Galileo Millenium Mission Status 6 Aug 2001

NASA’s Galileo spacecraft has successfully completed a
flyby of Jupiter’s moon Io, skimming about 200 kilometers (124
miles) above the surface of the highly volcanic moon at 0459
Universal Time today (9:59 p.m. Sunday, Pacific Daylight Time).

Engineers at NASA’s Jet Propulsion Laboratory in Pasadena,
Calif., said that signals confirming the veteran spacecraft’s
basic health were received five and a half hours after the flyby
via a Goldstone, Calif., antenna of the Deep Space Network.

As of 1700 UT (10 a.m. PDT) today, the spacecraft had
recorded about three-fourths of the scientific data that its
instruments had been programmed to collect during this swing
through the inner portion of the Jovian system. Besides
studying Io, Galileo has made observations of cloud patterns
on Jupiter.

Initial telemetry did not reveal whether or not Galileo
passed through a volcanic plume on Io. Galileo’s route went
directly over a volcano named Tvashtar, which had been spouting a
tall plume of gases when last observed seven months ago. “As
expected, we don’t have any sign at this point that the plume was
still active, but whether it was or not, we expect this flyby
will give us valuable new information about changes in the
Tvashtar area from recent activity,” said JPL’s Dr. Eilene
Theilig, Galileo project manager. The area was to be examined by
Galileo’s camera and near-infrared mapping spectrometer.

Galileo’s camera, which has had an intermittent electronic
problem for more than a year, appears not to have been working
during the closest part of the flyby. Engineers have narrowed the
cause of the problem to one of two electronic components probably
damaged by radiation from Jupiter’s radiation belts. Nine or more
of the camera’s 16 planned observations during the encounter
period were probably lost, Theilig said. Engineers are attempting
to restore the camera to functioning status in time for more-
distant observations planned for Tuesday and Wednesday.

Recorded data from the camera and Galileo’s other
instruments will be transmitted to Earth over the next two
months. “We’re looking forward to getting data back from the
observations to confirm that the scientific instruments worked as
planned,” Theilig said.

The flyby’s polar route was selected so Galileo could
collect magnetic measurements that might indicate whether Io
generates its own magnetic field, like the Earth, Jupiter, and
Jupiter’s moon Ganymede. That information could give scientists a
better understanding of what goes on deep inside Io, the most
volcanically dynamic world in the solar system. The magnetometer
and other instruments for studying fields and particles appear to
have been working during the flyby.

Coming close enough to Jupiter to approach Io subjects
Galileo to intense natural radiation from Jupiter’s radiation
belts, increasing the risk to the spacecraft’s electronics.

“Galileo has already performed much longer than expected,
so we’re pleased every time it completes another encounter
without showing new problems,” Theilig said. “We’re especially
satisfied to get the magnetic field measurements that were the
highest priority science objective for this flyby.”

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.

Galileo will fly near Io again, over the south pole
instead of the north, on Oct. 16, 2001.

Additional information about the mission is available at
http://galileo.jpl.nasa.gov . Galileo was launched from NASA’s
Space Shuttle Atlantis on Oct. 18, 1989. It began orbiting
Jupiter on Dec. 7, 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.