New Horizons went into safe mode briefly on Saturday, but the glitch won’t affect the overall Pluto mission (Image: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)

A hiccup in the final days of New Horizons’ decade-long journey to Pluto won’t affect any important science results, NASA says.

Mission controllers are in regular contact with the spacecraft as it nears its final approach on 14 July, but at 5.54 pm GMT last Saturday it suddenly went silent. About 80 minutes later, the NASA tracking station at Tidbinbilla in Australia regained contact with the craft, which had gone into “safe mode”, where it stops collecting data.

“The spacecraft is in full contact again,” says Glen Nagle, a spokesman for the CSIRO’s Canberra Deep Space Communication Complex at Tidbinbilla. “So it’s OK. It’s downlinking data and receiving commands.”

Since it takes 4.5 hours for signals travelling at the speed of light to reach the craft – making 9 hours in total for the return journey – resuming normal operations was always going to take time. Later on, NASA revealed the fault wasn’t a result of software or hardware on board, but rather some commands sent to the craft. “The underlying cause of the incident was a hard-to-detect timing flaw in the spacecraft command sequence that occurred during an operation to prepare for the close fly-by,” NASA said in a statement. “No similar operations are planned for the remainder of the Pluto encounter.”

Normal operations should resume tomorrow, NASA says.

“It’s a good thing it happened now and not on Tuesday next week,” says Nagle, when the Pluto fly-by is due to occur. At the moment, the craft’s main job is taking increasingly close pictures of the dwarf planet. As a result, a couple of approach images will not have been recorded over the weekend.

The crucial science will be done as the craft passes Pluto, but Nagle says even if the fault had occurred closer to the crucial fly-by moment, data would not have been lost.

“Even if we stayed out of contact with the craft and re-established contact, say, two weeks from now, the spacecraft still would have done everything it needed to do at encounter time. The command set is on board,” says Nagle. “It would take an extraordinary set of circumstances [to make it fail] because each piece of equipment on New Horizons has a backup to keep it going.”

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