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Old 06-16-2018, 11:16 AM   #1
Stormcrow
 
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Default [Spaceships] Detecting hot reactionless

Hot reactionless engines (GURPS Spaceships, p. 24) have "a waste-heat signature equivalent to a conventional drive’s exhaust." What does this mean? Which conventional drive? What is the modifier for detecting a ship with a hot reactionless engine with passive sensors (pp. 44-5)?
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Old 06-16-2018, 11:35 AM   #2
PTTG
 
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Default Re: [Spaceships] Detecting hot reactionless

That means that it has a waste heat exhaust that's as bright as a chemical rocket engine, so passive sensors don't take any additional penalty.

The form that takes depends on the setting. In a fairly hard-science setting, that's a massive radiator array. In a soft-science-fiction setting, it's supertech acceleration engines that look just like regular rocket engines but don't need fuel.
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Old 06-16-2018, 03:26 PM   #3
AlexanderHowl
 
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Default Re: [Spaceships] Detecting hot reactionless

Which is ironic, considering that the only reactionless drives that seem even remotely possible are the NMP drives and, since they would probably not be high energy systems, they would actually produce less waste heat than any reaction engine. A spaceship with NMP drives would not even need specialized power plant compenents, unless they sported weapons of some sort (it would actually make morse sense for a merchant ship to carry missiles instead of high energy weapons because any excess weapon space could carry cargo instead of missiles and it would not have to waste space on a power plant).
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Old 06-16-2018, 07:31 PM   #4
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Default Re: [Spaceships] Detecting hot reactionless

Quote:
Originally Posted by Stormcrow View Post
Hot reactionless engines (GURPS Spaceships, p. 24) have "a waste-heat signature equivalent to a conventional drive’s exhaust." What does this mean? Which conventional drive? What is the modifier for detecting a ship with a hot reactionless engine with passive sensors (pp. 44-5)?
I interpret that as simply being up to the GM, with the modifiers from later being used as guides. If your hot reactionless drive outputs heat comparable to a jet engine system, the IR signature is good for a +4. If it instead outputs heat comparable to a super conversion torch, it's at +12. Personally, I'd lean toward either jet engine or chemical rocket (+5 for the latter).
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Old 06-16-2018, 07:54 PM   #5
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Default Re: [Spaceships] Detecting hot reactionless

Currently I use +6, so that a ship using standard thrusters (also called 'cold' in my campaign) and a non-nuclear power plant is noticeably stealthier. This is also high enough that hot thrusters are not stealthy (unless you're accelerating towards the sensor), while cold ones powered by solar panels or fuel cells are. It also makes using an old fission reactor slightly stealthier than a fusion plant, because the drives are less obvious than the latter.

It's not unknown for navies to have a few ships that have a cold thruster for low-signature manoeuvres and a fission plant and sometimes even a solar panel array just big enough to run the thruster. These are intended for quietly moving into low traffic systems to have a look around. Naturally such a ship has the Stealth and Dynamic Chameleon options, Enhanced Sensors, etc.
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