JPL Suggests Bouncing Off A Planet to Reach Another Available to Purchase

Space‐age Tarzans will substitute gravity for vines. Just as the Jungle Boy uses the tension in a conveniently placed suspension to lose potential energy he doesn't want and gain a momentum directed toward the place he wants to reach, interplanetary explorers should use gravitational acceleration from appropriately placed planets to whip them around into the trajectory they need. So says Gary Flandro of Jet Propulsion Laboratory, who has computed some journeys you can make that way in the 1970's.