Ulysses Solar Orbiter Switched Off

Controllers switched off the Ulysses joint European Space Agency/NASA solar orbiter June 30, almost 19 years after its launch on the space shuttle Discovery in October 1990.

The end-of-mission command from the Jet Propulsion Laboratory (JPL) turned off the spacecraft's radio into monitor-only status, and no further commands are planned.

Mission engineers managed to eke out an extra year of operations by firing Ulysses' thrusters every two hours to keep the fuel from freezing as the onboard radioisotope power system degraded.

Ultimately ESA and NASA decided to free up the 70-meter Deep Space Network antennas needed to collect data from Ulysses, and to save on the cost of operating it in the face of diminishing scientific returns.

"Although it is always hard to take the decision to terminate a mission, we have to accept that the satellite is running out of resources and a controlled switch-off is the best ending," said Paolo Ferri, head of the Spacecraft Operations Solar and Planetary Missions Division at JPL.

Ulysses was the first spacecraft to orbit the sun over its poles, orbiting Earth's star every six years after achieving solar orbit with the help of a gravity assist from Jupiter in 1992.

It took the first direct measurements of interstellar dust particles and helium atoms, and discovered that the dispersal of solar particles is not shaped solely by the latitude at which they are expelled from the sun.

That last finding will help planners protect astronauts on future deep-space exploration missions by giving them a better idea of the danger posed by activity on different areas of the sun's surface.

"Ulysses has taught us far more than we ever expected about the sun and the way it interacts with the space surrounding it," said Richard Marsden, ESA's Ulysses project scientist and mission manager. The spacecraft will continue in its solar orbit, which at apogee reaches the orbit of Jupiter.

Artist's concept of Ulysses: Jet Propulsion Laboratory