The Huygens probe didn't last long. What are the challenges of operating a rover on the surface of Titan for at least a few months and what technologies would be used to overcome these?


Titan's atmosphere is not extremely thick. Its only 1.5 bars at ground level. Its also not corrosive, consisting mostly of nitrogen and, to a lesser degree, methane.

The only real challenge is the distance from the sun. Reaching Titan requires a considerable amount of delta-v (about 20km/s from the earth's surface). Once you are on Titan, solar panels are unusable because of the low amount of light that reaches the surface (0.1% of the level at the earth's surface). Also because of this low energy input, temperatures are frigid cold, at about -180°C.

Space is also cold out there, but the atmospheric temperature is worse, because in space there is no convection. Heat can only be exchanged by radiation. In Titan's atmosphere, there is lots of convection, quickly cooling the spacecraft below the allowable temperatures of sensitive equipment, such as the batteries.

The only way to keep a spacecraft operating and supplied with energy for a longer period of time on Titan would be a nuclear power source. A nuclear reactor is possible, but it makes more sense to use a large radioisotope thermoelectric generator (RTG). Therein the heat from the decay of a plutonium ingot is converted to electrical power. RTGs have been used other space missions, such as Voyager or Curiosity, but in order to keep a titan probe warm, you would need a big one, and that makes it expensive to build and launch.

The required size, of course, depends on the amount of insulation, so its an optimization problem: Save some weight on the RTG, and carry more insulation, or carry a larger RTG and save some weight on the insulation.

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    $\begingroup$ Wouldn't it be very difficult to deal with the same heat generation during flight through vacuum as inside the Titan atmosphere? A heat source would need to be adjustable, and I don't think a plutonium RTG can do that. Or leaving a large heatsink in orbit before landing. And btw, did the Huygens finally fail by freezing? $\endgroup$ – LocalFluff Oct 30 '14 at 10:33
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    $\begingroup$ That is a design issue that certainly need to be addressed. $\endgroup$ – Rikki-Tikki-Tavi Oct 30 '14 at 10:51
  • $\begingroup$ Probably only the electronics should be kept warm, simply because we didn't develop the technology of the chips whose operating temperature is so low. Building electric motors and other electromechanical parts capable to to work in -180C would be easy. $\endgroup$ – peterh Aug 7 '18 at 21:29
  • $\begingroup$ @LocalFluff Huygens failed because its batteries ran out. $\endgroup$ – Hobbes Sep 18 '18 at 9:50
  • $\begingroup$ I've asked a separate spin-off question about whether or why we would need to keep (much of) the rover hotter than the Titanian environment. space.stackexchange.com/questions/30744/… $\endgroup$ – Steve Linton Sep 18 '18 at 10:20

Additional to @Rikki's answer in addition to heat and power you need to be able to move and explore, there are several challenges to this:

  • Titan is far from the sun, so has very little light. On Mars there's enough light for conventional camera instruments to work. Making navigation decisions is possible based mostly on visual information. On titan you'd need to design a system that can "see" terrain in a very dark environment
  • Titan is very far away from earth, so communications takes a great deal of time. It's unrealistic for a titan rover to be directed from earth as nothing would get done, so the rover would need to be able to navigate and use its science instruments with a great deal of autonomy, which means a high level of AI
  • Parts of Titan are covered with liquid hydrocarbons in which a rover would easily get mired. It is theorized that it rains hydrocarbons as well, so a rover would need to be able to recognize and avoid seas, rivers, ponds, and puddles of liquid methane which would be a hazard
  • We know comparatively little about the surface of Titan. Before committing a rover to the surface of a planetoid we would want to do extensive, accurate mapping of the surface, which would have to be incorporated as part of, or a separate mission to pave the way for a rover mission

So, for a rover to be successful it would need to independently move around largely unknown terrain which is pitch black, close to absolute zero, and covered with liquid hydrocarbon all the while being able to do meaningful science.

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    $\begingroup$ Well, the "system to see in a dark environment" is called a "lamp", and not all that uncommon ;). You're right about the additional hazards of moving around. The probe must be insulated very well against the ground, or else it will melt the more volatile hydrocarbons and sink in. $\endgroup$ – Rikki-Tikki-Tavi Oct 30 '14 at 17:13
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    $\begingroup$ I'm not sure lamps would be the best solution - probably less energy-intensive (and better images) by using sensitive CCDs that can see in low-light, or amplification equipment similar to "starlight" night-vision equipment on Earth. The RTG is a definite, that was my first thought as well. And the communications lag is a good point - so autonomy is huge. Also, an orbiting comm relay satellite to reduce rover's weight. I think possibly inflatable wheels that provide buoyancy and allow motion thru fluids (eg, rivers/lakes). $\endgroup$ – Kirkaiya Oct 30 '14 at 18:24
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    $\begingroup$ Lamps will certainly be useful, but not for navigation as you won't be able to power a strong enough one. Laser mapping would probably work, or radar. $\endgroup$ – GdD Oct 30 '14 at 19:19
  • $\begingroup$ The question of light levels is discussed here: space.stackexchange.com/questions/7849/…. Basically daytime under the clouds on Titan is comparable to full moonlight on Earth. Not a big problem, $\endgroup$ – Steve Linton Sep 18 '18 at 10:02

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