Just 10 days before its history-making flyby of Pluto and its moons, NASA's New Horizons spacecraft briefly lost communication with Earth.

While most of us were celebrating Independence Day, scientists and flight engineers for NASA's New Horizons mission were hunkered down at the control center at Johns Hopkins University's Applied Physics Laboratory in Laurel, Maryland. They weren't celebrating much, because yesterday at 1:54 p.m. Eastern Daylight Time contact was lost with the spacecraft for about 1½ hours, until communication was restored at 3:15 p.m. EDT.

Trajectory of New Horizons past Pluto and its moons
Timing will be everything when New Horizons dashes past Pluto and its moons on July 14, 2015. Key events are shown in Universal Time.

According to a NASA-issued announcement, "During that time the autonomous autopilot on board the spacecraft recognized a problem and — as it’s programmed to do in such a situation — switched from the main to the backup computer. The autopilot placed the spacecraft in 'safe mode,' and commanded the backup computer to reinitiate communication with Earth. New Horizons then began to transmit telemetry to help engineers diagnose the problem."

For now, the spacecraft's planned observations have been suspended. New Horizons is still roughly 6½ million miles (10½ million km) from Pluto, and it's been taking a series of long-range navigation images to fine-tune the trajectory and timing during its dash through the Pluto system on July 14th. It's also been recording the state of the solar wind along its trajectory.

Pluto-Charon color rotation movie June 23-29
New Horizons scientists combined images taken with the craft's color and black-and-white cameras from June 23rd to 29th to create this time-lapse view of Charon circling around Pluto. During this interval the distance to these targets decreased from 15 million to 11 million miles (24 million to 18 million km). Both bodies were already showing many surface details.

Right now the spacecraft is nearly 3 billion miles (31.82 astronomical units) from Earth, so it takes 8.8 hours to complete a single, two-way communication.

Fortunately, it didn't take long for an Anomaly Review Board to determine that the spacecraft has no hardware or software problems. Instead, as mission managers reported late today, the glitch resulted from a "hard-to-detect timing flaw in the spacecraft command sequence that occurred during an operation to prepare for the close flyby."

No similar sequences are planned before the upcoming encounter, and the team expects to resume normal activities on July 7th. Overall the consequences of the operational hiccup will be minimal. "We may lose a few appetizers off the planned menu," notes mission participant Richard Binzel (MIT), "but right now the focus is on delivering the main course."

That "main course" is an intense, tightly scripted sequence of observations centered on July 14th at 11:49:58 Universal Time (7:49:58 a.m. EDT), when the spacecraft will come within 7,800 miles (12,500 km) of Pluto's surface as it zips past at 8.6 miles (13.8 km) per second. Because of its great distance from Earth, the spacecraft will transmit its results at a low data rate, and mission scientists won't have all of the flyby data in hand until mid-November.

Emily Lakdawalla's 8-page preview article in the July issue provides all the info you'll need to prepare for New Horizons' historic flyby.


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July 5, 2015 at 9:34 pm


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Anthony Barreiro

July 6, 2015 at 5:20 pm

alfaragalli -- Yes, November. Emily Lakdawalla's cover story in the July 2015 Sky and Telescope provides a very thorough overview of the New Horizons mission, including the timeline for data collection and transmission. New Horizons will be gathering a huge amount of data, and during the closest part of the flyby the probe will be fully occupied with gathering data, and mostly unable to transmit data. Even once the probe starts transmitting data, it will take a long time to download all of those data to the Earth. Exploring Kuiper belt objects that are four or five light hours distant from Earth is not a good hobby for the impatient.

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July 6, 2015 at 6:31 pm

Well, that's full resolution and not compressed images. But the probe will send compressed versions first, so we will have something to look at. Just hope there's no more safe modes right at the closest part of the flyby.

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