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JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
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Galileo Millennium Mission Status
May 23, 2001
NASA's Galileo spacecraft today passed the closest
point to Jupiter of the spacecraft's current orbit of the giant
planet, and remains healthy as it heads for a flyby of Callisto,
the outermost of Jupiter's four largest moons.
Galileo swung within about 460,000 kilometers (about 285,000
miles) of Jupiter's cloud tops at 10:33 a.m. PDT time, according
to engineers managing the spacecraft from NASA's Jet Propulsion
Laboratory, Pasadena, Calif. Flying that close to Jupiter
exposes the spacecraft's electronics to potential harm from
intense radiation belts.
"We have indications Galileo is bearing up well to the harsh
environment, but it is still in a challenging environment," said
Dr. Eilene Theilig, Galileo project manager at JPL. "As
anticipated, we are seeing an intermittent anomalous behavior in
the camera, similar to what we saw during Galileo's last
encounter five months ago. Prior to high-priority observations,
we plan to cycle power to the instrument off and on to decrease
the risk of losing images. Cycling the power has cleared the
intermittent anomaly in the past."
Galileo is on course to pass within about 123 kilometers (76
miles) of Callisto at 4:24 a.m. PDT on Friday. Galileo has
succeeded at more flybys of assorted worlds -- including Venus,
Earth, and two asteroids as well as Jupiter's four largest moons
-- than any other spacecraft, and Friday's will be its closest
As of 2 p.m. PDT today, Galileo had recorded about 30
percent of the scientific data that its instruments had been
programmed to collect during this swing through the inner
portion of the Jupiter system. The images and other data will
be transmitted back to Earth over the next two months, with an
interruption of three weeks in June when Jupiter and Galileo
will be behind the Sun from Earth's perspective.
The scheduled observations so far have included studies
of Jupiter's clouds in infrared wavelengths, to improve
understanding of the structure and dynamics of the planet's
atmosphere and distant observations of Io, innermost of
Jupiter's large moons, to monitor its volcanic activity. High-
resolution images of Callisto's surface are planned for
studies of how loose debris on the surface may be obscuring
some of the smaller craters. Callisto is about the size of
Mercury, with a heavily cratered surface that reveals billions
of years worth of information about the size and frequency of
comets and other objects hitting Jupiter and its moons.
Galileo has already received more than three times the
cumulative radiation exposure it was designed to withstand and
has continued making valuable scientific observations more
than three years after its original two-year mission in orbit
around Jupiter. Its nuclear electrical power source -- two
radioisotope thermoelectric generators -- continues to provide
power to the instruments, computers, radio and other systems
on the spacecraft.
Additional information about the Galileo mission is
available at http://galileo.jpl.nasa.gov .
Galileo was launched in 1989 and has been orbiting
Jupiter since 1995. JPL, a division of the California Institute
of Technology in Pasadena, manages the Galileo mission for NASA's
Office of Space Science, Washington, D.C.