Today, NASA’s Lucy will speed towards Jupiter’s Trojan asteroids using Earth’s gravity

NASA’s Lucy spacecraft is preparing to swoop near Earth on October 16 to use our planet’s gravity to set itself on a course toward the Jupiter Trojan asteroid, reported a NASA statement on Thursday. But this might be easier said than done.

A 1-10,000 chance that Lucy will collide with space objects

Mission engineers will have to track the Lucy spacecraft nonstop, along with more than 47,000 satellites, debris, and other objects circling our planet. This is due to a greater than 1-10,000 chance that Lucy will collide with one of these objects forcing mission engineers to slightly adjust the spacecraft’s trajectory.

This is more common than one would think. The International Space Station, for instance, has maneuvered out of the way of space debris 31 times since 1999, including three times since 2020.

“Low-Earth orbit is getting more crowded, so that has to be part of the consideration nowadays, especially for missions that fly low, like Lucy,” said Dr. Dolan Highsmith, chief engineer for the Conjunction Assessment Risk Analysis group at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

The group is responsible for evaluating the probabilities of collisions between NASA’s robotic spacecraft and Earth-orbiting objects.

Lucy was first launched on October 16 of last year. The craft is now on a 12-year-journey to study multiple Trojan asteroids up close and is the first spacecraft to visit these remnants from the early solar system.

It is set to arrive at the Trojans in 2027 and the upcoming gravity assist is one of three the spacecraft will have to perform to catapult itself to its target.

Collision analysis

Engineers started collision analysis for Lucy a week before the spacecraft’s Earth approach. This might seem like a short time but starting the process any earlier would render collision predictions futile, Highsmith said.

“The further you're predicting into the future, the more uncertain you are about where an object is going to be.”

Evaluating the positions of spacecraft, plus orbiting satellites and debris, is challenging, particularly when trying to predict the future. This is because the Sun plays a major role in pulling or pushing objects around, and future solar activity is hard to predict.

This means that the closer the collision assessment is to the Earth flyby time, the better. Therefore Lucy’s whereabouts are sent to the Space Force squadron daily. If the squadron speculates that Lucy could intersect with something, Highsmith’s group acts to move the spacecraft.

“With such a high value mission, you really need to make sure that you have the capability, in case it's a bad day, to get out of the way,” Highsmith said.

Lucy navigation engineers rely on two maneuver options in case the spacecraft needs to avoid an object. Both maneuvers require engine burns to speed up the spacecraft and can move Lucy’s closest approach to Earth up by 2 seconds or 4 seconds, respectively.

“That's enough to avoid any one thing that could be in the way,” said Kevin E. Berry, Lucy’s flight dynamics team lead from NASA Goddard.