Defense Secretary Ashton B. Carter has signed off on a plan to fly a pair of giant radar balloons over Aberdeen Proving Ground again, military officials said Thursday.

The unmanned balloons have been grounded since October, when one broke free of its moorings and drifted 160 miles north into central Pennsylvania.

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Army investigators have concluded that a series of errors combined to rip the balloon from the ground.

"Design, human, and procedural issues all contributed to the incident," said Maj. Beth Smith, a spokeswoman for the North American Aerospace Defense Command.

NORAD launched the system, known as JLENS, last year to see if it could help spot cruise missiles being shot at Washington. The pair of balloons carried specialized radars for the task.

The company that makes the balloons said the chance of breaking the tether that held them to the ground was less than one in a million. Investigators said a combination of circumstances caused the cable to fail.

The full report has not been made public, but Smith provided a summary.

The problems began when the wind picked up, Smith said. The pressure inside the balloon was supposed to increase in response, but a device intended to detect changes in pressure — called a pitot tube — malfunctioned.

A fin sagged and a lightning rod cable wrapped around it, tearing the tail. That made the whole aircraft unstable and broke the tether that held it to the ground.

Once free, the balloon began floating toward Pennsylvania, defying the predictions of military planners who expected it would fall into the Chesapeake Bay.

The military scrambled F-16 jets to chase it, and authorities warned people on the ground away. It trailed thousands of feet of cable at an average speed of 40 mph, snapping power lines and causing outages along the way.

At least $300,000 in claims have been filed with the Army.

The balloon's journey came to an end in rural Moreland Township, Pa., where it crashed into some woods and was deflated with shotgun blasts before being untangled from trees.

Smith said NORAD wants to resume the test, which was scheduled to run for three years. But getting the system aloft again would require congressional approval, more money, training personnel and manufacturing a new balloon.

Congress cut three-quarters of the funding for the project in an end-of-year budget deal to reflect a "test schedule delay."

Aides have said the money could be restored.

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""The way ahead at this point is a little unclear," Smith said.

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