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Ulysses says goodbye.

The odyssey of Ulysses is coming to an end after a successful 18-year mission orbiting the Sun.

Ulysses was one of the European Space Agency's first deep-space projects, following the Giotto comet probe. It had a tortuous gestation as a joint NASA/ESA out-of-ecliptic mission and then as the international Solar Polar Mission, featuring twin probes-one of which was cancelled when the US dropped out, leaving bitter transatlantic feelings.

The mission faced further delays following the Challenger accident in 1986 and the cancellation of the Shuttle-Centaur upper stage. In October 1990, however, the Space Shuttle Discovery deployed the probe with a three-stage solid-rocket system that accelerated it to 15.2 km (9.4 miles) per second toward an encounter with Jupiter-the fastest Earth escape until the New Horizons launch in 2006.

The Jupiter flyby in February 1992 sent Ulysses into the first artificial-satel lite orbit to pass over the poles of the Sun. The initial swing overthe solar south pole in 1994 was followed by the first northern pass in 1995. Two orbits later, Ulysses was completing its third northern polar pass at the start of 2008.

As its aging radioisotope generators continued to run down, the probe's hydrazine fuel was in danger of freezing. But the loss of the main X-band radio transmitter on January 15th prompted researchers to wrap up the science program by the end of June. The backup S-band transmitter can't return enough data to make it worthwhile continuing.

Ulysses leaves an extensive scientific legacy. It discovered thatthe solarwind at high latitudes flows a fast and steady 750 km per second compared to a wildly fluctuating and slower 400 km per second near the ecliptic. The fast wind is also cooler, thinner, and more directly reflects the composition of the Sun's photosphere than the slow wind, which is affected by conditions in the chromosphere.

Ulysses also discovered thatthe magnetic field in the solarwind has a similar strength at all latitudes, disproving earliertheoriesthat predicted stronger fields near the poles.

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Title Annotation:Mission Update
Author:McDowell, Jonathan
Publication:Sky & Telescope
Geographic Code:1USA
Date:Jun 1, 2008
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