By March 2019, two test articles of Starship were being built, and three by May. The low-altitude, low-velocity Starship test flight rocket was used for initial integrated testing of the Raptor rocket engine with a flight-capable propellant structure, and was slated to also test the newly designed autogenous pressurization system that is replacing traditional helium tank pressurization as well as initial launch and landing algorithms for the much larger 9 meters rocket.