Balloon tank

A balloon tank is a style of fuel tank utilized in the Atlas ICBM and Centaur upper stage that does not utilize an internal framework, but instead rely on a constant internal pressurization to keep their shape.

Design

Balloon tanks get their name from the use of the cylindrical party balloons in which inspired Karel Bossart, a junior engineer on Werner von Braun's design team who later designed both the Atlas and Centaur rockets for the U.S. Air Force and NASA. Constructed of very thin stainless steel, the tanks, prior to integration into the Atlas or Centaur rocket body, are inflated with nitrogen to give the tanks their shape and strength. While other rockets, including the Titan and Saturn rockets (and even the Space Shuttle's external tank) can remain rigid due to the internal framework, balloon tanks must always remain presurrized, as any drop in pressurization will result in the failure of the vehicle.

History

The use of balloon tanks in the Atlas ICBM was the brainchild of rocket designer Karel Bossart. Instead of utlizing the traditional internal framework used on the rockets available at that time (especially the Redstone IRBM, a direct descendant of the V-2 rocket), the Atlas ICBM under development at that time used the balloon tank concept to allow the rocket to be lightweight and able to hurl a 5 megaton thermonuclear weapon to a target in the former Soviet Union from launch pads in the United States. This application allowed the Atlas to utlize 1.5 staging instead of the more complicated staging utilized in later Titan ICBMs.

After its initial development in the Atlas rocket, Bossart utilized the same technology with the high-energy Centaur upper stage. Utilizing liquid oxygen and liquid hydrogen (the Atlas rocket used LOX and RP-1, a highly-refined kerosene used in liquid-fueled rockets), the Centaur rocket, powered by its powerful RL-10 engine was originally planned to be used with the Saturn V rocket for high-energy mission to the Solar System, but was later adapted for use as part of the Atlas and Titan rockets.

With the introduction of the Atlas V EELV, balloon tanks and "1.5 staging" are no longer utilized on the Atlas rocket – only the Centaur retains this feature and has not undergone a single catastropic failure since the Atlas V's first flight.