Vulcan Centaur is a two-stage-to-orbit, heavy-lift launch vehicle under development by United Launch Alliance (ULA) since 2014. It is principally designed to meet launch demands for the U.S. government's National Security Space Launch (NSSL) program for use by the United States Space Force and U.S. intelligence agencies for national security satellite launches. It will replace both of ULA's existing launchers (Atlas V and Delta IV Heavy) in this role, as these launchers are retiring.