Inside the loop or outside the loop.

[therealcrow999]

This question is about real life rockets. This would be easier to answer thinking of the craft of the Gemini missions.

I got a question about when the rocket turns east doing the orbital inclination, are the astronauts inside the loop for the turn? Like are their heads toward the ground or are they on the outside of the loop doing a negative G turn, with the stars above them?

Some stock footage I was looking at from Gemini launches and the missions, they look like they are on the outside of the loop. So when they are done with the turn they have the ground below them, like if they were in a jet aircraft.

Because the way the default set up of a capsule in KSP, they are set up to do the east turn sideways. I tried rotating the capules left from default so when rocket takes off its on the outside of loop. When craft levels off in orbit, the navball look normal, as if what a pilot would see in earth atmosphere. The blue area on top and brown ground on bottom.

[FlamedSteak]

To be honest, I don't really care about my rotation until I get out of the atmosphere. And only then because it make navigating a little easier when docking.

[FITorion]

I'm not sure about the Gemini and Apollo era rockets. I don't think it'd matter too much in terms of +or- g on the crew in a capsule since they're directly over the thrust vector.

I do Know that the Shuttle rotated to be heads down or inside the loop as you put it almost immediately after launch.

[Urban_K]

Apollo: Inside/down.

[Pipcard]

Inside the loop, because the human body has a lower tolerance for negative Gs.

[Kasuha]

For astronauts it is irrelevant whether they travel with their heads towards Earth or towards space, the only force they feel is pushing them against their ship's engines.

[SpaceSphereOfDeath]

Inside, where they experience positive gee's.

Outside, they would have negative gee's and that could lead to SPONTANEOUS UNPLANNED DIS-ASSEMBLY OF YOUR SKULL

[Starwhip]

Inside, where they experience positive gee's.

Outside, they would have negative gee's and that could lead to SPONTANEOUS UNPLANNED DIS-ASSEMBLY OF YOUR SKULL

I gots an ideases...

[Traches]

The gravity turn is caused by exactly that -- gravity. You pitch over a few degrees at launch, and then let gravity pull your prograde vector down towards the earth as you accelerate. Since gravity pulls on everything exactly the same, there are no positive or negative G's to worry about, except for those created by the rocket engine.

[KerbMav]

Because the way the default set up of a capsule in KSP, they are set up to do the east turn sideways. I tried rotating the capules left from default so when rocket takes off its on the outside of loop. When craft levels off in orbit, the navball look normal, as if what a pilot would see in earth atmosphere. The blue area on top and brown ground on bottom.

This is by design to make it easier for the player to comprehend what is going on:

Visualizing the turn to the east while looking south-north onto your rocket, pressing the right-arrow key to turn the craft in the same direction ...

What you did is easy to do after playing for some time, because you learned to think with what the navball tells you, not what the craft looks like.

The gravity turn is caused by exactly that -- gravity. You pitch over a few degrees at launch, and then let gravity pull your prograde vector down towards the earth as you accelerate. Since gravity pulls on everything exactly the same, there are no positive or negative G's to worry about, except for those created by the rocket engine.

Someone in the mood to calculate the forces that are perceived by the crew of a rocket travelling at x m/s and flying a curve of y degrees?

And compare it to the force of its acceleration?

Edited October 30, 2013 by KerbMav

[Kasuha]

Someone in the mood to calculate the forces that are perceived by the crew of a rocket travelling at x m/s and flying a curve of y degrees?

And compare it to the force of its acceleration?

Engine - pushes the rocket in the direction of its movement (gravity turn)

Atmospheric drag - pushes against the movement, i.e. directly against engine acceleration

Gravity - pulls everything with the same force, cannot be perceived within the cabin frame of reference

Gravity has zero effect, coriolis effects are negligible, the only thing they feel is engine acceleration minus atmospheric drag.

If the rocket was not doing gravity turn i.e. engines were not accelerating directly prograde, they might feel effects of atmospheric drag. They would probably feel many other things too as the rocket would probably disintegrate in such situation.

[DChurchill]

Didn't Gemini go up sideways? That is with the astronauts on their side?

Edit: can't find anything on a Google search, but I swear I read it somewhere. Something with the Titan guidance system caused it.

Edited October 30, 2013 by DChurchill

[Pipcard]

For astronauts it is irrelevant whether they travel with their heads towards Earth or towards space, the only force they feel is pushing them against their ship's engines.

Inside the loop is essentially like pulling up towards the horizon (positive Gs)

Outside the loop is essentially like pulling down towards the horizon (negative Gs)

[KerbMav]

.

