[Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

It started as a tagline in a post, but as I considered it took on the dimensions of a real question. When the Pyramid #3/34: Alternate GURPS article "Alternate Spaceships" introduced the concept of Spaceships as Buildings (page 9) I wondered if putting heat producing systems in the basement levels would reduce their IR signature from outside. How would I determine and calculate this? (Remember sensor readings on a building would not serve the same purposes as those on a spaceship.)

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

Earth is an insulator, so you'd need somewhere to vent your heat if you don't want to cook your inhabitants. That's either out to the surface, probably with air or water cooling systems, or maybe into the surrounding bedrock, which would require more extensive heat exchange piping.

The other problem is that on Earth-like planets, the rock gets warmer as you go deeper, so how effective your cooling is depends a lot on the planet and local geological conditions.

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

Presumably for some sort of bunker?

The thick layer of dirt would be a good insulator and diffuse the heat signature over a larger area, but the heat still has to go somewhere so IR sensors would be a bit spot of slightly warmer dirt rather than a sharp point of heat.

Maybe a "Planetary Cooling System" that reduces IR signature by 1 per system, presuming there's enough space around the building for the buried radiators, +1 effective SM per -1 to IR signature. I have no numbers to back this up, just eyeballing it.

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

Well my current project is a base on Mars that is mining a frozen underground aquafer for ice so cooling isn't a problem. I was more interested in what kind of barrier being underground would be to IR sensors. Also, could exposed radiators use the surrounding dirt/rock as a heat sink?

I'm more interested in IR detection than cooling at the moment but that is a concern for structures on warmer planets.

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

Okay, but how effective your cooling is limits how much you can supress your IR sig. If your local geology is no good for cooling, you have to shed heat to the atmosphere and generate an IR sig. But as Tyneras said, you might be able to spread that out and keep it close to background levels.

This helps, obviously. I think you'd be looking at flowing meltwater as your heat medium, instead of the ice itself, as the ice in contact with your radiators would melt soon anyway. This might pose some engineering challenges, but the idea of dirt muffling your IR sig is okay. You'd probably have a heat reflective layer under the dirt too, to keep your heat loss directed downward.

Yes, but not as effectively as flowing air or water. Rock has a greater thermal mass than air, but once all the rock next to your radiators heats up, its efficiency as a heat sink drops (heat transfer is proportional to the difference in temperature between the two heat masses). Thus you'd need to spread out your radiators over a large underground volume.

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

Okay, the big problem with infrared signatures is that heat, once produced, can't be destroyed; it has to go somewhere. Thus, the aim of IR shielding, to the degree it's realistic at all, is to make the heat go somewhere where it can't easily be detected. This generally involves one of four strategies:

1. Efficiency: if you can improve your systems so they produce less heat to start with, your signature is reduced. Note that solar panels are using energy that would otherwise have been producing heat anyway, and thus have no net signature (they are usually visible for other reasons, however).
2. Diffusion: you can spread your heat out over a large area, hopefully falling below the noise threshold of enemy sensors. Spreading the heat emissions over 100 times the area doesn't actually reduce the amount of heat, but it increases the background noise by a factor of 100, making any signal much more difficult to identify. This is more practical for air and water vehicles, as there is a large quantity of fluid available to mix in, but can be done on the ground as well.
3. Storage: you don't have to radiate heat away at all, you can store it somewhere. It will probably eventually radiate away, but you can possibly delay for long enough to make the issue moot, and you can certainly delay by enough to smooth out any heat spikes (with similar benefits to diffusion).
4. Directionality: it is in principle possible to block heat emissions in particular directions. Unfortunately, this requires you to know what directions likely sensors are. For ground-based facilities this is mostly equivalent to diffusion (you put up an umbrella to prevent heat going upwards, it goes sideways, heats up the stuff to the sides, and you wind up with a large diffuse blob).

