Preliminary guidance and navigation design for the upcoming DLR reusability flight experiment (REFEX)

The experience of SpaceX's Falcon 9 and Blue Origin's New Shepard shows that reusability is becoming an important feature for the sustainability of future space missions. The German Aerospace Center (DLR) is developing the Reusability Flight Experiment (ReFEx), which is scheduled for launch on a Brazilian VSB-30 sounding rocket in 2021. The mission shall enable the development of key technologies necessary for future reusable launch vehicle applications, culminating in their demonstration with a controlled autonomous return flight in a representative regime. This paper presents the proposed architecture for the guidance and the navigation subsystems. We elaborate on the proposed optimal-trajectory based guidance strategy and on the hybrid navigation subsystem. Additionally, we present a study of different sensor configurations and their achievable performances through covariance analysis, and describe the preliminary functional and algorithmic structure of the navigation process as well as the fault detection, isolation, and recovery strategy.