Gravity Assist

space · physics · clever trick

What is it?. A gravity assist is when a spacecraft zooms past a planet and uses that planet's gravity to change direction and gain speed, like swinging around on a playground swing.

Saves money and fuel. By borrowing a planet's gravity, spacecraft don't need to carry as much fuel, which means missions cost way less money and can travel farther.

Planet acts as helper. Planets are moving through space really fast, and when a spacecraft flies close by them at just the right angle, it can catch a ride and get a huge speed boost.

Used by real missions. NASA and other space agencies use gravity assists all the time, like when the Cassini spacecraft zoomed past Venus and Jupiter to reach Saturn.

Speed boost works both ways. The spacecraft gets faster, but the planet slows down just a tiny bit because of physics, though planets are so massive we never notice the change.