Gravity assist facts for kids
A gravitational slingshot, gravity assist maneuver or swing-by is the use of the relative movement and gravity of a planet to alter the path and speed of a spacecraft, typically in order to save fuel, time, and expense. Gravity assistance can be used to speed up, slow down and/or change the path of a spacecraft. The "assist" is provided by the motion of the gravitating body as it pulls on the spacecraft. The Soviet Union used it first for the Luna 3 probe that photographed the far side of the Moon. The later Pioneer program used gravity assist in several missions.
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Example encounter.In the planet's frame of reference, the space probe leaves with the exact same speed at which it had arrived. But when observed in the reference frame of the Solar System (fixed to the Sun), the benefit of this maneuver becomes apparent. Here it can be seen how the probe gains speed by tapping energy from the speed of the planet as it orbits the Sun. (If the trajectory is designed to pass in front of the planet instead of behind it, the gravity assist can be used as a braking maneuver rather than accelerating.) Because the mass of the probe is many orders of magnitude smaller than that of the planet, while the result on the probe is quite significant, the deceleration reaction experienced by the planet, according to Newton's third law, is utterly imperceptible.
Gravity assist Facts for Kids. Kiddle Encyclopedia.