Time for grisly questions:
Suppose an Apollo command module had had a cracked heat shield. How long do the astronauts suffer during reentry before dying?
The hot plasma would enter the spacecraft interior and presumably melt away their clothing before melting their bodies. Maybe 15 seconds of pain?
And unrelated question: Why isn’t the command module’s exterior still hot on the outside after splashdown in the Pacific (that is, the parts that don’t touch seawater?)
Your second question: the heat shield deflects the “burn” around the capsule; it doesn’t touch the other parts.
Because the heat shield is designed to melt, carrying away the heat along with the melted droplets that stream off the side. Imagine blowing an ice cube with a hair dryer–the ice cube slowly shrinks as water is blown backwards off the cube in the stream of hot air from the drier. The bulk of the ice remains cold. The heat shields are made thick enough that it isn’t all used up before the capsule slows down too much to melt it.
I would suspect that the capsule would start tumbling uncontrollably due to unbalanced aerodynamic forces and be torn apart by the airstream (as was the case for Challenger & Columbia) before the plasma entered the crew compartment. If that were the case, the immediate cause of death might instead be blunt-force trauma, rather than being burned.
Interesting username/question combo!
If the plasma enters the part of the spacecraft where the crew is I’d expect them to be dead is a LOT less than 15 seconds.
I was thinking it would be like this:
Vaporizing the spacesuit = maybe 2 seconds?
Vaporizing skin and several layers of underneath flesh = maybe another 2 seconds?
The head is the toughest part, it is also surrounded by the protective helmet, and the brain itself has a thick skull around it. Maybe the helmet = 3 seconds, then the skull = another 3 seconds, before the plasma gets to the brain? By this time, the plasma has probably already vaporized the flesh outside of the heart and other organs, or maybe even is already vaporizing the organs.
Maybe less than 15 seconds from plasma breaching the crew compartment, to astronaut death, but not a whole lot less. Probably still a few seconds of agony…?
I recall reading in the book* Riding Rockets* by astronaut Mike Mullane that if the Space Shuttle suffered a heat-shielding breach, that he hoped that he would be unconscious before the flames began to consume his flesh. That seems to suggest that he anticipated that he’d feel the burning briefly; maybe the astronauts had been told that it would feel like that. But the Space Shuttle’s reentry temperatures are lower than the Apollo crafts, I think 1,500-2,000 degrees lower? So in the Apollo missions they’d die even faster?
Plasma is several thousand degrees Celsius. It’s as hot as or hotter than molten steel, which will vaporize a human body pretty much instantly if flesh contacts molten metal.
The astronauts might die slower from the entire crew compartment heating up as the spacecraft gets plasma-blasted, but if actual plasma gets inside and hits someone they’ll be gone, as I said, a lot faster than 15 seconds.
No sensible answer - it could be anything from seconds to minutes. Depends on the location and extent of the crack. It could be as trivial a failure as a tiny crack that causes the capsule to lose pressurisation. In which case the failure is survivable.
Otherwise you end up with a whole raft of possible disasters. Columbia was dying long before it broke up. All the control systems in the left wing had been destroyed, the landing gear gone, and control surfaces out. They could have never landed it safely even if it had made it to the landing area. They might (very very big might) have been able to hold level flight long enough to bail out, but I don’t think anyone seriously thinks they would have managed even that.
For an Apollo capsule similar loss of control systems would doom the craft. Once it started to tumble it would break up and every dies as close to instantly as you like.
A major failure might see the heat shield fracture and large part fall off whilst still in re-entry. Sudden and violent destruction of the craft from aerodynamic forces.
The heat shield was over designed. Although designed as a single use disposable item, it had enough reserve that it might actually have been safely reflown. Not that anyone would have seriously suggested it.
Just one quibble Francis Vaughan, depressurisation at altitude during reentry would likely have been fatal, they did not wear pressure suits during re-entry.
Just found this page of notes on heat shield development.
I think that any sort of fault that allowed any sort of leakage at all would also result in basically instantaneous disintegration of the entire craft.
With hot plasma coming in, or extremely violent gyrations of the craft, depressurization would surely be the slowest-acting threat that would be killing the astronauts…?
Soyuz 11 showed that depressurisation acts pretty swiftly too.
According to that Wikipedia page, it took 40 seconds for cardiac arrest to kick in after capsule pressure loss.
Don’t know how long violent gyrations would take to kill the crew, but as **Broomstick **mentioned earlier, hot plasma would probably kill in less than 15 seconds, so that depressurization would really be the least of the killing concerns.