Lucy in the sky

NASA's Jupiter asteroid probe gets a crucial boost from Earth's gravity

A trip home will help Lucy get through the asteroid belt.


NASA's Goddard Spaceflight Center

On October 16, 2021, NASA launched its Lucy spacecraft on a mission to study asteroids around Jupiter.

Southwest Research Institute

But before it gets there, Lucy paid a quick visit to Earth

To reach its first target in the asteroid belt, Lucy needs a little boost. So exactly one year after launch, Lucy swung by Earth for what’s known as a gravity assist.

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First used by the Soviet probe Luna 3 in 1959, the maneuver uses a planet’s gravity and velocity to speed a craft up while changing its course.

Artemis I will use the same principle to enter an elliptical orbit around the Moon after its long-delayed launch finally happens.

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Lucy’s gravity assist is just one step on its way to observing asteroid Donaldjohanson in 2025 and the Trojan asteroids later.

Getting a craft like Lucy to slingshot around Earth in exactly the right way is even more complicated than it sounds.

Lockheed Martin Space


Lucy will actually dip below the altitude of the International Space Station on its flyby, bringing it into an area swarming with dangers.

Earth isn’t as alone as it seems.

Our planet is surrounded by thousands of satellites and other objects, all of which Lucy needs to dodge for a gravity assist.

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NASA's Goddard Space Flight Center

NASA engineers tracked Lucy and the roughly 47,000 objects that might pose a danger during its flyby, ready to adjust the craft’s trajectory if things looked dicey.

This act of astronomical acrobatics isn’t a one-time deal for Lucy.


A second gravity assist will get Lucy through the asteroid belt to reach its first target, and another in 2030 will send it toward to Patroclus-Menoetius asteroid pair.

NASA's Goddard Space Flight Center
Lucy is NASA’s first mission to the Trojan asteroids.

It’s designed to give us a glimpse of Jupiter’s two asteroid swarms, believed to consist of the material that formed our Solar System more than 4 billion years ago.

NASA's Goddard Space Flight Center

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