Solar probe Ulysses ends historic mission of discovery
Ulysses, a joint mission of NASA and the European Space Agency, officially ceased operations on Tuesday after operating for more than 18 years and charting the region of space above the poles of the sun, Xinhua reported.
A statement from NASA's Jet Propulsion Laboratory in Pasadena, California, said Ulysses followed programmed commands and switched off its transmitter completely at 4:15 p.m. EDT (2015 GMT).
When Ulysses was launched from the space shuttle Discovery on Oct. 6, 1990, it had an expected lifetime of five years. However, the mission gathered unique information about the heliosphere, the bubble in space carved by the solar wind, for nearly three times longer than expected.
"This has been a remarkable scientific endeavor," said Richard Marsden, Ulysses mission manager and project scientist at the European Space Agency. "The results Ulysses obtained have exceeded our wildest dreams many times over."
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 them to observe the sun 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."
In addition to measuring the solar wind and charged particles, Ulysses instruments measured small dust particles and neutral gases from local interstellar space that penetrate into the heliosphere. The spacecraft had an unprecedented three chance encounters with comet tails, registered more than 1,800 cosmic gamma-ray bursts, and provided findings for more than 1,000 scientific articles and two books.
"The breadth of science addressed by Ulysses is truly astonishing," said Ed Smith, Ulysses project scientist at NASA's Jet Propulsion Laboratory. "The data acquired during the long lifetime of this mission have provided an unprecedented view of the solar activity cycle and its consequences and will continue to keep scientists busy for many years to come."
The extended mission also presented significant challenges to the NASA-European operations team. In particular, critical parts of the spacecraft became progressively colder with time. In recent years, a major effort was made to prevent the onboard hydrazine fuel from freezing. The operations team continually created methods to allow the aging space probe to continue its scientific mission.