The ThorAblestar, or Thor AbleStar, also known as ThorEpsilon was an early American expendable launch system consisting of a PGM17 Thor missile, with an Ablestar upper stage. It was a member of the Thor family of rockets, and was derived from the ThorAble.. The Ablestar second stage was an enlarged version of the Able, which gave the ThorAblestar a greater payload capacity compared to ...