Temperature and you

>If I understood correctly:
>
>You indicated that ships without thermal protection are visible at 1 LS
and
>hard to detect at 10 LS. 
>
>You worked with 300K temp I believe. 
>
>You indicated ships could disperse their heat (or maybe even store it
>internally by some method instead?) and thus (because radiation is a
T^4
>property), decrease their luminosity by 16 for every halving of
temperature.
>

Yep,  I am working on the assumption that you are trying to detects
using IR radiation emitted from the ship.  If the ship does something
(turns on reaction drives, fires somethign) all of this goes out
the window.

>
>So, this to me says that if I could drop my temp to 150 K (a long way
from
>absolute zero) on the hull, I'd be visible only at 1/16th of a LS
(300,000
>km/16 is roughly 20,000 km) . If I could drop my temp to 75K, I'd be
visible
>at 1/256th of a LS (1500 km?). 
>
>So, if I read you right, and I can drop my hull temp by even half (to
150K),
>I can make detection difficult to inside of 60,000 km (which I'd call a
>tactical range). If I can drop it to 75K, I can probably sneak right up
to
>within 6000 km (6") in a tactical scale. 
>

This would be again to Cloaking.  

>Or am I missing something? I'd be interested to see some of the
>math/assumptions/physical constants you used to back your calculations.

>
>

So the math is really simple.  The luminosity of a blackbody is

L = 4PI Radius^2 Temp^4

The flux of received is

F = L/(4PI * Distance^2)

So, the flux then becomes:

F = (Radius^2 Temp^4)/(Distance^2)

So, any thing that keeps your temperature down (for a fixed radius)
makes
you harded to detect in the IR.  The other thing to look at the equation
above (L = 4PI Radius^2 Temp^4), is if you make your radius bigger, you
lower your temperature.  Your luminosity will not change, but the
cooler you are the more you blend into the background (most things in
our galaxy are around 20 of degrees Kelvin).  

None of this talks about reflecting light, or any kind of active systems
like radar.  This is just thermal radiation from a an object.  The
problem
is you ship will generate a certain amount of heat, and you will have
to get rid of it.  However, something like the cloak from FT could be
mimiced by having something that you dump the heat into temporarily,
( a really big vat of Liguid Helium) which lets you "hide" as long as
you don't turn on the engines or shoot at people.

Is that clearer?

cheers
Brad Holden

"If Winston Churchill were alive today and could read that, he'd roll
over in his grave." - J. Kemp