What you are describing is similar to the Scottish dance, "Strip the willow," where people pull around each other. The flaw is the acentrists inherent assumptions as to the size of the so-called 'solar system'. There would simply be nothing close enough to overcome Jupiter's gravity. Regards, Neville. Ok ... so ignoring Jupiter and just coming closer to easily discernable gravitational bodies, "strip the willow" can in fact work a slingshot manouvre as I described. Can you discuss the physics, without being sidetracked by the accentrists flawed assumptions. I am not an accentrist, and I am not making assumptions. Since I last posted I discovered some more detailed information which also makes more sense and adds energy to my projectile. As usual I convert the math to practical realities, so that all can see my point. When a cricket ball is hit by the force of the bat swung with great force, some of the batsmans energy is added to the ball. The back swing sends it for six behind the wicket. Do the vectors. If I threw a "perfect bouncy ball" at the moon as it was coming towards me over the horison at thousands of miles per hour, (GC speed) It would hit the ball like a cricketers bat, and bounce it off even further into space, adding part of its own kinetic energy . Do the vectors. I followed the vectors. The equations made no sense to me. But you can verify them for me if you will Neville. At the following sites. http://www.mathpages.com/home/kmath114.htm http://www.egglescliffe.org.uk/physics/gravitation/slingshot/sling.html gravity like a magnetic field would I think make for an almost perfect bouncy medium for transferring energy or work.Therefore as in practise we cannot bounce our projectile off the surface, we can bounce it off by absorbtion in the gravitational field. A poor analogy of what I mean. A diagram should not be needed, but consider a cricket ball that is a theoretical North magnetic Pole being thrown at velocity in the direction of rotation close to a rotating South magnetic field. Ok so its Don Bradman swinging his bat which has a south polarity at its extremity. Its a close miss pass the end. No collission damage. But no doubt the ball will get an injection of momentum... (Basic electric motor?) regards, Philip.