Assertion: cesium | /r/ObjectUse | used as propellant
Facets:
value: in early ion engines
type: LOCATION
Source sentences:
text: Caesium and mercury were used as a propellant in early ion engines designed for spacecraft propulsion on very long interplanetary or extraplanetary missions.
text: Cesium was used as propellant by early ion propulsion engines for space exploration until xenon became the standard.
text: Caesium was used as a propellant in early ion engines.