The Thor-Able (Thor DM-18-Able) was an American expendable launch system and sounding rocket used for a series of re-entry vehicle tests and satellite launches between 1958 and 1960. It was a two-stage rocket, consisting of a Thor IRBM as a first stage and a Vanguard-derived Able second stage. On some flights, an Altair solid rocket motor was added as a third stage. It was a member of the Thor family and an early predecessor of the Delta.