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On the use of a failure emulator mechanism at nanosatellite subsystems integration tests

The increase number of CubeSat based space missions in the last decade shows the new possibilities for cheaper, faster but not so better projects. This lack of quality in a mission completeness point of view is associated to lack of good practices at developing, assembly and testing phases. Addressing such problem, this work presents a fault injection tool for nanosatellite robustness testing, named Failure Emulator Mechanism (FEM). The goal of the FEM is to emulate at the subsystems interface level faults that could be presented during the mission operation of the spacecraft. Working at the communication bus, the FEM is capable to intercept the exchanged messages between two subsystems under test and inject different faults: (i) time related faults, i.e. delay; (ii) value related faults, i.e. bitflip and; (iii) specific communication bus faults, i.e. a verbose subsystem. The FEM was developed to support the integration tests of the software-intensive NanoSatC-BR2 On Board Data Handling Software (OBSw) and its Payloads. The NanoSatC-BR2 is the second scientific nanosatellite developed jointly by the Brazilian National Institute for Space Researches (INPE) and Santa Maria Federal University (UFSM). As this spacecraft works with a full shared I2C communication bus, the FEM was implemented to support and work at this communication protocol and electric interface. The use of FEM has proved to be helpful along all phases of nanosatellite development. In the early phase, FEM supports robustness requirement validation by means models in the loop (MIL). In the nanosatellite integration phase, FEM supports robustness testing of the communicating subsystems under integration, configuring hardware in the loop (HIL). In this paper, we present the design, implementation and results of FEM as MIL tool for robustness requirement validation of OBSw and Langmuir Probe, a particular NanoSatC-BR2 Payload.