The Atlas-Able was an American expendable launch system derived from the SM-65 Atlas missile. It was a member of the Atlas family of rockets, and was used to launch several Pioneer spacecraft towards the Moon. Of the five Atlas-Able rockets built, two failed during static firings, and the other three failed to reach orbit.The Atlas-Able was a three-and-a-half-stage rocket, with a stage-and-a-half Atlas missile as the first stage, an Able second stage, and an Altair third stage.