Ulysses solar probe ends historic mission

Computerworld - A solar orbiter that was expected to last just five years in the harsh environment of outer space had the final day of its 18-year mission come to a close yesterday.

The Ulysses spacecraft, which launched as a joint NASA and European Space Agency mission, ceased operations Tuesday afternoon. The craft, which made nearly three full orbits of the sun during its lifespan, helped scientists chart what had been unexplored regions of space.

"This has been a remarkable scientific endeavor," said Richard Marsden, Ulysses mission manager and project scientist at the European Space Agency, in a statement. "The results Ulysses obtained have exceeded our wildest dreams many times over."

When space shuttle Discovery launched Ulysses on Oct. 6, 1990, the unmanned orbiter had an expected lifetime of five years, according to NASA.

The spacecraft is credited with gathering new information about the heliosphere, the area of space affected by the sun and its magnetic field. While Ulysses enabled scientists to map constituents of the heliosphere, the fact that it worked for nearly four times longer than expected means it was able to send back long-term observations and build a more detailed map.

NASA also noted that Ulysses sent back information about the three-dimensional character of galactic cosmic radiation, the energetic particles produced in solar storms and solar wind.

"The sun's activity varies with an 11-year cycle, and now we have measurements covering almost two complete cycles," Marsden said. "This long observation has led to one of the mission's key discoveries, namely that the solar wind has grown progressively weaker during the mission and is currently at its weakest since the start of the Space Age."

Ulysses' orbital path is carrying the spacecraft farther away from Earth. The increasing distance has limited the amount of data that could be transmitted back and forth. Yesterday, a ground team sent commands to Ulysses that basically shut down its transmitter and kept its antenna system from receiving information from Earth.

Despite the demise of Ulysses, NASA still has several orbiters to deal with.

The Mars Reconnaissance Orbiter has been sending back information about massive buried glaciers on the Red Planet, as well as data about fractures in that planet's surface and evidence of ancient Martian water flows.

And earlier this month, NASA launched two orbiters that are designed to send back more detailed information about the moon and help scientists find the best landing spot for the next time humans visit Earth's satellite.

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