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Balloon tank
Lightweight tank that needs to be pressurized to keep its shape / From Wikipedia, the free encyclopedia
A balloon tank is a style of propellant tank used in the SM-65 Atlas intercontinental ballistic missile (ICBM) and Centaur upper stage that does not use an internal framework, but instead relies on a positive internal pressurization to keep its shape.
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![](http://upload.wikimedia.org/wikipedia/commons/thumb/0/00/Centaur_stage_during_assembly_1962.jpg/640px-Centaur_stage_during_assembly_1962.jpg)
![](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Centaur-propellant-system.jpg/640px-Centaur-propellant-system.jpg)
Balloon tanks are very light, and this permits a good propellant mass fraction. A disadvantage of balloon tanks is that if pressurization fails, the vessel collapses.