Balloon Array for RBSP Relativistic Electron Losses (BARREL) is a NASA mission operated out of Dartmouth College that works with the Van Allen Probes mission (formerly known as the Radiation Belt Storm Probes mission). The BARREL project has launched 20 balloons from Antarctica during each of two balloon campaigns in January 2013 and January 2014. Unlike the football-field-sized balloons typically launched at the Poles, these are each just 90 feet in diameter.

A barrel, cask, or tun is a hollow cylindrical container, traditionally made of wooden staves bound by wooden or metal hoops. Traditionally, the barrel was a standard size of measure referring to a set capacity or weight of a given commodity. For example, in the UK a barrel of beer refers to a quantity of . Wine was shipped in barrels of .