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NASA's Lucy spacecraft prepares to swing by Earth

The NASA Lucy spacecraft, the first expedition to the Jupiter Trojan asteroids, will pass just 220 miles (350 kilometres) over the Earth's surface on October 16 at 7:04 a.m. EDT. Lucy will obtain part of the orbital energy it needs to reach this unexplored group of asteroids by passing Earth on the first anniversary of its launch.

Trojan asteroids are trapped in Jupiter-parallel orbits around the sun, either  in front of or far behind the big planet. Currently, Lucy has travelled for twelve years. Following a two-year orbit on a revised track thanks to the gravity assist, Lucy will come back to Earth for a second gravity assist. Lucy will have the energy it needs to traverse the main asteroid belt and examine asteroid after this second help. Travel to the leading Trojan asteroid swarm after Donaldjohanson. There, Lucy will fly through six Trojan asteroids, including Orus, Polymele, Eurybates, and its unidentified satellite Queta. Then, in 2030, Lucy will make a third gravity assist to the planet in order to re-target the spacecraft for a rendezvous with the binary asteroid pair Patroclus-Menoetius in the trailing Trojan asteroid swarm.

Lucy will appear to be travelling toward Earth from the direction of the sun during this initial gravity boost. This prevents spectators on Earth from seeing Lucy in the days leading up to the event, but Lucy will be able to capture photographs of the almost full moon and Earth. These photos will be used by mission scientists to calibrate the equipment.

Because of its trajectory, Lucy will pass through an area populated by debris and earth-orbiting satellites as it passes very close to Earth, even lower than the International Space Station. NASA created protocols to foresee any potential threat and, if necessary, carry out a minor maneuver to prevent a collision in order to protect the safety of the spacecraft.

According to Coralie Adam, Lucy's deputy navigation team chief from KinetX Aerospace in Simi Valley, California, "the Lucy team has prepared two possible maneuvers." "The spacecraft will carry out one of these 12 hours prior to its closest approach to Earth if the team determines that Lucy is in danger of colliding with a satellite or piece of debris, which will move the closest approach time by two or four seconds. Even though this is a little adjustment, it is sufficient to prevent a potentially disastrous collision."

Lucy will be passing the 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 arrays increase this effect.

According to Rich Burns, Lucy's project manager at NASA's Goddard Space Flight Center in Greenbelt, Maryland, "in the original plan, Lucy was actually scheduled to pass about 30 miles closer to the Earth." But when it became obvious that we might have to carry out this flyby with one of the solar arrays unlatched, we made the decision to use a little bit of fuel so that the spacecraft passes the Earth at a little bit higher altitude, reducing the disturbance from the atmospheric drag on the spacecraft's solar arrays.

Lucy will initially become visible to viewers on the ground in Western Australia at roughly 6:55 a.m. EDT (6:55 p.m. for those observers). At 7:02 a.m. EDT, Lucy will quickly pass above and be visible to the unaided eye for a short period of time before fading away as it enters the Earth's shadow. At 7:26 a.m. EDT, Lucy will remain in complete darkness over the Pacific Ocean before leaving the Earth's shadow. Sky observers in the western United States should be able to see Lucy with the aid of binoculars if the clouds cooperate.

Hal Levison, Lucy's chief investigator at the Southwest Research Institute (SwRI) Boulder, Colorado office, said, "The last time we saw the spacecraft, it was being encapsulated in the payload fairing in Florida." "It is amazing that we will be able to watch the spacecraft from here in Colorado once more. And Lucy will be in the skies this time.

After taking a few more calibration photographs of the moon and quickly reentering interplanetary space, Lucy will then quickly leave the Earth's atmosphere.

John Spencer, acting deputy project scientist at SwRI, remarked, "I'm really excited by the last few photographs that Lucy will capture of the moon." The science that Lucy will do is crucially dependent on counting craters, and this will be the first chance to calibrate Lucy's crater detection capabilities by comparing them to earlier moon observations made by other space missions.

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