The solar probe Ulysses has circled the sun for more than 18 years–almost as long as the Greek hero Odysseus, also called Ulysses, was absent from home due to the Trojan War and his prolonged journey home–but the space probe doesn’t have a homecoming in its future. Ulysses will receive its final transmission tomorrow, as researchers say the scientific findings sent home by the failing spacecraft no longer justify the mission’s costs. After shut-off, Ulysses will continue to orbit the Sun, becoming in effect a man-made ‘comet’. “Whenever any of us look up in the years to come, Ulysses will be there, silently orbiting our star, which it studied so successfully during its long and active life” [SPACE.com], says mission manager Richard Marsden.
The craft has already exceeded expectations. In February 2008, mission engineers announced with great solemnity and with heaps of praise for the orbiter that the craft would fall silent within a few months. Its power supply had grown too weak to keep the craft’s fuel lines from freezing. Not so fast: Engineers figured out that they could keep the lines warm by firing the craft’s thrusters in short bursts every couple of hours [The Christian Science Monitor]. Using that clever fix, Ulysses soldiered on for another year.
The probe, a cooperative mission between the European Space Agency and NASA, has studied the solar wind, the stream of charged particles ejected by the sun. Last year researchers announced that Ulysses’s observations showed that the sun was in the doldrums, with solar winds dropping to the weakest level ever since recording began. The scientific legacy of Ulysses also includes a study of helium isotopes created shortly after the Big Bang. By measuring their abundance, Ulysses found evidence to support the theory that the universe will keep expanding forever, because not enough matter was created in the Big Bang to halt the expansion through gravitational attraction.
Researchers say that the bold voyage of Ulysses should be celebrated and applauded. Now, however, the craft is moving away from Earth in its solar orbit. It’s no longer able to send data at a speedy enough rate to merit yet another “season” [The Christian Science Monitor]. Perhaps the poet Alfred Tennyson would have approved of the probe’s final resting place in orbit around the sun; in his poem about Ulysses he imagines the aging king exhorting his sailors to take to the sea again. Ulysses says he hopes to “sail beyond the sunset, and the baths/ Of all the western stars, until I die.”
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