One of the two JLENS aerostats on the ground at Aberdeen Proving Ground, Maryland. Two aerostats make up a JLENS “orbit”.

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One of the two tethered aerostats that make up the Joint Land Attack Cruise Missile Defense Elevated Netted Sensor System (JLENS), broke loose from its moorings today and drifted across the skies of Maryland and  Pennsylvania, before coming down to earth 160 miles away. Two Air National Guard F-16 fighters were scrambled to monitor its movements, while its trailing tether took out power lines in Pennsylvania, causing blackouts across the state.

JLENS’ twin aerostats are (or were) supposed to provide airborne early warning and targeting of low-flying airborne threats coming in from the Atlantic, covering a radius of 300 miles with their look down search and targeting radar. They have been the subject of much controversy because of the cost of the program; a recent Los Angeles Times report called the $ 2.7 billion dollar project delivered by Raytheon a “zombie” program: “costly, ineffectual and seemingly impossible to kill.”

The twin white balloons with their radomes are usually visible from Baltimore and much of surrounding Maryland, flying on tethers at sites in Baltimore County and Harford County near the Army’s Aberdeen Proving Ground.The 242-foot long JLENS aerostats are designed to operate at altitudes of up to 10,000 feet, and can stay aloft for up to 30 days at a time before being retrieved for maintenance. The tethers, made of Vectran (a substance similar to kevlar), are 1 1/8 inches thick, and are designed to withstand 100 mile-per-hour winds. However, the Harford County tether, near Aberdeen Proving Grounds’ Edgewood Arsenal facility, broke today, about halfway up to the JLENS aerostat, allowing the unmanned, unpowered blimp to be carried off while trailing 6,700 feet of cable. High winds during a storm that passed through the Baltimore region, or perhaps wind shear associated with the storms, snapped the tether just after noon local time, setting the aerostat adrift.