How Does The Slingshot Effect (Or Gravity Assist) Work To Change The Orbit Of A Spacecraft?
“It’s called Gravity Assist. Overcoming gravity is all about velocity. Escaping Earth’s gravity requires approximately 25,000 mph. Escaping the Solar System needs more than 45,000mph. We don’t have a large enough rocket to achieve that speed so spacecraft can use a planets gravity to increase its velocity and then the planet can “slingshot” it onto a new trajectory toward the next target. The gravity of a large object can “pull” something to a higher velocity and then, rather than crash into the object, the craft can just miss the planet or moon and, for a moment, go into orbit.
gravity assist Also known as the slingshot effect, an important spaceflight technique used successfully on a number of interplanetary missions, including Voyager, Galileo, and Cassini, whereby the gravitational field of a planet is used to increase the speed and alter the course of a spacecraft without the need to expend fuel. The inbound flight path is carefully chosen so that the spacecraft will be whipped around the assisting body, being both accelerated and deflected on a hyperbolic trajectory. At first sight, it may seem as if something has been gained for nothing. However, the additional speed of the spacecraft has been won at the planet’s expense which, as a result of the encounter, slows imperceptibly in its orbit and, as a result, moves fractionally closer to the Sun. One of the earliest, and most dramatic applications of the technique came in 1970 when the world watched as NASA used a lunar gravity-assist to rescue the Apollo 13 astronauts after an onboard explosion had sever
Suppose that you are a “stationary” observer and that you see: a planet moving left at speed U; a spaceship moving right at speed v. If the spaceship is on the right path, it will pass close to the planet, moving at speed U + v relative to the planet’s surface because the planet is moving in the opposite direction at speed U. When the spaceship leaves orbit, it is still moving at U + v relative to the planet’s surface but in the opposite direction, to the left; and since the planet is moving left at speed U, the spaceship is moving left at speed 2U + v from your point of view – its speed has increased by 2U, twice the speed at which the planet is moving. It might seem that this is oversimplified since we have not covered the details of the orbit, but it turns out that if the spaceship travels in a path which forms a hyperbola, it can leave the planet in the opposite direction without firing its engine, the speed gain at large distance is indeed 2U once it has left the gravity of the pl
