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Viewing Single Post From: The giant space ship example
Chris Ho-Stuart
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The easiest way to answer the original question is to simply use a Nitrogen/Oxygen mix in the starship atmosphere. Nitrogen and Oxygen are almost totally transparent to infrared radiation, which means that there is no greenhouse effect in the starship atmosphere. The thermal radiation emitted from the surface will pass straight out into space, pretty much the same as if there was no atmosphere at all.

The starship surface is at a temperature of 10 C, or 283 K. The Stefan Boltzmann relation gives a very good approximation for the thermal radiation from most conceivable surfaces. This relation is
      Q = sigma.T4
where

  • Q is the energy per unit area, in Watts/m2
  • T is the temperature in Kelvins
  • sigma is the Stefan-Botzmann constant, 5.67e-8

For T = 283, this gives Q = 364.

Now the surface area of the starship is 4.pi.R2, with R = 1.2e6 m. So surface area is 1.8e13 m2 (18 million sq km).

Combining, the total thermal energy being emitted out to space is 364 * 1.8e13 = 6.58e15 Watts, or 658,000 6,580,000 GigaWatts!

     (Value in GigaWatts corrected with a late edit.)

That's the power that will need to be supplied by the onboard heating system. It's several hundred times greater than all power generated world wide today. Wikipedia tells me (at Electricy Generation) that the total power output from electricity generation over a year (2008) is now up to 20,261 TWh. A year has 8760 hours, so that works out to 2313 GigaWatts.

The starship engineers would love to reduce that... how much benefit could they get from an atmospheric greenhouse effect? That's what I have to consider next.
Edited by Chris Ho-Stuart, Dec 4 2011, 09:57 PM.
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The giant space ship example · Physical theory for climate