In an exciting new chapter for NASA’s Lucy spacecraft, the spacecraft is now just days away from its second asteroid flyby. On April 20, 2025, Lucy will closely approach Donaldjohanson, a small asteroid located in the main asteroid belt. This encounter marks a major milestone in Lucy’s mission to explore the solar system’s Trojan asteroids, which share Jupiter’s orbit. As NASA’s Lucy mission prepares for this crucial event, the spacecraft’s team is also using this encounter to fine-tune systems and observation techniques that will be pivotal in its upcoming encounters with the Trojan asteroids.
NASA’s Lucy mission, launched in 2021, has already made strides in understanding the earliest building blocks of the solar system by exploring these distant objects. With Donaldjohanson being one of the youngest and most intriguing asteroids in the main belt, this upcoming encounter presents an opportunity to learn more about the origins of the solar system.
The Encounter: A Step Toward the Trojan Asteroids
Lucy’s upcoming flyby of Donaldjohanson will take place on April 20, 2025, at approximately 1:51 PM EDT, at a close distance of 596 miles (960 km). This encounter will serve as a “dress rehearsal” for the more complex and crucial observations that Lucy will make when it reaches the Trojan asteroids in the coming years. Lucy will begin orienting itself to track the asteroid about 30 minutes before its closest approach, and it will carry out an advanced observation sequence.
The spacecraft will use its three science instruments—the L’LORRI greyscale imager, the L’Ralph color imager and infrared spectrometer, and the L’TES far-infrared spectrometer—to take high-resolution images and analyze the asteroid’s composition. This will be more advanced than the previous flyby of the Dinkinesh asteroid in 2023, which served as a preliminary systems test for the spacecraft.
Autonomous Operations and Instrument Protection
As Lucy approaches Donaldjohanson, the spacecraft will briefly suspend communication with Earth to focus on its observations. This is because the high-gain antenna will be turned away from Earth to ensure that Lucy remains properly oriented toward the asteroid. Lucy will perform a more complicated sequence of observations than it did during the flyby of Dinkinesh, which will involve all three of its instruments.
However, Lucy’s instruments will not be exposed to direct sunlight as it passes by the asteroid. “If you were sitting on the asteroid watching the Lucy spacecraft approaching, you would have to shield your eyes staring at the Sun while waiting for Lucy to emerge from the glare,” said Michael Vincent, the encounter phase lead at Southwest Research Institute in Boulder, Colorado. “After Lucy passes the asteroid, the positions will be reversed, so we have to shield the instruments in the same way.” This is an important consideration to prevent damage to the sensitive instruments, which are designed to photograph objects illuminated by sunlight 25 times dimmer than what we see on Earth.
Navigating Deep Space: Lucy’s Communication Delay
After the flyby, Lucy will reorient itself to communicate with Earth, but there will be a significant communication delay due to its distance from Earth. “One of the weird things to wrap your brain around with these deep space missions is how slow the speed of light is,” said Vincent. At 12.5 light minutes away, it will take a total of 25 minutes for the spacecraft to send and receive signals—12.5 minutes for the signal to reach Lucy, and another 12.5 minutes for Lucy’s response to return to Earth. Once the spacecraft’s health is confirmed, engineers will begin transmitting the science data from the encounter, a process that will take several days to complete.
What’s Next for Lucy?
As Lucy continues its journey, it will eventually move on to its primary mission: exploring the Trojan asteroids, which share Jupiter’s orbit. These asteroids are remnants of the early solar system and are believed to hold clues about the formation of the planets. Lucy’s journey promises to revolutionize our understanding of the origins of the solar system and help scientists unlock the secrets of these ancient objects.
With this second asteroid encounter, Lucy is proving to be an indispensable tool in the search for answers about the history of our solar system. Each encounter brings scientists closer to understanding the building blocks of life and the role asteroids played in the formation of planets and moons.
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