Ulysses mission finally ended today

Ulysses, the joint ESA/NASA solar orbiter mission, finally ended today when ground controllers sent commands to shut down the satellite's communications. The event marks the conclusion of one of the longest and most successful space missions ever conducted.

The mission had been predicted to end in July 2008, when the satellite's weakened power supply was expected to fall below the minimum required to keep fuel lines from freezing, without which Ulysses would be uncontrollable. At that time, the ESA/NASA operations team planned to continue operating the spacecraft in a reduced capacity for a few more weeks.

However, through smart engineering and realtime innovation, controllers determined they could keep the lines from freezing by briefly firing the thrusters every few hours. In fact, Ulysses has continued gathering valuable scientific data throughout most of the past year - until today, after a decision was taken to end the mission due to continuing weak power and the unavailability of ground station time.

Today's final communication pass via NASA's 70-m Deep Space Network started at 17:35 CEST and the satellite's radio communications switched into receive-only mode at 22:10 CEST. Last telemetry was received as expected at 22:15 CEST. No further contact with Ulysses is planned

Launched by Space Shuttle Discovery on 6 October 1990, the 18-year, 8-month mission has returned a wealth of scientific data on the space environment above and below the poles of the Sun. The spacecraft and its suite of nine instruments had to be highly sensitive yet robust enough to withstand some of the most extreme conditions in the Solar System, including a close fly-by of the giant planet Jupiter.

During its life, Ulysses made nearly three complete orbits of the Sun. The probe revealed for the first time the three-dimensional character of galactic cosmic radiation, energetic particles produced in solar storms and the solar wind. Not only has Ulysses allowed scientists to map constituents of the heliosphere in space, its longevity enabled the Sun to be observed over a longer period of time than ever before.

"The Sun's activity varies with an 11-year cycle, and now we have measurements covering almost two complete cycles," said Marsden. "This long observation has led to one of the mission's key discoveries, namely that the solar wind has grown progressively weaker during the mission and is currently at its weakest since the start of the Space Age."

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