2023-11-01 23:38:27
“Lucy” is not an acronym. Rather, the NASA probe launched in October 2021 was named after the pre-human female of the species Australopithecus afarensis named, whose skeleton was discovered in Ethiopia in 1974. The famous fossil find now also has an Amharic name, namely “Dinkinesh”, which is also the name of the barely one kilometer wide asteroid that Lucy came within 425 kilometers of on the afternoon of November 1st, trying out a new optical navigation method.
Ulf von Rauchhaupt
Editor in the “Science” department of the Frankfurter Allgemeine Sonntagszeitung.
The main belt asteroid 52246 Donaldjohanson was actually intended as Lucy’s first target – it is named after the American paleanthropologist Donald Johanson, one of the discoverers of Lucy, the pre-human lady. The asteroid 152830 Dinkinesh only came onto the program in January 2023, when it became clear that a small change in course was enough to get even closer to the new intermediate goal than Donaldjohanson, who nevertheless remains on the agenda. In April 2025, Lucy will flyby within 922 kilometers of it.
The actual target of the mission, however, is not the asteroid belt between Mars and Jupiter, but a pair of enormous asteroid clouds that probably contain as many chunks as the main belt and that move in front of and behind Jupiter on its orbit around the sun. Such celestial mechanically fixed asteroids also exist in the orbits of other planets.
They are called “Trojans” because, in the case of Jupiter, they are named after characters from Homer’s Iliad, the great epic about the Trojan War. Asteroids with namesakes on the side of Troy, i.e. Trojans in the narrower sense, are those who move behind Jupiter, and those who move ahead of him are the “Greeks”. Unfortunately, this naming custom only emerged when the first Jupiter Trojans had already been named, which is why two do not fit into the literary scheme: 624 Hektor is a “Greek” and 617 Patroclus is a “Trojan”.
Among Trojans: Some of Lucy’s targets: Image: NASA
Patroclus will visit the probe, but only in March 2033 as the culmination of its official program, because with a diameter of 113 kilometers it is the largest asteroid on Lucy’s list. It also has a 104-kilometer-wide companion named Menoetius, which has only been known since 2001, as the two orbit each other only 680 kilometers apart and can therefore only be distinguished from Earth using very large telescopes.
Lucy will spend the years before visiting this double asteroid in the Trojan camp with the Greeks: first she will fly past 3548 Eurybates in August 2027, then the following month past 15094 Polymele, in April 2028 past 11351 Leucus and the following November past 21900 Orus . In order to get from the Greek to the Trojan camp to Patroclus and Menoetius, Lucy will first have to fly past Earth again in December 2030. It had already gained momentum a year after it started and will do so again in December 2024.
These flybys are unexpectedly important for the Lucy team. The probe not only gains momentum, but also enables NASA engineers to manage a problem: After launch, one of the space probe’s two disk-shaped solar panels could not be fully unfolded and locked. The unfolding is now 98 percent successful. This would not affect the mission as long as the panel remains stable. But that remained the case despite the lack of a lock when Lucy approached the Earth on her first flyby in 2022 to within 392 kilometers and thus into the area of the Earth’s outer atmosphere. The second approach to Earth next year could then provide an opportunity to completely solve the problem.
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First, the probe completed its first dress rehearsal at 152830 Dinkinesh. Since it passed the mini-asteroid in an orbit geometry similar to that planned for the Trojans at the end of the decade, NASA engineers were now able to test Lucy’s optical navigation system. The vehicle began aligning itself with the target asteroid about an hour before the flyby. But because Dikinesh is so tiny, the actual “lock-on”, in which Lucy holds him in the field of vision of her instruments, only occurred a few minutes before the encounter.
Because the high-performance antenna is not aligned with Earth during the encounter, Lucy had to carry out the pre-programmed maneuver autonomously and then turn back to Earth independently. Only then could we begin sending the images of Dikinesh and other instrument data from the flyby to the control center over the next few weeks. NASA confirmed that the relevant order was sent to Lucy after ensuring that the probe survived the flyby unscathed.
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