The NASA Space Shuttle (SS) Orbiter Vehicle (OV) portion of the Space Transportation System (STS) comprises a series of spaceplanes numbered by OV-100 series. These have also been referred to as Constitution-class space shuttles, due to the fact the first anticipated working example was originally named Constitution, prior to being renamed Enterprise. These spaceplanes were originally provisioned with turbofans for in-atmosphere propulsion after re-entry, but these were deleted early in the design stage, and the shuttles are purely gliders during their atmospheric operation phase.