NASA’s Lucy spacecraft is about to pass in front of Earth

On October 16, 2022, Lucy will fly over Earth like a partner in a swing dance, increasing her speed and lengthening her orbit around the Sun. At 7:04 a.m. EST, Lucy will make her closest approach just 219 miles above the planet: lower than the International Space Station. This exceptionally close shave will increase her speed by four and a half miles per second, putting Lucy on track to gain even more speed when she returns to Earth for her second gravity assist in December 2024. Credit: Goddard Space Flight Center The NASA

launch, Lucy will gain some of the orbital energy it needs to travel to this never-before-visited population of asteroids.

Discovered in February 1906 by German astrophotographer Max Wolf, the Trojan asteroids are trapped in orbits around the Sun at the same distance as Jupiter. They’re essentially following the same orbit, just either far ahead of or behind the giant planet. Lucy is currently one year into a twelve-year, 4-billion-mile voyage to study these ancient asteroids.

This gravity assist will place Lucy on a new trajectory for a two-year orbit, at which time it will return to Earth for a second gravity assist. This second assist will give Lucy the energy it needs to cross the main asteroid belt, where it will observe asteroid Donaldjohanson, and then travel into the leading Trojan asteroid swarm. There, Lucy will fly past six Trojan asteroids: Eurybates and its satellite Queta, Polymele and its yet unnamed satellite, Leucus, and Orus. Lucy will then return to Earth for a third gravity assist in 2030 to re-target the spacecraft for a rendezvous with the Patroclus-Menoetius binary asteroid pair in the trailing Trojan asteroid swarm.

NASA’s Lucy spacecraft will make an exceptionally close flyby of Earth on October 16, 2022. Credit: NASA Goddard Space Flight Center

For this first gravitational assist, Lucy will appear to be approaching Earth from the direction of the Sun. While this means observers on Earth won’t be able to see Lucy in the days leading up to the event, Lucy will be able to take images 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, lower even than the International Space Station (ISS), which means that Lucy will pass through a region full of Earth-orbiting satellites and debris. 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 maneuvers,” says Coralie Adam, assistant navigation team leader for Lucy at KinetX Aerospace in Simi Valley, Calif. “If the team detects that Lucy is at risk of colliding with a satellite or debris, then – 12 hours before the closest approach to Earth – the spacecraft will execute one, changing the time of the closest approach two or four seconds in. It’s a small correction, but it’s enough to avoid a potentially catastrophic collision.

Spacecraft Lucy near a large asteroid

Illustration of the Lucy spacecraft near a large asteroid with Jupiter visible in the distant background. Credit: Southwest Research Institute

Lucy will pass Earth at such a low altitude that the team had to include the effect of atmospheric drag when designing this flyby. Lucy’s large solar panels increase this effect.

“In the original plan, Lucy was actually going to pass about 30 miles closer to 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 run this flyby with one of the unlocked solar panelswe chose to use some of our fuel reserves to have the spacecraft pass Earth at a slightly higher altitude, reducing atmospheric drag disturbance on the spacecraft’s solar panels.

At approximately 6:55 a.m. EDT, Lucy will first be visible to ground observers in Western Australia (6:55 p.m. for those observers). Lucy will quickly pass overhead, clearly visible to the naked eye for a few minutes before disappearing at 7:02 a.m. EDT as the spacecraft passes through Earth’s shadow. Lucy will continue over the Pacific Ocean in the dark and emerge from Earth’s shadow at 7:26 a.m. EDT. If the clouds cooperate, skywatchers in the western United States should be able to see Lucy through binoculars.

Flyby of the Earth by Lucy Trajectory

Lucy’s trajectory during Earth flyby seen from above Earth’s North Pole, a red dot every 10 minutes. Location at certain key moments indicated in white. Credit: SWRI

“The last time we saw the spacecraft, it was locked in the payload fairing in Florida,” said Hal Levison. He is Lucy’s Principal Investigator in the Boulder, Colorado office of the Southwest Research Institute (SwRI). “It’s exciting that we can stand here in Colorado and see the spacecraft again. And this time Lucy will be in the sky.

Lucy will then quickly move away from the vicinity of Earth, passing by the Moon and taking a few more calibration images before continuing into interplanetary space.

“I’m particularly excited about the final images Lucy will take of the Moon,” said John Spencer, the project’s acting assistant scientist at SwRI. “Counting craters to understand the history of Trojan asteroid collisions is key to the science that Lucy will conduct, 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.

Panoramic view of Lucy’s first Gravity Assist Earth (EGA). The camera follows Lucy as the spacecraft approaches the sunlit side of Earth before crossing into Earth’s shadow as it orbits the planet. Credit: NASA Science Visualization Studio

The public is invited to join the #WaveToLucy social media campaign by posting images of themselves saluting the spacecraft and tagging the @NASASolarSystem account. Also, if you find yourself in an area where Lucy will be visible, take a photo of Lucy and post it on social media with the hashtag #SpotTheSpacecraft. Instructions for viewing Lucy from your location are available here.

Hal Levison from South West Research Institute (SwRI), in the Boulder Colorado office is the Principal Investigator. SwRI, headquartered in San Antonio, also leads the science team and science observation planning and data processing for the mission. NASA Goddard provides overall mission management, systems engineering, and safety and mission assurance for Lucy. Lockheed Martin Space in Littleton, Colorado built the spacecraft, primarily designed the orbital path, and provides flight operations. Goddard and KinetX Aerospace are responsible for navigating the Lucy spacecraft. Lucy is the thirteenth mission in NASA’s Discovery program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama.

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