The Block II vehicles (SA-5 to SA-10) included two powered stages, and went into orbits. Beginning with SA-5, the guidance instruments were carried on the instrument unit (IU), just ahead of the S-IV stage. The first version of the IU was in diameter and high, and was both designed and built by Marshall Space Flight Center. Guidance, telemetry, tracking, and power components were contained in four pressurized, cylindrical containers attached like spokes to a central hub. This version flew on SA-5, SA-6, and SA-7.