Space Colonization
Terra-forming
ASTR 1420
Lecture 25
Not in the Textbook
Space Colonization
Space colonization in this lecture is in a narrow sense : colonization by human
and in the Solar System only (say within next few millennia).
• Also known as space settlement, space habitation, etc.
Space colonization = self-sufficient human habitation outside the Earth
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on planets
on satellites
free space
outside of the Solar System
Reasons why some humans living in Space
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Survival of our species
$$$ : solar power satellites, asteroid mining, space manufacturing, etc.
Resources : sufficient supply of rare materials
lesson the burden on the Earth
spread our beauty(?) to the Universe
Insulin crystal growth in space (left) versus on Earth (right)
“The long-term survival of the human race is at risk as
long as it is confined to a single planet. Sooner or later,
disasters such as an asteroid collision or nuclear war
could wipe us all out. But once we spread out into space
and establish independent colonies, our future should be
safe.”
Stephen Hawking
Space solar power station (immediate feature)
A space-based solar power station will use an array of mirrors to concentrate
the sun’s rays on photovoltaic cells. The electricity produced is converted
into a powerful microwave beam directed at an antenna on Earth, where it is
converted back into electricity and fed to the grid.
This simple design can generate 13.4 billion
watts per second which is ~15 times more than
annual energy consumption of USA
Things to be considered…
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mass per person
radiation shielding
minimum size
leakage rates
cost
schedule
Materials and Energy
• using material from Earth is very expensive due to larger gravity of Earth.
o Also, large-scale project will impact the Earth community
o Need to use materials from Moon, Mars, large asteroids
however, these objects lack volatiles (Hydrogen and Nitrogen).
solution? Jupiter’s Trojan asteroids have high content of water ice and other
volatiles.
• Solar energy is abundant in the space (no night, no cloud, no atmosphere).
o Energy on the top of Earth Atmo. (watts/m2) = 1366 / d2, (d is distance in AU)
o In developed countries, energy usage ~ 1000 watts/person
o Export created energy back to Earth
• Mars and Moon colonies may need to use nuclear energy
o waste heats?  requires a large radiator!
Transportation and Communication
• Transportation
o expect millions of shuttle launches.. 
requires cheaper and less pollutant
transportation devices.
o hypersonic spaceplane, space elevator, mass
driver, etc.
o all other rocket technologies we studied last
lecture!
• Communication
o for more distant colonies (e.g., Mars), a real
time communication is impractical due to the
light travel time (7 – 44 minutes lag).
o email or voice mails…
Minimum population size
• To prevent inbreeding  reduced fertility, genetic disorders, infant
mortality, malfunctioning immune system, etc.
• In 2002, anthropologist, John H. Moore.
population of 150-180 would allow normal reproduction for 60—80
generations (~2,000 population for long survival).
• “50/500” rule: conservation biologists, 50 is the minimum to prevent an
unacceptable rate of inbreeding, 500 is required to main overall genetic
variability.
 minimum “isolated” habitat population = 500
Life support
• We need air, water, food, mild temperature, and gravity.
• In space, closed ecological systems must recycle (or import) resources
• Nuclear submarine : carry out missions for months without resurfacing
o although they recycle oxygen, it is not “closed” system.
o they extract oxygen from sea water and dump CO2 outside.
• Radiation protection: against harmful cosmic rays and solar wind.
o Either we need 5—10 tons of blocking (absorbing) material per square
meter of surface habitat area. Or we can make the hull-metal electric to
protect against charged particles.
o Two experiments in 1991 and 1994
Biosphere 2 : experiment of a “closed” ecosystem
• Biosphere 2 in Arizona
savana and ocean
o a small, complex, manmade biosphere supported
8 people for 1+ years!
o after 1 year, oxygen had to be replenished.
coastal desert
crew quarters
Size of 2.5 football field. $200 million dollars. 1987-2007
Bernal Sphere
• a type of space habitat intended as a long-term home for permanent
residents, first proposed in 1929 by John Desmond Bernal (Irish Scientist).
O’Neil’s habitat (1974)
• Good locations are L4 & L5 points.
one of O’Neil’s three designs called “Island Three”: two very large, counterrotating cylinders, each 5 miles (8 km) in diameter and 20 miles (32 km) long
Other variants
Toroidal and Spherical colonies. Bernal Spheres.
Objections
• Even if the technology was available, and the costs of deploying a program
relatively low, and the likelihood of success relatively high, only a small
number of people would directly benefit from a colony (either enthusiastic
colonists or high risk commercial interests), leaving most of financial
burden on the public.
• Humans are treated as assets
• If the main reason is “insurance” against the annihilation of human, then
why people on Earth need to pay for something useful only after their
deaths?
Counter arguments
• argument of need
“population growth and limited
resources on Earth”
By 2040, population will be 10 billion!,
gem stones, power, etc.
• argument of cost
Cost of wars since 2001 = $1.32 trillion USD
• argument of benefits
despite the high cost of initial investment…
space colonies can provides precious metals, gem stones, power, etc.
 the smallest Earth-crossing asteroid 3554 Amun (~2km): iron, nickel, cobalt, platinum etc
(30x the amount ever mined. $20 trillion USD)
Terraforming
planetary engineering :
process of deliberately
modifying atmosphere,
temperature, surface
topography, or ecology of
celestial objects to fit our
purposes
Terraforming Mars
• Two things: atmosphere and heating
• Once it is terraformed to be similar to Earth, will it be able to sustain the
condition over geological timescales (10s Myr to 100 Myr)?
• How ?
o Small size is the main issue…
o Re-heating the core of Mars is considered an impractical solution
o the slow loss of atmosphere could possibly be counteracted with ongoing lowlevel artificial terraforming activities.
Method?
• Put several, large solar mirrors to direct light to the Martian surface (to
increase T)
• Bring one of ice moons of Jupiter or Saturn  induce an impact with an
~1,000 km object to melt the whole thing which will re-liquefy the core 
magnetic field!
Terraforming Venus
Requirements :
• removing most of the
planet's dense 9 MPa
carbon dioxide
atmosphere
• reducing the planet's
450 °C (850 K) surface
temperature
• Addition of O2
• Reduce the length of
day(?) : 117 Earth days
How?
• Solar shade at L1
• reflector on the ground
or in the atmosphere
• use of genetically
engineered bacteria
which can turn CO2 into
other organics
• induce an impact with
500-700km asteroid (to
eliminate atmosphere
fast)
Europa
• a good potential candidate for terraforming
• One clear advantage of Europa is the
presence of liquid water
Difficulties
• huge radiation (in the middle of Jupiter’s
radiation belt; On Europa, a human would
die from the radiation within ten minutes on
the surface)
o require the building of massive radiation
deflectors, which is currently impractical
• satellite is covered in ice and would have to
be heated
• need for oxygen  electrolysis of ocean
water
In summary…
Important Concepts
Important Terms
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Closed ecosystem experiments
Space habitat
Pros and cons of space habitats
Terraforming Mars, Venus, etc.
Terraforming
Biosphere 2
Bern sphere
ONeil’s habitats
Chapter/sections covered in this lecture : Not from the textbook
Human and Environment : next class!