On Monday, October 16, at 1:04 p.m. Spanish peninsular time, a NASA spacecraft launched into space a year ago will return to graze the Earth’s atmosphere. It will pass exceptionally close, just 350 kilometers above the surface, even lower than the International Space Station (ISS), risking colliding with the many satellites and debris that cross Earth’s orbit. This is the Lucy mission, destined to be the first to visit the mysterious Trojan asteroids that orbit the Sun alongside Jupiter.
But Lucy’s twelve-year journey is not in a straight line. The Trojans are stuck in orbits around the Sun at the same distance as Jupiter, either far ahead of or behind the giant planet. Monday’s maneuver, called gravitational assist, uses the planet’s gravity like a colossal slingshot to put the spacecraft on a new trajectory for a two-year orbit.
Then, in December 2024, it will return to Earth for a second ‘push’, which will give it the energy it needs to cross the main asteroid belt, where it will observe a rock called Donaldjohanson. You will then travel to the Trojan asteroid swarm where you will visit six rocks: Eurybates and its satellite Quetta, Polymele and his unnamed satellite, Leucus y In the valley.
For this first gravitational assist, Lucy will appear to approach Earth from the direction of the Sun. While this means observers on Earth won’t be able to see the s in the days leading up to the event, Lucy will be able to take images of the Earth and Moon. almost full. Mission scientists will use these images to calibrate instruments.
Two seconds to avoid a collision
Lucy will come very close, below the space station’s altitude and low enough that the spacecraft will be visible to the naked eye from Western Australia for a few minutes. This proximity also means passing through a dangerous region in Earth’s orbit with more than 47,000 satellites, debris and other objects revolving around our planet. NASA calculates a probability greater than one in 10,000 that the device collides with one of these bodies. In the event of imminent danger, mission engineers will slightly adjust the spacecraft’s trajectory.
“The Lucy team has prepared two different maneuvers,” explains Coralie Adam, deputy leader of the Lucy navigation team at KinetX Aerospace in Simi Valley, California. “If the team detects that Lucy is at risk of colliding with a satellite or with debris, then 12 hours before closest approach to Earth, the spacecraft will execute one of these, altering the closest approach time by two. or four seconds. This is a small correction, but it’s enough to avoid a potentially catastrophic collision,” she notes.
“In the original plan, Lucy was actually going to go about 30 miles closer to Earth,” says Rich Burns, project manager for Lucy at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. However, they chose to use some of their fuel reserves to fly the spacecraft past Earth at a slightly higher altitude, reducing the disturbance from atmospheric drag on the spacecraft’s solar arrays.
the craters of the moon
Lucy will then zoom out of Earth’s neighborhood, pass by the Moon and take a few more calibration images before continuing on into interplanetary space.
“I’m especially excited about the latest images Lucy will take of the Moon,” said John Spencer, a scientist at the Southwest Research Institute (SwRI) in San Antonio, Texas. “Counting craters to understand the history of Trojan asteroid collisions is key to Lucy’s science, and this will be the first opportunity to calibrate Lucy’s ability to detect craters against previous observations of the Moon by NASA. other space missions.
The mission is named Lucy after the 3-million-year-old australopitheca skeleton discovered by US paleoanthropologist Donald Johanson, which in turn gives its name to a main-belt asteroid. If this finding gave clues about how the human being originated, the Trojan asteroids, intact since their formation about 4,500 million years ago, can help to understand how the Solar System originated and the planets were formed.