Ulysses Mission Extension Approved
14 November 2007Meeting in Paris on 12-13 November, ESA's Science Programme Committee unanimously approved a proposal to continue operating the highly successful Ulysses spacecraft until March 2009. This latest extension, for a period of 12 months, is the fourth in the history of the joint ESA-NASA mission.
"This new lease of life is great news for the international heliophysics community," said Richard Marsden, ESA's Mission Manager and Project Scientist for Ulysses. "No other spacecraft can provide the out-of-ecliptic measurements made by Ulysses. The Sun's activity will soon pick up again, and there are plenty of unsolved questions for the Heliospheric Network to tackle." Among these is an apparent asymmetry in the temperature of the Sun's polar coronal holes, which appears to be related to the magnetic polarity. This was discovered during the first high-latitude passes in 1994 and 1995, when the magnetically positive northern polar coronal hole was found to be cooler than the southern pole. Data acquired during the coming months will hopefully shed new light on this puzzle.
For a satellite in its 18th year in space, Ulysses is in remarkably good health. Nevertheless, in order to compensate for the steadily diminishing power output of the onboard radioisotope thermoelectric generator (RTG), the spacecraft operations team has had to devise a new operational strategy that will allow the majority of the scientific instruments to operate throughout the period covered by the extension without the need for large-scale power-sharing. This entails switching part of the communications sub-system off when the spacecraft is not transmitting data in order to provide the power needed for the payload. During downlink sessions, the power needed for the transmitter will be provided by temporarily switching off one of the large onboard heaters. "Even though this will cause the spacecraft to cool, it is expected to happen slowly enough to avoid problems," said Marsden.
So what will the future have in store for Ulysses? "We're all very pleased to be able to continue getting great scientific data for another year," said Marsden. "Beyond that, we'll have to wait and see." As noted by Prof. Lennard Fisk of the University of Michigan, "To be sure, Ulysses has a finite lifetime, determined by technical limitations. There are no limitations to the science that we can still do. We are on an exploratory mission, probing the most fundamental processes of our solar system. Every bit of new data holds the promise of a new discovery of profound importance."