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V infinity

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#1 Mr Astro

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Posted 27 July 2019 - 07:22 AM

Hello,

 

Can any one give more details about V infinity in the attached pictures..

couldn't get the meaning.. while the V relative is clear..

i am wondering what is massless earth ?:confused:

 

Thanks 

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Edited by Mr Astro, 27 July 2019 - 07:26 AM.


#2 Mr Astro

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Posted 27 July 2019 - 07:24 AM

att. 2

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Edited by Mr Astro, 27 July 2019 - 07:27 AM.


#3 StupendousMan

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Posted 30 July 2019 - 07:27 PM

The quantity "V infinity" represents the speed that an object would have if it were to fly through an alternate universe in which everything was exactly the same as ours -- except that Earth was a little pebble of negligible mass.  

 

The point is that the real Earth is massive enough to modify the speed and direction of asteroids or other objects which fly past it.  Suppose that a rock moving through the Solar System just happens to zoom past the Earth.  As it comes within a few million km of the Earth, it starts to fall into the Earth's gravitational field, and speed up.  When it flies past the Earth, it will be moving very fast, due in part to the energy it gained by falling towards the Earth.  As it flies away from the Earth, it slows down, as it is now pulled backwards by the Earth's gravity.  

 

"V infinity" is the speed that it would have had, at its closest approach to Earth, if the mass of the Earth had not pulled on it and sped it up.



#4 llanitedave

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Posted 01 August 2019 - 10:41 AM

I'm not sure what the utility of the "V infinity" concept even is.  It basically creates a "what if" scenario of the Earth not being there.  But the Earth is there, and it would seem we're better off simply acknowledging reality.



#5 EJN

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Posted 01 August 2019 - 04:28 PM

I'm not sure what the utility of the "V infinity" concept even is. It basically creates a "what if" scenario of the Earth not being there. But the Earth is there, and it would seem we're better off simply acknowledging reality.


V infinity is used in calculations of other orbital elements, the semi-major axis (a), and the eccentricity (e).

Edited by EJN, 01 August 2019 - 04:34 PM.


#6 llanitedave

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Posted 01 August 2019 - 04:36 PM

V infinity is used in calculations of other orbital elements, the semi-major axis (a), and the eccentricity (e).

Do you mean to backtrack the orbit of a body that we're unaware of until close approach?



#7 EJN

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Posted 01 August 2019 - 09:16 PM

Do you mean to backtrack the orbit of a body that we're unaware of until close approach?

 

Not exactly, it can be considered initial conditions if the Earth wasn't there, from

which you can compute the deflection during flyby. Locally it can be described

as a hyperbolic transition from one ellipse to a (slightly) different one.

 

Knowing Vinf and the mass of the Earth allows the calculation of the amount the

initial trajectory is deflected by, called the impact parameter.

 

See this:

http://curious.astro...ravity-advanced


Edited by EJN, 01 August 2019 - 10:56 PM.


#8 llanitedave

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Posted 02 August 2019 - 10:55 AM

Not exactly, it can be considered initial conditions if the Earth wasn't there, from

which you can compute the deflection during flyby. Locally it can be described

as a hyperbolic transition from one ellipse to a (slightly) different one.

 

Knowing Vinf and the mass of the Earth allows the calculation of the amount the

initial trajectory is deflected by, called the impact parameter.

 

See this:

http://curious.astro...ravity-advanced

Thanks.  I've done a number of toy n-body orbital calculations, but flyby characteristics is never something I looked into.  I'm still not comfortable with the wording of the description here, though.  It's not so much the velocity of the object if Earth wasn't there, it's the initial velocity of the object before the beginning of the encounter, as I read it.  There may be nuances that I'm missing.



#9 Mr Astro

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Posted 08 August 2019 - 05:17 PM

Thank you all for enriching the post..

As i got your points and not a pro. in physics .. i end up with the following:

V infinity is calculated to get more information about any moving objects approaching the solar system and make a good picture of the values of that objects in their journey in space.

while its a supposed value but it gives more accurate calculations about the moving things near us..smirk.gif

  


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