Washington, Feb 23 : The joint NASA and European Space Agency (ESA) Ulysses mission to study the sun and its influence on surrounding space is likely to cease operations in the next few months, after the weathering down of its machinery.
A major reason for the mission's closure is that the spacecraft, which has lasted more than 17 years - almost four times its expected mission lifetime, is succumbing to the harsh environment of space.
Since its Jupiter flyby in 1992, Ulysses has been in a six-year orbit around the sun.
Its long path through space carries it out to Jupiter's orbit and back. The farther it ventures from the sun, the colder the spacecraft becomes. If it drops to 36 degrees Fahrenheit, the spacecraft's hydrazine fuel will freeze.
Another factor contributing to the degradation of the spacecraft is the steadily dropping power of a radioactive isotope, which has run for well over 17 years.
Also, the spacecraft no longer can run all of its communications, heating and scientific equipment simultaneously. "We expect certain parts of the spacecraft to reach 36 degrees pretty soon," said Richard Marsden, ESA project scientist and mission manager.
This temperature drop will block the fuel pipes, making the spacecraft impossible to maneuver.
The failure of the X-band transmitter aboard the spacecraft had further heightened the problems for the proper functioning of the mission.
After many attempts, the Ulysses project team now considers it highly unlikely that the X-band transmitter will be recovered. As a result, the spacecraft has lost its ability to send large quantities of scientific data back to Earth and is facing the gradual freezing of its fuel lines.
The team plans to continue operating the spacecraft in its reduced capacity, using the alternate S-band transmitter, for as long as they can over the next few weeks.
Ulysses was the first mission to survey the space environment above and below the poles of the sun. The reams of data Ulysses returned have forever changed the way scientists view our star and its effects.
Science findings and discoveries from the mission were numerous and unprecedented.
Examples include taking the first direct measurements of interstellar dust particles and interstellar helium atoms in the solar system and the discovery that the magnetic field leaving the sun is balanced across latitudes.