to mitigate the negative effects of
overpopulation.
[clarification needed]
If the resources of space were opened to use and viable life-supporting
habitats were built, Earth would no longer define the limitations of
growth. Although many of Earth's resources are non-renewable, off-planet
colonies could satisfy the majority of the planet's resource
requirements. With the availability of extraterrestrial resources,
demand on terrestrial ones would decline.
[23]
Other arguments
Additional
goals cite the innate human drive to explore and discover, a quality
recognized at the core of progress and thriving civilizations.
[24][25]
Nick Bostrom has argued that from a
utilitarian
perspective, space colonization should be a chief goal as it would
enable a very large population to live for a very long period of time
(possibly billions of years), which would produce an enormous amount of
utility (or happiness).
[26]
He claims that it is more important to reduce existential risks to
increase the probability of eventual colonization than to accelerate
technological development so that space colonization could happen
sooner. In his paper, he assumes that the created lives will have
positive ethical value despite the problem of
suffering.
In a 2001 interview with Freeman Dyson, J. Richard Gott and Sid
Goldstein, they were asked for reasons why some humans should live in
space.
[6] Their answers were:
Goals
Although
some items of the infrastructure requirements above can already be
easily produced on Earth and would therefore not be very valuable as
trade items (oxygen, water, base metal ores, silicates, etc.), other
high value items are more abundant, more easily produced, of higher
quality, or can only be produced in space. These would provide (over the
long-term) a very high return on the initial investment in space
infrastructure.
[27]
Some of these high-value trade goods include precious metals,
[28][29] gemstones,
[30] power,
[31] solar cells,
[32] ball bearings,
[32] semi-conductors,
[32] and pharmaceuticals.
[32]
The mining and extraction of metals from a small asteroid the size of
3554 Amun or
(6178) 1986 DA,
both small near-Earth asteroids, would be 30 times as much metal as
humans have mined throughout history. A metal asteroid this size would
be worth approximately US$20 trillion at 2001 market prices.
Space colonization is seen as a long-term goal of some national
space programs.
Since the advent of the 21st-century commercialization of space, which
saw greater cooperation between NASA and the private sector, several
private companies have announced plans toward the
colonization of Mars. Among entrepreneurs leading the call for space colonization are
Elon Musk,
Dennis Tito and
Bas Lansdorp.
[33][34][35]
The main impediments to commercial exploitation of these resources are the very high cost of initial investment,
[36] the very long period required for the expected return on those investments (
The Eros Project plans a 50-year development),
[37] and the fact that the venture has never been carried out before — the high-risk nature of the investment.
Major governments and well-funded corporations have announced plans
for new categories of activities: space tourism and hotels, prototype
space-based solar-power satellites, heavy-lift boosters and
asteroid mining—that create needs and capabilities for humans to be present in space.
[38][39][40]
Method
Building colonies in space would require access to water, food, space, people, construction materials, energy, transportation,
communications,
life support,
simulated gravity,
radiation
protection and capital investment. It is likely the colonies would be
located near the necessary physical resources. The practice of
space architecture
seeks to transform spaceflight from a heroic test of human endurance to
a normality within the bounds of comfortable experience. As is true of
other frontier-opening endeavors, the capital investment necessary for
space colonization would probably come from governments,
[41] an argument made by John Hickman
[42] and
Neil deGrasse Tyson.
[43]
Materials
Colonies on the Moon, Mars, or asteroids could extract local materials. The Moon is deficient in
volatiles such as
argon,
helium and compounds of
carbon,
hydrogen and
nitrogen.
The LCROSS impacter was targeted at the Cabeus crater which was chosen
as having a high concentration of water for the Moon. A plume of
material erupted in which some water was detected. Mission chief
scientist Anthony Colaprete estimated that the Cabeus crater contains
material with 1% water or possibly more.
[44] Water
ice
should also be in other permanently shadowed craters near the lunar
poles. Although helium is present only in low concentrations on the
Moon, where it is deposited into
regolith by the solar wind, an estimated million tons of He-3 exists over all.
[45] It also has industrially significant
oxygen,
silicon, and metals such as
iron,
aluminum, and
titanium.
