Lucy completes key Earth gravity assist maneuver

Lucy completes key Earth gravity assist maneuver
by Clarence Oxford
Los Angeles CA (SPX) Dec 13, 2024

NASA's Lucy spacecraft executed a critical gravity assist maneuver on Dec. 12, 2024, skimming just 220 miles (360 kilometers) above Earth's surface. This close approach, occurring at 11:15 p.m. EST, propels the spacecraft on a new trajectory through the asteroid belt and toward the Jupiter Trojan asteroids - objects never previously visited by any spacecraft.

The maneuver marks Lucy's second Earth gravity assist, coming three years into its ambitious 12-year journey. Lucy's first such maneuver, on Oct. 16, 2022, transitioned the spacecraft from a one-year orbit to its current two-year orbit, enabling encounters with the asteroid Dinkinesh and its satellite Selam. The new gravity assist boosts Lucy into a six-year orbit, targeting its first Trojan asteroid encounter in 2027, after a planned flyby of the main belt asteroid Donaldjohanson in 2025.

Approaching Earth from the Sun's direction, Lucy was invisible to observers as it entered Earth's shadow at 6:14 p.m. HST. However, viewers in Hawaii may have briefly glimpsed the spacecraft shortly after sunset. Lucy's shadowed transit over the continental U.S. occurred at an astonishing speed of over 33,000 miles per hour (14.8 kilometers per second). Emerging from Earth's shadow at 11:34 p.m. EST, Lucy became visible again to observers with telescopes in western Africa and eastern South America as sunlight reflected off its expansive solar panels. For observers in the eastern U.S., the "back" side of the solar panels made the spacecraft harder to detect.

NASA implemented careful measures to ensure Lucy's safety during this low-altitude pass, which took it beneath the International Space Station and through Earth's crowded orbital environment. A contingency plan allowed for a small trajectory correction maneuver, if necessary, 12 hours before closest approach to avoid collisions with satellites or debris.

Lucy's close encounter increased its velocity relative to the Sun by more than 16,000 miles per hour (7.31 kilometers per second), allowing it to continue its journey through the asteroid belt. During the spacecraft's first Earth gravity assist in 2022, Lucy captured images of Earth and the Moon for calibration purposes. However, no instrument imaging occurred during this maneuver, as calibrations are no longer required.

The next milestone for Lucy is its encounter with Donaldjohanson, a small main belt asteroid, scheduled for April 20, 2025.