Here’s a question -
If a hypothetical ‘spaceship’ were to set off from the earth’s surface, what is the fastest time it could reach the outer limits of earth’s atmosphere, yet ensure the survivability of the crew (thought not necessarily conscious)?
ie, what is the fastest survivable time for a theoretical movement from the planetary surface to space?
Hm…would I need to ask Cecil?
That would depend on the maximum acceleration the human body can take and survive, which as I understand it, is about 10 g. If we take the limit of the atmosphere to be 1000 km (a roughly averag evalue, since the actual thickness is difficult to define) then at 10g or 98 m/s[sup]2[/sup], it would take a bit over 3 seconds (if I’ve done my math right).
Damn unit conversions. Let me go do that over, and I’ll be right back. :smack:
With a 500 mile escape distance estimate, and 10g acceleration, I come up with just over 2 minutes.
I make it 104.1 seconds or 1.7 minutes with the revised calculations.
Is 10g survivable for that length of time though ?
Pilots being tested in that spinning arm thing, usually pass out before 8g, let alone 10g.
I know the human body can survive much higher than 10g, in crashes for example, but SUSTAINED ?
I guess you would survive it, but you wouldnt feel very well at all.
You might squeeze a few more gees of acceleration out of the human body if you immersed it in fluid capable of carrying oxygen - such a fluid support system has been suggested many times, but I don’t know if any fluid has been developed which is suitable.
So it is speculative nonsense- (but so is a 10 gee rocket at the moment).
Even more acceleration could be had by replacing the blood system with a shockproof vasculoid working fluid-
what?
you say they aren’t human any more?
ah well…
A 10g rocket is not speculative at all. Id do agree that sustaining that rate for two minutes is speculative, however.
Does the atmosphere really go up to 500 miles?
Actually thought more on the lines of 20 miles - I’m thinking of edge of the atmosphere, rather than satellite orbit. I think. 
Two more questions -
How would the calculations be affected if kept under 8g?
I’m a long time out of school, but isn’t 98m/s/s 1/4 of the speed of sound?
Thanks for the replies - much appreciated.
I think you’ll find its 9 point 8 meters per second per second, not 98.
20 miles is still well within the Stratosphere. Most graphs you see in weather books give a breakdown of the different atmospheric layers up to at least 60 miles when you are in the Thermosphere, I guess at a push, you could say ‘space’ starts after that.
ChalkPit, you’re thinking acceleration of gravity, and I, Bryan is talking about the speed of sound. 98m/s is more like one third the speed of sound, but that’s at sea level - the speed of sound decreases as you increase in altitude.
Also, defining “the edge of the atmosphere” is very subjective. The highest cruising altitude for an airplane is around 100,000 feet, or 20 miles (I’m thinking SR-71 here). On the other hand, even though the space shuttle orbits at around 10 times as high, at 200 miles, it’s still subject to a LOT of atmospheric drag. So I guess it depends on the context…
Nasa seem to define ‘space’ as >50 miles- below that you are still a pilot, I believe they say.
Is there a limit on how fast you can go if you use hydrogen/oxygen fuel? Assume you get a fixed energy yield per kilo and jettison the fuel.
If you don’t jettison there is a limit, as chemical energy in the fuel increases linearly with mass, but kinetic energy after accelerating increases quadratically. I can’t put a figure to it though.
For aerodynamic purposes- the point at which the Shuttle starts experiencing drag and heating upon reentry- NASA considers “nominal reentry” to begin at 400,000 feet, about 75 miles. And I belive some special reconnaissance satellites have apogees that dip as low as 85 miles. So somewhere in that range.
I don’t think 10 G’s is sustainable, but maybe 8 G’s for well-conditioned crew and definitely 6 G’s.
:smack: perigees.
Ok, let me rephrase my reply to I, Brian
10g (10*9.8) is 98m per sec per sec, which is an acceleration.
The speed of sound is a constant (for a particular altitude), so the two are not really comparable - one is an acceleration and one a speed.
Thanks for all the comments. 
As for the difference between speed and acceleration - yes, I know - it was simply for noting that 10g from rest would result in a sonic boom approximately every 3-4 seconds (at sea-level). I found that interesting.
I’m under the impression that multiple sonic booms occur, anyhow.