Launching materials from Earth is expensive, so bulk materials for colonies could come from the Moon, a
near-Earth object (NEO),
Phobos, or
Deimos. The benefits of using such sources include: a lower gravitational force, no
atmospheric drag
on cargo vessels, and no biosphere to damage. Many NEOs contain
substantial amounts of metals. Underneath a drier outer crust (much like
oil shale), some other NEOs are inactive comets which include billions of tons of water ice and
kerogen hydrocarbons, as well as some nitrogen compounds.
[46]
Farther out,
Jupiter's Trojan asteroids are thought to be rich in water ice and other volatiles.
[47]
Recycling of some raw materials would almost certainly be necessary.
Energy
Solar energy
in orbit is abundant, reliable, and is commonly used to power
satellites today. There is no night in free space, and no clouds or
atmosphere to block sunlight. Light intensity obeys an
inverse-square law. So the solar energy available at distance
d from the Sun is
E = 1367/
d2 W/m
2, where
d is measured in
astronomical units (AU) and 1367 watts/m
2 is the energy available at the distance of Earth's orbit from the Sun, 1 AU.
[48]
In the weightlessness and vacuum of space, high temperatures for industrial processes can easily be achieved in
solar ovens
with huge parabolic reflectors made of metallic foil with very
lightweight support structures. Flat mirrors to reflect sunlight around
radiation shields into living areas (to avoid line-of-sight access for
cosmic rays, or to make the Sun's image appear to move across their
"sky") or onto crops are even lighter and easier to build.
Large solar power photovoltaic cell arrays or thermal power plants
would be needed to meet the electrical power needs of the settlers' use.
In developed parts of Earth, electrical consumption can average 1
kilowatt/person (or roughly 10
megawatt-hours per person per year.)
[49]
These power plants could be at a short distance from the main
structures if wires are used to transmit the power, or much farther away
with
wireless power transmission.
A major export of the initial space settlement designs was anticipated to be large
solar power satellites that would use wireless power transmission (phase-locked
microwave
beams or lasers emitting wavelengths that special solar cells convert
with high efficiency) to send power to locations on Earth, or to
colonies on the Moon or other locations in space. For locations on
Earth, this method of getting power is extremely benign, with zero
emissions and far less ground area required per watt than for
conventional solar panels. Once these satellites are primarily built
from lunar or asteroid-derived materials, the price of SPS electricity
could be lower than energy from fossil fuel or nuclear energy; replacing
these would have significant benefits such as the elimination of
greenhouse gases and
nuclear waste from electricity generation.
Transmitting solar energy wirelessly from the Earth to the Moon and
back is also an idea proposed for the benefit of space colonization and
energy resources. Physicist Dr. David Criswell, who worked for NASA
during the Apollo missions, came up with the idea of using power beams
to transfer energy from space. These beams, microwaves with a wavelength
of about 12 cm, will be almost untouched as they travel through the
atmosphere. They can also be aimed at more industrial areas to keep away
from humans or animal activities.
[50] This will allow for safer and more reliable methods of transferring solar energy.
In 2008, scientists were able to send a 20 watt microwave signal from a mountain in Maui to the island of Hawaii. Since then
JAXA
and Mitsubishi has teamed up on a $21 billion project in order to place
satellites in orbit which could generate up to 1 gigawatt of energy.
[51]
These are the next advancements being done today in order to make
energy be transmitted wirelessly for space-based solar energy.
However, the value of SPS power delivered wirelessly to other
locations in space will typically be far higher than to Earth.
Otherwise, the means of generating the power would need to be included
with these projects and pay the heavy penalty of Earth launch costs.
Therefore, other than proposed demonstration projects for power
delivered to Earth,
[39]
the first priority for SPS electricity is likely to be locations in
space, such as communications satellites, fuel depots or "orbital
tugboat" boosters transferring cargo and passengers between
low-Earth orbit (LEO) and other orbits such as
geosynchronous orbit (GEO),
lunar orbit or
highly-eccentric Earth orbit (HEEO).
[52]:132
The system will also rely on satellites and receiving stations on Earth
to convert the energy into electricity. Because of this energy can be
transmitted easily from dayside to nightside meaning power is reliable
24/7.
[53]
Nuclear power
is sometimes proposed for colonies located on the Moon or on Mars, as
the supply of solar energy is too discontinuous in these locations; the
Moon has nights of two Earth weeks in duration. Mars has nights,
relatively high gravity, and an atmosphere featuring
large dust storms to cover and degrade solar panels. Also, Mars' greater distance from the Sun (1.5 astronomical units, AU) translates into
E/(1.52 = 2.25) only ½-⅔ the solar energy of Earth orbit.
