 SpaceX originally developed their reusable booster technology for the 3-meter-diameter Falcon 9 from 2012 to 2018.The "Starhopper" prototype was also the platform for the first flight tests of the full-flow staged combustion methalox Raptor engine, where the "Starhopper" was flight tested with a single engine in July/August 2019, but could be fitted with up to three engines to facilitate engine-out tolerance testing.The high-altitude, high-velocity 'Starship orbital prototypes' (everything after "Starhopper") are planned to be used to develop and flight test thermal protection systems and hypersonic reentry control surfaces.