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Ulysses is a joint space mission between the European Space Agency (ESA) and NASA, designed to explore the unknown region of space above the poles of the Sun.
It was launched in 1990 and travelled to Jupiter to where a gravity-assist manoeuvre put it in orbit around the poles of the sun. Its orbit varies from a distance of about the same as the Earth to about five times that distance.
(Diagram courtesy NASA)
Ulysses will also undertake investigations of the heliosphere, the large bubble of space dominated by the Sun's extended atmosphere and magnetic field. The diagram below shows how, as the Sun moves through space (from right to left in the diagram), its radiating fields plough through interstellar space creating a bow wave - at this point the pressure from the solar wind will just balance the pressure of the local Interstellar Medium. This boundary is thought to be positioned many times further away than the outermost planet of the Solar System.
(Picture courtesy NASA)
Voyager 1 (see link at bottom of page), the farthest man- made object in the Solar System, finally crossed the boundary bow wave in May 2005, after 28 years of travel through space. Scientists are using data from a number of spacecraft to try and gain a better understanding of the heliosphere.
Ulysses flew over the south pole of the Sun in 1994 and the north pole in 1995, with a second flight over the north pole during October-December 2001. It will then, for the second time in its 11-year lifetime, head out towards Jupiter's orbit in the long leg of its six-year circuit around the Sun. It will continue to monitor the state of the heliosphere as solar activity calms down, from the maximum in 2000, towards the next solar minimum.
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