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Titan is a shrouded moon, cloaked in a dense haze that obscures its surface to direct visual observation. Cassini, when it visited, had to rely on radar and near infrared imaging to see the surface [https://science.nasa.gov/mission/cassini/spacecraft/cassini-orbiter/imaging-science-subsystem/]).

As potential source of plot points for my world and others, I was thinking that would make it potentially quite easy to hide from prying eyes in the sky. On Earth, space is ultimate high ground and spysats are very effective. But on Titan, they'd need to rely almost exclusively on Radar and Infrared, and we already have tech that can work against those here on Earth.

I am not especially familiar with this aspect of military technology so the feedback I was looking for here is:

  • (a) wargaming a potential counter for an opposing faction, assuming current levels of technology
  • (b) other considerations/options for stealth I might have missed.

At least as I understand it, Titan's dense atmosphere would potentially make stealth very effective there and difficult to counter. Even crewed vehicles would be very hard to find from orbit if they didn't wish to be, and uncrewed ASAT launchers wandering the surface with minimal power would be very dangerous to anything in orbit.

https://science.nasa.gov/resource/cassinis-three-views-of-titan/

Left to Right: Visible, Monochrome Infrared, False Color Composite (green is where Cassini can see down to the surface) https://science.nasa.gov/resource/cassinis-three-views-of-titan/

Scenario

Location: Saturn's moon Titan (in setting it does have about the population of a mid-size city (3-4 million), with a colony beginning to establish itself)

Trying to avoid being detected: Ground vehicle (possibly automated)

Trying to detect target: Orbiting satellites (for simplicity assuming no ground detectors to work with)

Radar detection: I'm most hazy on this but as I understand this can be done by making use of radiation-absorbent materials.[https://en.wikipedia.org/wiki/Stealth_technology]

Infrared: This could be helped by leaving a gap between the outer layers and interior layers of the vehicle like the GTX Boxer [https://en.wikipedia.org/wiki/Stealth_ground_vehicle], which you would probably want anyway for insulation in Titan's frigid temperatures. Using nuclear/battery power would also help (and again would be practical on Titan regardless of stealth). Plus other measures like active cooling.

Edit: I had a very hard time picking an answer, since there was a lot of helpful ones. And I'm actually planning to use a combination of the suggestions here. Marked Mon's though since I am planning to use their suggestion and Pica's for engineering, Matthieu's for support infrastructure, and the considerations from Chris and Starfish. Like I said, if I could give an answer to all of you I would, but I can only pick one.

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6 Answers 6

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Thermal detection will definitely be an issue. BUT ...

You might however be able to temporarily mitigate the risk of detecting the heat signature of a manned vehicle on the surface of Titian using a modification of your original design i.e. installing pressurized tanks of a gas with a very low boiling point. (Given the extreme cold of Titan's environment (-175C?) liquid hydrogen or helium would be best). This gas could be then used to cool a separate 'outer shell' (in effect a hollow outer skin) of the vehicle. The inner surfaces of the vehicle have to be separated from this outer shell by a vacuum. So the order would be;

(1) inner (manned) airtight compartments

(2) Vacuum shell

(3) Outer (cold gas) shell.

No matter how well insulated the inner compartments are radiative heating from the will still reach the outer shell across the vacuum especially since the inner compartments need to be heated just to keep the crew alive. And please note there is nothing you can do to prevent that. Left to itself the outer shell will then heat up in turn - eventually. But, that said you can use a tank of ultra cold gas to cool the outer layer of the hull down to something approaching surface conditions by pumping small quantities of the coolant out into the atmosphere from the outer shell (under the vehicle would be best). This process 'draws' heat away with it. Your engineers would design the system to give it a set range based on the amount of heat generated by the crew and the vehicles systems per a given volume of coolant.

In effect its a bit like having an internal combustion engine i.e. your car has a finite amount of fuel that will let you drive X hours on one tank. In this case? You get X hours of mobile thermal screening before you need to stop to fill up on coolant again. And given how cold Titan is? You wont get a huge range per quantity of coolant expelled per hour.

