Horizontal takeoff and vertical landing (HTVL) is the spaceflight equivalent of aviation HTOVL (and its subtypes CTOVL, STOVL, CATOVL). This mode of operation has not been used, but has been proposed for some systems that use a two-stage to orbit launch system with a plane based first stage, and a capsule return vehicle. One of the few HTVL concept vehicles is the 1960s concept spacecraft Hyperion SSTO, designed by Philip Bono.[17]