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I was going to put a whole back-story for this question here, but thought it'd be better as a Google+ post instead, for reasons that should be obvious to anyone who reads it.

So, during high velocity returns, is there a chance that a parachute will fail if the capsule is travelling too fast when it's deployed? If so, what's the optimal speed/altitude range for deployment?

If speed is not the cause of these failures, what is, and how can I mitigate it?

I should also say that I'm using Mechanical Jeb. For reasons explained in this question, I now always bring the MechJeb unit back with me. In the case of the most recent failure, the MechJeb unit was positioned between the capsule and the parachute, something that had worked for me before. But for my rendezvous mission, I used one of the radial mount options, keeping the (proper sized) parachute connected to the top of the capsule.

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Possibly related: kerbalspaceprogram.com/forum/showthread.php/… – kalina Sep 22 '12 at 16:43
@MBraedley Have you looked at the flight log after impact? It won't (usually) tell you what caused a failure, but it should tell you where the failure is occurring, which might give some insight into your issue? – GnomeSlice Sep 22 '12 at 16:58
indeed, you should get something along the lines of "Structural failure on linkage between Mk16 Parachute and Mk1-2 Command Pod" – kalina Sep 22 '12 at 17:01
@pixel: Hmm, there is some useful information there that makes me think of another possibility. I've updated the question. – MBraedley Sep 22 '12 at 17:38
in one of my ships everything below the command pod breaks away.. which is fine by me as I don't need a separator. – reto Jan 7 at 12:49

1 Answer

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The rule of meassure I use is to only deploy the parachute when below the speed of sound (330 m/sec). I tend to wait until 250 m/sec, but I've never had a parachtute ripped off when under 330 m/sec.

The parachute doesn't do much anyway until you hit 500-1500m (Kerbin) altitude (most videos on Youtube show 500m, I'm playing 0.19.1 and it's usually roughly 1350m for me.). If at that point you're still going faster than 330 m/sec; may Kerbal God have mercy on your poor Kerbals' souls...

Edit: I do not use MechJeb, so I have no idea of its weight. The figures above are for a pod (doesn't matter how many Kerbals) and a parachute. If it's heavier, I'd scale those numbers accordingly.

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parachutes will start stabilising the flight path as soon as deployed AFAIK as drogue chutes, but won't fully open until 500m above ground level (which can be a ways up if you're landing in a mountain region). – jwenting Apr 16 at 9:22
Yep, but if you're still going too fast when deploying, it'll be ripped off. I haven't landed on a celestial body with an atmosphere other than Kerbin, so I'm not sure if variations in atmosphere (pressure, density, ...) will have an effect on those numbers. – Flater Apr 16 at 12:45

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