 The second stage of Starship is designed as a long-duration cargo and passenger-carrying spacecraft in its own right, and is expected to be initially used without any booster stage at all, as part of an extensive development program to get launch and landing working and iterate on a variety of design details, particularly with respect to atmospheric reentry of the vehicle.Two ("Starhopper", Mk1) test articles were being built by March 2019, and three ("Starhopper", Mk1, Mk2) by May.The low-altitude, low-velocity "Starhopper" 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 rocket.