NASA’s Lucy Spacecraft Prepares for Second Earth Gravity Assist

On Dec. 12, at 11:15 p.m. EST, NASA's Lucy spacecraft, currently in a two-year orbit around the Sun, will skim Earth's atmosphere, passing only about 220 miles (360 kilometers) above the surface. This close flyby will result in a "gravity assist," putting the spacecraft on a new trajectory that travels through the main asteroid belt and out to the never-before-explored Jupiter Trojan asteroids, small bodies that orbit the Sun at the same distance as Jupiter.

[Link]NASA Lucy Spacecraft's second Earth gravity assist (EGA) dramatically alters the spacecraft's trajectory, enabling it to travel through the Jupiter Trojan asteroids. Lucy's trajectory prior to the EGA is shown in solid red, while the trajectory afterward is shown by a dashed red curve. The orbits of the nearby planets are shown for reference, and the grey regions indicate the approximate location of the main asteroid belt and the leading (L4) Jupiter trojan asteroids. The main belt asteroid, Donaldjohanson, and the Trojan asteroid, Eurybates, are shown at the time of Lucy's encounters. Credit: NASA/SwRI

This second Earth gravity assist occurs three years into the Lucy spacecraft's 12-year voyage. Its first gravity assist on Oct. 16, 2022, one year after launch, boosted the spacecraft from an initial one-year orbit onto the present two-year orbit that reached into the inner limits of the main asteroid belt. This enabled Lucy's first asteroid encounter with the small asteroid Dinkinesh and its satellite Selam. The upcoming gravity assist will boost the spacecraft into a six-year orbit, one that will carry Lucy through the main asteroid belt (where it will fly past the asteroid Donaldjohanson) and into the Trojan asteroid swarm that leads Jupiter in its orbit, for the first Trojan asteroid encounter in 2027.

During the gravity assist, the Lucy spacecraft, from Earth's perspective, will approach from the direction of the Sun. This means that observers on Earth will not be able to see Lucy approaching, as it will be lost in the Sun's glare. Lucy's trajectory will bring the spacecraft very close to the Earth, even lower in altitude than the International Space Station. To ensure the safety of the spacecraft as it passes through this region full of Earth-orbiting satellites and debris, NASA has procedures to anticipate and avoid potential collisions. If needed, the spacecraft will execute a small trajectory correction maneuver 12 hours before closest approach to alter the time of closest approach by 1 or 2 seconds - enough to avoid a potential collision.

[Link]The trajectory of NASA's Lucy spacecraft during its second Earth gravity assist on December 12, 2024, as seen looking down on the Earth. The dots along the trajectory mark the position of the spacecraft every 10 minutes. Credit: NASA/SwRI.

Shortly after sunset, keen observers in the Hawaiian Islands may be able to catch a glimpse of Lucy as the spacecraft approaches Earth before it passes into Earth's shadow at 6:14 p.m. HST. Lucy will speed over the continental U.S. in darkness, travelling over 33,000 miles per hour (14.8 kilometers per second), and emerge from Earth's shadow 20 minutes later at 11:34 p.m. EST. At that time, Lucy may be visible to observers with a telescope in the western regions of Africa and the eastern regions of South America as sunlight reflects off the spacecraft's large solar panels (observers in the eastern United States will be looking at the much dimmer "back" side of the solar panels, making Lucy harder to see; go here for more information about observing Lucy during this gravity assist). Lucy will then rapidly recede from Earth and return to interplanetary space, the gravity assist having increased the spacecraft's speed with respect to the Sun by over 16,000 miles per hour (7.31 kilometers per second).

During the first Earth gravity assist in 2022, the spacecraft imaged the Earth and the Moon as part of an instrument calibration. As no further calibrations are needed at this time, the instruments will be off during this encounter. Lucy's next asteroid encounter will be with the small main belt asteroid Donaldjohanson on April 20, 2025.

Public link

Please use the above public link if you want to share this noodl on another website.