Towards an H/W-S/W Interface description for a comprehensive space systems simulation environment

In the development of space instruments it is common practice to analyze the software, developed in the course of the project, for errors by extensive tests as well as to simulate the different application scenarios to determine the behavior of the software. The hardware is often only modeled as a black box to the software and is usually not an active part of the simulation. In general, the interface between hardware and software is described and analyzed by a Hardware/Software Interaction Analysis (HSIA) at a late stage of the project, when the development of the hardware has generally been completed. In order to be able to integrate the hardware into a representative simulation of the system, especially with regard to Fault Detection Isolation and Recovery (FDIR), it is necessary to develop an interface that contains all important information about the structure of the hardware and its behavior. Thus the current state of the hardware can be described at any stage of the project and can be taken into account for software development. This paper describes a hardware/software-interface description using HSIA and Fault Tree Analysis (FTA) as a baseline. The overall goal is to model the interaction of hardware and software as accurately as possible in order to identify errors both in the software and in the hardware design. The description can also be used at a later stage to implement it into the Model-Based Systems Engineering framework Virtual Satellite (VirSat), developed by the German Aerospace Center (DLR). Concept and implementation of the hardware/software-interface with special focus on fault cases, detectability and fault mitigation will be described. The benefits of an interface description in an early stage of the hardware design are discussed. On the basis of an actual project, a hardware analysis is performed and the interface is described with the developed approach in order to evaluate its suitability. Finally, the feasibility and limits of this approach are assessed.