P.S. You also need to maintain a strict radio silence/zero EM emissions policy.

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  • $\begingroup$ Thanks, this is a genuinely interesting idea. Considering I'm realizing I underestimated the scale of the temperature problem, I was thinking it might make sense to combine your suggestion with @Starfish 's point that drone's may be a bit more practical than crewed if stealth is the goal. Stick some uncrewed drone launchers out there with the coolant suggestion here, engineered to operate with as little waste heat as is practical. That does lead to a new consideration of where is the coolant being topped up but that'd be out of scope I think. (Sympathizers at distant mining outposts maybe?) $\endgroup$
    – Wavedash
    Commented Apr 18 at 1:52
  • $\begingroup$ @Connor Higgins thanks I got the idea from a website called 'Tough SF' whose author addresses a lot of the hard science behind future space travel. One of which was the 'there's no such thing as stealth is space' trope. He suggested this solution of an unmanned space ship. Basically its a ship inside a giant tank of leaking liquid hydrogen that's kept at the same temperature as local space using this method. The other site I recommend even more strongly is called 'Atomic Rockets'. Its almost a bible for hard SF enthusiasts. $\endgroup$
    – Mon
    Commented Apr 18 at 5:53
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    $\begingroup$ "You also need to maintain a strict radio silence/zero EM emissions policy" <- not necessarily, As long as you keep repeater stations in known locations, you can use directional radio or lasers to communicate. This is how US stealth aircraft are able to communicate without being detected. $\endgroup$
    – Nosajimiki
    Commented Apr 18 at 21:45
  • $\begingroup$ @Mon The "there's no such thing as stealth is space" trope is easily countered with the "space is big" trope. While you can't closely orbit a highly developed planet and expect to go unnoticed, you can easily be a glowing white blob against the background of space and be totally undetectable at ranges of several light minutes because you are so small that you are still less luminous than the noise of the distant stars behind you. $\endgroup$
    – Nosajimiki
    Commented Apr 19 at 16:12
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    $\begingroup$ @Mon Yes, sustained stealth at 1000km in a vacuum is a Hard Scifi no-go. Thus my second comment about atmospheres. But my major point was that it's easy to over apply a World Building principle when you don't consider the exact implementation of it. $\endgroup$
    – Nosajimiki
    Commented Apr 22 at 14:13
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Heat seems like a serious problem that you can't simply handwave away. On Earth, people and equipment are warm compared to their surroundings. Titan is significantly colder, and that temperature differential is going to be much larger and hence easier to detect. Slow drone vehicles might be possible to make and operate at very low temperatures, but human-crewed things, or anything that needs to move fast is probably out of luck.

The best way to avoid detection is with the availability of cheap ASAT weapons, and a willingness to pollute low orbits with debris, I suspect.

