jennings@AEROSPACE.ARPA (Richard K. Jennings) (11/16/85)
Consider a small space probe passing close to (within the gravitational field of) a somewhat larger mass (say the planet Jupiter). Jupiter is speeding around the Sun. Mutual attraction causes the probe to (negligibly) pull Jupiter along its velocity vector (proportional to its mass) and vice versa -- except the force exerted by Jupiter is much much larger. Since Jupiter has more mass, the force exerted by the probe isn't easily observed. Since the probe is quite light, and Jupiter's gravitational field is quite strong, an easily observable acceleration is observed. In short, Jupiter through the wonders of gravity imparts a very small fraction of its *orbital* energy to the probe -- which then goes shooting out of the solar system like a bat of of h*ll! This effect is also possible with the Sun, since the Sun is also moving. Previous comments pertaining to the efficient use of propellant in gravity wells, while true, do not account for the energy gain produced by the slingshot effect. Regards, Rich