This fall, two high-flying, blimp-like craft may take flight over the northeast corner of Maryland, carrying a radar system capable of detecting trains, boats, cars, and — the Pentagon hopes — cruise missiles. The Washington Post reports that in October, the Aberdeen Proving Ground military base plans to start a three-year test of how surveillance aerostats (essentially large, tethered balloons) could improve missile defense systems on the Eastern Seaboard. The two craft would float up to 10,000 feet above the ground for 30 days at a time, and their attached radar system is supposed to be able to detect airborne objects from up to 340 miles away — which means it could reach as far as Boston — and vehicles on the surface from up to 140 miles away, closer to the distance between the base and New York City.

The aerostats, designed by defense contractor Raytheon, can be mounted with extremely sensitive sensors that can capture a live video feed of vehicles from "dozens" of miles away. But the Army denies that it has any current plans to mount cameras or infrared sensors, nor to share the information it captures with law enforcement at any level, though the Post reports that it wouldn't rule either possibility out. The system has previously been tested in Utah, where small planes simulated the flight of missiles, and similar tests will be carried out in Maryland.

The Raytheon system, known as JLENS, is meant to quickly detect flying objects, like missiles, that might be difficult or impossible to see from the ground in time to alert officials of an attack on the nearby capital. But civil liberties advocates worry that it will be hard to resist turning its formidable surveillance capabilities inward. Even without camera systems, it could be possible to detect and track civilian vehicles across a large expanse of space, though the technical limits of the aerostats' radar isn't clear. Areas around the US border can already be patrolled with drones by the Department of Homeland Security, and Customs and Border Protection has carried out hundreds of missions for other agencies, including the Coast Guard, Drug Enforcement Administration, and local law enforcement.