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All manned spacecraft to date have come back to Earth eventually, and when they do it's through a flaming ball of plasma.

It seems too probable that this plasma would have a way of breaking things like parachutes, which are kind of important so that you don't go splat upon contact with the water/ground. Has any spacecraft had a means for the crew to escape upon the event of a parachute failure or other catastrophic failure?

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In some Mercury flights, the astronaut had a personal parachute with them. The Gemini program used ejection seats, which could be used during launch and reentry. Later on, they realized that igniting a rocket-propelled ejection seat wasn't a good idea in a pure-oxygen atmosphere.
The Vostok capsule also had an ejection seat, but not as a backup: the designers hadn't yet developed a soft-landing system they were confident in. In both cases, the ejection seats were deleted in the successors (Apollo, Soyuz).
During the reentry phase where plasma occurs, the parachutes are safely stowed inside the spacecraft. If the plasma can get at them, it has penetrated the hull and the crew are in imminent danger as well. They can't eject at this stage: if they eject, the heat shield no longer protects them so they're exposed to the same plasma they were trying to escape from.
The backup system for landing generally consists of having 3 parachutes, any 2 of which can safely land the capsule. See this earlier question.

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    $\begingroup$ It's not so much that they're exposed to the plasma; they'd be generating it. Reentry velocity of a craft like Apollo is around Mach 25, and the heat generated is not so much because of friction against the air as it is compression of the air in front of it. This is in fact a critical design feature of spacecraft, to use the atmosphere as an air brake, slowing the craft down to speeds where aerodynamic control and/or parachutes would be useful. $\endgroup$ – KeithS Nov 25 '13 at 23:35
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The Space Shuttle Orbiter had a flight mode whereby, at or below ~50,000 feet of altitude during the reentry (or, in the event of an ascent abort, the gliding, unpowered phase of flight), the commander could command an autopiloted, wings level glide at about 190 knots equivalent airspeed (KEAS).

The plan was then, while the Orbiter was gliding, that the crew could execute a manual bailout procedure via the side hatch, utilizing the egress pole system. Said bailout could be initiated at or below ~30,000 feet of altitude during the glide.

Said bailout procedures were initiated after the Challenger mishap.

References:

To reference some of the bailout procedures (what we called a "Mode 8 egress"), please see the Shuttle Crew Operations Manual (page 2.10-13 for information about the Egress Pole System and starting on page 2.10-18 for information about the crew bailout procedures).

FYI, the 190 KEAS figure I stated above is from a crew training workbook that I still have on hand - specifically, there is a depiction therein of the "BAILOUT MODE 8" crew cue card that states (among other things) that the commander is to take manual control of the Orbiter, establish level flight, then, as the airspeed bleeds down to 185-195 KEAS, is to engage the autopilot. Said autopilot would then establish a glide at about those airspeeds.

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    $\begingroup$ Oooh, you're an astronaut. You were on one of those things. Okay, i guess that is sort of an automatic pass... still, it would help to make that clear, because an answer of this kind should have a reference to back it up. Maybe you remember the section in the Operators Manual :D $\endgroup$ – kim holder Nov 24 '15 at 23:21
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Consider that, in order for the escaping crew to survive outside the re-entering capsule, they'd need a heat-shielded, thick-walled escape pod; in order not to hit the ground at fatal speed, the escape pod would need to be broad and blunt in order to bleed off speed via aerodynamic drag.

You'd basically be talking about another re-entry capsule inside your re-entry capsule. From an engineering standpoint, it makes far more sense to build redundancy (multiple parachutes) and reliability into the single capsule.

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  • $\begingroup$ In regards to surviving an ejection at high speeds and capsule inside a capsule, note that the experimental XB70 bomber aircraft had an ejection capsule inside the cockpit. ejectionsite.com/xb70caps.htm And this was at a max of about Mach 3. It was used once (not at Mach 3) during a promotional photo shoot where planes collided and the XB70 crew bailed. One made it safely to the ground, and sadly one didn't as his clamshell ejection seat didn't close properly so he couldn't eject. $\endgroup$ – Milwrdfan Jul 30 at 16:23

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