Editing Helium (section)

==== Flight ====
[[File:Goodyear-blimp.jpg|thumb|left|Because of its low density and incombustibility, helium is the gas of choice to fill airships such as the [[Goodyear blimp]].|alt=The Good Year Blimp]]
Because it is [[lighter than air]], [[airship]]s and balloons are inflated with helium for [[Lifting gas|lift]]. While hydrogen gas is more buoyant and escapes permeating through a membrane at a lower rate, helium has the advantage of being non-flammable, and indeed [[fire-retardant]]. Another minor use is in [[rocket]]ry, where helium is used as an [[ullage]] medium to backfill rocket propellant tanks in flight and to condense hydrogen and oxygen to make [[rocket fuel]]. It is also used to purge fuel and oxidizer from ground support equipment prior to launch and to pre-cool liquid hydrogen in [[space vehicle]]s. For example, the [[Saturn V]] rocket used in the [[Apollo program]] needed about {{convert|370,000|m3|e6ft3|abbr=off}} of helium to launch.<ref name="LANL.gov" />