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Juno spacecraft slips into safe mode, putting science on hold

(NASA/European Pressphoto Agency)

Wednesday was meant to be a momentous day for NASA's Juno spacecraft. The robot, which entered orbit around Jupiter in July, was set to fire its main engine for the first time. That would have maneuvered Juno into a new trajectory where it could pass close to Jupiter's surface more often.

But last week, some of Juno's pieces weren't working quite as they should. A set of valves in the fuel pressurization system — components that help facilitate the firing of the main engine — were a bit sluggish when scientists executed a command sequence. The mission team decided to hold off on the scheduled burn, which meant keeping the craft's current orbit until December. Yet they hoped to have all of the spacecraft's instruments turned on for the planetary pass it would make Wednesday, making the most of a close encounter with Jupiter as consolation for the passes they'd miss.

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Instead, NASA reports, Juno went into safe mode several hours before that flyby. This happened automatically — it seems a software performance monitor prompted Juno to reboot its main computer — and isn't necessarily a horrible sign. Safe mode is what's supposed to happen when the spacecraft senses something unexpected. It battens down the hatches: The spacecraft ensures that it's facing the sun to receive solar power, then turns off its scientific instruments and any nonessential components to protect them for several hours or days.

Juno was still about 13 hours away from its planned close encounter when it entered safe mode, so scientists think it unlikely that the spacecraft encountered any truly troublesome radiation that would cause permanent damage.

“We were still quite a ways from the planet’s more intense radiation belts and magnetic fields,” Rick Nybakken, Juno project manager from NASA’s Jet Propulsion Laboratory, said in a statement. “The spacecraft is healthy, and we are working our standard recovery procedure.”

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Unfortunately, the safe-mode procedure kept Juno from collecting any scientific data during Wednesday's flyby. The next chance for close-range data collection will come Dec. 11. At that time, depending on Juno's condition, NASA may again try to slip it into the new orbit. If the transition is successful, the orbiter will make close passes of Jupiter every two weeks instead of every two months.

The team is analyzing data from Juno's initial flyby in late August, which gave scientists their first tantalizing glimpse below Jupiter's roiling clouds.

NASA is optimistic that Juno will behave normally for the next flyby. But it's been a rough week for space robots across the solar system: On Wednesday, the European and Russian space agencies were able to insert a satellite into orbit around Mars as part of the ExoMars mission. But the mission's second goal — touchdown of the Schiaparelli lander on the Red Planet's surface — seems to have failed.

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