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Old 09-30-2017, 12:01 PM   #5
Michael Thayne
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Join Date: May 2010
Default Re: [Spaceships] IR Signatures for the power plants and drives in Spaceships 7

Originally Posted by Anthony View Post
Note that the existing rules for IR signature don't bear a lot of resemblance to reality.

The minimum energy output of a drive is 0.5 * thrust * ISp; if we convert to spaceships this works out to 7.2MW * (accelerator/1g) * (delta-V per tank/1 mps) * 10^(SM/2). Looking at a couple of examples:

Chemical: 3G, 0.15 mps/tank, so 3.2MW * 10^(SM/2).
Ion drive (fission reactor): 0.0005G, 3 mps/tank, so 11kW * 10^(SM/2).
Nuclear thermal (TL 9): 0.5G, 0.45 mps/tank, so 1.6* 10^(SM/2).

IR signature should probably be something like 3 * log10(power) - 7 (+0 at 200W), so at SM +6 we get:
Chemical: 3.2GW, log10(power) = 9.5, signature = +21 (SS1: +11)
Ion: 11 MW, log10(power) = 7, signature = +14 (SS1: +12)
NTR: 1.6GW, log10(power) = 9.2, signature = +20 (SS1: +12)
Is it possible for a more efficient drive to have a reduced IR signature? I assumed this was the rationale for higher-TL drives with increased delta-V per fuel tank having the same IR signature. But maybe it doesn't work that way.
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