From: spike66 (spike66@attbi.com)
Date: Wed Jul 17 2002 - 22:46:40 MDT
Robert J. Bradbury wrote:
>I tend to disagree with spike in that I don't think small
>people will buy you that much. And we certainly aren't
>going to have the ability to engineer them anytime soon.
>My bets would be on real AIs before munchkins. Robert
>
OK, so let us ask the question now: how *does* mass scale with height?
Robert is aware that much of my career was in weights engineering. This
discipline uses scaling all the time. I used the example of half scale
humans: could we build a half scale lunar module that would weigh
one eighth as much? Turns out, the answer is no. Some systems scale
as the cube of the linear dimension, such as the pressure vessel, the
atmosphere inside and the propulsion systems. Fortunately, most of
the really heavy stuff scales as the cube of the linear dimension.
Some systems scale as the square of the linear dimension, such as
the coatings on the surface of the vehicle. Paint, for instance, would
not be any thinner on a half scale vehicle, so you would need a
quarter as much as the full scale model.
Some systems would scale at less than the square but more than
linear dimension. One example would be the heating system. The vehicle
loses heat to space by radiation, which is a function of surface
area, however, the half scale vehicle has walls half the thickness,
so they conduct more heat. So all else equal, the half scale vehicle
has a heater that scales as about the 1.7 power.
Some systems would scale linearly, such as wire for most control
and communications functions: the half scale vehicle would need
wires of the same diameter in many places, and only their lengths
would be half.
Finally, some systems would not scale at all. The half scale vehicle
would need control computers and communications antennas
exactly the same size as the full scale vehicle.
All told, for a given mission to the moon, if we could find 5 sigma
small people currently living on earth, and these 5 sigma people
are about half the scale of our current average astronaut, I estimate
we could build a moon mission that would weigh about a fifth as
much and cost about a half as much as a full scale mission.
spike
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