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

You can't just insulate and keep the heat from getting out. You'll melt. What you could do is use the water table to spread out your heat and make your heat signature less distinct.

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

For what it's worth, using infrared sensors to detect houses that are being used for pot production was a thing a few years back (might still be) so I doubt a basement helps meaningfully.

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

Yeah, it's not really a barrier situation. IR signature isn't about directly seeing the heat-producing system, anyway, at least in a realistic treatment: it's about seeing the external radiators that are connected to the heat-producing system. Which section the system itself is in doesn't make an appreciable difference.

Being embedded in the ground means that the vacuum radiators can be replaced with a ground-conduction heat sink, probably consisting of a network of heat conductors buried in the surrounding rock. This doesn't reduce the amount of heat available for people to see, but it does make it pretty easy to spread the heat over a large area and a lower visible temperature. It also would be possible to put the heat sink displaced from the main installation.

In addition to making detection harder as Anthony notes, this means that when someone does spot your heat signature they still don't know where you are with any precision. So they'll have to do more work before they can shoot you or land an assault team on your roof.

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

You can also create heatsinks to store the heat for later dissipation. The simplest of this would be Frozen water which you then melt and heat up. Eventually, though, you're going to start boiling it and will have to deal with the steam. Something like salts or rocks can take a lot of heat, and in the right conditions can store it for quite a while. You can also use heat transfer pipes which you drill both very deep and very wide, and you just dump the waste heat into the ground. Using these methods you can spread the heat out quite a bit, but eventually it will start to show up on IR meters. The simple problem is that no matter what you do with the heat it still exists and will still show up eventually.

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

Another possible strategy is disguise. You could join the heat sink for a covert element to a larger legitimate one and hope that the overall difference isn't noticed, you can make your signature look like something else (for example, a tank with a heat signature which mimics a truck's), or try to make it look 'noisy' by blocking patches (in the same way that conventional camouflage can break up a solid shape into a confusing mess). None of those seem like great strategies for hiding an industrial operation in your basement though.

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

Thank you everybody! I had no idea the issue was so complicated. (Silly me, looking for a simple answer.) Still, a lot of good advice here that I will take into account if I design an underground base that really needs to stay hidden. The surface features of my Martian “Gas” Station would make it pretty obvious. Now though you've got me worried about heat management. Mars is pretty cold so you sink a lot heat there but do I need any special provisions for a long term base with an underground reactor? (Please reply through the above thread.)

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

The heat will find its' own way out. Your only issues are it doing it too slowly or having too much go through the hman-inhabited areas. Several usable suggestions have been made.

You might not need an. Subteranean tunnels could be too cold and if you pump in any outside atmosphere that's going to need a lot of warming. There's even a fair bit of temprature range between "melted ice" and "human friendly environment".

I think it extremely likely that any problems are solvable without excessive difficulty.

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

A thermal satellite image is going to look something like this:

https://thermal.kk7.ch/

Unfortunately, it doesn't list a scale showing what temperature the colour grades indicate, but it's probably a sensitivity of a couple of degrees C between red and blue.

As you can see, there's a lot of variation, so one trick you might get away with is to disguise your thermal plume as a natural feature.

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

Not especially. The rock around will soak up the heat. It's just going to be obvious on Mars where the epicenter of the heat bloom is.

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

Of course, with good heat pumps and enough heat pipes spreading out in the right direction it is be possible to move the center of the heat away from where the base is actually located. The farther away you move it the more it'll cost in time, resources, and thus money, but you can certainly move it away from the base.

What you won't be able to do is cover up the heat signature; you can move it, you can spread it out, but you can't hide it. And, of course, what do you do with all your excess heat if they find your underground heatpipe network and disable it?

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

You have exactly the same problem as you would with any other type of radiator system being disabled?

Re: [Spaceships] Query: Can dirt shielding reduce an IR Signature?
 

More or less my point, with the added problem that the excess heat is going to build up at your actual base negating the stealth advantage you were trying to create.