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Recently I did a Duna mission in Kerbal Space Program. I was landing my capsule on Kerbin (from Duna). I had a Heat Shield (0.625m), a Mk1 Cockpit, parachutes and a SAS. My periapsis was 19 kilometers. So everything was set.

When I entered the atmosphere at 2500 m/s everything was going fine until I started getting heat warnings and eventually everything exploded/burned up, including the heat shield. How do I prevent that?

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    What was your apoapsis before hitting atmosphere? (Steepness of entry matters as much or more than raw speed at entry, since it determines whether you hit thick air at high speed or low speed. Telling us apoapsis will give us that information.) – SevenSidedDie Dec 13 '16 at 16:27
  • Well, it's hard to say by your description, but I would suggest the following: Hit the atmosphere gently! Make an orbit around Kerbin with approximately 71K for both apoapsis and periapsis. when you are at the apoapsis, make your periapsis 69K. When you arrive at your periapsis, make your apoapsis something around 68K. That's enough... let the atmosphere remove those 2500m/s to something way easier for your ship to take. And remember to set your SAS to periapsis so all the heat will be taken by the heat shield. – vianna77 Dec 13 '16 at 17:10
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    Can you include a screenshot of the craft? – SevenSidedDie Dec 14 '16 at 17:24
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The 0.625m heat shield is inappropriate for an 1.25m stack. The MK1 cockpit has a diameter of 1.25m.

There is no need to circularize around Kerbin first as other comments suggest. It is perfectly possible to re-enter from an interplanetary trajectory.

19km might be a bit deep, though. I usually aim at 25km for a return from the mun and would not aim deeper for an interplanetary return. I'd say 25-35km should be deep enough to capture but high enough to trouble with overheating, if you have the right heat shield.

Remember that you want to minimize two things: Peak heat flux, and total heat energy absorbed. Coming in too shallow will mean you don't capture (which isn't as bad in KSp as IRL due to unlimited life support), coming in a bit too shallow will mean you spend too much time breaking and absorb too much total heat, and coming in too steep means the peak heat flux is bigger then what your craft can tolerate.

From your description, it is not entirely clear whether or not you had a problem with total heat absorbed or peak heat flux, so react accordingly.

Further good reading is here:
How do you tell if re-entry will destroy your ship?

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    Using a 0.625m heat shield on the MKI cockpit makes me think the entry into the atmosphere may have been the wrong way around... that heat shield fits perfectly on the pointy end, but that's not the way to come back! – tpg2114 Dec 14 '16 at 16:12
  • No, its not. You want the blunt end forward in order to slow down enough. – Polygnome Dec 14 '16 at 17:55
  • @Polygnome its not a case of what you want - its a case of what aerodynamics makes happen! – Qwerky Dec 21 '16 at 14:36
  • @Qwerky No, its not. The pods are aerodynamically stable without SAS with the blunt end forwards. Thats what they are designed for. Going with the pointy end forwards means that the hull is directly exposed to the airflow, and you go kaboom. You always want a heat shield that is at least as big as the stack pointing forward. Having a 0.625m heat shield on a 1.25m stack means the heat shield does not protect the stack, and the air flow touches the unprotected parts. Boom. There really isn't more to it. If your vessel flips, its badly designed with an imbalanced CoM, and needs redesign. – Polygnome Dec 21 '16 at 14:46
  • @Polygnome - The pods are aerodynamically stable without SAS with the blunt end forwards yeah, that's what I'm saying. – Qwerky Dec 21 '16 at 14:49

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