# The Naked Scientists Forum

### Author Topic: Do we really understand the 'Slingshot Effect'?  (Read 5523 times)

#### Joe L. Ogan

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##### Do we really understand the 'Slingshot Effect'?
« on: 14/12/2009 00:20:09 »
Do we really understand the Slingshot Effect?  I have been looking at some of the explanations and they leave me wondering if they are really true?  Thanks for your comments.  Joe L. Ogan

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##### Do we really understand the 'Slingshot Effect'?
« Reply #1 on: 14/12/2009 08:41:56 »
We do, what's basically happening is that the slingshotted object is stealing some kinetic energy off the body it slingshots off.

#### graham.d

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##### Do we really understand the 'Slingshot Effect'?
« Reply #2 on: 14/12/2009 08:43:56 »
I don't see your problem. I think the slingshot ideas are well understood and don't need any great subtlety of insight. The mathematics is calculable and accurate, although I expect numerical techniques are employed in practice. If you have a specific question, that may be easier to address.

#### Fozzie

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##### Do we really understand the 'Slingshot Effect'?
« Reply #3 on: 14/12/2009 11:46:36 »
We do, what's basically happening is that the slingshotted object is stealing some kinetic energy off the body it slingshots off.

OK, so what is the situation where the object is a spacecraft launched from Earth which does an orbit of the sun, then slingshots back past the Earth out into the outer reaches of the Solar System? Energy was put into the spacecraft in the first place to get it into orbit, so if it is stealing some kinetic energy off the body it slingshots off, does that mean even more goes into the spacecraft than would have done if it had not been launch from Earth?

#### graham.d

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##### Do we really understand the 'Slingshot Effect'?
« Reply #4 on: 14/12/2009 14:43:19 »
The maths is well understood but not necessarily easy :-) In the case you describe I don't think you would have any net gain. In order to get into a hyperbolic orbit around the sun you must decrease your orbital velocity below that of the earth from which you are launched. This would be the only way (I think) that you could re-intersect with the earth orbit. Your launch vector will therefore not make best use of your initial orbital speed. Any additional gain on further encounter with the earth would only, at best, put back what you sacrificed by direction of the initial launch.

I think it is possible to get a net gain if you permit use of thrusters (and some fuel) to alter the trajectory at key points.

In theory, with a perfectly (and highly unlikely) set of fortuately positioned planets in a solar system, you can attain very high speeds indeed. The limitation, I believe, is how close you can get to a planet without effects from the atmosphere. I don't think you can get much (if anything) from one planet and a sun when launched from the planet. I could be wrong though :-)

#### Geezer

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##### Do we really understand the 'Slingshot Effect'?
« Reply #5 on: 16/12/2009 02:01:38 »
The maths is well understood but not necessarily easy :-) In the case you describe I don't think you would have any net gain. In order to get into a hyperbolic orbit around the sun you must decrease your orbital velocity below that of the earth from which you are launched. This would be the only way (I think) that you could re-intersect with the earth orbit. Your launch vector will therefore not make best use of your initial orbital speed. Any additional gain on further encounter with the earth would only, at best, put back what you sacrificed by direction of the initial launch.

I think it is possible to get a net gain if you permit use of thrusters (and some fuel) to alter the trajectory at key points.

In theory, with a perfectly (and highly unlikely) set of fortuately positioned planets in a solar system, you can attain very high speeds indeed. The limitation, I believe, is how close you can get to a planet without effects from the atmosphere. I don't think you can get much (if anything) from one planet and a sun when launched from the planet. I could be wrong though :-)

Thanks Graham. Nice post!

#### Zufolek

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##### Do we really understand the 'Slingshot Effect'?
« Reply #6 on: 17/12/2009 14:13:48 »
If you play with some gravity simulation software, it will make more sense. In the real world, there might however be a tiny bit of newbielink:http://en.wikipedia.org/wiki/Flyby_anomaly [nonactive].

#### PAOLO137

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##### Re: Do we really understand the 'Slingshot Effect'?
« Reply #7 on: 28/04/2015 13:34:06 »
Can somebody explain to me in simple words how the slingshot effect is working? If a lighter and fast object passes by an heavy one which we can suppose not moving in the space (with respect to the high speed of the first) it looks to me that the trajectory of the lighter object should be symmetrical with respect of the heavier one. I know to be wrong, but where? Thanks, Paolo, Rome.

