October 1,1994
On Tuesday, September 13, the Jupiter-bound Galileo spacecraft experienced a failure in one memory cell of an on- board computer -- one bit out of more than 3 million bits total in the computer. This is the only memory failure to have occurred on Galileo in the 5 years of its flight to date.
During the development of the advanced computer memories, it was recognized that perhaps dozens of cells would randomly fail over the 8-year mission lifetime. To protect against such failures, special fault protection was included in the spacecraft flight software. Immediately upon detecting the failure on Sept. 13, that fault protection software executed as it was intended to. This stopped the sequence of commands then being carried out to play back science data from Galileo's observation of Comet Shoemaker-Levy 9 impacts at Jupiter in July, and reconfigured the spacecraft in a safe state.
By Sept. 25, the failure had been traced and programmed around, and the transmission of Shoemaker-Levy data resumed. No long-term mission impacts of the memory failure are expected. Some of the data lost due to the problem will be recovered by changing the priorities in a later transmission of data stored on Galileo's on-board tape recorder. Transmission of Shoemaker-Levy data is planned to continue through January 1995.
Currently, data from Galileo's near-infrared mapping spectrometer of Comet Shoemaker-Levy's fragment G impact are being transmitted and will be followed later this month by data from the imaging cameras's observations of the impacts of fragments K and N.
The spacecraft continues to operate normally, spinning at
about 3 rpm and transmitting at 10 bits per second to ground
stations at NASA/JPL's Deep Space Network. The spacecraft will
reach Jupiter on December 7, 1995, when its probe will descend
into the Jovian atmosphere and the orbiter spacecraft will begin
two years of observation and measurement of the planet, its moons
and magnetosphere.