For every action there is an equal and opposite reaction...

[7499275]

I was watching a show on tv the other day that said because of this law of physics every rocket launch (especially the Saturn V launches because it was so powerful) will eventually millions of years from now will throw the earth out of its perfect orbit. I'm confused, if every action has an EQUAL but OPPOSITE reaction, wouldn't that not affect the earth at all? because the earth would push back "up towards" the Saturn with as much force as Saturn is pushing down.

Maybe I'm missing a key little bit of information I'm not sure could someone please clear this up for me?

[andrewas]

Draw all the interactions. Rocket throws exhaust out the back. Exhaust dumps its momentum in the atmosphere which in turn pushes on Earth. The net effect is that Earth is pushed 'down' with the same force that is pushing the rocket 'up', at least while the rocket is still flying vertically, it gets a bit more complex after it starts to pitch.

However, this is a tiny effect due to the Earth's much higher mass than the rocket, and its not in a consistent direction, so it won't be changing Earth's orbit any time soon.

[7499275]

Wait... That law only states that in Saturn context... The force pushing "down" is essentially what moves the rocket "up" and not the rocket it self?

[K^2]

Whoever said that does not understand anything about celestial mechanics. With the exception of the few launches that result in debris or ships escaping Earth's gravity completely, all of the things either remain in Earth's orbit or decay back to Earth. That means that the total momentum of the Earth system is preserved, and Earth will continue on the same exact trajectory around the Sun, no matter how many satellites we launch.

[Kerbin Dallas Multipass]

There are no perfect orbits in the universe. Everything is elliptical and wobbly, Nothing will last until eternity.

Earth is subject to all sorts of quite significant forces and changes. There are tidal forces, pressure by solar wind, loss of mass by blown away atmosphere, gain of mass by captured asteroids and probably even aerodynamic drag since space is not a perfect vacuum. Similar for the sun: It is blowing vast amonts of matter into space and therefore changes mass which influences earth's orbit.

Compared to these forces a saturn V is... well.. .undetectable. Even if you launch billions of them without returning anything to earth

[78stonewobble]

Well according to wikipedia the mass of the earth is 5,97218 x 10 to the 24th power.

Meaning, if I do this correctly, that the earth "weighs":

5.972.190.000.000.000.000.000.000 Kg ...

I'll let someone much more savvy at maths attempt to calculate how many saturn 5's on mountain tops (or more likely xx km high towers) we would need to fire to catastrophically change the orbit of the earth.

I think that it will take more saturns than there is room for, or even mass enough in the earth to build.

[7499275]

This show said it would barely alter the orbit, just by a few km, in millions of years.

[lajoswinkler]

The effect is negligible and undetectable. Statistical noise and falls into the domain of the chaos theory.

Was it by any chance aired on Discovery channel?

[thescientist]

This show said it would barely alter the orbit, just by a few km, in millions of years.

The Moon has a much stronger effect, and we didn't launched it with a rocket. Dont' worry about the Saturn V.

[ZetaX]

As K^2 already said, it won't change the orbit at all, and not due to being irrelevant but due to how impulse works.

[7499275]

As you guys asked the channel I believe it was either History or National Geographic.

[deadshot462]

Any impulse changes due to rocket launches is dwarfed by the superior amount of space debris (meteors, etc.) that hit the Earth every year.

[softweir]

Well according to wikipedia the mass of the earth is 5,97218 x 10 to the 24th power.

Meaning, if I do this correctly, that the earth "weighs":

5.972.190.000.000.000.000.000.000 Kg ...

I'll let someone much more savvy at maths attempt to calculate how many saturn 5's on mountain tops (or more likely xx km high towers) we would need to fire to catastrophically change the orbit of the earth.

I think that it will take more saturns than there is room for, or even mass enough in the earth to build.

I am sure I have heard it said that even if the moonshots had missed and gone into interplanetary space, the change in Earth's orbit would have been down at the subatomic-particle scale.

@O.P.: You mention the Earth's "perfect orbit". It doesn't have one. It's elliptical, and prone to tiny shifts due to gravitational interactions with other, larger planets such as Jupiter. Not to mention that 28-day wobble caused by our moon!

[MatixCubix]

Well, This perfect orbit is more like an orbit in the future If the rocket didnt launch, now as most people here might know,

a little change in speed over an enormous lapse of time, would create a quite different distance from the original without that acceleration (this is wrong for orbits) Edited

,And is important to add that gravity follows the R^2 so a change in distance between 2 celestial objects (for ex: Earth and jupiter) would create a quite difference also in the attraction between both, and thus changing alot more its original orbit.

Edited January 7, 2014 by MatixCubix
I said something false

[K^2]

Well, This perfect orbit is more like an orbit in the future If the rocket didnt launch, now as most people here might know, a little change in speed over an enormous lapse of time, would create a quite different distance from the original without that acceleration

Orbits don't work this way. Earth's orbit is stable. So a small deviation results in planet still returning to the point at which deviation occurred a year later.

