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.
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.
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.