International Mission Studying Sun to Conclude
PASADENA, Calif. - After more than 17 years of pioneering solar science,
a joint NASA and European Space Agency mission to study the sun
will end on or about July 1.
The Ulysses spacecraft has endured for almost four times its expected
lifespan. However, the spacecraft will cease operations because of a
decline in power produced by its onboard generators. Ulysses has forever
changed the way scientists view the sun and its effect on the surrounding space.
Mission results and the science legacy it leaves behind were reviewed today
at a media briefing at European Space Agency Headquarters in Paris.
"The main objective of Ulysses was to study, from every angle, the heliosphere,
which is the vast bubble in space carved out by the solar wind," said Ed Smith,
Ulysses project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
"Over its long life, Ulysses redefined our knowledge of the heliosphere and
went on to answer questions about our solar neighborhood we did not know to ask."
Ulysses ends its career after revealing that the magnetic field emanating from
the sun's poles is much weaker than previously observed. This could mean the
upcoming solar maximum period will be less intense than in recent history.
"Over almost two decades of science observations by Ulysses, we have learned a
lot more than we expected about our star and the way it interacts with the space
surrounding it," said Richard Marsden, Ulysses project scientist and mission manager
for the European Space Agency (ESA). "Solar missions have appeared in recent years,
but Ulysses is still unique today. Its special point of view over the sun's poles
never has been covered by any other mission."
The spacecraft and its suite of 10 instruments had to be highly sensitive, yet
robust enough to withstand some of the most extreme conditions in the solar system,
including intense radiation while passing by the giant planet Jupiter's north pole.
The encounter occurred while injecting the mission into its orbit over the sun's poles.
"Ulysses has been a challenging mission since launch," said Ed Massey, Ulysses project
manager at JPL. "Its success required the cooperation and intellect of engineers
and scientists from around the world."
Ulysses was the first mission to survey the environment in space above and below the
poles of the sun in the four dimensions of space and time. It showed the sun's magnetic
field is carried into the solar system in a more complicated manner than previously
believed. Particles expelled by the sun from low latitudes can climb to high latitudes
and vice versa, sometimes unexpectedly finding their way out to the planets. Ulysses also
studied dust flowing into our solar system from deep space, and showed it was 30 times
more abundant than astronomers suspected. In addition, the spacecraft detected helium
atoms from deep space and confirmed the universe does not contain enough matter to
eventually halt its expansion.
Ulysses collected and transmitted science data to Earth during its 8.6 billion kilometer
journey (5.4 billion miles). As the power supply weakened during the years, engineers
devised methods to conserve energy. The power has dwindled to the point where thruster
fuel soon will freeze in the spacecraft's pipelines.
"When the last bits of data finally arrive, it surely will be tough to say goodbye,"
said Nigel Angold, ESA's Ulysses mission operations manager. "But any sadness I might
feel will pale in comparison to the pride of working on such a magnificent mission.
Although operations will be ending, scientific discoveries from Ulysses data will
continue for years to come."
Ulysses was launched aboard space shuttle Discovery on Oct. 6, 1990. From Earth orbit,
it was propelled toward Jupiter by solid-fuel rocket motors. Ulysses passed Jupiter on
Feb. 8, 1992. The giant planet's gravity then bent the spacecraft's flight path downward
and away from the ecliptic plane to place the spacecraft in a final orbit around the sun
that would take it past our star's north and south poles.
The spacecraft was provided by ESA. NASA provided the launch vehicle and upper stage
boosters. The U.S. Department of Energy supplied a radioisotope thermoelectric generator
to provide power to 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.
More information about the joint NASA/ESA Ulysses mission is available at
Media contacts: Dwayne Brown 202-358-1726
NASA Headquarters, Washington
DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.