![Centaur-propellant-system](https://upload.wikimedia.org/wikipedia/commons/f/f1/Centaur-propellant-system.jpg)
A balloon tank is a style of propellant tank used in the
SM-65 Atlas
The SM-65 Atlas was the first operational intercontinental ballistic missile (ICBM) developed by the United States and the first member of the Atlas rocket family. It was built for the U.S. Air Force by the Convair Division of General Dy ...
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.
Balloon tanks are very light, and this permits a good
propellant mass fraction
In aerospace engineering, the propellant mass fraction is the portion of a vehicle's mass which does not reach the destination, usually used as a measure of the vehicle's performance. In other words, the propellant mass fraction is the ratio bet ...
. A disadvantage of balloon tanks is that if pressurization fails, the vessel collapses.
Design
Balloon tanks get their name from the cylindrical party balloons that inspired
Karel Bossart
Karel Jan Bossart (February 9, 1904 – August 3, 1975) was an innovative rocket designer and creator of the Atlas ICBM. His achievements rank alongside those of Wernher von Braun and Sergei Korolev. But as most of his work was for the United ...
, who designed both the Atlas and Centaur rockets for the
U.S. Air Force
The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Sign ...
and
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...
. Constructed of very thin 301 extra-full-hard stainless steel 0.014–0.037 inch (0.3556–0.9398 mm) thick, prior to integration into the Atlas or Centaur rocket body the tanks are inflated with nitrogen to give them their shape and strength. As such, balloon tanks must always remain pressurized, as any appreciable drop in pressurization will result in failure. However, the airframes could be handled without tank pressurization through the use of a "stretch" mechanism (which basically helped support vehicle weight and prevented collapse). By contrast, non-balloon tanks in other liquid-propelled rockets remain rigid while empty due to an internal framework, although they do also depend on internal pressurization to support thrust and launch loads.
History
The use of balloon tanks in the Atlas ICBM was the brainchild of rocket designer Karel Bossart. Instead of the traditional internal framework used on the rockets available at that time, especially the
Redstone short-range ballistic missile
A short-range ballistic missile (SRBM) is a ballistic missile with a range of about or less. In past and potential regional conflicts, these missiles have been and would be used because of the short distances between some countries and their rela ...
(SRBM), a direct descendant of the
V-2 rocket
The V-2 (german: Vergeltungswaffe 2, lit=Retaliation Weapon 2), with the technical name ''Aggregat 4'' (A-4), was the world’s first long-range guided ballistic missile. The missile, powered by a liquid-propellant rocket engine, was develop ...
, the Atlas ICBM designers used the balloon tank concept to lighten the rocket enough to hurl up to a 3.75 megaton
thermonuclear warhead
A thermonuclear weapon, fusion weapon or hydrogen bomb (H bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a low ...
at a target in the
Soviet Union
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...
from a launch pad in the
contiguous United States. This tank technology made feasible a relatively simple
stage-and-a-half design for Atlas instead of the more complicated
staging
Staging may refer to:
Computing
* Staging (cloud computing), a process used to assemble, test, and review a new solution before it is moved into production and the existing solution is decommissioned
* Staging (data), intermediately storing data b ...
used in later
LGM-25 Titan ICBMs.
After its initial development in the Atlas rocket, Bossart used the same technology with the high-energy
Centaur upper stage. The Centaur rocket, fueled with liquid hydrogen and powered by an
RL10
The RL10 is a liquid-fuel cryogenic rocket engine built in the United States by Aerojet Rocketdyne that burns cryogenic liquid hydrogen and liquid oxygen propellants. Modern versions produce up to of thrust per engine in vacuum. Three RL10 ve ...
engine, was originally planned to be used with the
Saturn V
Saturn V is a retired American super heavy-lift launch vehicle developed by NASA under the Apollo program for human exploration of the Moon. The rocket was human-rated, with three stages, and powered with liquid fuel. It was flown from 196 ...
rocket for high-energy missions to the Solar System, but was later adapted for use as part of the Atlas and Titan rockets.
In May 1963 at
Vandenberg Air Force Base Vandenberg may refer to:
* Vandenberg (surname), including a list of people with the name
* USNS ''General Hoyt S. Vandenberg'' (T-AGM-10), transport ship in the United States Navy, sank as an artificial reef in Key West, Florida
* Vandenberg Sp ...
an Atlas–
Agena vehicle under static testing suffered a pressurization failure, leading to the total collapse of the vehicle that was scheduled to carry a
KH-7
BYEMAN codenamed GAMBIT, the KH-7 (Air Force Program 206) was a reconnaissance satellite used by the United States from July 1963 to June 1967. Like the older CORONA system, it acquired imagery intelligence by taking photographs and returnin ...
spy satellite. The Agena upper stage was repaired and used for later flight. A 2009 article mentions a review of hardware serial numbers which lead to the conclusion that the satellite payload had not yet been mounted on the rocket during the failed test. A history of the program, however, written in 1973 (declassified in 2011) states that the satellite was damaged beyond repair.
With the introduction of the
Atlas V
Atlas V is an expendable launch system and the fifth major version in the Atlas launch vehicle family. It was originally designed by Lockheed Martin, now being operated by United Launch Alliance (ULA), a joint venture between Lockheed Mart ...
Evolved Expendable Launch Vehicle
National Security Space Launch (NSSL) — formerly Evolved Expendable Launch Vehicle (EELV) from 1994 to 2019 — is a program of the United States Space Force (USSF) intended to assure access to space for United States Department of Defense and ...
(EELV), balloon tanks and half-staging are no longer used on the Atlas rocket. Centaur, however, retains this feature, yet it has not undergone a single catastrophic failure since the Atlas V's first flight.
References
{{Reflist
Rockets and missiles