When the Spacecraft Goes Silent, Engineers Awake

The New Horizons mission to Pluto suffered glitches that had to be solved 4.67 billion miles away.

The New Horizons interplanetary space probe went silent on July 4, 2015, just a week before the craft was scheduled to begin delivering photos and data from Pluto. After 9.5 years traveling to the far off once-planet, there was suddenly nothing. At first, the 40 members of the Space Mission Operations Group that manages NASA's New Horizons mission were stunned.

New Horizons, NASA, spacecraft

Yet according to Alice Bowman, New Horizons Mission Operations Manager (MOM) at the Johns Hopkins University Applied Physics Laboratory in Maryland, there wasn’t time for panic. When asked about the team’s emotional response during the hours it looked like the mission might possibly be doomed, she told Design News, “We didn’t have time for an emotional reaction. We had to get to work.”

The malfunction occurred just as the spacecraft was approaching Pluto. “The flyby was scheduled for nine days, from July 7 to July 16. This nine-day sequence took up 80% of our memory,” said Bowman. “On July 4th we stared loading the sequence to the spacecraft. The set of commands took two hours to radiate. At 1:55 pm, we lost communication with the spacecraft. That happened right at the time everybody was interested.”

Over the next few days, the team explored a number of scenarios that might have caused the glitch. “We thought the problem could be the switch from the main computer to the backup, so we switched to the backup computer. This was at 3:11 pm on July 4th,” said Bowman. “We have a process we follow when we have anomalies. We pretty much knew what to do. Over the next couple days, we got it back into configuration with four hours to spare. We didn’t leave the Command Center for three or four days, but that’s what made it successful.”

Maryland, We’ve Solved the Problem

The malfunction took days to solve simply because of the distance from Earth to Pluto, 4.67 billion miles. Communication with the craft to fix the malfunction was maddeningly slow at 4.5 hours each way. And that’s at the speed of light. The team would receive a response to communication nine hours after sending a message. The team discovered the spacecraft experienced a software anomaly and went into safe mode, preventing it from performing scientific observations.

Team engineers went to work to resolve the problem, and on July 5, NASA announced that the problem was determined to be a timing flaw in a command sequence used to prepare the spacecraft for its flyby. The spacecraft resumed scheduled science operations on July 7. The science observations lost because of the anomaly were judged to have no impact on the mission's objectives.

15 Years And the Project’s Still Going

Bowman told the dramatic story of the New Horizons Pluto mission in a keynote presentation at ESC Silicon Valley last week. The project has been operating for 15 years. “We proposed a mission to Pluto. Many projects were proposed but they were not funded. In 2001 NASA funded the mission. From the launch of the spacecraft, it would take 9.5 years to reach Pluto. We launched in 2006,


I would have thought that the software would have been more carefully checked, probably line by line, by a group who understood that language and the satellite system very well. But evidently not quite that well. But it certainly is good that they did know the system well enough to understand the problem and fix it. Hopefully a lesson was learned and no mistakes or errors next time. I do not like this 500 character limit. It REALLY STINKS!!!

Hey William. Alice said the problem is that when you add a new function, you don't know how the new code might affect a line of code for another function. That's apparently what happened.

If the team has to send the same satellite to the Pluto today again; Is it possible to power the satellite with the high efficiency (25-30 %) solar cells of today, instead of using nuclear power?

Even with so-called "high efficiency" solar cells of today, there isn't enough photon density at that distance to provide enough power, especially with degradation of the solar array from cosmic radiation exposure.

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