Arent they lying on their backs in the seats actually, belly towards the top of the rocket? Then it is the same as sitting in a plane flying almost vertically upwards.

The rocket is flying a curve, so changing its flight vector continuously, which creats g-effects like pulling/pushing a plane up/down, depending on the rotation of the rocket/capsule.

[Smidge204]

Inside the loop is essentially like pulling up towards the horizon (positive Gs)

Outside the loop is essentially like pulling down towards the horizon (negative Gs)

No. I have no idea how this even comes up. To be honest I don't even know what "positive" and "negative" mean in this context.

If you cut the engines, and neglect air resistance, crew would experience no G-forces. They would be in a free-fall trajectory along with the rocket and thus feel "weightless." This is exactly what an orbit is, BTW.

Ideally, the turning of the rocket is done by gravity, as already explained. That means the only force the crew experiences is net force of the rocket minus air resistance pushing them from directly behind, because that's the only force present that's not present during an orbit.

A rocket is not like a car, where you feel "pushed" to one side when you take a sharp turn. In that scenario, the force causing the turn is the friction between the wheels and road, and the only way that force can be transmitted to you is through contact between you and the vehicle. This is not true for ballistic trajectories because the "turning force" - gravity - is applied directly to you.

Now, in the "reality" of KSP the rockets don't really turn by gravity... they are forced to turn. In this case and this case only, There would be an additional, not-aligned-with-thrust-vector force. However, that force would be radial to the curve and would be entirely "positive" if you use a sensible frame of reference. There might be a difference in the magnitude of the force from one side of the pod ("inside") to the other ("outside") but since the difference in radius would be measured in parts per thousand it would be completely undetectable and insignificant to the crew. Remember that the radius of the turn is on the order of kilometers (10km+) while the height of the crew would be less than two meters.

F = (m*V^2)/r

Change r by +/-0.01% and see who gives a Kerbal's ass!

=Smidge=

Edited October 30, 2013 by Smidge204
Clarified some wording

[KerbMav]

When talking about flying and steering, g-forces are not quite the same as gravity.

Here g-forces describe the feeling you have on a swing or a karussel or what keeps water in a bucket if you swing it real fast over your head - which pushes blood into your head or feet, depending on positive or negative g.

[AmpsterMan]

For what it is worth, I like to curve with the Kerbals' heads toward the ground just because that is what the shuttle did.

[KerbMav]

A rocket is not like a car, where you feel "pushed" to one side when you take a sharp turn.

My old buddy Newton would like a word with you.

Whenever an object that moves at a specific speed in a straight line (or sits still, which is basically the same from the POV of said object) is made to move in another direction or change its velocity it experiences a force, g-force, because of the laws of inertia. My question aimed at, if the curve the rocket flies during its gravity turn - and at a very high speed that is - would exert a noticalbe force on the crew in regards to the acceleration forces they experience by the rocket firing and getting faster.

In that scenario, the force causing the turn is the friction between the wheels and road,

Stop right there!

The force the driver feels is caused by the car starting to go into a different direction.

This is not true for ballistic trajectories because the "turning force" - gravity - is applied directly to you.

Again, g-forces deal with inertia, not gravity.

Now, in the "reality" of KSP the rockets don't really turn by gravity... they are forced to turn.

Irrelevant, they are forced to turn, and that is what it is all about.

In this case and this case only, There would be an additional, not-aligned-with-thrust-vector force.

The thrust vector is changing as the rocket turns.

Imagine being grabbed by the hand by someone running who suddenly runs around a corner.

However, that force would be radial to the curve and would be entirely "positive" if you use a sensible frame of reference. There might be a difference in the magnitude of the force from one side of the pod ("inside") to the other ("outside") but since the difference in radius would be measured in parts per thousand it would be completely undetectable and insignificant to the crew. Remember that the radius of the turn is on the order of kilometers (10km+) while the height of the crew would be less than two meters.

You are so close!

Yes, the crew would not feel a difference between the force exerted on their heads or feet, but the force as a whole ... ?!

Edited October 30, 2013 by KerbMav

[csanders]

My old buddy Newton would like a word with you.

Whenever an object that moves at a specific speed in a straight line (or sits still, which is basically the same from the POV of said object) is made to move in another direction or change its velocity it experiences a force, g-force, because of the laws of inertia.

A body in low Earth orbit is accelerating at 9.8m/s^2, but experiences 0 Gs.

