An artist's concept of Ulysses. Photo: ESA

The European Space Agency has agreed to fund the Ulysses mission for an extra 2 years and 9 months. At its meeting in Paris on June 5-6, ESA's Science Programme Committee approved the funds to continue operating the spacecraft from the end of 2001 to September 30, 2004.

Ulysses is a joint ESA/NASA mission and NASA's approval is also required for the mission extension. So far, NASA has approved funding until December 2002 and a decision on further funding is expected in mid-2001. If that decision is positive, Ulysses will remain in operation to observe the Sun's environment as sunspot activity gradually declines after this year's sunspot maximum.

Over the past ten years, Ulysses, launched on October 6, 1990, has made many remarkable discoveries about the heliosphere, the vast bubble blown out into space by the solar wind, from its unique solar polar orbit. The extension to September 30, 2004 would allow the spacecraft to complete two full orbits around the poles of the Sun and make further discoveries throughout a full 11-year solar cycle.

"Ulysses has already changed our view of the heliosphere in many fundamental ways. We are delighted that the SPC has approved the extension and we are now looking forward to a positive decision by NASA," says Richard Marsden, ESA's Ulysses Project Scientist.

Ulysses second solar orbit diagram. Photo: ESA

Around solar maximum, the polarity of the Sun's magnetic field reverses, causing corresponding changes to the heliosphere. Ulysses is expected to make new discoveries about how this readjustment takes place in the months following the field reversal. Extending the mission will allow the spacecraft to gain a clear picture of the behaviour of the heliosphere as it settles down once again to quiet times from the Sun.

"We'll be watching carefully as the relative chaos of the active Sun makes way for a more stable pattern," says Marsden. "The effects will be most readily seen in the behaviour of cosmic ray particles arriving from outside the heliosphere."

In the early years of this decade, during the declining phase of the previous solar cycle, Ulysses was en-route to Jupiter, and all measurements were made near the ecliptic (the plane in which the planets orbit) rather than at high solar latitude. The extension would allow Ulysses to make the first-ever set of high-latitude observations over a full solar cycle.

The extension would also allow Ulysses to continue addressing a broad range of astrophysical phenomena, which include locating gamma-ray burst sources, studying the interstellar abundance of rare species like deuterium and 3He, and increasing the precision of cosmic ray isotopic abundance measurements.

After a detailed study, ESA concluded that there are sufficient on-board consumables to keep a core payload operating continuously provided there is some time-sharing among other scientific instruments. The additional cost to ESA represents excellent value-for-money in return for a significant enhancement to the scientific harvest of the Ulysses mission.