Just days away from its rendezvous with Pluto, the New Horizons Spacecraft experienced a communications glitch that temporarily halted its science operations, NASA says.

Communications with the probe were lost on the afternoon of the Fourth of July holiday and remained silent for more than an hour before controllers at the space agency's Deep Space Network were able to reestablish contact.

The spacecraft's autopilot system, recognizing a problem, followed its programming and put the probe into "safe mode" while it switched control from the primary onboard computer to a backup one that restored communications.

"Full recovery is expected to take from one to several days; New Horizons will be temporarily unable to collect science data during that time," NASA said in a statement.

Due to its location almost 3 billion miles from earth, commands from controllers take 4.5 hours to reach the spacecraft and any response from the probe takes another 4.5 hours to return, the agency explained.

In preparation for its flyby of the dwarf planet set for July 14, controllers had already sent a new set of instructions dubbed the "encounter program" to the spacecraft.

One of the features of the program would override any attempt by the spacecraft to put itself into the automatic safe mode as it did on July 4.

"Encounter mode short-circuits the onboard intelligent autopilot so that if something goes wrong, instead of calling home for help, which is what most spacecraft do and what New Horizons does during cruise flight, it will just stay on the timeline," explained New Horizons lead scientist Alan Stern.

The spacecraft would attempt to fix any problem it encountered but would not enter safe mode -- what Stern called going "fetal" -- because "if it just called home for help, it could miss the flyby," he said.

New Horizons has been on a long voyage toward Pluto -- the only major object in our solar system not yet visited by a robotic space probe -- since 2006.

For most of that time it has been in a sort of technical hibernation, brought back to life in January of this year to begin science operation as it approaches the dwarf planet and its moons.

The spacecraft, controlled by the backup computer, is healthy and sending data back to Earth, NASA said, as controllers continue to work to investigate the cause of the communications glitch.

NASA released a statement early Monday that the spacecraft returns to normal science operations.

"I'm pleased that our mission team quickly identified the problem and assured the health of the spacecraft. Now - with Pluto in our sights - we're on the verge of returning to normal operations and going for the gold," said Jim Green, NASA's Director of Planetary Science.