[54]
Another method would be transmitting energy wirelessly to the lunar or
Martian colonies from solar power satellites (SPSs) as described above;
the difficulties of generating power in these locations make the
relative advantages of SPSs much greater there than for power beamed to
locations on Earth. In order to also be able to fulfill the requirements
of a moon base and energy to supply life support, maintenance,
communications, and research, a combination of both nuclear and solar
energy will be used in the first colonies.
[50]
For both solar thermal and nuclear power generation in airless
environments, such as the Moon and space, and to a lesser extent the
very thin Martian atmosphere, one of the main difficulties is dispersing
the
inevitable heat generated. This requires fairly large radiator areas.
Life support
In space settlements, a life support system must recycle or import
all the nutrients without "crashing." The closest terrestrial analogue
to space life support is possibly that of a
nuclear submarine.
Nuclear submarines use mechanical life support systems to support
humans for months without surfacing, and this same basic technology
could presumably be employed for space use. However, nuclear submarines
run "open loop"—extracting oxygen from seawater, and typically dumping
carbon dioxide overboard, although they recycle existing oxygen.
[citation needed] Recycling of the carbon dioxide has been approached in the literature using the
Sabatier process or the
Bosch reaction.
Although a fully mechanistic life support system is conceivable, a
closed ecological system is generally proposed for life support. The
Biosphere 2
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.
The relationship between organisms, their habitat and the non-Earth environment can be:
A combination of the above technologies is also possible.
Radiation protection
Cosmic rays and
solar flares create a lethal radiation environment in space. In Earth orbit, the
Van Allen belts
make living above the Earth's atmosphere difficult. To protect life,
settlements must be surrounded by sufficient mass to absorb most
incoming radiation, unless magnetic or plasma radiation shields were
developed.
[55]
Passive mass shielding of four metric tons per square meter of surface area will reduce radiation dosage to several
mSv or less annually, well below the rate of some populated
high natural background areas on Earth.
[56]
This can be leftover material (slag) from processing lunar soil and
asteroids into oxygen, metals, and other useful materials. However, it
represents a significant obstacle to maneuvering vessels with such
massive bulk (mobile spacecraft being particularly likely to use less
massive active shielding).
[55]
Inertia would necessitate powerful thrusters to start or stop rotation,
or electric motors to spin two massive portions of a vessel in opposite
senses. Shielding material can be stationary around a rotating
interior.
Self-replication
Space manufacturing could enable self-replication. Some think it's the ultimate goal because it allows an
exponential increase in colonies, while eliminating costs to and dependence on Earth.
[57] It could be argued that the establishment of such a colony would be Earth's first act of
self-replication.
[58]
Intermediate goals include colonies that expect only information from
Earth (science, engineering, entertainment) and colonies that just
require periodic supply of light weight objects, such as
integrated circuits, medicines,
genetic material and tools.
Psychological adjustment
The
monotony and loneliness that comes from a prolonged space mission can
leave astronauts susceptible to cabin fever or having a psychotic break.
Moreover, lack of sleep, fatigue, and work overload can affect an
astronaut's ability to perform well in an environment such as space
where every action is critical.
[59]
Population size
In 2002, the
anthropologist John H. Moore estimated that a population of 150–180 would permit a stable society to exist for 60 to 80 generations — equivalent to 2000 years.
A much smaller initial population of as little as two women should be viable as long as human
embryos are available from Earth. Use of a
sperm bank from Earth also allows a smaller starting base with negligible
inbreeding.
Researchers in conservation biology have tended to adopt the "50/500"
rule of thumb initially advanced by Franklin and Soule. This rule says a
short-term
effective population size (
Ne) of 50 is needed to prevent an unacceptable rate of
inbreeding, whereas a long‐term
Ne of 500 is required to maintain overall genetic variability. The
Ne = 50
prescription corresponds to an inbreeding rate of 1% per generation,
approximately half the maximum rate tolerated by domestic animal
breeders. The
Ne = 500 value attempts to balance the rate of gain in genetic variation due to mutation with the rate of loss due to
genetic drift.
