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A tethered balloon is an inflated fabric structure, often shaped like an airship and usually filled with helium, that is restrained by a cable attached to the ground or a vehicle. Tethered balloons differ from airships and free balloons in that it is not free-flying.
Tethered balloons are sometimes called aerostats.
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Tethered balloons come in three forms:
- 1) Traditional sausage-shaped (i.e., blimp-shaped) balloons with fins to stabilize them, but relying on helium alone for lift;
- 2) Simple round balloons relying on helium alone, but without stabilisation. These are sometimes used to carry passengers or support advertisement, like the aerophile balloons;
- 3) Hybrid tethered balloons are systems that use both buoyancy and aerodynamic lift.
Designed by Albert Caquot, French engineer, in 1914, the barrage balloons of World War I and World War II were examples of tethered balloons. Today, tethered balloons are used for lifting cameras, radio antennas, electro-optical sensors, radio-relay equipment and advertising banners - often for long durations. Tethered balloons are also used for position marking and bird control work.
During the 1990 Invasion of Kuwait, the first indication of the Iraqi ground advance was from a radar-equipped tethered balloon that detected Iraqi armor and air assets moving south. Surveillance tethered balloons were used in the 2004 American occupation of Iraq. They utilized a high-tech optics system to detect and observe enemies from miles away. They have been used to over watch foot patrols and convoys in Baghdad, Afghanistan and several other contingency operations.
The United States Geological Survey uses tethered balloons to carry equipment to places where conventional aircraft cannot go, such as above an erupting volcano. Tethered balloons are ideal as they can easily remain more or less in one place; are less likely to be damaged by volcanic ash and are less expensive to operate than a helicopter.
The Drug Enforcement Administration has contracted with Lockheed Martin to operate a series of radar-equipped tethered balloons to detect low-flying aircraft attempting to enter the United States. A total of twelve tethered balloons, called Tethered Aerostat Radar System, are positioned approximately 350 miles apart, from California to Florida to Puerto Rico, providing unbroken radar coverage along the entire southern border of the US.
Lockheed Martin is the global leader in Aerostat technology and production.
Worldwide Aeros Corp. manufactures a family of tethered balloon systems for a variety of uses.
Aerophile is one of the world leaders along with Lindstrand Technologies in large tethered gas balloons for passengers.
Tethered balloons can be used as temporary transmitters, instead of a radio mast, either by using the tether which holds the balloon as the antenna, or by carrying antennas on the balloon fed by a fiber optic or radio frequency cable contained inside the tether. The advantage of tethered balloons is that great antenna heights are easily realizable and they can stay aloft for months.
Tethered balloons are sometimes used for advertisement, either by lifting advertisement signs, or by using a balloon with advertisements on it. Often both methods are combined. It is not uncommon to use specially designed balloons. By suspending a light source within the envelope, the balloon can be made to glow at night, drawing attention to its message.
See also 
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- Lockheed Martin PTDS Aerostat ISR system
- Vigilance Rapid Deployable Aerostat
- Raven Aerostar - aerostat manufacturer
- SkyDoc Aerostat resources
- Worldwide Aeros Corp – a manufacturer of aerostats
- TCOM – a manufacturer of aerostats
- Top I Vision – video surveillance aerostats
- Aerophile SA – manufacturer of aerostats
- Aerostat based communications and surveillance
- SkyDoc Aerostat resources
- Air-Foil Aerostat