#### Colin2B

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##### Re: Do we really understand the 'Slingshot Effect'?
« Reply #8 on: 28/04/2015 14:53:39 »
Can somebody explain to me in simple words how the slingshot effect is working? If a lighter and fast object passes by an heavy one which we can suppose not moving in the space (with respect to the high speed of the first) it looks to me that the trajectory of the lighter object should be symmetrical with respect of the heavier one. I know to be wrong, but where? Thanks, Paolo, Rome.
No you can't assume the heavy planet is not moving, that's the whole point of the slingshot effect, the planet is moving.
Try thinking through with planet moving and come back if you have problems.

#### chiralSPO

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##### Re: Do we really understand the 'Slingshot Effect'?
« Reply #9 on: 28/04/2015 15:18:49 »
Can somebody explain to me in simple words how the slingshot effect is working? If a lighter and fast object passes by an heavy one which we can suppose not moving in the space (with respect to the high speed of the first) it looks to me that the trajectory of the lighter object should be symmetrical with respect of the heavier one. I know to be wrong, but where? Thanks, Paolo, Rome.
No you can't assume the heavy planet is not moving, that's the whole point of the slingshot effect, the planet is moving.
Try thinking through with planet moving and come back if you have problems.

How does the slingshot maneuver appear in the frame of reference of the planet? (...where the planet is not moving...)

#### Colin2B

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##### Re: Do we really understand the 'Slingshot Effect'?
« Reply #10 on: 28/04/2015 17:12:17 »
How does the slingshot maneuver appear in the frame of reference of the planet? (...where the planet is not moving...)
Good question.
If incoming is head on planet would see it as faster than the spacecraft would think it's own v relative to sun, when goes round planet it's outgoing v would appear less than spacecraft view rel to sun. Does that sound right?
If incoming is from behind, spacecraft would appear slower to planet than spacecraft view, until it passed, when it appears to speed up from both frames.
Relatively speaking do you think Planet might have kindly slowed down to let it overtake?

Not sure about the above, talking top of head, need to think! I'll put on some Holst.
Nice courteous planet though

#### wolfekeeper

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##### Re: Do we really understand the 'Slingshot Effect'?
« Reply #11 on: 29/04/2015 16:15:30 »
From the point of view of the planet, the speeds towards and away from the planet are the same.

It's very similar to a bat hitting a ball. The speed of the bat towards a ball is (ignoring some losses in the collision) the same as the speed of the bat away from the ball afterwards. But of course the bat is moving!!!

The slingshot effect is the same; the planet is moving and you bounce off the planet- except because gravity is attractive you swing behind the planet and get pulled, but otherwise it's exactly the same principle.

#### chiralSPO

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##### Re: Do we really understand the 'Slingshot Effect'?
« Reply #12 on: 29/04/2015 19:21:22 »
From the point of view of the planet, the speeds towards and away from the planet are the same.

It's very similar to a bat hitting a ball. The speed of the bat towards a ball is (ignoring some losses in the collision) the same as the speed of the bat away from the ball afterwards. But of course the bat is moving!!!

The slingshot effect is the same; the planet is moving and you bounce off the planet- except because gravity is attractive you swing behind the planet and get pulled, but otherwise it's exactly the same principle.

That was my intuition, but I wasn't entirely sure. I am glad to see that it was correct :-)

#### diethyl

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##### Re: Do we really understand the 'Slingshot Effect'?
« Reply #13 on: 30/04/2015 06:54:01 »
I just simply think of it as 'very very fast'. [:I]

#### PAOLO137

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##### Re: Do we really understand the 'Slingshot Effect'?
« Reply #14 on: 09/07/2015 19:30:20 »
Thanks for all the comments. My original mistake was based on the assumption that the "heavy" body was at rest.
I figured out the lighter body approaching the heavy one, accelerating like falling pulled by the gravity. Then , symmetrically, the lighter object goes away with a slowing down speed symmetrical to the incoming trajectory.

#### wolfekeeper

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##### Re: Do we really understand the 'Slingshot Effect'?
« Reply #15 on: 09/07/2015 21:54:14 »
There's always a heavy body that is 'at rest', for the purposes of the slingshot.

In the solar system, that's the typically the Sun- you're trying to gain (or lose) energy relative to that, but you can also slingshot around the moon relative to the Earth, to gain speed relative to the Earth.

#### The Naked Scientists Forum

##### Re: Do we really understand the 'Slingshot Effect'?
« Reply #15 on: 09/07/2015 21:54:14 »