ESG7@DFVLROP1.BITNET (10/14/86)
In an earlier posting, I attacked the idea of a free floating space
colony and suggested an alternative space colony through construction of
cavities in the Lunar or Martian crust. Paul Dietz provided the best
counter attack and I shall respond to his arguments. He raised the
first point:
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Gary claims a space colony will require 30 million tons of shielding.
Where he gets this number from, I don't understand. Perhaps he is
discussing a very large space colony?
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I got this number from "Space Settlements - A Design Study",
NASA SP-413, page 44, Table 4-1. The shielding mass ranged from
9.9 megatons to 46.7 megatons, with populations ranging from
10,000 to 820,000 people. The designs considered are among those that
L-5 and other groups have advocated. Paul's analysis on shielding
based on the Earth's atmosphere is faulty. I recommend that he
review the literature on space colonies where the calculations on
habitat shielding are done in detail. Paul's second point considers
the colony's bearings between it's rotating pressure vessel and its
stationary 30 megaton radiation shield:
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Gary poo-poos the idea of mounting a spinning space colony inside
a stationary shield. He states that the colony would have to rest on a
bearing that would have to withstand megatons of force. Why?
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There's no such thing as a frictionless bearing. Even a magnetic
levitation system has "friction" due to eddy currects.
Also there is the question of starting the system into rotation
with the colony being initially out-of-round. In addition with
such an enormous structure you would find that the structure would
be quite elastic. The action of starting or of the colony being hit
by a large meteorite would cause the structure to oscillate. This
oscillation would likely couple into the rotation causing large
lateral loads on the bearing. The bearing would have to be designed to
take this into account, and I strongly suspect that such a bearing is
impossible due to strength of materials considerations. Paul then took
the offensive and attacked my idea of constructing a Lunar colony:
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Gary suggests using "clean" nuclear weapons to dig holes in the lunar
crust to build colonies. Wouldn't such a hole be structurally
unsound? After all, the blast wouldn't destroy the rock's atoms,
it would just force them violently outward. Rock would be fractured
and deformed for a considerable distance. The result on Earth
is that the resulting cavity (which isn't very large) collapses
quickly. I'll add that lunar regolith isn't terribly strong,
and that on Mars one is likely to encounter permafrost, which could
make living deep underground difficult.
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The cavities made in the Nevada desert from nuclear tests are enormous.
The cavity I suggested would be even bigger because it would be made
in the soft lunar stone and the 6 meter diameter bore hole would be
left unblock when the nuclear explosive (not weapon) was detonated.
I wouldn't care to be anywhere near the mouth of that bore hole
when a jet of megatons of vaporized lunar stone came blasting by.
However it would leave a nice cavity afterwards. An additional
thought just popped into my head that this would be a very good way
of propelling an asteroid into a new orbit. Structural instability
would be a problem afterwards, which is why I suggested bricking the
interior and using a ceramic liner. Paul then went on to try and
defend the idea of Powersats. This is a concept that has been beat to
death. There are probably hundreds of reports in various Energy and
Aerospace publications showing the infeasibility of this idea. It's
absolutely dead-as-a-doornail. I will not weary the readers by
repeating these arguments. Just go to your local library and pull
aerospace journals made around 1980 and you'll find articles about this
thing. Before finishing up, I should reemphasize that I am **for**
Martian colonization. Mars is the place in terms of gravity,
atmosphere, and availablitiy of all of the elements for life and
industrial activity. It would be difficult to find a world **better**
suited for space industrialization than Mars. It has an atmosphere
thick enough for aerobraking and winged vehicles but thin enough to not
be a major bother for launch into orbit. Its 1/2 G gravity is stong
enough for the health of the colony, but weak enough for cheap launches
into space. Phobos and Demios are ideal for forming the nucleus of
orbital stations. While I see the moon as a dead end for space
colonization and free floating colonies as a pipe dream, I find Mars
very exciting indeed. However the big question as alway is: How are we
going to economicly justify this Martian colony?
Gary Allen