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From what I understand you can't use aerobraking on Mars for landing as the atmosphere is too thin. From what I understand Mars is quite problematic because the atmosphere is too thin to benefit from parachutes, but not thin enough like the moon where you can enter in whatever angle you want.

So I wondered if there are any significant reductions in required energy to enter Venus compared to Mars. And also how it compares to the Earth. E.g. would the heat-shield need to be thicker or lighter. Will it be easier or harder to enter Venus than Earth?

I assume parachutes would be more effective on Venus.

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Aerobraking is most definitely used at Mars. Going from about 6000 m/s down to 100 m/s is done entirely with aerobraking, first with a heat shield, and then with a parachute. The last bit from 100 m/s to about 1 m/s is done with rockets. (There seems to be a lot of excitement about the bit at the end for some reason, but by then nearly all the work has already been done.)

Venus entry velocities are higher, so it is much rougher on the heat shield. Once you're past that part, the atmosphere is much thicker than Mars' and far enough down, much thicker than Earth's. The atmosphere is so thick that a small metal structure can serve as a sufficient parachute for a slow descent to the surface.

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  • $\begingroup$ Is aerobraking still useful for capture and orbital insertion if one wants to put an Earth Return Vehicle in a high Mars orbit, to lower fuel need for the return flight? Isn't the low periapsis a problem then, or is it just a high apoapsis that counts for cheaper return? $\endgroup$ – LocalFluff Aug 22 '15 at 9:37
  • $\begingroup$ Why are Venus entry velocities higher? Due to higher gravitational pull? But just for comparison. At equal velocity would aerobraking on Venus work better? $\endgroup$ – Erik Engheim Aug 22 '15 at 10:18
  • $\begingroup$ Yes, higher gravity, as well as steeper entries due to the larger scale height. I'm not sure you mean by "better". $\endgroup$ – Mark Adler Aug 22 '15 at 14:00
  • $\begingroup$ Yes, aerocapture works at Mars. I don't understand the question about apoapsis and periapsis. After an aerocapture the periapsis must be raised using a propulsive maneuver at the first apoapsis. $\endgroup$ – Mark Adler Aug 22 '15 at 14:02
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    $\begingroup$ It is much better than Mars in that there is no problem whatsoever slowing down enough by the time you get to 50 km. It is much worse than Mars in that you need a much thicker, denser, and heavier heat shield (made of materials we have forgotten how to make) to survive the high heat phase of that entry, due to the high entry velocity and steeper flight path angle. $\endgroup$ – Mark Adler Aug 23 '15 at 15:11

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