G-forces on Earth and in space

Glad to find a board where I can finally post this question.

I've got a little argument going with a friend over whether or not there is a difference between 12G's in space and 12G's on earth. I declare that 12G's is about the maximum that a human body can take with conditioning and pressure suit aid before G-LOC. This should be true, but say otherwise if I am incorrect in this assumption. If this is true, astronauts experiencing 12G's in say, a slingshot maneuver around the moon (ala Apollo 13, but with more speed in this case), they would be susceptible the the same intense G-forces as a pilot when performing intense aerial maneuvers. How long is the human body capable of enduring these forces before it becomes fatal, or at least until G-LOC typically sets in? My argument is that nobody can survive a sustained 12G environment for the amount of time it would take to burn around the moon towards a return trajectory to Earth. Oh, and assuming that they are positive G's, not the kind of negative G's that cause the blood to rush to your head, causing red-out.

I've been told by someone who supposedly is majoring in physics that I am wrong in assuming that there is no difference in space and on Earth. This person also told me that astronauts experience up to 60g's during liftoff, which sounds preposterous to me. I know that the human body can survive high G-forces for brief periods of time, but for 10 minutes? I don't think so.

I have also been told by a reliable source that I am totally correct and my friend and this other source are completely retarded. Discuss...

I do believe you are right. "G-forces" is a measurement of force in units of g, the acceleration due to gravity on the earth at sea level, about 9.8m/s^2 (there is a defined value for g, to keep everyone on the same page.) So if you accelerate at 18.6m/s^2 you are pulling 2 g's, 98m/s^2 is 10 g's. It's just a way of mentally understanding forces you are dealing with.

Whether by gravity or a rocket up your butt, the effects are the same, otherwise you are arguing with Einstein over general relativity.

Sources on the web says that they Space Shuttle accelerates at about 3 g on lift off. See also the life and works of one John Stapp, who survived 46.2 times g.

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

So yeah, you're right, friends need to hit the books more.

Yes, I read that about the shuttle. Not only is it safer for the astronauts, but it is also safer for the shuttle. The Saturn V rocket was capable of outputting up to 10G's of force.

Does anyone have any kind of chart that shows what humans are capable of withstanding? Something like the x-axis being length of time and the y-axis being amount of G-force. I still need to also prove that nobody could take 12G's for 10 minutes... let alone maybe ONE minute.

I think 8gs is accepted as what a human body can take, with proper suit and training and genetic predisposition, for extended periods of time (a few seconds). This is why they don't build military jets to take much more than 8gs. They could, but it would be useless because the human body can't take it.

As has been mentioned, the human body can take more (up to 45gs as far as we know, apparently), but that's for only a split second and therefore does not apply to this discussion.

And yes, if you were in a sealed box with no input from the outside, you would not be able to tell, using any instrument, whether the box is standing on the earth or accelerating at 1g in space.

What is this? How can the moon accelerate something at 12gs if its gravity is only a fraction of the earth's (which is 1g)?

Further evidence for my belief that schooling and education doesn't make a person intelligent.

Lsos,

IN the same way a person experiences > 1g at the bottom of a roller coaster, i believe.


Frothy,

Hmmm, good luck for that. If you can find out something that shows enough g-s that would cause a pilot to pass out with a pressurised suit on, an equal g-s for 3-4 minutes should cause brain damage or death, as the passing out is due to blood being unable to make it to the brain...

Damn it, now I'm curious...

pub med abstract on high "Gz" tests

Okay, here is something but it also brings to mind that seat position, that is direction of the Gz (Gz seems to be the symbol) comes into play.

Chart of Gz and seat tilt to brain blood pressure

I believe that the astronaghts have somethng close to the 90 degree tilt, so it seems that 12 Gz isn't all that dangerous, at least to the brain. At 0 tilt, which i take the Gz to be head to foot, you have 0 blood pressure to the brain, which means you are dead in a couple of minutes.

Anyhoo, good luck

On a roller coaster we are accelerated by forces exerted by a sturdy structure consisting of steel tubes anchored in concrete. I understand we can experience even greater Gs simply by jumping off the roller coaster and hitting the sidewalk below.

But...I don't see how this has anything to do with being accelerated by the moon in the nothingness of space, where the only force acting upon us in a slingshot maneuver would be the moon's gravity...which I understand not to be that large.

Okay, I got this from the movie Armageddon. I got into this argument because I was making fun at how horribly the movie was written from a scientific standpoint. I basically said that whoever wrote that movie has never taken a science class in their lives. I know it's just a movie, but you know, you gotta make it at least remotely believable, or else nerds like me will pick it apart.

In the movie, they were trying to come up behind the asteroid that was heading to Earth. In order to pick up the speed they need, they were using the moon's gravity to combine the acceleration given from their engines to hit, I think 26000 MPH. While going around the moon, they burn their engines at full throttle to pick up the speed they need to catch up to the backside of the asteroid. They tout that the burn will last 9 1/2 minutes and that someone in the movie says that it will be something like a 10G burn. When you see the LED in the movie, you see that the G-forces actually exceed 12G's. This is where I was saying "That's f***ing bulls***. Nobody can survive that!"

I am pretty sure that if the acceleration is constant, the G-forces should actually be about the same. The LED was showing the G-forces increasing during the entire burn.

This was just one of the many huge mistakes made in the movie. You can make a humongous thread listing out all of the other mistakes that were made, but nobody really cares anyways. I just want to get the evidence I need to support my opinion.

Sure - the movies get it wrong. They know it! Its part of their "artistic" license.
They make roaring noises when the burn goes on too!

