This paper deals with the system design of the USV1, the first Space experimental vehicle funded by the Italian National Aerospace Research Program (PRORA). The Unmanned Space Vehicle 1 (USV1) is a multi-mission, re-usable vehicle under development in CIRA, the Italian Aerospace Research Centre. The first USV1 mission is scheduled for the end of 2005 and is aimed at experimenting the transonic flight of a re-entry vehicle. In addition, being a multi-mission flying laboratory, USV1 will perform three flights, each one of them simulating the final portion of a typical re-entry trajectory. USV1 is basically composed by a Flying Test Bed (FTB1) and a Carrier based on a stratospheric balloon. The FTB1 is a slender, not-propelled, winged vehicle able to perform experiments on Structure and Aeroelasticity behaviour identification, Autonomous Guidance Navigation and Control, and Thermo-Aerodynamics. During the missions the balloon will carry the FTB1 up to the desired altitude (25 Km for the first mission) and then, after having established a cruise horizontal trajectory, will release it from the gondola. At this moment FTB1 will start its proper flight following the designed trajectory. In the frame of a step by step approach the FTB1 will reach during each subsequent mission an increasing number of Mach, starting from Mach 1 during the first mission up to Mach 2 during the fourth flight. At the maximum velocity it will perform the experiments and by means of a pull up manoeuvre it will decelerate in order to enter in the safe parachute opening regime. The final recovery will be performed from the sea. After a brief description of the missions the paper will present the system architecture and the adopted solution able to match the mission and experiment requirements for all the foreseen missions. At the time of the conference the FTB1 shall be performing the integration and test phase and all the subsystem shall be delivered to CIRA.