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C00002 00002 Humans will eventually settle the universe unless someone
C00003 00003 The Habitability of Space:
C00005 00004 Science fiction and reality:
C00010 00005 How do we get off the planet?
C00012 00006 How do we get to the stars?:
C00015 00007 The space program:
C00016 00008 Societies in space:
C00017 ENDMK
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Humans will eventually settle the universe unless someone
stops us. There are several reasons.
1. The interplanetary space surrounding ours and other suns
is entirely habitable by humans. As it becomes economically more
feasible, the same motivations that produced every previous human
expansion will operate.
2. Given the danger of nuclear wars, expansion into space
is an important way of dispersal so that no single war could wipe
out humanity.
3. Having a frontier is an attractive feature of a society.
The Habitability of Space:
While the planets are all less habitable than Antarctica,
it appears that interplanetary space is habitable and probably
even enjoyable by humans. Some will prefer adapting their physiology ---
if necessary, irreversibly --- to absence of gravity. Others will
maintain their fitness for life on a planet by using centrifugal
force to simulate gravity.
Interplanetary space has the following advantages over
the surface of planets.
1. The absence of gravity permits very large structures ---
very much larger than buildings on earth.
2. Solar energy is readily collectable in interplanetary
space, because the collectors can maintain a fixed orientation
toward the sun.
3. Travel within the solar system that does not involve
descending to the surface of a planet can be very cheap and
easy. There is an incredible amount of space in space.
There is the problem of materials. These will be obtained from
the earth (at great expense), from the moon (at lesser expense because of
the moon's lower gravity and lack of atmosphere) and from the asteroids at
still lower expense, because they have very low gravity and large surface
to volume ratios.
Science fiction and reality:
Many people's ideas of life off the planet have been formed
by reading science fiction. Sometimes the authors do their best
to base their stories on the scientific possibilities, but more
often their entertainment or propaganda motives win out.
Here are some of the science fiction motifs and their comparison
with reality.
1. Alien civilizations. It would be great fun to live
in a galaxy with thousands of civilizations, with most at a technological
level not too far from our own, with alien beings with lives and
motivations not too far from our own. It would be best if they
were reachable in journeys of a few weeks to a few months. These
possibilities make for great stories, but reality seems to be different
in a number of ways.
2. If present science is correct, there isn't any way of going
faster than light and very difficult to achieve speeds close to
that of light. This means 4 years to the nearest star and something
like 30 thousand years to the center of the galaxy. We have to think
about migration rather than travel under these circumstances. Travel
will be a reasonable concept if we can extend our lives to be many
hundreds of thousands of years. However, unless this is to be the
theme of the story, the idea isn't congenial to a science fiction
writer --- better write something fuzzy about hyperspace. A
literary layman can't quarrel with this literary decision.
3. If most stars will support intelligent life, then there
will eventually be a hundred billion civilizations in our galaxy.
Who needs that many in a story unless that is to be the story's theme?
4. Aliens might be quite different from us. For example,
some of them might have neural times much faster than ours.
Conversation with us would be very dull for such an alien.
Better make them more like us.
5. The biggest difference appears to be that there may not
be any other civilizations in our galaxy, and there may not be very
many planets where humans could survive with ordinary clothing.
6. Closer to home, all science fiction greatly underestimated
the cost and organizational complexity of space travel by factors of
many thousands. The typical 1930s and 1940s story had the cost
of going to the moon about a million dollars or less, judging from
the number of people apparently involved in the project. There
was nothing like the million people who worked at one time or another
on aspects of the Apollo project. Moreover, they didn't just make
a few isolated landings on the moon.
As literature generally does for the sake of the story,
the importance of a few key individuals is exaggerated, and the
amount of division of labor and responsibility is underestimated
by an enormous factor.
7. The other planets of the solar system are all less
habitable for humans than Antarctica. This isn't faced unless
it's the theme.
How do we get off the planet?
This problem has technological, political and social aspects.
An important technological consideration is that the main
problem is getting people and materials to low earth orbit as the
Shuttle does. For travel in space beyond low earth orbit there are
low thrust high exhaust velocity rockets like ionic rockets.
There are several technological possibilities.
1. Like the Shuttle only bigger and better. That will work;
only it will cost more money than the U.S. has been willing to spend.
2. There's the NERVA style nuclear powered rocket.
A major ideological obstacle is the attitude of a large
part of the scientific and intellectual community. They just don't
like manned space travel, and find every possible reason to oppose
it.
How do we get to the stars?:
Getting to the stars is entirely feasible with technology
based on present science provided we are willing to accept multi-generation
journeys. One scheme involves using a nuclear reactor to generate
electricity and using the electricity to eject matter at a suitable
velocity from the rear of the space ship. It turns out that the
optimal velocity depends on the length of the journey and should
vary during the journey. Under reasonable assumptions, one can
derive a formula for the time taken for a journey as it depends
on the length of the journey and the power to mass ration of
the reactor and propulsion system. The formula, derived and
discussed in Appendix A, is
%
$$t = 2 pā{-1\over 3}sā{2\over 3},$$
%
where the time is in seconds, the distance in meters and the power
to mass ration in watts per kilogram. It is assumed that the
velocities remain small compared to the speed of light and that
the journey is less than 600 light years.
The formula has three interesting consequences. First, with
any reasonable power to mass ratios, it will take hundreds of
years to get to the nearest star. Second, it doesn't take a qualitatively
different time to get anywhere within 600 light years and there
are plenty of stars within that distance. Third, the time is not
very sensitive to the power to mass ratio, so there isn't an
enormous premium to be gained from making it better.
The space program:
I begin by expressing disappointment that the United States
hasn't pursued its space program more vigorously and expressing
some bitterness at the people who have prevented it.
Societies in space: