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NASA plans to renew the solar system passport of the Galileo
spacecraft by extending the mission exploring Jupiter and its
moons through the end of 2000, when Galileo may embark on a joint
scientific expedition with another solar system explorer, the
Saturn-bound Cassini spacecraft.

“This extended travel ticket enables us to continue studying
Jupiter and its fascinating moons,” said Jim Erickson, Galileo
Project Manager at NASA’s Jet Propulsion Laboratory, Pasadena,

During this new extension, called the Galileo Millennium
Mission, tour planners hope to include three high-priority
scientific observations in 2000:

Galileo would team with Cassini for simultaneous
observations of the Jupiter system and its magnetic environment
from two vantage points. Cassini will visit Jupiter’s
neighborhood in December 2000. Jupiter’s powerful gravity will
be used to “slingshot” Cassini toward Saturn.

Galileo will perform two additional flybys of Jupiter’s moon
Ganymede, the largest moon in the solar system, on May 20 and
December 28. Scientists hope these flybys will tell us more
about Ganymede’s geologic history, including the highest
resolution pictures ever taken of this icy world.

Results will be analyzed from the January 3 flyby of
Jupiter’s moon Europa and the closest-ever flyby of the volcanic
moon Io on February 22. That encounter, at an altitude of only
200 kilometers (124 miles), may have been the last tour of that
unique environment for years to come. The close-up images will
add to Galileo’s bulging scrapbook, which already contains about
14,000 pictures beamed back to Earth so far.

By April 2001, after the spacecraft transmits to Earth
pictures and scientific information stored on its tape recorder
during the flybys in 2000, Galileo will have traveled nearly 4-
1/2 billion kilometers (2.8 billion miles). Here on Earth, that
mileage would earn a frequent flyer nearly 85,000 free round-trip
tickets to Hawaii, an area with volcanoes remarkably similar to
those observed by Galileo on Io.

“For the first time ever, two spacecraft will simultaneously
explore an outer planet,” Cassini Project Scientist Dr. Dennis
Matson said about the planned Jupiter observation by Cassini and
Galileo. “One spacecraft will be inside Jupiter’s magnetic
envelope, with the other outside where it can observe the
powerful solar wind pressing on the envelope. From the two
vantage points, we’ll watch cause and effect as the wind changes
the magnetic properties around Jupiter.”

“We have a unique opportunity to study this dynamic system
with two highly capable spacecraft at the same time,” added
Galileo Project Scientist Dr. Torrence Johnson. “It’s a real
bonus for both missions.”

Galileo’s original two-year mission ended in December 1997,
and a two-year extension called the Galileo Europa Mission, ended
on January 31, 2000. Galileo engineers are fond of saying that
the spacecraft has lived well past its warranty. The spacecraft
has already endured nearly three times the radiation it was
designed to withstand, but repeated exposure to Jupiter’s
radiation has taken its toll. Galileo was zapped with
particularly high doses of radiation during recent flybys of Io,
which lies deep within Jupiter’s radiation belts.

“As Galileo continues operating in Jupiter’s harsh radiation
environment, it’s a challenge for our operations team to keep the
spacecraft healthy,” Erickson said. “But we like to think of
Galileo as the ‘little spacecraft that could.'”

Galileo mission planners are currently exploring various
options for the mission’s eventual conclusion, including possible
further encounters with Io and another Jovian moon, Callisto.
Planners are looking into a possible impact with Io or Jupiter
for a mission finale, with other options are also being
considered. They are trying to avoid an impact with Europa
because recent evidence suggests there may be a liquid ocean
beneath its icy crust, raising the possibility that life could
exist there.

More information on the Galileo mission is available at . Additional information about
the Cassini mission is available at .

Galileo was launched aboard the Space Shuttle Atlantis on
October 18, 1989, and it entered orbit around Jupiter on December
7, 1995. Cassini was launched on October 15, 1997 and it will
arrive at Saturn in 2004. JPL manages the Galileo and Cassini
missions for NASA’s Office of Space Science, Washington, D.C.
JPL is a division of the California Institute of Technology,



03/08/00 JP