A Gravity Assist maneuver is a space-based launch technique through which a vehicle, most frequently some kind of probe,

but theoretically any kind of satellite or spacecraft could utilize this approach,

is launched in what would seem to be the wrong direction in order to more efficiently

make its way to its proper location. Sometimes this means using the gravity of a planet or

moon to slow a vehicle down, as was the case with the

1959 Soviet Luna 3 probe, which not only sent back the first images of the far side of the Earth's moon, its mission was also, the first time we as a species utilized a gravity assist maneuver, in this case to swing up from below the

moon up around toward the top, with the gravity of the moon itself pulling on the probe

as it passed by, slingshoting it back toward Earth as it reemerged around the top side of the

moon. The 1973 U.S. built Mariner 10 probe was the first craft to use gravity assist to explore

a planet.

In this case, the Mariner 10 was launched toward Venus, but primarily for the purpose of using

the larger Earth-neighboring planet to slingshot toward Mercury, something that conceivably

could have been accomplished by aiming at Mercury instead, but because of the nature of the planets,

their orbital trajectories, and relative locations in space, it made a lot more sense in terms

of time and efficiency at that moment to lob the craft toward another target,

using that target's gravity to sling it in the proper direction,

as a consequence using less fuel and taking less time to get there.

Maybe the most famous, and one of the more impressive early uses of gravity assist in spaceflight and exploration, though, was utilized

by the Voyager program with the Voyager 2, which launched in 1977, flying by Jupiter to take

a look at the planet, but also to get a trajectory boost to reach Saturn, and the Voyager 1,

which launched the following month, doing pretty much the same thing,

and reaching Jupiter before the Voyager 2, because the arrangement of the planets had changed by

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