A U.S. Army tethered aerostat broke free from its mooring station at Aberdeen Proving Ground, Md., on October 28 and drifted in a northerly direction over Pennsylvania with a length of tether attached. The airship came down about four hours later and 160 miles away, apparently after knocking out power to thousands of utility customers.
The North American Aerospace Defense Command (NORAD) said two Air National Guard F-16s from Atlantic City, N.J., were dispatched to monitor the runaway aerostat, which rose to about 16,000 feet as it floated north. The command worked with the Federal Aviation Administration to ensure air traffic safety after the airship broke loose at 12:20 p.m. Later that afternoon, the command announced on Twitter that the aerostat had landed near Moreland Township in north central Pennsylvania, about 130 miles northwest of Philadelphia. “The area is secured and a military recovery team is enroute,” NORAD said.
The airship was one of two helium-filled, tethered aerostats comprising the Army’s Joint Land Attack Cruise Missile Defense Elevated Netted Sensor (JLENS) system, which NORAD has been evaluating as part of its multi-layered aerial surveillance and defense strategy. One of the aerostats in a JLENS orbit carries a 360-degree VHF surveillance radar, the other an X-band fire-control radar. According to the system concept, once the surveillance radar detects an airborne threat such as a cruise missile or a drone, ground operators then slew the fire-control radar on the other aerostat to the area to provide precise targeting information for air-launched or ground air defense weapons. The aerostats are supposed to fly at 10,000 feet above sea level for 30 days at a time, coming down only for maintenance or in the event of severe weather.
The Army launched a surveillance aerostat from Aberdeen Proving Ground north of Baltimore last December to begin the three-year evaluation. It launched the second, fire-control aerostat in mid-August. It was not immediately known which airship broke free from its mooring station.
The 243-foot-long aerostats are held aloft by a tether made of Vectran, a manufactured fiber spun from liquid crystal polymer. The tether carries power to the JLENS radar and sends data down to a computer. The tether has withstood winds in excess of 100 knots, and the chance of it breaking “is very small,” according to JLENS prime contractor Raytheon. “However, in the unlikely event it does happen, there are a number of procedures and systems in place which are designed to bring the aerostat down in a safe manner,” the manufacturer added. Raytheon referred inquiries about the runaway aerostat to NORAD.
According to media reports, the rogue aerostat dragged a mile-long section of tether that disrupted the electrical grid on its path. PPL Electric Utilities, which serves central and eastern Pennsylvania, reported that 18,000 customers lost power. “We are assessing and responding to damage to our system reportedly caused by the tether line of the runaway blimp,” the utility tweeted late in the afternoon. “We are working to switch many affected customers to other circuits, restoring power. It has not been determined how long repairs will take.” Broadcast media later showed the aerostat deflated and wrapped around a tree.