Flight controllers are working to return Galileo to normal operations after the spacecraft unexpectedly went into safing mode this week.
Although controllers do not know what caused the incident, it is not expected to have any permanent effect on the Jupiter-bound Galileo, which has been in relatively quiet cruise en route to an asteroid flyby next October.
The spacecraft apparently went into safing mode at about 6:10 a.m. Pacific Standard Time on Tuesday, March 26.
In safing mode, the spacecraft turned off science instruments and went into an "all-spin" configuration in which all parts of the spacecraft spin. Galileo previously had been in a "dual-spin" configuration, in which part of the spacecraft spins and part remains fixed in relation to space.
The spacecraft also carried out a Sun-pointing maneuver to orient itself properly in relation to the Sun as part of the safing response. In safing mode this maneuver is automatically carried out every 12 hours.
Finally, also as a part of the safing response, Galileo dropped the speed of the digital data it sends to Earth from 40 bits per second (bps) to 10 bps.
According to the flight team, data from Galileo show that the incident was caused when one of the spacecraft's two redundant Command & Data Subsystem computers detected a problem with itself, prompting it to take itself off-line. The other computer continued to function properly and carried out all intended operations.
The cause of the problem in the computer is unknown, but has been confirmed to have been a transient signal of some kind. There is no evidence of any permanent damage to any hardware onboard the spacecraft, flight controllers said.
Project officials intend to reconfigure Galileo to resume normal activities by the time the next major sequence of commands is scheduled to be sent to the spacecraft April 25.
On April 10 Galileo had been scheduled to unfurl its high-gain antenna, a large umbrella of metal fabric that the spacecraft will use to communicate with Earth. Project officials said that the antenna unfurling will be delayed, but will be carried out before the April 25 uplink of the next major command sequence.
The event is the second time Galileo has entered safing mode since launch in October 1989. In both cases, the spacecraft responded exactly as intended, project officials noted.
The Galileo Project is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science and Applications.
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