This paper describes the hardware components and the embedded software of a self-designed unmanned aerial system (UAS) to fulfill the task of an autonomous indoor exploration. The project, the paper is based on, was conducted at the University of Braunschweig - Institute of Technology by students and scientific researchers studying and working at the Institute of Flight Guidance. The paper is structured as follows. The first part deals with the development, selection, collocation and assembling of the appropriate hardware to obtain a reliable and robust system which suits the task of controlling the UAS, collecting information about the environment and providing the computational resources to execute the implemented algorithms. The second part deals with the software architecture that generates the control commands for the quadrotor UAS and ensures the execution of the mission by the stepwise fulfillment of single tasks.