Assuming a journey of 6,300 years, the astrophysicist Frédéric Marin
and the particle physicist Camille Beluffi calculated that the minimum
viable population for a
generation ship to reach
Proxima Centauri would be 98 settlers.
[60][61]
Location
Location is a frequent point of contention between space colonization
advocates. The location of colonization can be on a physical body
planet,
dwarf planet,
natural satellite, or
asteroid or orbiting one. For colonies not on a body see also
space habitat.
Near-Earth space
The Moon
Due to its proximity and familiarity, Earth's Moon is discussed as a
target for colonization. It has the benefits of proximity to Earth and
lower
escape velocity,
allowing for easier exchange of goods and services. A drawback of the
Moon is its low abundance of volatiles necessary for life such as
hydrogen, nitrogen, and carbon. Water-ice deposits that exist in some
polar
craters
could serve as a source for these elements. An alternative solution is
to bring hydrogen from near-Earth asteroids and combine it with oxygen
extracted from lunar rock.
The Moon's low surface gravity is also a concern, as it is unknown whether 1/6
g is enough to maintain human health for long periods.
[citation needed]
The Moon's lack of atmosphere provides no protection from space
radiation or meteoroids. The early Moon colonies may shelter in ancient
Lunar lava tubes to gain protection. The two-week day/night cycle makes use of solar power more difficult.
Lagrange points
Another near-Earth possibility are the five Earth–Moon
Lagrange points.
Although they would generally also take a few days to reach with
current technology, many of these points would have near-continuous
solar power because their distance from Earth would result in only brief
and infrequent eclipses of light from the Sun. However, the fact that
the Earth–Moon Lagrange points
L4 and
L5 tend to collect dust and debris, whereas
L1-
L3 require active
station-keeping
measures to maintain a stable position, make them somewhat less
suitable places for habitation than was originally believed.
Additionally, the orbit of
L2–
L5 takes them out of the protection of the Earth's
magnetosphere for approximately two-thirds of the time, exposing them to the health threat from cosmic rays.
The five Earth–Sun Lagrange points would totally eliminate eclipses, but only
L1 and
L2 would be reachable in a few days' time. The other three Earth–Sun points would require months to reach.
The inner planets
Mercury
Colonizing
Mercury would involve similar challenges as the Moon as there are few
volatile elements, no atmosphere and the surface gravity is lower than
Earth's. However, the planet also receives almost seven times the solar
flux as the Earth/Moon system. Geologist Stephen Gillett has suggested
this will make Mercury an ideal place to build
solar sails, which could launch as folded up "chunks" by
mass driver from Mercury's surface. Once in space the solar sails would deploy. Since Mercury's
solar constant
is 6.5 times higher than Earth's, energy for the mass driver should be
easy to come by, and solar sails near Mercury would have 6.5 times the
thrust they do near Earth. This could make Mercury an ideal place to
acquire materials useful in building hardware to send to (and terraform)
Venus. Vast solar collectors could also be built on or near Mercury to
produce power for large scale engineering activities such as
laser-pushed lightsails to nearby star systems.
[62]
Asteroid belt
Colonization of asteroids would require space habitats. The
asteroid belt has significant overall material available, the largest object being
Ceres,
although it is thinly distributed as it covers a vast region of space.
Unmanned supply craft should be practical with little technological
advance, even crossing 500 million kilometers of space. The colonists
would have a strong interest in assuring their asteroid did not hit
Earth or any other body of significant mass, but would have extreme
difficulty in moving an asteroid
[citation needed]
of any size. The orbits of the Earth and most asteroids are very
distant from each other in terms of delta-v and the asteroidal bodies
have enormous
momentum. Rockets or mass drivers can perhaps be installed on asteroids to direct their path into a safe course.
Moons of outer planets
Jovian moons – Europa, Callisto and Ganymede
The
Artemis Project designed a plan to colonize
Europa, one of
Jupiter's moons. Scientists were to inhabit
igloos
and drill down into the Europan ice crust, exploring any sub-surface
ocean. This plan discusses possible use of "air pockets" for human
habitation. Europa is considered one of the more habitable bodies in the
Solar System and so merits investigation as a possible abode for life.
NASA performed a study called
HOPE (Revolutionary Concepts for
Human
Outer
Planet
Exploration) regarding the future exploration of the Solar System.