The G-Forces you actually experience very much depend on your motion.
If you were hurtling toward Earth on a slingshot near-miss path, at a speed so fast that it exceeded escape velocity, your speed would increase some, the closer you came. It would be fastest when you were closest. You can change exit direction with a well timed burn, (and stay high enough to avoid atmospheric drag).

The point is, except for the time the burn was on, the force you feel internally is ZERO !!

We are nearly at the heart of the key thing we just don't understand about gravity!
You feel G-forces when your velocity changes ie. accelerations It does not matter if you used a thruster, or spent awhile dropping on a rollercoaster before changing direction, or did figure-of-eights in a Zifko Edge 540 at a Red Bull Air Race

You do not feel any internal forces when you agree to be accelerated by a gravity effect of a nearby large mass. You only feel the force when you resist that motion. Astronauts are being accelerated continuously toward the Earth. They feel no force! Only when they fire retros, or eventually reach a terminal velocity of a parachute, or finally step out of a shuttle...then they feel it, and only because what they are not doing is falling toward Earth gaining speed at 9.81m/sec/sec.

So - the G- Force you feel from accelerations is indistinguishable from the tug you get from a planet, except that the planet kind is this stuff called gravity, which reaches through everything, at any range, to pull on every particle of you equally, as opposed to the rocket motor, which shoves under, and lets the internal stresses in you make you aware of a "force". I guess thats why they called it "the acceleration due to gravity"

Check out a whole lot of fun Bending Spacetime in the Basement

Oops - I missed on this bit

Yeah - this actually happens. With a constant shove from the motor, as the mass of fuel gets used up, what is left gets accelerated faster. Astronauts notice this during launch.

I totally agree with what you just said. During spaceflight, there should not be any G-forces acting on the astronauts. Only during acceleration/deceleration and/or change in direction will G-forces be felt by the occupants in the vessel.

My point is that when 12G's are being exerted on the astronauts, it is the same force felt by pilots in the atmosphere. The difference is that there is always that 1G of gravity pulling the pilots towards the surface. In the movie, they are accelerating the shuttles AND going around the moon in a circular motion, causing up to 12G's for over 9 minutes. They shouldn't even be able to last 30 seconds before brain asphyxiation sets in and becomes fatal. 12G's for 30 seconds on Earth has the same effect, correct?

We all know that 1G is the measurement of the Earth's gravity at sea level and at the median distance from the center of the planet.

Is it accurate to say that when a pilot is doing a loop at 13G's (hypothetically), that they will feel a NET force of 12G's from downwards from their head to their feet at the very apogee of the loop?

Er.. not quite. The "going round the moon in a circular motion" has a moon orbit component. It all depends how high and how fast, and how much of that motion is forced by the motor. Take it in small pieces.

First, for a given size of orbit or approach there is only one speed that seemingly allows no forces on the astronaut. All other combinations require engine burn, and so also, forces on the folk.

The moon gravity pulls on all the particles of them equally. The local tug between bits of his body, and even the mass of the spacecraft hardware is too small to feel. You are completely un-affected by even very large gravitational tugs provided you allow yourself to be continuously falling towards it. An orbit is a special case of "continuously falling" where you manage to avoid ever making it to the ground, because the entire acceleration is devoted to keeping you continuously changing direction.

Next - you can simply add the forces, but it is important to know when they are there. If you are (say) over Earth, near the ground, at steady speed, in a (say) aerobatic plane capable of pulling a few G. You feel only your own 1G weight because you are not in free fall. If you fly in a horizontal circle, you feel your 1G weight downward, and also the plane shoving you inward toward the circle centre (which feels like you shoving the plane outward - but thats a body frame-of-reference illusion).

In a vertical loop, as you go over the top and free fall while the plane obligingly keeps itself around you, you feel zero G. As you hit the bottom, you feel your regular 1G (from not agreeing to be in free fall) plus added to that whatever force is needed to keep your body in the loop circle. Notice that the speed in the loop can be constant. The change of direction is enough to constitute acceleration. Revving around in movie spaceships is just a scaled up version of this. Generally, going round a moon or planet always would have a substantial orbit (free fall) component.

If you could afford the fuel, and the fuel to lift the fuel, you could fire retros to match the surface rotation speed of a planet, and fall straight down with parachutes and no violent re-entry! Unfortunately, we still have to send anything anywhere in space by flinging mass we brought along, out of the back at high speed, hoping to get within range of a moving planet "gravity well". Then, we can steal some of the planet's momentum, in the famous "slingshot" effect.

The movie "Apollo 13" was about the only one that got the fuel budget right. In just about all others, they ignore it. "Star Trek" invented transporters because they didn't want the expense of sets for landing and takeoff scenes. Its sad that modern polsters can have a substantial proportion of the population thinking "di-lithium crystals" is a fabulous rocket fuel.

How fast must a person be falling to experience a "G" force?

How many "G" forces are too many for the human body?

There is no way that a human could take 9g's for mor than a few seconds(let alone 12). The f-16 and f-15 pilots pulling hard g's pull a max of 9, any more and it would be black out.
Astronauts, on lift of only pull about 3 g's, and thats with a seat angle of 90 degrees (no y-axis g's).

just to let you guys know most of you are wrong... the body even untrained has been shown to accept about 17 g's without apparent harm, not to mention the 1973 crash of David Purley in which he experienced 179.8 g's after his throttle got stuck and he hit a wall. he survived. As well as the voluntarily applied g forces that John Paul Stapp experienced equaling 46.2 g's