Re: Dyson shell redux

From: Anders Sandberg (
Date: Wed Feb 21 2001 - 04:11:24 MST

You would need a gas pressure counteracting the weight of one square
meter of the shell, or P=GmM/r^2. The ideal gas law (insert wild
handwaving here) PV=nRT gives us VGmM/(Rr^2)=nT or 4*pi*GmMr/(3R)=nT
when we factor in the volume.

Putting in numbers,
R=8.31451 m^2 kg/s^2 K mol
G=6.673e-11 m^3/kg s^2
M=1.989e30 kg
m=42 kg/m^2 (from my own FAQ,
r=1.50e11 m
gives us nT=4.2e32.

Assuming we spread out all of the sun as hydrogen gas, we get
n=1.989e30/2.016e-3 =9.8e32 mols. Wow, same order of magnitude! So in
this case you could manage with a mere T=0.42 K gas. However, this is
of course unrealistic as the gas itself will start contracting if it
is cold.

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.

Anders Sandberg                                      Towards Ascension!                  
GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y

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