Stent-graft delivery systems having a tip capture mechanism with a plurality of elongated cables that allow for gradual deployment and repositioning of a stent-graft prosthesis. The tip capture mechanism includes a guiding assembly, a distal tip assembly, and a plurality of cables. In a first relative position, the distal tip assembly extends the guiding assembly to temporarily constrain the distal ends of the cables and an intermediate portion of each cable constrains an endmost crown of the prosthesis. In this first relative position, tension on the cables may be selectively adjusted to allow for both gradual continuous radial expansion and contraction of the endmost crowns of the stent-graft prosthesis. In a second relative position, the distal tip assembly does not extend over the guiding assembly and thus does not constrain the distal ends of the cables, and thereby the cables do not constrain the endmost crowns.