International Ulysses Team Meets At SwRI.

Business Editors & Science Writers

SAN ANTONIO--(BUSINESS WIRE)--Oct. 11, 2002

As the Ulysses spacecraft is completing its second pass around the sun in its unique high-latitude orbit over the sun's poles, an international group of Ulysses mission scientists are gathering at Southwest Research Institute(tm) (SwRI(R)) in San Antonio on October 10-11.

Launched in 1990 from space shuttle Discovery, Ulysses is a joint mission of NASA and the European Space Agency. The spacecraft, built by ESA and launched by NASA, achieved its polar solar orbit using a gravity assist from Jupiter to slingshot the craft into its high-latitude orbit, perpendicular to the ecliptic plane where the planets orbit the sun. The 48th working meeting of the mission science team will cover science, business, and operations aspects of the mission, including reports that instruments continue to perform well and return unique data, and that the spacecraft has adequate energy available.

"Ulysses is a tremendous science mission," says Dr. David J. McComas, executive director of Space Science and Engineering at SwRI, who is hosting the meeting. McComas is principal investigator of the Solar Wind Observation Over the Poles of the Sun instrument, one of 11 experiment packages aboard Ulysses.

"Hundreds of scientific papers have been written as a result of the mission, and we've learned a tremendous amount about the high-latitude solar wind and the heliosphere -- a previously unexplored region of space."

The Ulysses spacecraft is named for the protagonist in Homer's The Odyssey, which chronicles his adventures as he journeys home to Greece. Designed originally for just one orbit of the sun, the Ulysses space mission made some of its most interesting observations during the second solar orbit, when the spacecraft made measurements during solar maximum, the most turbulent portion of the 11-year solar cycle.

During the first orbit, the sun emitted a low-speed, variable wind in the low-latitude ecliptic plane, while at high latitudes towards the sun's poles, scientists observed a very fast, stable solar wind. The second orbit observed conditions at solar maximum, when completely chaotic fast and slow winds prevailed at all latitudes. Most recently, a somewhat simpler, less chaotic structure has returned, although not as simple as was previously observed.

"I think that as Ulysses heads back down to lower latitudes, the sun is getting quieter and quieter as the large polar coronal hole that emits the high-speed stable solar wind reopens behind us," said McComas. "We're seeing some fast winds and think a growing polar coronal hole must be responsible."

Just as The Odyssey's adventures didn't end with landfall in Greece, so the spacecraft's journey holds more possibilities, including a pass close to Jupiter.

"There are no technical reasons why we can't do a third orbit and continue to get these extremely valuable data," continues McComas. "The interesting and different things observed in the second orbit compared to the first are clearly a very strong function of the solar cycle.

"If you really want to understand the three-dimensional solar wind and the heliosphere, you need to sample it at different points in the solar cycle to see if the current model repeats itself as we head towards solar minimum," said McComas. "We've seen how very different things are at different points in the solar cycle, and there's much more to be learned about variation from one cycle to the next."

SwRI is an independent, nonprofit, applied research and development organization based in San Antonio, Texas, with more than 2,700 employees and an annual research volume of more than $319 million.