It's only for 5 seconds, but that is an awful lot of force. The Falcon system is similar and presumably also involves very high-g forces. Could injury result from the abort itself in either case?
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asked Feb 14, 2015 at 17:52
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$\begingroup$ Are you interested in flights on the Soyuz or on the Falcon (or both)? $\endgroup$– HDE 226868Commented Feb 14, 2015 at 18:30
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$\begingroup$ both. I should probably edit the question to reflect that. $\endgroup$– kim holderCommented Feb 14, 2015 at 18:31
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7$\begingroup$ Less uncomfortable than the alternative? $\endgroup$– Nate BarbettiniCommented Feb 14, 2015 at 18:34
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2$\begingroup$ @NateBarbettini - i'm not sure, with some alternatives you might not have time to feel anything at all ;) $\endgroup$– kim holderCommented Feb 14, 2015 at 18:35
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$\begingroup$ Presumably the crew have high-G training, are wearing G-suits, and don't need to be conscious for the vehicle to land normally? $\endgroup$– A ECommented Feb 15, 2015 at 21:01
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3 Answers
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14G sounds like a lot. To put it in context:
- the acceleration you can endure depends on the force vector. The position in which we can withstand G-forces best is forward (using the directions from the XKCD diagram), so spacecraft seats are placed to take advantage of this. When the rocket sits on the pad, the astronauts lie on their back.
- fighter pilots are trained to function at peaks of 9G upward. They use special flight suits to achieve this much. Much higher than that and people lose consciousness.
- we know from tests (John Stapp) that a human can survive peak loads of 45G (backward, or 'eyeballs out') but he suffered vision damage at these loads. People have survived higher loads in car crashes, but injuries are likely.
- untrained humans can survive 20G for 10 seconds.
- fighter pilots who have to eject, experience 12-22G peak loads upward and often have some health problems afterward, and are usually grounded after their second ejection to prevent worse.
- NASA did some research into parachute harnesses. The opening of a parachute also induces a large G-load upward, and they found:
For such harnesses the NASA/AGARD researches indicate a 5% injury risk at 12.1G,
Sitting in a well-designed seat the forces are spread out much better than in a harness. I suspect the injury risk at 14G is pretty low. The crew won't be able to move for those few seconds, but they should be okay.
From the XKCD site:
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$\begingroup$ Interesting that the tolerance varies with a factor of ten depending on orientation. I wonder if orientation has a similar importance, in the long term, for medium gravity 0.1g-1g. $\endgroup$ Commented Feb 14, 2015 at 23:17
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$\begingroup$ From Stapp's Wikipedia page: ["The acceleration requirement for fighter seats was increased considerably up to 32 g"] (en.wikipedia.org/wiki/John_Stapp). That's upward. 14 g eyes-out sounds not too bad. $\endgroup$– MSaltersCommented Feb 15, 2015 at 0:05
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$\begingroup$ @LocalFluff I don't think this is surprising. We're a bunch of vital organs stuck together with differing kinds of connective tissue that responds to loads highly anisotropically. $\endgroup$ Commented Feb 21, 2015 at 8:46
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When I worked with Vladimir Titov on STS-86 he was fine after experiencing such an abort years earlier. If your question is could an injury happen, sure, anything can happen.
answered Feb 14, 2015 at 18:53
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EDIT: I had missed that this was about abort, not launch. The answer below has been changed to reflect that.
The G-force estimations here seem to generally be expecting the feet of the crew to be toward the pull. This is not so.
Crew are positioned with their backs to the ground at launch in all spacecraft designs I've ever seen (almost always in the descender part of the craft), specifically because this is the best position from which to resist high G forces.
A few fighter ejection seats are rated for a 14G force, though for lesser duration, with the additional detrimental points that it is a downward directed force and subjects the pilot to windblast (which, if anything kills them, this or a collision is the most likely thing to do it).
With this taken into account, 5 seconds at 14Gs is not pleasant, but its not going to cripple or incapacitate a healthy human, as evidenced by all the healthy folks walking around the planet who have ejected from fighter aircraft. Of course, there may be side effects, but its a lot better than the alternative.
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$\begingroup$ The healthy folks who have been to space have experienced a normal launch at 3-6G, not a launch abort at 14G. The portion of ascent with the highest G-loads is usually just before first stage separation, because the stack has its highest power-to-weight ratio at that point. Initial acceleration off the pad is not that rapid because the fuel tanks are full and the power-to-weight ratio is low. $\endgroup$– HobbesCommented Feb 16, 2015 at 8:18
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$\begingroup$ @Hobbes Bzz! You are indeed correct, I somehow missed the fact this was about launchpad abort, not launch. With that in mind, the 14G is a rather standard rate for ejection seats on fighter craft (with the added effects of being upright and subjecting the pilot to windblast). I've adjusted the answer to reflect this. $\endgroup$– zxq9Commented Feb 16, 2015 at 9:35