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  • $\begingroup$ Thank you, definitely is an issue I mis-understood the scale of. Drone ASAT launchers sound like the most feasible way to go, and free trigger finger. Possibly combined with Mon's suggestion to give them a little leeway with excess heat. (As a side note, I found it hilariously on brand for user @StarfishPrime to be recommending me a solution that involves "a willingness to pollute low orbits with debris.") $\endgroup$
    – Wavedash
    Commented Apr 18 at 1:37
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    $\begingroup$ Actually you can- on earth as on titan. You drill a small hole in the ground an inject your surplus heat via a cooling liquid into the ground below. You get cooling liquid from your surroundings. The warmth shows, but with great delay and just as blotches- meanwhile you are miles away. $\endgroup$
    – Pica
    Commented Apr 18 at 7:03
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    $\begingroup$ Uhh isn't it possible to hide from infrared detection? Like if your heatsinks are covered by a layer of glass then you can't directly see the heatsinks temperature. Would need a large area for temperature to dissipate in atmosphere without being a visible plume. It might be enough to hide from sensors, or as @Pica has stated if you inject into the ground while making sure your surface is covered in glass or w/e IR blocking thing you have. $\endgroup$
    – HSharp
    Commented Apr 18 at 8:09
  • $\begingroup$ You can integrate a cooling system into your surface, adjusting the temperature to present with the background temperature. You can use any heatpump like for example: en.wikipedia.org/wiki/Thermoacoustic_heat_engine to pump the heat into a reservoir. $\endgroup$
    – Pica
    Commented Apr 18 at 8:12
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    $\begingroup$ @ConnorHiggins You could melt the ice, use it as a eat reservoir and pump that liquid down into some fracked cavity. But that overall approach needs - the ability to drill holes. And it would turn the ground beneath you into a ice slushy over time. So its constant drill, pump, shoot and scoot? $\endgroup$
    – Pica
    Commented Apr 19 at 7:29
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For hiding in infrared, a warm, busy background is your friend. You can't just insulate yourself, because you have waste heat to dispose of, which you will have to diffuse through large amounts of atmosphere to keep the heated atmosphere from being obvious. Meanwhile, you're glowing like a lightbulb compared to everything else, and have to contain all those thermal emissions. Oh, and you're probably surrounded by a big plume of hydrocarbons boiling off due to your waste heat. I think the only environment worse than Titan for thermal stealth would be an airless or near-airless iceball like Enceladus.

If you really want to hide on Titan in infrared, it may be helpful to use a vehicle that can at least partially submerge (perhaps with a tethered heat exchanger), so you can use the denser liquid to spread and obscure your thermal signature. This will only work in a geographically limited area, however. Alternatively, rather than trying to hide your thermal signature, try to look like something else...mimic the thermal and radar appearance of other vehicles on the surface. This of course requires that there be something to mimic.

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    $\begingroup$ +1 As well, an alternative to hiding outright could be to simply say there are many other civilian science/construction/mining/transport vehicles trundling around the surface for more benign reasons. And stick a few ASAT launchers in a few at random. That would be an escalation in tactics of the setting though, in that it might make civilian casualties more likely. Doesn't mean it wouldn't work of course (or that you don't make a good point) but that might have other implications on events that something like drone launchers wouldn't $\endgroup$
    – Wavedash
    Commented Apr 18 at 1:44
  • $\begingroup$ *Possibly wouldn't I should amend, considering my comment on Mon's $\endgroup$
    – Wavedash
    Commented Apr 18 at 1:54
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Have you considered Underground circulation?

While Titan does have an atmosphere, it's blistery cold out there. This means that vehicles will need to be heated, and even with good insulation, that'll quite a good chunk of energy. Furthermore, any breach of hull will be deadly, which means accidents -- even simple "fender benders" -- will be deadly.

Oh, and that cold atmosphere isn't breathable either, so on top manned vehicles also need to worry about oxygen, etc...

So why even tempt fate?

An underground tunnel -- not even a deep one -- can provide a much more friendly environment:

  • It can be heated more efficiently, due to permanent infrastructure. Not necessarily to 20C, -50C would be a solid improvement already.
  • It can contain a breathable atmosphere.
  • It can be made of sections that can be cordoned off in case of breach in one of them.

Vehicles circulated may additionally be heated, but they can be much more lightweight, and users should probably carry around warm clothing and small bottle of oxygen in case of breach, so they can reach the next section, on foot if necessary, but that's much easier already.

Underground is stealthy

Vehicles in the tunnel are hidden from detection, so if you only care about hiding the vehicles, not the tunnels themselves, the problem is solved.

Otherwise, the heat signature of a tunnel will depend how close to the surface it is, and whether radiators were used to disperse the leaking heat over a large surface, or not.

Going deeper will help hide the tunnel, as heat is conducted uniformly in a volume.

And with appropriate design, it should be possible to move most of the leaking heat to the radiators, thereby at worst showing the positions of the radiators but not the tunnels. And even then, if the radiators cover sufficient ground, possibly by going deep, the difference in temperature on the surface may be small enough as to look like noise.

