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C00002 00002	SPACE AS A FRONTIER
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SPACE AS A FRONTIER

	The public is disappointed with the progress of the space program,
and I think this disappointment is justifiable.  Early rhetoric on the
space program compared the exploration of space with the discovery of the
new world, although it was entirely vague about the nature of the
comparison.  In part, the disappointment was inevitable for the following
reasons:

	1. The planets of our solar system are not inhabited by intelligent
peoples.  In fact, they almost certainly don't support any life at all.
As places to live, they are all less hospitable than Antarctica, and no-one
(not one person in the whole world!) seems inclined to move to Antarctica.

	2. Space travel remains extremely expensive, and there are no plans
for reducing the cost to an extent that will permit even well-to-do people
to include it in their travel plans.

	In spite of these unpleasant facts, space does have the potential
of serving as a frontier, and this is very important to human society.

	The relevant scientific facts are as follows:

	1. Interplanetary space rather than the planets is reasonably
hospitable to human life.  This is because structures can exist without
support and because solar energy can be collected by structures with
a fixed orientation.  Moreover, people can live in weightlessness, and
there is good reason to hope that people will come to prefer a weightless
condition to one with gravity.
The only shortage is matter.  The cost of matter in interplanetary space
will depend mainly on the depth of the gravitational well out of which it
has to be taken.  Therefore, the planets are not as good places to get
matter as the asteroids.  All the main elements seem to be available in
the asteroid belts, and elements wanted only in trace quantities can be
obtained on earth.

	2. It is not immediately clear what would ultimately limit human
population in interplanetary space.  The energy limit is easiest to
calculate.  This limit would occur when the space rafts carrying people
completely englobed the sun and used all its energy.  If we imagine
people living so austerely that their major energy limit was food,
say 4000 calories per day, we get 10\F328\F0 people.  Present American
levels of energy consumption would give 10↑26 people.  Almost certainly,
we would run out of some material before we ran out of energy.  This depends
on whether matter could be obtained from the larger planets.
In any case, this Malthusian limit is not what we are concerned with.
Humanity would probably have aesthetic reasons to limit its population
long before the Malthusian limit was reached.