Galileo Millennium Mission Status November 25, 2002
Flight controllers have returned NASA’s Galileo spacecraft to normal
operation after the spacecraft put itself into a precautionary standby
mode about 16 minutes after flying near Jupiter’s inner moon Amalthea
on Nov. 5.
The veteran spacecraft is now functioning properly, except for its
tape recorder, which is used for storing data for later transmission
to Earth. The Galileo flight team is conducting tests to diagnose the
problem with the tape recorder and developing possible commands to get
it working again.
“It appears that the tape recorder has taken a hit from the intense
radiation Galileo passed through,” said Dr. Eilene Theilig, Galileo
project manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.
“Our efforts to restore the tape recorder may continue for a few
weeks.”
During the Amalthea flyby, the orbiter sped through an environment of
intense natural radiation close to Jupiter. Hits by radiation
triggered Galileo’s onboard computer to enter a “safe” mode, which
causes the spacecraft to suspend most activities until receiving
further instructions. At least five events occurred that each
individually would have put the spacecraft into this standby mode. The
problems were diagnosed and a new sequence of commands was sent to
Galileo. Normal operations, including the real-time collection of
scientific data from the magnetometer instrument, resumed on Nov. 13.
One possible cause for the tape recorder malfunction is radiation
damage to a light-emitting diode or an optical transistor in the
circuitry that controls the recorder’s motor. Diagnostic tests
indicate the situation is not the same as previous times when tape in
the recorder has become stuck.
In the hours before the Amalthea flyby and the minutes afterwards,
Galileo’s scientific instruments gathered information about the energy
fields and charged particles of the magnetic environment close to
Jupiter and about dust particles that make up a “gossamer” ring around
the planet. Most of that information is recorded on the tape
recorder, so getting the data into the hands of scientists depends on
reviving the tape recorder.
Information about Galileo’s path of movement during the flyby is
already on the ground. Researchers are analyzing it to determine
whether it will give a clear indication of how Amalthea’s gravity
affected the spacecraft, which would provide an estimate of that
moon’s density and a clue to its composition.
Galileo, launched in 1989, has been orbiting Jupiter since 1995 —
nearly five years longer than planned for its original prime mission.
Passes through Jupiter’s radiation belts have exposed the orbiter to
more than four times the cumulative dose of radiation it was designed
to withstand.
The Amalthea encounter was Galileo’s final flyby. The spacecraft has
nearly depleted its supply of the propellant needed for pointing its
antenna toward Earth and controlling its flight path. While still
controllable, it has been put on a course for impact into Jupiter next
September. The maneuver prevents the risk of Galileo drifting to an
unwanted impact with the moon Europa, where it discovered evidence of
a subsurface ocean that is of interest as a possible habitat for
extraterrestrial life.
Additional information about Galileo and the discoveries is available
at
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.
