Kenneth Ellison asked:
How do space vehicles pick up speed by using other planetsí gravity to slingshot them on their way?
Dave - This is a really neat trick which NASA and all the space agencies use called the gravitational slingshot. The way it works is that, because the planets are orbiting theyíre moving. Theyíre not stationary so if you imagine firing yourself if youíre a space probe, going outwards towards a planet. Imagine going just behind the planet. The planetís gravity is going to pull you towards it and because the planet is moving away from you all the time itís going to pull you towards it more than it would do if it were stationary because youíve got to catch up with it as keeps moving away from you. You donít move towards it as quickly as you would have done so you gain energy. Once you have left the planet you actually gain a load of energy from the planet and you slow the planet down a bit.
Chris - Do you have to get the angle of attack or approach to the planet so that as the planet moves away from you it doesnít pull you off course again.
Dave - The whole point is that itís using the planet to pull you off course in a way that helps you. Youíve got to have a very careful approach. If you want to speed up youíre behind the planet . If you want to slow down you go in front of it. Overall this will give you more energy or less energy and get you to where you want to be.