[63] The target chosen was
Callisto
due to its distance from Jupiter, and thus the planet's harmful
radiation. It could be possible to build a surface base that would
produce fuel for further exploration of the Solar System.
Three of the
Galilean moons (Europa, Ganymede, Callisto) have an abundance of volatiles that may support colonization efforts.
Moons of Saturn – Titan, Enceladus, and others
Titan is suggested as a target for colonization,
[64]
because it is the only moon in the Solar System to have a dense
atmosphere and is rich in carbon-bearing compounds. Titan has ice water
and large methane oceans.
[65] Robert Zubrin identified Titan as possessing an abundance of all the elements necessary to support life
[where?],
making Titan perhaps the most advantageous locale in the outer Solar
System for colonization, and saying "In certain ways, Titan is the most
hospitable extraterrestrial world within our solar system for human
colonization".
Enceladus
is a small, icy moon orbiting close to Saturn, notable for its
extremely bright surface and the geyser-like plumes of ice and water
vapor that erupt from its southern polar region. If Enceladus has liquid
water, it joins Mars and Jupiter's moon Europa as one of the prime
places in the Solar System to look for extraterrestrial life and
possible future settlements.
Other large satellites:
Rhea,
Iapetus,
Dione,
Tethys, and
Mimas, all have large quantities of volatiles, which can be used to support settlements.
Trans-Neptunian region
The
Kuiper belt is estimated to have 70,000 bodies of 100 km or larger.
Freeman Dyson has suggested that within a few centuries human civilization will have relocated to the Kuiper belt.
[66]
The
Oort cloud is estimated to have up to a trillion comets.
Outside the Solar System
Looking beyond the Solar System, there are up to several hundred
billion potential stars with possible colonization targets. The main
difficulty is the vast distances to other stars: roughly a hundred
thousand times further away than the planets in the Solar System. This
means that some combination of very high speed (some percentage of the
speed of light), or travel times lasting centuries or millennia, would be required. These speeds are far beyond what current
spacecraft propulsion systems can provide.
Many scientific papers have been published about
interstellar travel.
Given sufficient travel time and engineering work, both unmanned and
generational voyages seem possible, though representing a very
considerable technological and economic challenge unlikely to be met for
some time, particularly for manned probes.
[citation needed]
Space colonization technology could in principle allow human
expansion at high, but sub-relativistic speeds, substantially less than
the speed of light,
c. An interstellar colony ship would be
similar to a space habitat, with the addition of major propulsion
capabilities and independent energy generation.
Hypothetical
starship concepts proposed both by scientists and in
hard science fiction include:
- A generation ship
would travel much slower than light, with consequent interstellar trip
times of many decades or centuries. The crew would go through
generations before the journey is complete, so that none of the initial
crew would be expected to survive to arrive at the destination, assuming
current human lifespans.
- A sleeper ship, in which most or all of the crew spend the journey in some form of hibernation or suspended animation, allowing some or all who undertake the journey to survive to the end.
- An embryo-carrying interstellar starship (EIS), much smaller than a generation ship or sleeper ship, transporting human embryos
or DNA in a frozen or dormant state to the destination. (Obvious
biological and psychological problems in birthing, raising, and
educating such voyagers, neglected here, may not be fundamental.)
- A nuclear fusion or fission powered ship (e.g. ion drive) of some kind, achieving velocities of up to perhaps 10% c permitting one-way trips to nearby stars with durations comparable to a human lifetime.
- A Project Orion-ship, a nuclear-powered concept proposed by Freeman Dyson which would use nuclear explosions
to propel a starship. A special case of the preceding nuclear rocket
concepts, with similar potential velocity capability, but possibly
easier technology.
- Laser propulsion concepts, using some form of beaming of power from the Solar System might allow a light-sail
or other ship to reach high speeds, comparable to those theoretically
attainable by the fusion-powered electric rocket, above. These methods
would need some means, such as supplementary nuclear propulsion, to stop
at the destination, but a hybrid (light-sail for acceleration,
fusion-electric for deceleration) system might be possible.
