Ulysses ends long trek

The mission of the spacecraft Ulysses, which studied the far-flung polar regions of the sun, has come to an end after 18 years of exploration far outlasting its original life expectancy.

The spacecraft was a joint mission between Jet Propulsion Laboratory/NASA and European Space Agency. Throughout its long mission it entered unexplored regions of the solar system, gathering information about the sun and its environment.

“We lasted almost four times longer than planned and a year longer than we thought we would,” said Ed Massey, Ulysses NASA/JPL project manager.

The spacecraft was initially launched from the space shuttle Discovery on Oct. 6, 1990, with a life expectancy of five years.

The information gained by Ulysses will continue to be studied and help future missions, scientists said. Some of its highlights include taking the first direct measurements of interstellar dust particles and helium atoms in the solar system, and showing that the magnetic field leaving the sun is balanced across latitudes.

The science community hailed the discovery as an important development for future space missions because it meant regions of the sun that weren't previously considered as sources of hazardous particles for astronauts and satellites would now have to be carefully monitored.

“We were able to see solar pole reversal and measure the winds, fast and slow, and investigate the source of those winds,” Massey said.

The spacecraft was not able to forecast weather, such as the solar flares that create technical problems on Earth, “but we were able to see how solar storm shocks change,” he added.

Ulysses' orbit takes it out past Jupiter and back. As it flies through cold space, it maintains its heaters while running its communications and scientific equipment, but as it aged the power steadily dropped.

At this point, it cannot maintain its equipment, and its fuel will likely freeze. Its radio transmitter has also failed to turn on, so the time had come to shut it down, Massey said.

“We could not recover recorded data, and we were not gaining any science,” he said.

The decision to end a mission is never easy, but Massey said it was the right decision at the right time. Ulysses now joins Voyager I and II as it travels into unexplored space alone.

“It will be in orbit around the sun indefinitely,” he said. “It may be thrown out by Jupiter. We have no idea how fast it will go.”

Massey added the small team left to monitor Ulysses will now move on to other projects.

“Over the years we have made a lot of friends in house and the European science team,” he said. “We can be proud that as a group we did a wonderful thing.”

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