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 http://galileo.jpl.nasa.gov. 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.
Contacts: JPL/Guy Webster (818) 354-6278