Let me see if I can explain this. The secret is thinking about it in the right frame. In this case, that is the center of mass of the planet and spacecraft. in this frame, the planet appears to be moving very slowly in from (say) the left and the spacecraft is coming in very fast from the right, accelerating as they approach each other (again, the planet hardly changes its speed but the satellite is accelerated quite a bit). after they pass each other, they start to both decelerate until, when they are far away, they have the same speed as when they both started just as you expect. Now, however, switch your view to the orginal frame. The speed of planet has hardly changed by its encounter with the spacecraft but its moment has decreased. The decrease in the planet moment's must be balanced by an equal increase in the spacecraft's momentum (which is mass times velocity). Since the relatively light weight spacecraft has gained the momentum that the massive planet lost, its change in velocity must be huge. Incidently, you can slow a spacecraft down by approaching it from the direction that the planet is moving in. NASA used this reverse sling shot when it sent a space craft to venus (or was it mercury?) in a very long and complicated trajectory. I hope that helps. Best, Geoff Quoting Jeff Umbarger <jumbarger2000@yahoo.com>: > Hey All, > I know that this is somewhat off thread but can > someone explain how a planet can "slingshot" a > satellite that has come near it at a *higher* velocity > than before the satellite reached the planet? Here is > where I struggle with this idea: if satellite is > approaching a planet, then that planets gravity should > begin to accelerate that satellite towards it. But as > the satellite *departs* the planet after making > closest approach that same gravity should decelerate > the satellite by just as much - with no net positive > gain, right??? > > Regards, > Jeff Umbarger > ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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