I have gone through the slingshot for the Juno with the earth. I have also seen the train and ball example as given by NASA. [http://solarsystem.nasa.gov/basics/grav/primer.php]

But, I am still unable to visualize and think on how it is working.

My assumption and thinking:-

So, earth gravity will be more when the Juno is close to it and the vehicle have to maintain its constant speed [not more and not less, since it will go out of the track or it will fall in the earth]. So it is doing a elliptical rotational around the earth.

Original Juno Path: enter image description here

So, we are starting to slow the speed at the point "A" and juno will travel along with the earth, due to gravity, upto point "B". Lets consider it is going to acquire the speed of some "5 kms". And while it reaches the point "B", we are going to apply extra speed by turning on the main ignition, to escape from the earths' gravitational orbit and to follow back the juno's orbit and we are going to turn off the main engine back and allow the juno, to travel with its original speed.

"A" and "B" points, just marked approximately.

Since, juno crossed the earths' gravitational pull, [and no more earth's gravity is applicable] the juno will travel with the extra gained speed in some straight line/or its own elliptical orbit, and since in space there is no resistance to reduce its speed so it will not lose the speed unless some thing is happening.

This is what I am assuming.

So my question is :-

  • In the original image, the earth is not in the center of the elliptical path of the juno.

My Image Path:-

enter image description here

  • Regret for the bad drawing skill. Lets assume the earth be in the center of the juno's slingshot travel.

    1. If the earth's flyby is providing extra speed to the vehicle, why the juno is following its own trajactory path. It can loop the earth continuously as much as possible, so it will travel with more speed like more than "5kms" and after some time, we can turn on the main ignition to escape from the earth gravitational pull. Right.. Why they have decided the juno's some thing to be different?

    2. Is there any reason why, we have to maintain some distance between the surface of the earth and the juno. I mean, the elliptical path seems to be away from the earths atmosphere atleast by some 100kms.

    3. Is there any reason/advantage why the juno have to follow some thing like the perigee and apogee position as the earth is doing with the sun or the moon is doing with the earth.

Could somebody one, kindly correct me/my assumption and the thought, if wrong.


  • $\begingroup$ That link is dead. Possible replacement: Interplanetary Trajectories $\endgroup$
    – user10509
    Aug 7, 2016 at 11:11
  • $\begingroup$ The link isn't dead, it just contains one ] too much at the end. Correct link: solarsystem.nasa.gov/basics/grav/primer.php $\endgroup$
    – Polygnome
    Aug 7, 2016 at 21:18
  • $\begingroup$ Hi @Polygnome I have seen the link which u pinged, already. But still I am unable to understand. Could u kindly help me to understand... Thanks. $\endgroup$ Aug 8, 2016 at 2:59
  • $\begingroup$ Not really. A lot of your assumptions seem either to be flat out wrong or explained in a way that they don't make any sense. If you want to understand gravity assists, don#t make any assumptions. only newtons three laws + the law of universal gravitation, and then read the link again. $\endgroup$
    – Polygnome
    Aug 8, 2016 at 8:00


Browse other questions tagged or ask your own question.