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An aerostat (From Greek ἀήρ aer (air) + στατός statos (standing) through French) is a craft that remains aloft primarily through the use of buoyant lighter than air gases, which impart lift to a vehicle with nearly the same overall density as air. Aerostats include free balloons, airships, and tethered balloons. An aerostat's main structural component is its envelope, a lightweight skin containing a lifting gas to provide buoyancy, to which other components are attached. One of the most recent deployments of an aerostat was seen at the opening ceremony of the nineteenth 2010 Commonwealth Games, held in Delhi, India. The aerostat used in the ceremony was the largest in the world.
Aerostats are so named because they use "aerostatic" lift which is a buoyant force that does not require movement through the surrounding air mass. This contrasts with aerodynes that primarily use aerodynamic lift which requires the movement of at least some part of the aircraft through the surrounding air mass.
There are two distinct senses for the scope of the term aerostat. In the broader sense, the term refers to all systems that remain aloft primarily using aerostatic buoyancy. In the narrower sense, the term is used to refer to the most common type of aerostat which is the Tethered balloons. This article uses the term in its broader sense. For the narrower sense, see tethered balloon. Moored means on a platform; tethered means secured to one location and not manned or flight controlled.
Tethered balloons 
Systems that are connected to the surface via one or more tethers: In contrast to the other types of aerostats, tethered balloons are non-free flying. A notable example of tethered balloons are barrage balloons. Some tethered balloons obtain aerodynamic lift via the contours of their envelope or through the use of fins. Tethered balloons are also used for military purposes, border protection, sight seeing and advertising.
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Helikite is a trademarked name given to a patented combination of a helium balloon and a kite to form a single, aerodynamically sound tethered aircraft, that exploits both wind and helium for its lift. The attached balloon is generally oblate-spheroid in shape although this is not essential. A Helikite is not a moored balloon, because a Helikite is not a balloon. A Helikite is a tethered aerostat. The US Customs classifies a Helikite as "other non-powered aircraft" not as balloons. The British Civil Aviation Authority's Air Navigation Order gives Helikites its own classification as "Helikites" as opposed to "kites" and "balloons". A Helikite is not just a kite because Helikites fly in nil wind and kites need wind to fly. A Helikite is not just a balloon because Helikites can fly even if weighed down to be heavier than air whereas balloons will never fly if heavier than air. A Helikite is a new type of tethered aerostat with its own official classification. Trials have shown that Helikites fly to greater altitudes than tethered balloons and in far higher winds. They stay stationary and steady in the air in more conditions and for longer than any other type of aerostat. If the word aerostat comes from the greek "aer" + "statos" then Helikites are a pure form of aerostat.
Free balloons 
Free-flying buoyant aircraft that can be propelled and steered. Some airships obtain aerodynamic lift via the shape of their envelope or through the addition of fins or other shape. These types of craft are called hybrid airships.
Tethered balloons can carry instruments and sensors for long durations that are impractical for other aircraft.
Airships are free flying aerostats that can be propelled and steered.
See also 
- Airship resources
- Aerophile web page
- Tactical Aerostats
- Raven Aerostar web page
- DJ's Zeppelin page
- "Illustrations of the Five Major Types of Lighter-Than-Air-Aircraft" Popular Mechanics, June 1930