Donald Savage
Headquarters, Washington, DC                  March 15, 2001
(Phone: 202/358-1547)

Guy Webster
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-5011)

RELEASE: 01-41

GALILEO GETS ONE LAST FREQUENT-FLYER UPGRADE

     The resilient Galileo spacecraft doesn't know when it 
call it quits. So, NASA has outlined the details of one last 
mission extension, which includes five more flybys of the 
Jovian moons before a final plunge into the crushing pressure 
of the giant planet's atmosphere.

Galileo has been orbiting Jupiter for more than five years and 
survived radiation exposure more than three times what it was 
built to withstand. Galileo's mission has previously been 
extended twice and during that time it has returned an 
enormous wealth of scientific information, including evidence 
of a sub-surface ocean on Jupiter's moon Europa.

"We're proud that this workhorse of a spacecraft has kept 
performing well enough that we can ask it to keep serving 
science a little longer," commented Dr. Jay Bergstralh, Acting 
Director of Solar System Exploration at NASA Headquarters, 
Washington, DC.

On May 25, Galileo should pass about 123 kilometers (76 miles) 
above the moon Callisto, the second largest of Jupiter's 28 
known moons. The effects of Callisto's gravity will set up the 
space probe for a swing over both polar regions of the 
intensely volcanic moon Io in August and October.

Galileo will take pictures, measure magnetic forces, and study 
dust and smaller particles. Science goals include studying the 
extent of volcanism on Io, both in new and previously active 
sites; determining whether Io generates its own weak magnetic 
field; and gaining a better understanding of a doughnut-shaped 
ring, the Io Torus, that encircles Jupiter and contains 
electrically charged gases. 

In 2002, having completed its imaging mission, Galileo will 
continue studies of Jupiter's massive magnetic field with 
seven instruments. In January, the orbiter will fly near the 
equator of Io.

In November, it will swing closer to Jupiter than ever before, 
dipping within about 500 kilometers (about 300 miles) of the 
moon Amalthea, which is less than one-tenth the size of Io and 
less than half as far from Jupiter. Scientists will use 
Galileo measurements to determine the mass and density of 
Amalthea. They will also study dust particles as Galileo flies 
through Jupiter's gossamer rings and seek new details of the 
magnetic forces and the densities of charged particles close 
to the planet.

Galileo's final orbit will take an elongated loop away from 
Jupiter. Then in August 2003, the spacecraft will head back 
for a direct impact and burn up as it plows into Jupiter's 
60,000 kilometer-thick atmosphere. This final act was approved 
by the National Research Council of the National Academy of 
Sciences last December.

"Galileo has already succeeded beyond expectations, and we 
have the opportunity to learn still more in coming months, but 
it is sad to see the end of the road up ahead," said Eilene 
Theilig, Galileo project manager at NASA's Jet Propulsion 
Laboratory, Pasadena, CA. "Exposure from Jupiter's intense 
radiation belts has impaired some of Galileo's instruments, 
but it is still producing valuable scientific results."

The science program for the Galileo mission extension was 
recommended to NASA by a blue-ribbon panel of planetary 
scientists, who met last July, and will cost $9 million. "This 
mission extension accomplishes the highest priorities of the 
review panel in a cost effective way," said Paul Hertz, 
Galileo Program Executive at NASA Headquarters.

Galileo was launched Oct. 18, 1989, aboard NASA's Space 
Shuttle Atlantis. On Dec. 7, 1995, a probe released earlier 
from Galileo made measurements while dropping through 
Jupiter's upper atmosphere. Galileo's top scientific 
accomplishments include:

*  Produced strong evidence that Europa has a melted saltwater 
ocean under the ice layer on its surface. The spacecraft has 
also found indications that Ganymede and Callisto have layers 
of liquid saltwater, too.
*  Detailed the varied and extensive volcanic processes on Io, 
catching plumes erupting, fire fountains in process and lava 
flows expanding, among other observations.
*  Delivered a probe that made the first measurements of 
Jupiter's atmosphere from within the atmosphere.
*  Made the first close approach to an asteroid and made the 
first discovery of a satellite orbiting an asteroid.
*  Discovered the first internal magnetic field of a moon. 
Ganymede's intrinsic magnetic field actually creates a "mini-
magnetosphere" embedded within Jupiter's vast magnetosphere.
*  Provided the only direct observation of Comet Shoemaker-
Levy's impact into Jupiter.

JPL, a division of the California Institute of Technology in 
Pasadena, manages Galileo for NASA's Office of Space Science, 
Washington, DC. 

More information about Galileo is available on the Internet 
at:

                http://galileo.jpl.nasa.gov/

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