Unmanned airships and blimps, also known as LTA (lighter than air) vehicles or aerostats, use a buoyant gas such as helium to provide lift. Some may be tethered in place, while others use motors, fins and rudders for propulsion and steering. Hybrid aerostats also exist that incorporate design principles from kites, allowing them to stay aloft in stronger winds than would otherwise be possible.
Due to the fact that airships undergo passive lift that is used to gain altitude, their power requirements for staying airborne are much lower than other UAVs (unmanned aerial vehicles) such as fixed-wing drones and multicopters. This means that they typically have much longer endurance than other unmanned aircraft, and can lift relatively heavy loads.
They are usually powered by batteries, and some may also use solar panels. Solar power is suitable for many blimps as they have a large surface area, and unlike fixed-wing UAVs, solar panels will not interfere with the aerodynamics of the aircraft.
Blimps typically move much slower than other UAV platforms, and this low kinetic energy means that they are safer for operations over people and in urban environments. Blimps are also relatively easy to repair, as holes in the material can simply be patched up, and most damage to the ship will not result in an immediate catastrophic drop.
Tethered aerostats are connected to their base station by a cable that provides power and communications. Depending on their size, they may be launched from trucks and other vehicles, or even boats. They can be used to quickly and easily set up a persistent aerial presence.
Blimps and aerostats are used for a wide variety of military and civilian applications, including ISR (Intelligence, Surveillance & Reconnaissance) and SIGINT (Signals Intelligence), supporting forward operating troops, communications relays, broadcasting and advertising, and weather monitoring and environmental research.