[MatixCubix]

Orbits don't work this way. Earth's orbit is stable. So a small deviation results in planet still returning to the point at which deviation occurred a year later.

Yes, I got a little confused by that statment I said , you are correct, the statment I said is only available if it is a liniar movment (and dosen´t come back later at the original place that was accelerated). Imagine we have a system of 2 orbits and the celestial objects orbiting we have, do not interact gravitationally ( because in this example the 2 orbits are the 2 probabilities of orbits that we can have if and if not we launch the rocket) , well let´s say that one orbit is more excentrical than the other and the periapsis (because the excentrical orbit apoapsis is higher than the other orbit apoapsis) of the more excentrical orbit passes through the first orbit trayectory, the distance of both would have a pattern and they might even crash if we had enough time, now lets imagine we have another celstial object that interacts with both, and it has a higher orbit rotating the same way as the others, the more excentrical orbit would be more close to this orbit and it would cause a more stronger gravity assist and this would cause a much more different orbit than the original, so in conclusion the change of the orbit would be variable(if we have the masses constant) by the speed of both object and the distance between both.

I got confused when you said year, is year an entire rotation of the new orbit? or is it a time period?

Edited January 5, 2014 by MatixCubix
Didnt explain well the model , lol

[K^2]

Imagine we have a system of 2 orbits and the celestial objects orbiting we have do not interact gravitationally

If you assume something that's false, you can arrive at any conclusion you like. Real planets interact. Their orbits are stable even with respect to each-other.

I got confused when you said year, is year an entire rotation of the new orbit? or is it a time period?

I was just being lazy. Since we are talking about planets, by "year", I mean one full revolution around the parent star. So yeah, the former. But if we are talking about Earth, there shouldn't be a difference, since changing period requires significant change in semi-major axis, which you won't get with any minor boost. So it should be the same thing to any significant precision.

[MatixCubix]

If you assume something that's false, you can arrive at any conclusion you like. Real planets interact. Their orbits are stable even with respect to each-other.

Yeah, when I referred to the two orbits the more eccentric orbit was the result of the diversion created by the acceleration, so when I said that the two do not interact is because in reality there is only one

Sorry for dont explaining that

[Drunken Hobo]

I did read something quite plausable on the same subject. I can't remember the numbers exactly, but it was something like a single Saturn V rocket launch would change the position of Earth in its orbit by 60° over a few hundred million years.

The concept was to demonstrate why we can't predict Earth's orbit accurately over very long timescales, rather than any genuine fear that rocket launches will ruin Earth's orbit. If even a rocket launch can change it that much, then imagine the unpredictability caused by plate tectonics, asteroids etc.

[K^2]

I did read something quite plausable on the same subject. I can't remember the numbers exactly, but it was something like a single Saturn V rocket launch would change the position of Earth in its orbit by 60° over a few hundred million years.

No, it wouldn't. Earth system's barycenter would continue on exactly the same orbit.

[Kerbin Dallas Multipass]

No, it wouldn't. Earth system's barycenter would continue on exactly the same orbit.

Even if the Saturn V was .. like ... huge? The size of the moon for example?

[K^2]

Even if the Saturn V was .. like ... huge? The size of the moon for example?

If it was size of the Moon, the Earth-SV system would interact with other planets a little differently, which could result in a difference. But from a rocket launch, you take a tiny perturbation to Earth's position times tiny perturbation from interaction with the planets, yielding a perturbation so tiny that it does absolutely zip.

What these people did was actually take the momentum of the rocket out of Earth's. And that's not how it works, because Saturn V does not escape Earth's gravity. So total Earth system momentum remains the same. It might get distributed slightly differently between Earth, Moon, and all satellites natural or artificial, but the total is exactly the same, resulting in exactly the same motion of Earth system around the Sun.

[Kerbin Dallas Multipass]

@K^2 Parts of it do seem to leave earth/moon gravity system http://forum.kerbalspaceprogram.com/threads/48694-Strange-Asteroid-J002E3

I understand this as a hypothetical discussion and agree with you thus far that it causes no measurable change (as I posted above), but I'm skeptical that it causes no change at all.

[K^2]

That's not result of a Saturn V launch. That's a result of a specific mission. Yes, Lunar missions ejected some junk from the system. This would make a contribution. But Saturn Vs were also used to launch Skylab. That resulted in no debris leaving Earth system. I've pointed out that there are some insignificant exceptions in the first post I've made in this thread. But claim that Saturn V launch causes any changes to Earth orbit is false. The launch itself does absolutely nothing. If you end up accelerating something past escape velocity, that's a different story.

[Kerbin Dallas Multipass]

EDIT: I'm trolling. No need to answer this seriously.

K^2

If there was a headline "SATURN LAUNCH TURNS DAY INTO NIGHT (in 1,2 billion years)" would you say yay or nay?

Edited January 6, 2014 by Kerbin Dallas Multipass