Aerostat

An aerostat is a tethered, lighter-than-air platform, a balloon on a cable, carrying sensors that stay aloft for days or weeks at a time. No pilot, no fuel burn to stay up, no orbit to maintain. The tether carries power up and data down, which is the whole trick: an aerostat at 10,000 feet gives radar a horizon hundreds of miles wide for a fraction of what it costs to keep surveillance aircraft in a 24-hour rotation.

What they actually do

Persistence is the product. A radar aerostat watches for low-flying aircraft and cruise missiles that terrain masks from ground radars, and it does so continuously. The US Tethered Aerostat Radar System (TARS) has flown along the southern border and the Caribbean since the 1980s, mostly hunting drug-running aircraft. Israel fields aerostats over its borders, and both sides in Ukraine have lofted them for communications relay and surveillance. Payloads run from surveillance radar to electro-optical turrets to signals-intelligence receivers, and swapping payloads is a ground-crew job, not a redesign.

The failure modes are just as concrete. Weather is the classic one. High winds have destroyed more aerostats than enemies have. The JLENS program, meant to cover the US East Coast against cruise missiles, died in large part because one of its aerostats broke loose in 2015 and dragged its tether 160 miles across Pennsylvania, cutting power to thousands of homes. Survivability against a capable adversary is the other standing question, since a large, stationary, radar-reflective target invites cheap kills.

Why use one when drones exist?

Cost per hour of coverage. A Reaper-class drone gives you a sensor for 20-odd hours, then lands, and the next one launches, with crews around the clock. An aerostat holds station for two weeks on one ground crew. For fixed-site or border surveillance, where the watch area never moves, the balloon wins the arithmetic. Drones win everywhere the target moves.

Who builds them?

TCOM in Maryland builds most Western military aerostats, with Raytheon and Lockheed Martin as the traditional radar integrators. RT Aerostat Systems of Israel supplies the smaller tactical class used widely by border agencies, and Aerostar covers high-altitude free-flying variants.