ESA's Ulysses Spacecraft, the first probe ever to fly over the poles of the Sun, climbed to its maximum latitude of 80.2 degrees north of the Sun's equator on Monday, 31 July, thereby passing another milestone on its historic mission to survey the Sun's environment from a unique vantage point in space.
All operations and science experiments continue to go well and NASA's tracking facilities near Madrid and Goldstone, California, are monitoring the spacecraft 24 hours a day as manoeuvres are performed to keep Ulysses' radio antenna pointing toward the Earth.
Launched in October 1990 aboard the space shuttle Discovery, the 370-kilogram spacecraft was designed to study the heliosphere - that region of space dominated by the solar wind -at all latitudes above and below the Sun's equatorial plane. These high latitude regions have never been explored before.
Named after the legendary adventurer who journeyed to the "hidden" side of the Sun, Ulysses carries nine scientific instruments provided by research institutes in Europe and the United States to make detailed studies of solar wind, magnetic fields, energetic solar and cosmic ray particles, natural radio waves, and interplanetary dust and gas. In addition, a gamma- ray burst detector helps determine the source of the brightest cosmic gamma-ray bursts. In a permanent 6-year orbit about the Sun, the spacecraft is currently travelling at about 90,000 kilometers per hour with respect to the Sun. Having made its greatest northern excursion, Ulysses is now gradually descending in latitude. On 29 September 1995, the spacecraft will complete the northern polar pass and begin to travel back out to the orbit of Jupiter, reaching Jupiter's distance of about 800 million kilometers in April, 1998. Ulysses will then head back on its high latitude trajectory toward the Sun, returning first to the south polar regions in the year 2000, followed by a second flight over the north pole in 2001.
Initial results from the climb to high northern latitudes have already confirmed a number of the findings from Ulysses' southern polar pass that took place last year. As expected, once the spacecraft moved away from the equatorial regions heading north, it became permanently immersed in fast solar wind from the northern polar cap.
Another feature of the southern polar regions, the uniform radial magnetic field (with no evidence of a "magnetic pole"), is also characteristic of the northern hemisphere. "We don't expect the Sun's northern hemisphere to be fundamentally different from the South", said Dr. Richard Marsden, the European Space Agency's project scientist for Ulysses. "On the other hand, the Sun is less active now, and this may influence the observations".
The scientists will have a special meeting next fall to discuss the detailed findings from the northern solar pass. The Ulysses mission is a collaborative project managed jointly by ESA, the European Space Agency, and NASA's Jet Propulsion Laboratory.
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