The above concepts all appear limited to high, but still
sub-relativistic speeds, due to fundamental energy and reaction mass
considerations, and all would entail trip times which might be enabled
by space colonization technology, permitting self-contained habitats
with lifetimes of decades to centuries. Yet human interstellar expansion
at average speeds of even 0.1% of
c would permit settlement of
the entire Galaxy in less than one half of a galactic rotation period of
~250,000,000 years, which is comparable to the timescale of other
galactic processes. Thus, even if interstellar travel at near
relativistic speeds is never feasible (which cannot be clearly
determined at this time), the development of space colonization could
allow human expansion beyond the Solar System without requiring
technological advances that cannot yet be reasonably foreseen. This
could greatly improve the chances for the survival of intelligent life
over cosmic timescales, given the many natural and human-related hazards
that have been widely noted.
If humanity does gain access to a large amount of energy, on the
order of the mass-energy of entire planets, it may eventually become
feasible to construct
Alcubierre drives.
These are one of the few methods of superluminal travel which may be
possible under current physics. However it is probable that such a
device could never exist, due to the fundamental challenges posed. For
more on this see
Difficulties of making and using an Alcubierre Drive.
Intergalactic travel
Looking
beyond the Milky Way, there are at least 2 trillion other galaxies in
the observable universe. The distances between galaxies are on the order
of a million times farther than those between the stars. Because of the
speed of light limit on how fast any material objects can travel in
space, intergalactic travel would either have to involve voyages lasting
millions of years,
[67] or a possible faster than light propulsion method based on speculative physics, such as the
Alcubierre drive. There are, however, no scientific reasons for stating that
intergalactic travel is impossible in principle.
Funding
Space colonization can roughly be said to be possible when the necessary methods of space colonization become
cheap enough (such as space access by cheaper launch systems) to meet the cumulative funds that have been gathered for the purpose.
Although there are no immediate prospects for the large amounts of
money required for space colonization to be available given traditional
launch costs,
[68][full citation needed]
there is some prospect of a radical reduction to launch costs in the
2010s, which would consequently lessen the cost of any efforts in that
direction. With a published price of
US$56.5 million per launch of up to 13,150 kg (28,990 lb) payload
[69] to
low Earth orbit,
SpaceX Falcon 9 rockets are already the "cheapest in the industry".
[70] Advancements currently being developed as part of the
SpaceX reusable launch system development program
to enable reusable Falcon 9s "could drop the price by an order of
magnitude, sparking more space-based enterprise, which in turn would
drop the cost of access to space still further through economies of
scale."
[70]
If SpaceX is successful in developing the reusable technology, it would
be expected to "have a major impact on the cost of access to space",
and change the increasingly
competitive market in space launch services.
[71]
The
President's Commission on Implementation of United States Space Exploration Policy suggested that an
inducement prize
should be established, perhaps by government, for the achievement of
space colonization, for example by offering the prize to the first
organization to place humans on the Moon and sustain them for a fixed
period before they return to Earth.
[72]
Terrestrial analogues to space colonies
The most famous attempt to build an analogue to a self-sufficient colony is
Biosphere 2, which attempted to duplicate Earth's biosphere.
BIOS-3 is another
closed ecosystem, completed in 1972 in
Krasnoyarsk,
Siberia.
Many
space agencies build testbeds for advanced life support systems, but these are designed for long duration
human spaceflight, not permanent colonization.
Remote research stations in inhospitable climates, such as the
Amundsen–Scott South Pole Station or
Devon Island Mars Arctic Research Station, can also provide some practice for off-world outpost construction and operation. The
Mars Desert Research Station has a habitat for similar reasons, but the surrounding climate is not strictly inhospitable.
History
The first known work on space colonization was
The Brick Moon, a work of fiction published in 1869 by
Edward Everett Hale, about an inhabited artificial satellite.
[73]
The Russian schoolmaster and physicist
Konstantin Tsiolkovsky foresaw elements of the space community in his book
Beyond Planet Earth written about 1900. Tsiolkovsky had his space travelers building greenhouses and raising crops in space.
[74] Tsiolkovsky believed that going into space would help perfect human beings, leading to immortality and peace.
[75]
Others have also written about space colonies as Lasswitz in 1897 and Bernal, Oberth, Von Pirquet and Noordung in the 1920s.
Wernher von Braun contributed his ideas in a 1952
Colliers article. In the 1950s and 1960s,
Dandridge M. Cole[76] published his ideas.
