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Comment by zachrose | Hacker News Reader

> Crew Dragon will accelerate from 0 to nearly 100 mph in one second. The entire test is less than two minutes long, with Dragon traveling over one mile in the first 20 seconds alone.

That sounds totally insane, and yet at 4.5 g's was what the Apollo crews experienced on a successful launch.

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That's actually fairly mild, as these things go.

The Apollo lunar missions experienced max G forces of 6.5-7.2g during reentry. (The Earth orbital missions only went to about 3.3g.) See: http://history.nasa.gov/SP-368/s2ch5.htm

Alan Shepard freaking flew Mercury 3 by hand during a 11.6g reentry.

Ejections seats are 12-14g or worse.

Of course, max G is only part of the equation; duration is the other. You can handle really high forces if they aren't for long. Given the short duration and lack of need to keep the occupants awake they could go a lot harder. I'm actually a little surprised it's so gentle.

One of the Soyuz (http://en.wikipedia.org/wiki/Soyuz_7K-T_No.39) hit 21.3g on re-entry.

Formula One drivers usually experience 5 g while braking, 2 g while accelerating, and 4 to 6 g while cornering.

If my mental math comes out correct, that's 25 m/s in one second, so assuming straight against gravity, that's a bit over 3g for one second. Not too bad, considering how extreme of a situation is involved.

100MPH is about 45m/s, not 25. Fighting gravity, that's 55m/s^s acceleration, or 5.5g.

Still fairly mild, considering. The Soyuz launch escape system, for example, subjects its occupants to 14-17g for five seconds. Incidentally this is the only LES that's seen actual use, when it saved a crew from an exploding rocket in 1983.

Whilst it is true that there has only been one launch abort so far, if the Shuttle had a launch abort system it would have saved the seven astronauts aboard. Just mentioning this in case someone mistakes your post as arguing that launch abort systems are rarely useful.

could, not would. Having a launch abort system is no guarantee that everybody will survive the ordeal.

That's a good point to raise. I didn't intend to make that statement but I can see how it could sound that way.

You are very correct.

On the ground, drag racing achieves similar levels of acceleration too:

http://en.wikipedia.org/wiki/Top_Fuel

And 7 g's on re-entry ...

I think the difference will be the Apollo crews were expecting it and it was sustained and constant.

A launch abort isn't something that you can really brace for.

Everyone aboard will be strapped down in a nice flight couch. It probably won't be pleasant, but will be easily survivable--which sitting on an exploding rocket, the alternative, would not be.

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