Re: Dyson shell redux

From: Jeff Davis (jdavis@socketscience.com)
Date: Wed Feb 21 2001 - 11:37:40 MST


Great post Anders, thanks.

Anders writes:

>If we accept T=1000 K as the maximum temperature our system can stand,
>then we just need a thousandth of this mass and things look a little
>better - but not much, since now we will have an active fusing star in
>the middle heating the gas up! A more likely gas temperature would be
>the sun's surface temperature 6000 K or solar wind temperature
>150,000K - ouch! And in this case the gas will not be as thin as the
>solar wind is now, it will really transfer heat to the
>construction. You better have good cooling.

Let me take it from here.

First let's flatten out the shell, dropping the caps down closer to the
star, and 'onto' the atmosphere. The equatorial region can be balanced
against gravitaional collapse by spin, so the caps are the only parts that
really need to be 'held up'.

Next, let's deal with the heat 'problem'. I'd like to imagine that the
'upper' atmosphere might not be hot--that it might somehow be coo. No way
are my skills up to the task of analyzing so unprecedented a condition of
atmospheric dynamics, so let me put my blissful ignorance to work and
suggest several mechanisms which might suggest the possibility of a
cool--or at least cooler--upper atmosphere: 1) the temperature profile of
other atmospheres provide examples: decreasing temperature with increasing
altitude; 2) the outer layers of atmosphere may 'launch' gas particles
outward, whose kenetic energy is then sapped (they're cooled) by
gravitation.

On the other hand, since the projected radiation from the star is almost
entirely hydrogen emission, and the upper atmosphere is yet again more
hydrogen (of mixed species: monotomic, diatomic, plus ionized versions of
both), it can hardly be expected that it would be transparent to the
outbound radiation. On the contrary, to whatever degree it is cooled, it
would seem to be primed to reabsorb and heat up. But as I said, this is
way too complex an issue for me to assert anything with confidence.

So maybe the supporting atmosphere is hot, maybe very hot. We'll just have
to convert that heat 'problem' into an advantage. That's what the Dyson
shell is about in the first place, right? So where the shell gets hot, we
just harvest the heat. Rather than photovoltaic energy harvesting, we go
for the old low-tech thermodynamic cycle, direct contact, heat source/heat
sink method.

We're cookin' now. Cookin' with gas.

Into the breech! (With two ee's this time.)

                        Best, Jeff Davis

           "Everything's hard till you know how to do it."
                                        Ray Charles



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