Welcome Guest [Log In] [Register]
Sky Dragon is up and running. We need people to sign up and add content. Introduce yourself at the General discussion forum. Speak up to welcome a few others, start a thread, or contribute to someone else's thread.
Viewing Single Post From: The giant space ship example
Chris Ho-Stuart
Member Avatar
Administrator
gbaikie
Dec 7 2011, 07:58 PM

So comparing to Earth. Dwarf at 65,800,000 GigaWatts [5.4e21 watts/joules]
"The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere.[petawatts 10^15 watts] en.wikipedia.org/wiki/Solar_energy
Earth gets 1.74e17 watts sunlight and much this isn't converted heat.


The starship is 6,580,000 Gigawatts surface emission. You've add a zero there.

Watts/Joules makes no sense. I don't know what you mean by 5.4e21. The starship atmosphere is 5.4e17 kg, which is a heat capacity of about 5.4e20 J/K.
[indentblock]Aha! I think you must have used my value for heat capacity. And I was the one who got the error by a factor of ten! Sorry about that; I've gone back to fix up the original, leaving my original mistake there with the strikeout format and with the correct numbers added in. So it seems you have used heat capacity for the power requirements. You have to be careful with units.[/indentblock]

Quote:
 
Dwarf needs 5.4e21 watts or 30,000 times more energy.


No, the wattage we've calculated for maintaining the starship temperature is 6.58e15 Watts.

Of the 1.74e17 W that Earth gets from the Sun about 30% is lost by reflection. The rest goes to heat in the sense that the rest is what maintains Earth's temperature. The proper comparison is therefore as follows.

Earth. Surface temperature of about 15C (but varying over the surface) maintained by 1.22e17 W of solar heating; with the benefit of an atmospheric greenhouse to give about 33K higher temperature that what this much heating would give to a bare surface.

Starship. Surface temperature of about 10C (pretty constant over the surface) maintained by 6.58e15 W of fusion heating; with no atmospheric greenhouse effect to help.

Quote:
 
Something seems very wrong about this.


You used the wrong number for the power in watts heating the starship.

Edited by Chris Ho-Stuart, Dec 7 2011, 10:09 PM.
Offline Profile Quote Post
The giant space ship example · Physical theory for climate