The Thor-Ablestar, or Thor Able-Star, also known as Thor-Epsilon was an early American expendable launch system consisting of a PGM-17 Thor missile, with an Ablestar upper stage. It was a member of the Thor family of rockets, and was derived from the Thor-Able.The Ablestar second stage was an enlarged version of the Able, which gave the Thor-Ablestar a greater payload capacity compared to the Thor-Able.