The Reusability Flight Experiment (ReFEx) is based on results of the the DLR research and development program on re-usable launch vehicle and re-entry vehicle technologies.
The Department of Guidance, Navigation and Control Systems is contributing to the ReFEx mission with the development of a hybrid navigation system (HNS) and the flight guidance. Both elements will allow an autonomous navigation and flight guidance of the vehicle during every phase of its mission. The stabilization of the vehicle is realized by an active aerodynamic control system, which transforms the inputs of the navigation system and the guidance into control commands for the individual actuators. Innovative approaches – such as the hybridization of the navigation system – will be investigated during the project.
The navigation system will be developed as hybrid, compact, and highly reliable navigation system on the basis of existing technologies like the navigation experiment aboard the SHEFEX II mission, among others. In this context, the combination of measurements of different sensors into a common navigation solution is referred to as hybridization. To achieve the required accuracy for position and attitude of the vehicle, the navigation system combines the measurements of gyroscopes, accelerometers, GPS receivers, and Sun sensors – with the option to include additional sensors. Apart from the increased accuracy of position and attitude determination, the HNS technology developed in ReFEx represents the test of an experimental, integrated navigation system capable of combining the aforementioned components with each other.
During flight, the guidance system will analyze possible trajectories and compute a modified, near-optimal flight trajectory on board in real time. A non-linear controller ensures that the deviations from the selected trajectory and planned landing site are kept minimal. This is done by calculating the error between the current vehicle state and the selected trajectory to derive the required corrections.
The development of such a complex and demanding system requires an intensive collaboration and interactions with the fields of aerodynamic flight control (DLR Institute of Flight Systems, Braunschweig), aerodynamics (DLR Institute of Aerodynamics and Flow Technology, Braunschweig/Göttingen), and mission analysis (DLR Institute of Space Systems, Bremen).