Tethered aerostats are unmanned non-rigid lighter-than-air vehicles (a.k.a. blimps), which remain anchored to the ground by one or more ropes. They are used for various surveillance tasks, where a low-cost long-endurance (up to a month) stationary aerial platform is needed. In all tethered aerostat systems, the main tether not only holds the blimp in position, but also provides electrical power to the vehicle's systems as well as a data link (via fiber optics in all modern systems) to communicate with the on-board sensors. The main envelope of an aerostat is filled with helium, while the stablizing tail fins are normally filled with air. The payload is located in a ventral dome under the envelope. The aerodynamic shape of the envelope and the tail fins provide a stable platform in the presence of modest winds and gusts. However, for each aerostat system there is a maximum wind speed in which it can safely operate. Loss of blimps to suddenly deteriorating weather conditions can be a problem for operators of tethered aerostat systems. When moored to the ground, large aerostats are anchored to a rotating mast so that they can freely weathervane in the wind.
Military - Aerostat