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09-28-2017, 10:38 PM | #1 |
Join Date: May 2010
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[Spaceships] IR Signatures for the power plants and drives in Spaceships 7
One omission from Spaceships 7 is the heat signatures produced by the drives therein. Here's my best attempt to extrapolate the values from known data, feedback welcome. I'm going to ignore paranormal technologies, for realistic and quasi-scientific designs:
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09-28-2017, 11:18 PM | #2 |
Join Date: Jun 2013
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Re: [Spaceships] IR Signatures for the power plants and drives in Spaceships 7
I think those are probably mostly close enough, with the possible exception of the vacuum energy power plant. Antimatter, fusion, and total conversion are, unless I'm mistaken, basically all really advanced heat engines (much as modern nuclear power plants are). A vacuum energy plant would, presumably, only produce heat as waste, not as an intrinsic part of its general operation, so I'd expect it to have a smaller signature, if any. I could see vacuum energy plants, depending on fluff, being anywhere from +3 (no difference from the systems it powers) to the +7 of total conversion, or possibly even higher; personally I'd peg it at +4 or so.
For the solar mirror systems, I'd probably have those close to lightsails - just like the latter, solar mirrors are extremely reflective. Now, typically the brightest light source will be directed into the ship's bowels, so it probably won't be quite as bright as a lightsail. +6, perhaps? Note that makes the signature of the system it powers academic, as the mirror itself is far easier to detect.
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09-29-2017, 03:47 PM | #3 | |
Join Date: May 2010
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Re: [Spaceships] IR Signatures for the power plants and drives in Spaceships 7
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I'm a little disappointed I haven't gotten more pushback on the fusion-powered stealth bomber. Again, does anyone know enough about these hypothetical proposals to tell me if it's realistic? It has pretty big consequences for the design of aerospace craft! Notably, nuclear air-rams become strong choices for variations on a number of designs in Spaceships 4 if they can be stealthy. |
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09-29-2017, 04:21 PM | #4 |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: [Spaceships] IR Signatures for the power plants and drives in Spaceships 7
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) |
09-30-2017, 12:01 PM | #5 | |
Join Date: May 2010
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Re: [Spaceships] IR Signatures for the power plants and drives in Spaceships 7
Quote:
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09-30-2017, 12:16 PM | #6 |
Join Date: May 2010
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Re: [Spaceships] IR Signatures for the power plants and drives in Spaceships 7
I'm only learning about this because of GURPS, but as I understand it jet engines can be rated for ISP, which can't be inferred from GURPS stats because they don't carry reaction mass, but nevertheless because ramjets have relatively low ISP, a fission or fusion ramjet probably shouldn't have a higher IR signature than the jet engine in the original Spaceships volume, because that's described as representing a "a turbo ramjet or scramjet".
Am I looking at this right? |
09-30-2017, 12:23 PM | #7 | ||
Join Date: Jul 2008
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Re: [Spaceships] IR Signatures for the power plants and drives in Spaceships 7
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But...IR stealth for aircraft is a bit different, I think. A fusion reactor for your ramjet might give you considerably more heat to dispose of than a conventional fuel-burning turbine, but the main thing is to keep the externally visible heat diffuse and dissipate it into the air without presenting sharp 'hot spots' for IR sensors, I think. And that probably isn't impossible to do around a fusion reactor. Quote:
However, for thermal rockets the kinetic energy of the departing particles is proportional to their temperature, and I think there's basically nothing you can do about that.
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I don't know any 3e, so there is no chance that I am talking about 3e rules by accident. Last edited by Ulzgoroth; 09-30-2017 at 12:27 PM. |
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09-30-2017, 12:25 PM | #8 |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: [Spaceships] IR Signatures for the power plants and drives in Spaceships 7
Yeah, what's actually visible is the inefficiency of the drive. However, that's not going to vary all that dramatically (no more than a couple points).
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