Sky anchor
Encyclopedia
A sky anchor is a system of two balloons in tandem, with a "zero-pressure" lifting gas balloon
tethered to a superpressure balloon
"anchor". The gas balloon is filled with a lifting gas
and provides the buoyancy
, while the superpressure balloon is filled with air, and pressurized to provide the desired ballast weight. In a passive sky anchor, the superpressure balloon is sealed, while in an active system, its pressure can be varied. Both versions have been tested in flight, but have had frequent failures with only occasional successful outcomes. The tandem arrangement makes launching difficult, and this complexity can lead to mission failure.
The tandem balloon system is intended to increase the flight time of the zero-pressure balloon by damping the diurnal
altitude variations caused by solar heating of the lifting gas and its subsequent expansion. As the balloons descend, the superpressure balloon's constant volume displaces a larger mass of the denser air, and becomes more buoyant. Likewise as they rise, the system displaces less air mass, limiting the ascent to prevent the lifting gas from expanding too far and escaping from the zero pressure balloon.
The Sky Anchor system, originally developed at Texas A&M University
in 1976, is usually applied to unmanned balloons, but the concept was also applied to a piloted balloon. The "Earthwinds" balloon system used a tandem balloon arrangement for a planned circumnavigation
record attempt using the jet stream
winds. Five attempts at the circumnavigation in the early 1990s all failed early in the flight, with the fifth abort on January 1, 1995 blamed on a failure of the lower ballast balloon.
Gas balloon
A gas balloon is any balloon that stays aloft due to being filled with a gas less dense than air or lighter than air . A gas balloon may also be called a Charlière for its inventor, the Frenchman Jacques Charles. Today, familiar gas balloons include large blimps and small rubber party balloons...
tethered to a superpressure balloon
Superpressure balloon
A superpressure balloon is a style of aerostatic balloon where the volume of the balloon is kept relatively constant in the face of changes in the temperature of the contained lifting gas. This allows the balloon to keep a stable altitude for long periods...
"anchor". The gas balloon is filled with a lifting gas
Lifting gas
Because of the Archimedes' principle, a lifting gas is required for aerostats to create buoyancy. Its density is lower than that of air . Only certain lighter than air gases are suitable as lifting gases.- Hot Air :...
and provides the buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
, while the superpressure balloon is filled with air, and pressurized to provide the desired ballast weight. In a passive sky anchor, the superpressure balloon is sealed, while in an active system, its pressure can be varied. Both versions have been tested in flight, but have had frequent failures with only occasional successful outcomes. The tandem arrangement makes launching difficult, and this complexity can lead to mission failure.
The tandem balloon system is intended to increase the flight time of the zero-pressure balloon by damping the diurnal
Diurnal temperature variation
Diurnal temperature variation is a meteorological term that relates to the variation in temperature that occurs from the highs of the day to the cool of nights.-Temperature lag:Temperature lag is an important factor in diurnal temperature variation...
altitude variations caused by solar heating of the lifting gas and its subsequent expansion. As the balloons descend, the superpressure balloon's constant volume displaces a larger mass of the denser air, and becomes more buoyant. Likewise as they rise, the system displaces less air mass, limiting the ascent to prevent the lifting gas from expanding too far and escaping from the zero pressure balloon.
The Sky Anchor system, originally developed at Texas A&M University
Texas A&M University
Texas A&M University is a coeducational public research university located in College Station, Texas . It is the flagship institution of the Texas A&M University System. The sixth-largest university in the United States, A&M's enrollment for Fall 2011 was over 50,000 for the first time in school...
in 1976, is usually applied to unmanned balloons, but the concept was also applied to a piloted balloon. The "Earthwinds" balloon system used a tandem balloon arrangement for a planned circumnavigation
Circumnavigation
Circumnavigation – literally, "navigation of a circumference" – refers to travelling all the way around an island, a continent, or the entire planet Earth.- Global circumnavigation :...
record attempt using the jet stream
Jet stream
Jet streams are fast flowing, narrow air currents found in the atmospheres of some planets, including Earth. The main jet streams are located near the tropopause, the transition between the troposphere and the stratosphere . The major jet streams on Earth are westerly winds...
winds. Five attempts at the circumnavigation in the early 1990s all failed early in the flight, with the fifth abort on January 1, 1995 blamed on a failure of the lower ballast balloon.