Update 4:30pm Pacific: The spacecraft is healthy, but will be convalescing until Nov. 24, said Cassini program manager Bob Mitchell of NASA’s Jet Propulsion Lab.

NASA engineers determined that some command files were corrupted en route from Earth to Saturn. Usually Cassini’s computers reject any corrupted commands, but somehow this one got through, Mitchell said.

The data stream may have been interrupted by solar flares, which spew jets of charged plasma into space and are known to pose problems for Earth-orbiting satellites as well.

The craft automatically triggers its safe-mode settings whenever something happens that requires attention from mission controllers on the ground. Since going into safe mode (what NASA terms a “safing event”), Cassini has stopped collecting science data and sent back only data on engineering and spacecraft health.

That’s normal, Mitchell said. “The spacecraft did everything it was supposed to do,” he told Wired.com. When the satellite reboots, “it will be as though nothing had ever happened, as far as the spacecraft is concerned.”

But the Cassini team will probably elect to leave the orbiter in safe mode until the next scheduled data-collecting sequence begins on Nov. 24, Michell added. Engineers will need to reset a lot of values in Cassini’s software by hand, such as indicators for which instruments are on and how much power is being used.

“There’s a lot of housecleaning to be done,” Mitchell said. “Rather than risk another safing event, or do damage, my preference is to take it careful.”

This is the sixth time Cassini has gone into safe mode since its launch in 1997, and only the second since it arrived at Saturn in 2004. That time, the safety switch was thrown by a cosmic ray striking the computers and throwing a power switch.

“Considering the complexity of demands we have made on Cassini, the spacecraft has performed exceptionally well for us,” Mitchell said.

But the hiccup came at an awkward time. The spacecraft was scheduled to fly past Saturn’s largest moon, Titan, on Nov. 11. The flyby will still happen, but the scientific instruments won’t be up and running again in time.

“Losing one [Titan flyby] will hurt,” Mitchell said.

There’s a silver lining, though: Cassini has 53 more Titan flybys planned between now and the end of its extended mission in 2017.

Image: NASA/JPL

See Also:

• Cassini Gets Life Extension to Explore Saturn Until 2017
• Cassini Skims Through Titan’s Upper Atmosphere
• Cassini Captures First Video of Extraterrestrial Lightning
• This Summer’s Sexiest Images From Saturn

Authors: Lisa Grossman

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