Jet Propulsion Laboratory, Pasadena, Calif.
agle@jpl.nasa.gov 

Dwayne Brown    202-358-1726
NASA Headquarters, 
Washington                                                                                     

dwayne.c.brown@nasa.gov

NEWS RELEASE: 
2008-031                                                              
Feb. 22, 2008

*International Solar Mission to End Following Stellar Performance*

WASHINGTON - The joint NASA and European Space Agency Ulysses mission to 
study the sun and its influence on surrounding space is likely to cease 
operations in the next few months. The venerable spacecraft, which has 
lasted more than 17 years or almost four times its expected mission 
lifetime, is succumbing to the harsh environment of space.

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.

"I remember when we got those first pictures of Ulysses floating out of 
the space shuttle Discovery's payload bay back in October of 1990 and 
thinking we had a great five years ahead of us," said Ed Massey, Ulysses 
project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "I 
never dared think that we would be receiving invaluable science data on 
a near continuous basis for more than 17 years. Ulysses has set the bar 
on solar science data collection quite high."

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.

"The data and science output of this mission truly deserves to be named 
after the legendary explorer in Greek mythology," said Arik Posner, 
Ulysses program scientist, NASA Headquarters, Washington. "My 
compliments go out to the international team of scientists and engineers 
who built a spaceship and instrument payload that is highly sensitive, 
yet durable enough that it withstood the most extreme conditions in the 
solar system, including a polar passage of the giant planet Jupiter."

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 2 degrees Celsius (36 degrees 
Fahrenheit), the spacecraft's hydrazine fuel will freeze. This has not 
been a problem in the past because Ulysses carries heaters to maintain a 
workable onboard temperature.

The spacecraft is powered by the decay of a radioactive isotope. Over 
its 17-plus years, the power has been steadily dropping. The spacecraft 
no longer can run all of its communications, heating and scientific 
equipment simultaneously. "We expect certain parts of the spacecraft to 
reach 2 degrees Celsius 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 NASA/ESA project team approved a plan to temporarily shut off the 
main spacecraft's X- band transmitter. This would release 60 watts of 
power, which could be channeled to the science instruments and the 
heater. The team planned to turn the transmitter back on when data was 
to be transmitted back to Earth. This would have made it possible to run 
Ulysses for up to another two years.

Unfortunately, during the first test of this approach in January, the 
power supply to the radio transmitter failed to turn back on. Engineers 
believe the fault can be traced to the transmitter's power supply, 
meaning that the extra energy they hoped to gain cannot be routed to the 
heater and science instruments. "The decision to switch the transmitter 
off was not taken lightly. It was the only way to continue the science 
mission," Marsden said.

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. 

"We will squeeze the very last drops of science out of it that we can," 
Marsden said. "Ulysses is a terrific old workhorse. It has produced 
great science and lasted much longer than we ever thought it would."

The Ulysses spacecraft was built by Dornier Systems of Germany for ESA. 
NASA provided the launch and the upper stage boosters. The U.S. 
Department of Energy, Washington, supplied the generator that powers the 
spacecraft; science instruments were provided by both U.S. and European 
investigators. The spacecraft is operated from JPL by a joint NASA/ESA 
team and has employed NASA's Deep Space Network for communications.

More information about NASA's Ulysses mission is available on the Web at:

***http://ulysses.jpl.nasa.gov*