Updated 5 a.m. Eastern July 6.
WASHINGTON — NASA’s New Horizons spacecraft suffered an anomaly July 4 that put the spacecraft into a protective safe mode less than ten days before its flyby of Pluto, but should resume normal operations by July 7 with no effect on mission science.
In a statement issued late July 4, NASA said spacecraft controllers, working at mission control at the Applied Physics Laboratory in Maryland, lost contact with the spacecraft at 1:54 p.m. Eastern time July 4. Communications with New Horizons resumed at 3:15 p.m. Eastern time.
The communications blackout was apparently triggered by a problem with the main computer on New Horizons. The spacecraft’s autopilot placed the spacecraft into safe mode and switched to a backup computer to resume communications.
The cause of the problem that put New Horizons into safe mode wasn’t immediately known. NASA said in the statement that the spacecraft is “healthy” and flight controllers were working on a recovery plan. Returning New Horizons to normal operations could take “one to several days,” the statement advised, in part because of the nine-hour round-trip time for communications between the Earth and the spacecraft.
In a statement late July 5, NASA said that a “a hard-to-detect timing flaw,” and not a specific hardware or software fault, caused the safe mode. The set of operations that caused the timing flaw is not planned for the remainder of the flyby. Normal science observations should resume by July 7.
That gap in science observations caused by the safe mode was disappointing to scientists working on New Horizons, but they were hopeful the spacecraft will return to normal operations well before the flyby. “We may lose a few appetizers off the planned menu, but right now the focus is on delivering the main course,” said one scientist involved with the mission July 5.
The observations lost while the spacecraft is in safe mode will have only a “minimal effect” on some lower-priority science goals, mission principal investigator Alan Stern said in the July 5 statement. “In terms of science, it won’t change an A-plus even into an A.”
New Horizons had been in good condition prior to the July 4 anomaly. “The spacecraft is operating flawlessly,” Stern said in a June 29 interview. “It’s running on all of its prime systems. We are not using any of its backups.”
The project team announced July 1 that the spacecraft would remain on its planned trajectory, which will send the spacecraft to within 12,500 kilometers of Pluto’s surface at approximately 7:50 a.m. Eastern time July 14. That decision came after the project completed a seven-week search for any previously unknown moons or rings orbiting Pluto that could pose a hazard to the spacecraft, requiring the spacecraft to fly a safer, but more distant, trajectory past Pluto.
“As a scientist I’m a bit disappointed that we didn’t spot additional moons to study, but as a New Horizons team member I am much more atedieved that we didn’t find something that could harm the spacecraft,” said John Spencer, who led the search for potential hazards, in a July 1 statement.
