Dr. Jones, I remember actually hearing the explanation for a slingshot on network tv during what would have otherwise been and enjoyable cartoon time. Never liked the moon launches for that reason. Looking at them now it is easy for me to gravitate (pun intended) to the word "preposterous", but this does leave me close-minded the proponents would say. Therefore, I'll remain open enough to hear the reasoning, but I can't off-hand see how it would gain momentum for the reason you spelled out to Philip below. Whenever one tries to maintain a curve in a car at a steady speed, and then speeds up, does he not risk flying off the boundary of the curve? Then what direction is he going? Of course, one could argue easily that I am neither a professional driver nor a trained astrophysicist, but it seems a very difficult proposition to have a space probe match a planetary rotation at the right height off that planet so that the whole thing works. I am open, but I'd like to have that explained.... Sincerely, Gary Shelton > Philip, <snip> This is why I said that the acceleration it received on approach would be completely negated by the deceleration it experienced on recession. > > Besides all this, the accuracy required for this science fiction manoeuver, over billions of kilometres, is absurd. I will not produce detailed mathematics on the forum, because many would not follow it. I appeal to your common sense and everyday experience instead. <snip> > The alleged probe would be pulled back, with a force that is basically the same strength and the opposite direction to that which it would have received on approach. Gravity slingshots are nonsense. > > Neville. > -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.300 / Virus Database: 265.8.7 - Release Date: 2/10/05