LYCOS RETRIEVER 
Ulysses: Spacecraft
built 656 days ago
Ulysses is a robotic space probe designed to study the Sun at all latitudes. The spacecraft, named for the Latin translation of "Odysseus", was launched in October 1990 from the Space Shuttle Discovery (mission STS-41) as a joint venture of NASA and the European Space Agency. It was originally scheduled for launch in 1986 aboard the Space Shuttle Challenger. The spacecraft is equipped with instruments to characterize fields, particles, and dust, and is powered by a radioisotope thermoelectric generator (RTG). The Ulysses mission is ongoing, still collecting valuable scientific readings to this day.
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The Ulysses is the first spacecraft to explore the third dimension of space over the poles of the Sun. Scientists have found some surprising new discoveries about the polar regions of the Sun when the spacecraft passed over the regions in 1994 and 1995. The spacecraft revealed two clearly separate and distinct solar wind regimes, with fast wind emerging from the solar poles.
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During cruise phases, Ulysses is still providing unique data. As the only spacecraft out of the ecliptic with a gamma-ray instrument, Ulysses provides an important part of the InterPlanetary Network (IPN). The IPN detects gamma ray bursts (GRBs); since gamma rays cannot be focused with mirrors, it was very difficult to locate GRBs with enough accuracy to study them further. Instead, several spacecraft can locate the burst through triangulation (or, more specifically, multilateration). Each spacecraft has a gamma-ray detector, with readouts noted in tiny fractions of a second. By comparing the arrival times of gamma showers with the separations of the spacecraft, a location can be determined, for follow-up with other telescopes.
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The Ulysses spacecraft continues to go where no other spacecraft has gone before, namely, over the Sun's poles to study the Sun and Its Influence on the space environment. About a year after Ulysses once again crossed into the Sun's south polar cap, it has begun its journey over the north polar cap. Previous spacecraft have remained near the Sun's equator where the Earth and other planets are located... Ulysses' orbit is perpendicular or highly inclined to all other spacecraft orbits providing a unique perspective from which to study the Sun and its effect on surrounding space. Entry into the North Polar Cap is defined by the heliographic (solar) latitude of + 70 degrees. Ulysses will now proceed to its maximum latitude of 80 degrees and then return to 70 degrees in 15 March 2008 and exit the polar cap. Observations of the solar wind, magnetic field, solar energetic particles and cosmic rays obtained during this interval will be compared with those obtained in the South Polar Cap earlier this year in order to investigate differences, i.e., a North-South asymmentry or temporal differences - associated with changes on the Sun made evident by the network of in-ecliptic (solar equatorial) heliospheric spacecraft.
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Ulysses is spin-stabilized about the axis of the dish. The RTG, whip antennas, and instrument boom were placed to stabilize this axis. Spin is nominally 5 rpm. Inside the body is a hydrazine fuel tank. Hydrazine monopropellant is used for course corrections, and to repoint the spin axis (and ... the antenna) at Earth. The spacecraft is controlled by eight thrusters, in two blocks. Thrusters are pulsed in the time domain to perform rotation or translation.
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The Ulysses spacecraft is an international project to study the poles of the sun and interstellar space above and below the poles. The mission, managed jointly by NASA's Jet Propulsion Laboratory and the European Space Agency, is designed to study three major topics in solar physics: the sun, the solar wind and interstellar space. The instruments of Ulysses will study those phenomena at nearly all solar latitudes, but the most important work will be at high solar latitudes, near the polar regions of the sun that have not been explored by other spacecraft.
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