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In the discussion of this question it is assumed that we would need to heat the rover so that (most of) it's components were operating at temperatures much hotter than ambient (about 90K). Current mars rovers typically need to heat at least some of their components at night, or they fail. For Titan, with its thick atmosphere, this poses a bunch of design challenges, vaguely comparable to trying to operate a rover on Earth many of whose components were 200 or 300 C:

  • Power to keep it heated, given the thick atmosphere to convect away the heat
  • Melting or boiling many compounds in the environment when the come into contact. This is bad from scientific point of view, but also dangerous, it could sink in, or be thrown around by exploding pockets of volatiles
  • local "weather" system caused by heated gas rising from the rover
  • temperature changes in bits of the rover as they move into and out of contact with the ground, or liquids
  • "steam explosions" if it falls into a lake

The obvious solution is just not to do that -- try and operate as much of the rover as possible at or close to ambient temperature, cooling any heat generating components with local atmosphere.

How hard would that be to do? Can we build computers, sensors, motors, the cold side of the power source, etc. to operate at these temperatures? If not, what are the obstacles?

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    $\begingroup$ My first thought was that semiconductors cease to work at low temperatures, but it seems that transition is at a lower temp than Titan's surface: extremetemperatureelectronics.com/tutorial3.html $\endgroup$ – Hobbes Sep 18 '18 at 11:27
  • $\begingroup$ related only because of temperature extremes Would it be possible to build a probe that could operate at 900F degrees without insulation? and also Potential high temperature power sources for a Venus lander I think low temperature batteries might be a bit of a challenge; perhaps a wind-up spring instead? $\endgroup$ – uhoh Sep 18 '18 at 11:28
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    $\begingroup$ Is there a fundamental reason why low-temperature batteries (which don't have to work at higher temperatures) can't exist, or is it just that we have little experience? $\endgroup$ – Steve Linton Sep 18 '18 at 11:37
  • $\begingroup$ @SteveLinton that's a great question, and could conceivably be asked separately. I don't know the answer, but chemistry in general slows down exponentially with temperature. $\endgroup$ – uhoh Sep 18 '18 at 11:44
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    $\begingroup$ @SteveLinton Heat capacity of nitrogen and methane doesn't change much - only a few percent between 100K and 300K. And while pressure is only 1.5bar, density is 4 times higher than on Earth due to low temperature. Convection and heat conduction scales with the temperature difference, not with ratio of temperatures. $\endgroup$ – asdfex Sep 18 '18 at 16:27
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I think we should break this down in two parts: Operation at low temperature and impact of a "hot" rover on the environment.

Most semi-conductor based electronics as we have them today don't have an inherent problem operating at very low temperatures. The characteristics of e.g. diodes and transistors depend a lot on temperature, which plays an important role in all analog circuits (e.g. sensors) and less so in digital circuits (processors, memories). We can't assume to take conventional circuits to Titan and operate them there without issues, we have to design them specifically for low temperatures. This is, in general not too complicated, it mostly boils down to selecting the right components and defining things like working points and gain of transistors correctly. This can be tested and verified on Earth without too many difficulties.

One important issue is mechanical stress due to the huge temperature differences that can damage components as well as solder junctions if not done properly. Again, this can be mitigated without too much effort and a well made design.

Were we run into real problems are all chemical components like batteries. Chemical processes tend to slow down a lot at low temperatures, so most batteries won't work well at already moderately cold temperatures. One might think about replacing batteries by capacitors. But unfortunately high-capacity capacitors rely on electrolytic fluids and can't stand too low temperatures as well. There is still a possibility to not use batteries at all: In current rovers they are needed to be able to deliver enough power during operation of high-power devices while the power generator is only designed to deliver enough power for the average consumption. This saves a lot of weight on the generator side.

The only viable source of power for such a rover is some form of nuclear energy source (currently most likely RTG, but a fission or fusion reactor can be possible choices in the future). If the generator source is designed to be able to cope with the peak power usage of the rover, there is no need for batteries any more. The weight penalty will be high, but it's a working solution.

These power sources have the additional advantage of delivering a huge amount of direct heat that can be used to keep the rover warm. It's obvious that for operation at very low temperatures insulation must be much stronger compared to current Mars rovers, and there need to be (for example) heated storage places for sensitive equipment.

Compared to the statement in the answer, I don't see an actual problem of operating parts of the rover at temperatures that are at least 100K above ambient (that is, -50°C in an -150°C environment). Insulation is something that works very well and there is no reason to assume that any of the exposed parts of the rover will be anywhere close to this internal temperature. For comparison, people regularly move around at ambient temperatures of more than 60K below their body temperature and can stand this for hours with a heating power of just about 100 W.

Cooling due to heat transfer to the atmosphere on Titan is not that much more than on Earth: Atmospheric pressure is 1.5 times higher, density about 2.5 times higher, heat capacity a bit less - that's about a factor 4 under strong wind. If there is no wind, only convection will play a role, but this is less than on Earth due to the much lower gravity.

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  • $\begingroup$ That's really helpful. You discuss electronic and chemical concerns, although I wonder if there might not be a battery chemistry usable at those conditions, but far too reactive to be safe at Earth temperatures. What about mechanical? Are there usable lubricants or ways to avoid needing lubricants? $\endgroup$ – Steve Linton Sep 23 '18 at 13:46
  • $\begingroup$ @SteveLinton a "cyro-battery" that you have to keep cooled during transit or it'll explode? Sounds really interesting, but also sounds like the inverse of the problem. Shielding this battery from the sun for 2.5-6.5 years while it gets to Saturn could be worse. $\endgroup$ – Magic Octopus Urn Sep 23 '18 at 14:33
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    $\begingroup$ @SteveLinton: Battery chemistries too reactive to be safe at Earth temperatures would be difficult to test, build, and transport, and there's no particular need to keep such components at ambient temperature on the surface so you're not solving much of a problem. Note the opportunity for use of high temperature superconductors for components that can easily be kept near ambient temperature, though. And there's certainly cryogenic-safe lubricants, graphite for one. $\endgroup$ – Christopher James Huff Sep 23 '18 at 14:34
  • $\begingroup$ Transporting such batteries could use a 2-component design - fill the electrolyte into the battery only after arrival. Testing stuff in a closed chamber at -150°C isn't too complicated either. $\endgroup$ – asdfex Sep 23 '18 at 14:39
  • $\begingroup$ The heating power of a person at rest may be about 70 to 100 W, but if a person moves around at ambient temperatures of more than 60K below their body temperature, heating power may be around 200 to 600 W depending on physical activity. $\endgroup$ – Uwe Sep 23 '18 at 14:42

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