A Shuttle-derived launch architecture was selected by NASA for the Ares I. Originally, the crewed vehicle would have used a four-segment solid rocket booster (SRB) for the first stage, and a simplified Space Shuttle Main Engine (SSME) for the second stage. An uncrewed version was to use a five-segment booster with the same second stage. Shortly after the initial design was approved, additional tests revealed that the Orion spacecraft would be too heavy for the four-segment booster to lift, and in January 2006 NASA announced they would slightly reduce the size of the Orion spacecraft, add a fifth segment to the solid-rocket first stage, and replace the single SSME with the Apollo-derived J-2X motor. While the change from a four-segment first stage to a five-segment version would allow NASA to construct virtually identical motors, the main reason for the change to the five-segment booster was the move to the J-2X.