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  • $\begingroup$ I'd probably combine this idea with one of the others, i.e. hidden support bases that can provide repairs, coolant and other supplies. It is helpful, but in a tangential way. The original thought was to have a situation roughly analogous to nuclear submarines on Earth -- they could be anywhere and would be a constant worry for things in orbit. This would be closer to a silo -- stealthy, but once found (possibly after they fire an ASAT) they can't pack up and go. And they just fit plot needs for me. $\endgroup$
    – Wavedash
    Commented Apr 18 at 18:07
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Hide inside the Infrared Atmospheric Window

You don't actually need to be on a hot planet to hide from IR detection. There are are certain wavelengths at which different gases are opaque to Infrared. For example, if you cool your vehicle's exhaust to 89°C, then even though it is still quite warm, it will emit IR radiation in a frequency that methane is opaque to; so, orbital IR sensors will not be able to see you past all the methane in the way. Also, if your vehicle has a heated surface, you can make the skin of your vehicle stealthy too.

To prevent your exhaust from showing up as it cools, you should also use a thin, wide exhaust. This fans the gases out quickly so that by the time they cool enough to emit visible IR radiation, the gas is too thin to be detected.

This is far more efficient that cryogenics because the only cooling fluid you need is small amounts of Titan's atmosphere to premix with your exhaust and to AC your vehicle's interior. It only consumes marginally more power to heat up your hull by an extra 69°C vs trying to keep your hull and interior ~200-300°C appart.

enter image description here

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    $\begingroup$ This is a genuinely cool idea though a bit harder to understand intuitively. Presumably once the exhaust leaves at 89 degrees it will cool to a point that is not in the infrared window though correct? So the vehicle itself may be invisible but observers could see a trail around it from exiting exhaust as it cools? Analogous to Pica's idea leaving drilled holes that would be faintly visible. I'm wondering if this might be a better technique to use on something fast moving, like a missile/drone and its' exhaust. Exhaust would still be visible but object itself would be harder to find. $\endgroup$
    – Wavedash
    Commented Apr 19 at 19:09
  • $\begingroup$ @Wavedash This technique is used by actual combat vehicles on Earth. It's a proven, workable technology. As for the exhaust thing, I've updated my answer to explain how that is mitigated IRL. $\endgroup$
    – Nosajimiki
    Commented Apr 22 at 13:48
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How do they get to Titan?

Before you get to playing hide-and-seek on the surface of Titan, you have got to get there without anyone knowing. If someone has seen a craft go towards Titan, and then disappear around the far side, they are going to be suspicious. If they are badly worried, they will come and look. And, extrapolating only slightly from what has happened to sensor technology in my lifetime, they will find you.

I can imagine a plot where a base on Titan is decommissioned, but some people secretly stay behind. That might get around the problems of being spotted while getting there. There are probably other ways.

Once you are there, you can probably get around the heat problem in relatively low-tech ways, such as the Viet Minh used in the Cu Chi tunnels. If they had a cooking fire, they would let the heat and smoke out through several chimneys that moved the smoke a long way sideways, and dispersed it though several exists. Titan may not have hit springs, but there may be some natural hot spot that you can imitate. A vehicle could scoop up hydrocarbon slush, raise its temperature by not-too-many degrees, and then spray it around, including over itself. That way, the vehicle will not appear as a bright spot in a cold surround in a thermal imager.

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    $\begingroup$ Note that the question is specifically about vehicles, not cities, so presumably the existence on Titan is known. $\endgroup$
    – Matthieu M.
    Commented Apr 18 at 8:24
  • $\begingroup$ Yes, I avoided specifics because I wanted to keep the post generalizable and useful for other people. But the specifics in mine involves a rebelling colony that is outmatched in space situation, sneaking in there is not the issue. $\endgroup$
    – Wavedash
    Commented Apr 18 at 18:17

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