NASA's Lucy probe dodges space traffic around Earth in gravity-assist flyby

Spacecraft coming through, outta the way, watch your step, we're heading to Jupiter

NASA's Lucy spacecraft has successfully performed its first gravity-assist flyby of Earth, dodging tens of thousands of satellites and bits of debris.

The probe is named after the incomplete female skeleton discovered in Ethiopia in 1974 of an early human ancestor dating back more than three million years. The spacecraft is on a twelve-year mission to a more ancient type of relic: Jupiter's Trojan asteroids. NASA described the rocks as the "fossils of planetary formation," left over when the largest planets in the Solar System began to form more than 4.5 billion years ago.

To get Lucy closer to the Trojans, mission control will have the spacecraft perform multiple gravity assists around Earth to put it on a path toward Jupiter. NASA successfully completed the first one on October 16. Lucy came just 351 kilometres from Earth's surface, bringing it closer than most orbiting spacecraft, such as the International Space Station.

At these distances, Lucy faced a hazardous environment littered with more than 47,000 satellites, chunks of debris, and other objects orbiting Earth. Scientists had to monitor and track these bits and pieces while predicting the spacecraft's position to figure out how to avoid any collisions. If there was more than a one in 10,000 chance of impact with one of the objects, Lucy's trajectory would have to be adjusted before the orbital burn. 

The spacecraft managed to pull off the gravity assist with no hiccups. The team did, however, need to account for an increase in the Earth's atmospheric drag on the probe as it got closer to our planet: one of Lucy's solar panels had failed to latch into place, forcing the craft to flyby at a higher altitude.

"In the original plan, Lucy was actually going to pass about 30 miles (48 km) closer to the Earth," Rich Burns, Lucy's project manager at NASA's Goddard Space Flight Center, said in a statement.

"However, when it became clear that we might have to execute this flyby with one of the solar arrays unlatched, we chose to use a bit of our fuel reserves so that the spacecraft passes the Earth at a slightly higher altitude, reducing the disturbance from the atmospheric drag on the spacecraft's solar arrays."

The gravity assist with Earth boosted Lucy's speed and the spacecraft is now on a path toward Mars. It will need to perform a second assist in 2024 to get to Jupiter. Lucy will fly by 52246 Donaldjohanson, an asteroid in the inner main belt of our planetary system, and will then move towards visiting seven other Trojan asteroids over its twelve-year journey.

Four of these rocks are binary systems, while the other three are dark red-type asteroids that resemble Kuiper Belt objects beyond Neptune. These seven targets will give scientists a good representation of the major three C, P, and D-types of asteroids. Trojan asteroids are believed to be rich in dark carbon compounds, and may contain water and other volatile substances. 

"This is a unique opportunity," Harold Levison, principal investigator of the Lucy mission at the Southwest Research Institute in Boulder, Colorado, previously said. "Because the Trojans are remnants of the primordial material that formed the outer planets, they hold vital clues to deciphering the history of the solar system. Lucy, like the human fossil for which it is named, will revolutionize the understanding of our origins." ®