Another seminal book on the subject was the book
The High Frontier: Human Colonies in Space by
Gerard K. O'Neill[77] in 1977 which was followed the same year by
Colonies in Space by
T. A. Heppenheimer.
[78]
M. Dyson wrote
Home on the Moon; Living on a Space Frontier in 2003;
[79] Peter Eckart wrote
Lunar Base Handbook in 2006
[80] and then Harrison Schmitt's
Return to the Moon written in 2007.
[81]
As of 2013,
Bigelow Aerospace is the only
private commercial spaceflight company that has launched two experimental space station modules,
Genesis I (2006) and
Genesis II (2007),
[82] into
Earth-orbit, and has indicated that their first production model of the space habitat, the
BA 330, could be launched by 2017.
[83]
Planetary protection
Robotic spacecraft to Mars are required to be sterilized, to have at
most 300,000 spores on the exterior of the craft—and more thoroughly
sterilized if they contact "special regions" containing water,
[84][85] otherwise there is a risk of contaminating not only the life-detection experiments but possibly the planet itself.
It is impossible to sterilize human missions to this level, as humans are host to typically a hundred trillion
microorganisms of thousands of species of the
human microbiome,
and these cannot be removed while preserving the life of the human.
Containment seems the only option, but it is a major challenge in the
event of a hard landing (i.e. crash).
[86] There have been several planetary workshops on this issue, but with no final guidelines for a way forward yet.
[87] Human explorers would also be vulnerable to back contamination to Earth if they become carriers of microorganisms.
[88]
Objections
A corollary to the
Fermi paradox—"nobody else is doing it"—is the argument that, because no evidence of
alien colonization technology exists, it is statistically unlikely to even be possible to use that same level of technology ourselves.
Colonizing space would require massive amounts of financial,
physical, and human capital devoted to research, development,
production, and deployment. Earth's
natural resources
do not increase to a noteworthy extent (which is in keeping with the
"only one Earth" position of environmentalists). Thus, considerable
efforts in colonizing places outside Earth would appear as a hazardous
waste of the Earth's limited resources for an aim without a clear end.
The fundamental problem of public things, needed for survival, such as space programs, is the
free rider problem.
Convincing the public to fund such programs would require additional
self-interest arguments: If the objective of space colonization is to
provide a "backup" in case everyone on Earth is killed, then why should
someone on Earth pay for something that is only useful after they are
dead? This assumes that space colonization is not widely acknowledged as
a sufficiently valuable social goal.
Seen as a relief to the problem of overpopulation even as early as 1758,
[89] and listed as one of Stephen Hawking's reasons for pursuing space exploration,
[90] it has become apparent that space colonisation in response to overpopulation is unwarranted. Indeed, the
birth rates of many developed countries, specifically
spacefaring ones, are at or below replacement rates, thus negating the need to use colonisation as a means of population control.
[89]
Other objections include concerns that the forthcoming colonization and
commodification
of the cosmos may be likely to enhance the interests of the already
powerful, including major economic and military institutions e.g. the
large financial institutions, the major aerospace companies and the
military–industrial complex, to lead to new
wars, and to exacerbate pre-existing exploitation of
workers and
resources,
economic inequality,
poverty, social
division and
marginalization, environmental degradation, and other detrimental processes or institutions.
[2][3][4]
Additional concerns include creating a culture in which humans are no
longer seen as human, but rather as material assets. The issues of
human dignity,
morality,
philosophy,
culture,
bioethics, and the threat of
megalomaniac leaders in these new "societies" would all have to be addressed in order for space colonization to meet the
psychological and
social needs of people living in isolated colonies.
[91]
As an alternative or addendum for the future of the human race, many
science fiction writers have focused on the realm of the 'inner-space',
that is the computer-aided exploration of the
human mind and human
consciousness—possibly en route developmentally to a
Matrioshka Brain.
Robotic exploration
is proposed as an alternative to gain many of the same scientific
advantages without the limited mission duration and high cost of life
support and return transportation involved in manned missions.
Another concern is the potential to cause
interplanetary contamination on planets that may harbor hypothetical
extraterrestrial life.
Physical, mental and emotional health risks to colonizers
An additional concern is the health of the humans who may participate
in a colonization venture, including a range of physical, mental and
emotional health risks.
Involved organizations
Organizations that contribute to space colonization include:
In fiction
Although established space colonies are a stock element in science
fiction stories, fictional works that explore the themes, social or
practical, of the settlement and occupation of a habitable world are
much rarer.
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