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At orbital speeds around the Earth, things tend to burn up on striking the atmosphere, since they're going so fast. To get an astronaut (for example) home safely from those speeds, they need to have some kind of heat shield to protect them.

What if they were landing on Titan instead of Earth? At orbital speeds around Titan, how much heat shielding would you need to enter Titan's atmosphere without burning up?

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  • $\begingroup$ What do you think is the scenario for a spacecraft to go into orbit around Titan before landing? $\endgroup$ – Rikki-Tikki-Tavi Apr 4 '16 at 19:27
  • $\begingroup$ @Rikki-Tikki-Tavi Joe may be thinking of an orbiter-lander model. $\endgroup$ – called2voyage Apr 4 '16 at 20:24
  • $\begingroup$ @called2voyage Still wouldn't make much sense to deploy the lander from orbit, rather than directly from the escape trajectory. $\endgroup$ – Rikki-Tikki-Tavi Apr 4 '16 at 21:35
  • $\begingroup$ @Rikki-Tikki-Tavi I'm just saying that may be where he is coming from, and he might need the explanation you just provided. $\endgroup$ – called2voyage Apr 4 '16 at 21:37
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From this answer, we learn that sounding rockets typically don't have a heat shield, despite entering very quickly and at high angles (Although not orbital speeds). Huygens, which orbited Saturn, entered Titan's atmosphere at about 6 km/s. The increased atmosphere will allow for a more gradual entry into Titan's atmosphere. Bottom line, it should be possible to make a spacecraft that can enter Titan's atmosphere without a heat shield, if one does so carefully.

As for a human rated one, it would be a bit more difficult, but not terribly so. Heat is related to the speed at which the spacecraft slows down. One can slow down very carefully on Titan, and could probably glide for considerable range, which would allow one to build a spacecraft that could enter fairly easily without an ablative heat shield.

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    $\begingroup$ Just a sanity check, you don't make it clear that you are saying it should be possible to make a human rated spacecraft that can enter without a heat shield. $\endgroup$ – called2voyage Apr 4 '16 at 20:18
  • $\begingroup$ Fair point. I think it would be possible, but I'd have to think a bit more... $\endgroup$ – PearsonArtPhoto Apr 4 '16 at 20:20
  • $\begingroup$ Looks good to me. $\endgroup$ – called2voyage Apr 4 '16 at 20:23
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from wikipedia:

Observations from the Voyager space probes have shown that the Titanean atmosphere is denser than Earth's, with a surface pressure about 1.45 times that of Earth's. Titan's atmosphere is about 1.19 times as massive as Earth's overall,[6] or about 7.3 times more massive on a per surface area basis.

Just based on those two facts, I would assume that heat shielding would absolutely be needed, comparable or more massive than those for Earth reentry. Of course, the size of the TPS would depend on the relative speed between the craft and Titan.

If the object were in strict orbit around Titan (I assume 1000 km altitude for a stable orbit), the orbital speed would be around 1.6 km/s, which would not require that much heat shielding ("only" comparable to a hypersonic aircraft, not e.g. a Shuttle)

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  • $\begingroup$ I don't think you can answer the question just with the mass of the atmosphere. It depends if you can find a shallow trajectory, so you don't hit the atmosphere like a brick. Also, taking your 1.6 km/s, would mean that you only have about 5% of the energy of an earth orbit spacecraft to dissipate. $\endgroup$ – Rikki-Tikki-Tavi Apr 4 '16 at 19:27
  • $\begingroup$ @Rikki-Tikki-Tavi it's not just the mass of the atmosphere by itself - Titan's atmosphere appears to continue up to ~1000 km with not insignificant density (I'd compare it to 200-300 km Earth orbit). The total volume of the atmosphere is still less than that of Earth's, but with a greater mass, so greater density, generally, which means higher heating rates for comparable trajectories. $\endgroup$ – costrom Apr 4 '16 at 19:35
  • $\begingroup$ @Rikki-Tikki-Tavi and yes, if you were in a relatively circular orbit around Titan, the energy is much less than in a comparable Earth orbit, and could be dissipated fairly easily. $\endgroup$ – costrom Apr 4 '16 at 19:35

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