RE: [SG?] Cammo

On Aug 10, David Griffin <carbon_dragon@yahoo.com> wrote:
> 
> 
> --- Brian A Quirt <baqrt@mta.ca> wrote:
> ...
> >	 Assuming your spaceship is crewed by humans or
> > a near equivalent, they'll want an internal temperature of
> > somewhere around 20 degrees centigrade (close enough to 300
> > kelvins). Thus, their ship will be a blackbody emmitter at
> > roughly that temperature.
> >	 Unfortunately, you can't disguise your emmitted
> > heat with camo,...
> 
> Would it be possible to use some kind of refrigerated
> insulated outer hull to block the heat? Of course 
> this would give the ship a BIG problem of getting
> rid of waste heat, but it might work for short 
> periods. Of course I'm not a physicist, so there
> may be some fundamental problem I'm overlooking.

     Yes and no (hate to do that, but I'll continue with the full 
explanation).
     It IS possible to store your heat temporarily (eventually you 
have to get rid of it, and the longer you wait, the more you have to 
get rid of). Unfortunately, storing heat can be quite difficult.
     You could, for example, keep a tank full of liquid hydrogen (or 
oxygen, or nitrogen, or helium if you want, or whatever) onboard, and 
use it to store your waste heat. How long that'll give you depends on 
how much waste heat (crew + reactor + drive + whatever else) you 
generate and on how much cold stuff you have to absorb heat. 
Eventually, though, it's at the same temperature as your outer hull, 
and then you have to go on to the next paragraph.
     You can also store heat in something that's hotter than your 
outer hull. This runs you into the second law of thermodynamics. 
Essentially, it takes energy to move heat from a cooler object to a 
hotter object. The greater the difference in temperatures, the more 
energy (formulae are in my physics text which is stored in New 
Brunswick, a mere 1600km from my desk at work). And, of course, 
whatever reactor you're using to get this energy probably generates 
waste heat (ok, DEFINITELY generates SOME waste heat, it's just a 
question of how much), which is more heat you have to store into your 
heat sink, which requires more energy, which....
     How long you can keep all of that up depends on your tech level, 
your power requirements, how much heat you have to get rid of, who is 
(might be) looking for you, etc. Whether or not its worthwhile 
depends on the answer to the above, and also on the all-important 
question of how much it costs to be stealthy, and how effective it is.
     Of course, there is still a third option. If you are using a 
reaction drive, and you have it on, you can dump the heat into your 
rection mass. The less efficient your drive is (and hence, the higher 
thrust it has for a given power-density), the more heat you can get 
rid of this way. Of course, that means that your exhaust is heated, 
but I think the topic of how easy your drive plume is to detect 
should be given a brief rest. And, of course, if you don't have a 
drive plume, it doesn't matter anyway....