NASA’s Lucy spacecraft prepares for a near-Earth orbit

On Oct. 16 at 7:04 a.m. EDT, NASA’s Lucy spacecraft, the first mission to Jupiter’s Trojan asteroids, will fly through Earth’s atmosphere after passing just 220 miles (350 kilometers) above the surface. By flying past Earth on the first anniversary of its launch, Lucy will gain some of the orbital energy needed to travel to this never-before-visited group of asteroids.

Trojan asteroids are trapped in orbits around the Sun at the same distance as Jupiter, either far ahead or far behind the giant planet. Lucy is now one year into her twelve year journey. This gravity assist will put Lucy on a new trajectory for a two-year orbit, at which time she will return to Earth for a second gravity assist. This second helping will give Lucy the energy she needs to cross the main asteroid belt, where she will observe asteroid Donaldjahansson and then head to the leading Trojan asteroid swarm. There, Lucy will fly past six Trojan asteroids: Eurybates and its companion Queta, Polymele and its as-yet-unnamed companion Leucus, and Orus. Lucy will then return to Earth for a third gravity assist in 2030 to reorient the spacecraft to rendezvous with the Patroclus-Menoetius asteroid binary pair in the trailing Trojan asteroid swarm.

For this first gravity assist, Lucy appears to approach Earth from the sun’s side. Although this means that observers on Earth will not be able to see Lucy for several days before the event, Lucy will be able to take pictures of the near-full Earth and Moon. Mission scientists will use these images to calibrate the instruments.

Lucy’s trajectory will bring the spacecraft very close to Earth, even lower than the International Space Station, meaning Lucy will pass through a region full of satellites and debris orbiting Earth. To ensure the safety of the spacecraft, NASA has developed procedures to anticipate any potential danger and, if necessary, perform a small maneuver to avoid a collision.

“Lucy’s team prepared two different ones maneuvers” says Caroli Adam, deputy chief of Lucy’s navigation team at KinetX Aerospace in Simi Valley, Calif. “If the team detects that Lucy is in danger of colliding with a satellite or debris, then – 12 hours before closest approach to Earth – the spacecraft will perform one of them, changing the closest approach time by either two or four seconds. It’s a small fix, but enough to avoid a potentially catastrophic one collision.”

Lucy will pass by Earth at such a low altitude that the team had to take into account the effect of atmospheric drag when designing this a flight. Lucy’s large solar panels magnify this effect.

“The original plan was for Lucy to come within about 30 miles of Earth,” says Rich Burns, Lucy project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “However, when it became clear that we might have to complete this flyby with one of the solar panels disconnected, we decided to use some of our fuel reserves to allow the spacecraft to fly past Earth at a slightly higher altitude, reducing the interference from the atmospheric drag of the spacecraft’s solar panels. ship”.

Lucy will be first seen by observers on the ground in Western Australia around 6:55 a.m. EDT (6:55 p.m. for those observers). Lucy will quickly fly overhead, clearly visible to the naked eye for a few minutes before disappearing at 7:02 a.m. EDT as the spacecraft passes into Earth’s shadow. Lucy will continue over the Pacific Ocean in darkness and exit Earth’s shadow at 7:26 a.m. EDT. If the clouds cooperate, sky watchers in the western US will be able to see Lucy with binoculars.

“The last time we saw the spacecraft, it was in the payload fairing in Florida,” said Hal Levison, Lucy’s principal investigator at Southwest Research Institute (SwRI) in Boulder, Colorado. “It’s very exciting that we will be able to stand here in Colorado and see the spacecraft again. And this time, Lucy will be in heaven.”

Lucy then rapidly moves away from Earth’s vicinity, passing the Moon and taking a few more calibration shots before continuing its exit into interplanetary space.

“I’m especially excited about the last few pictures of the Moon that Lucy will take,” said John Spencer, SwRI’s acting associate scientist. “Counting craters to understand the impact history of Trojan asteroids is key to the science Lucy will be doing, and this will be the first opportunity to calibrate Lucy’s ability to detect craters by comparing it to previous observations of the Moon by other space missions. .”