With its nuclear power generator cooling and its maneuvering fuel about to freeze, ESA/NASA's Ulysses spacecraft is nearing the end of its 18-year voyage to study the sun and its impact on the solar environment, or "heliosphere."

 NASA and the European Space Agency are planning to pull the plug on Ulysses on July 1, ending the only mission ever sent to orbit over the north and south poles of the sun, rather than circling in the same plane as the planets. Launched in 1990, Ulysses flew out to Jupiter and used the giant planet's gravity to bend its trajectory so that it dove "down," below the orbital plane of the planets. It then circled back under the sun, swept "up" again and began its exploration of a region of the solar system that had never been visited before.  In two Jupiter flybys, it also added to our understanding of the Jovian system.

The mission lasted four times longer than its designers planned, and the German-built, NASA-powered craft has provided scientists with a long list or surprises and discoveries. You can read more about it here.