My question aimed at, if the curve the rocket flies during its gravity turn - and at a very high speed that is - would exert a noticalbe force on the crew in regards to the acceleration forces they experience by the rocket firing and getting faster.

Yes, the rocket is putting force on the crew, straight up through the stack. The crew (generally) are laying down facing up. It doesn't matter which way the rocket is rotated.

[AmpsterMan]

For wharever reason, I feel like a person with the ground below and behind them, experiencing a gravity turn, would be lifted slightly off the chair and pushed back into it. With the ground above it would be an opposite sensation.

[legodragonxp]

The space shuttle went up in to space inverted as part of the safety protocols should they need to separate from the tank prematurely (after SRB separation, tank separation prior to SRB separation is not an option). Once in space the shuttle normally remained inverted due to the needs of the radiators in the cargo bay doors unless dictated by mission parameters.

With 3g of launch force I do not think the effect the earth is all that great by being inverted (even after the initial roll), they are pretty much pinned in their seats during launch. Once the force is done they are in free fall.

[Traches]

Kerbmav, it's great that you've studied a little physics, but I promise you're mistaken.

In the real world, a gravity turn isn't "Fly to 10km, then pitch over to 45 degrees and burn till your apoapse is at 75km." Once clear of the launch tower, a real rocket will pitch over a few degrees (5 or so) and then gimbal the engines straight. It essentially pulls no lateral g's from then on-- only forward acceleration from the engines. Gravity does the rest-- it slowly pulls the velocity vector down towards the surface, so you are pointed more and more towards the horizon as you climb and accelerate. You basically let the rocket slowly "tip over" on its way up to orbit.

Since gravity is the only force acting laterally, and everything accelerates due to gravity at precisely the same rate, the occupants of a rocket feel no lateral g's during a launch.

[Eric S]

Whenever an object that moves at a specific speed in a straight line (or sits still, which is basically the same from the POV of said object) is made to move in another direction or change its velocity it experiences a force, g-force, because of the laws of inertia.

By the same logic, astronauts on the ISS would be pushed towards the "ceiling" instead of being in free fall. Instead, since every force that acts on the astronauts also acts on the ISS, the astronauts fall along the same path the ISS is taking. Since there's no difference in the path taken by the ISS and the astronaut, the ISS exerts no force on the astronaut to keep the astronaut confined within the ISS.

The reason the force of the wheels of a car was brought up for why you felt the turn is because that force is applied to the car, not to the passenger, causing the paths to diverge, which means that some force has to pull the passenger back into a path matching that of the car. This force is what you're feeling.

In the case of a rocket launch, there are only two forces that will act on the rocket but not the astronaut. The rocket's thrust, and atmospheric resistance. Since both of these forces are parallel to the movement of the craft, the net force is parallel to the movement as well. Hence the only force the astronauts feel is being pushed towards the direction of acceleration, which is to say, forward.

Gravity and intertia both affect both the rocket and the astronaut, any affect they have would have the same result on the rocket and the astronaut, meaning that their paths don't diverge, meaning that the astronaut won't feel anything from those forces.

Now, if the rocket were turning because the rocket was thrusting in a direction other than the one that it were moving in, then yes, the astronauts would feel some side to side force because atmospheric drag and thrust aren't parallel, resulting in some force not directly in line with the rocket. However, the point of a real gravity turn is that gravity itself is causing your trajectory to not follow a straight line.

[Smidge204]

My question aimed at, if the curve the rocket flies during its gravity turn - and at a very high speed that is - would exert a noticalbe force on the crew in regards to the acceleration forces they experience by the rocket firing and getting faster.

And the answer, again, is No... for the exact same reason that a crew in orbit does not experience a noticeable force. Provided it's a proper gravity turn, and not a forced turn.

If it's a forced turn, you can do the math for whatever radius and velocity you want to know about. If it's anything significant, chances are your rocket has spontaneously disassembled itself, or will very shortly.

=Smidge=

[csanders]

And the answer, again, is No... for the exact same reason that a crew in orbit does not experience a noticeable force. Provided it's a proper gravity turn, and not a forced turn.

If it's a forced turn, you can do the math for whatever radius and velocity you want to know about. If it's anything significant, chances are your rocket has spontaneously disassembled itself, or will very shortly.

=Smidge=

Even then, if you are "turning" with a rocket, that's done by rotating the rocket and having it's thrust vector be non-parallel from the velocity vector. Which again produces almost no lateral force.

EDIT: assuming one is in little to no atmosphere. If one is in atmosphere, any significant lateral force produced from drag would likely tear the rocket apart.

Edited October 30, 2013 by csanders