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Probe To Orbit Sun’s Poles

December 9, 1985

SAN FRANCISCO (AP) _ A probe called Ulysses will be launched from a space shuttle next May and use Jupiter as a gravitational slingshot to become the first spacecraft to orbit the sun’s poles, scientists said Monday.

″Over the poles of the sun, it’s going to be a very exciting time,″ David Bohlin, chief of solar physics for the National Aeronautics and Space Administration, told researchers attending the American Geophysical Union’s fall meeting.

″We have reasons for believing the properties of the solar wind and the magnetic field in the sun’s polar regions are quite different than near the sun’s equator,″ said Edward J. Smith, Ulysses project scientist for NASA’s Jet Propulsion Laboratory. ″So we need to go up there and see what kind of processes are going on.″

Peter Wenzel, Ulysses project scientist for the European Space Agency, said the $400 million, five-year international mission ″will solve some outstanding problems in solar physics,″ including the structure of the sun’s magnetic field and pathways of solar wind, a hot gas, or plasma, of electrically charged particles that speeds away from the sun at nearly 1 million mph.

Ulysses won’t actually get very near the sun, approaching only within 130 million miles, about 1.4 times Earth’s distance from the sun.

But it will travel farther out of the plane in which the planets lie than any other spacecraft, allowing it to reach previously unexplored portions of space above and below the plane of the solar system. That plane is called the ecliptic.

The 800-pound probe, which is about the size of a small car and was built for the European Space Agency, will be carried into Earth orbit aboard a NASA shuttle scheduled for launch May 15.

Ulysses will be dropped out of the shuttle’s cargo bay atop a new type of Centaur upper stage rocket, built by General Dynamics in San Diego.

The rocket will fire after it moves away from the shuttle, carrying Ulysses toward Jupiter at 45,000 mph, faster than any space probe has ever traveled, said Wenzel, who is from Noordwijk, The Netherlands.

In July 1987, Ulysses will swing above Jupiter and, deflected by the gravitational field of the solar system’s largest planet, will move around and beneath Jupiter and the ecliptic plane and back toward the sun.

″It is a gravitational slingshot,″ Smith said, explaining that no rocket engine is powerful enough to get Ulysses out of the ecliptic plane. The gravitational fields of smaller, closer planets are inadequate, he added.

Ulysses will pass under the sun’s south pole in March 1990, circle upward and fly over the sun’s north pole a year later before heading back out into space, Wenzel said.

The probe will be equipped with nine instruments to measure solar wind, magnetic fields, cosmic rays and dust, interplanetary gases, X-rays, radio waves, various particles and the sun’s corona, or hot atmosphere.

By studying solar wind plasma, scientists also hope to learn more about the hot gas that makes up most matter in the universe and which they are trying to harness on Earth to create fusion energy, Smith said.

Ulysses will reach the sun during the peak of sunspot and solar flare activity that occurs every 11 years, letting scientists learn more about how such phenomena affect weather and communications on Earth, Wenzel said.

Two space probes originally were planned, one European and one American. The American probe would have carried devices to take X-ray images and pictures of the corona.

″But due to budgetary actions of the Reagan administration, NASA canceled that (second) spacecraft,″ Wenzel said.

Ulysses will study Jupiter in passing. Another rocket from another shuttle later next May will carry the Galileo space probe toward Jupiter, which it will explore.

The Ulysses probe is named after the hero of Homer’s ″The Odyssey,″ who goes on a 10-year exploratory adventure. In ″The Inferno,″ Dante wrote that Ulysses was restless after returning home and implored his brethren to travel with him to ″the uninhabited world beyond the sun.″

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