Towards increasing nanosatellite subsystem robustness

Abstract

Short development life cycle and low cost of cubesat-based mission have motivated the growing number of nanosatellite launched in the last decade around the world. Fast and cheaper space project do not guarantee success in orbit. The lack of good practices on design, assembly and tests has been pointed out as one of the major causes to nanosatellite mission failures. Efforts on the use of verification and validation techniques are required. Because the increased use of nanosatellites missions for technology qualification of payloads on orbit, faulty behavior of those payloads can be expected. However, such malfunction shall not represent a risk to the whole mission. Robustness is an important property of reactive critical system not addressed properly in the cubesat standardization. Although significant mitigation of the interface failures has been observed at hardware level in the integration phase of the payloads with the nanosatellite platform, behavior aspects of the communicating subsystems on the use of these interfaces shall be verified. The test systematization of CubeSat-based nanosatellites supported by proper tools is necessary to reduce the mission development cycle in terms of the time consumed by the verification & validation activities. In this paper we present a failure emulator mechanism framework, named FEM, for robustness testing of interoperable software-intensive subsystems onboard nanosatellite. FEM acts in the communication channel being part of the integration test workbench in two phases of nanosatellite design: (i) robustness requirement specification using model in the loop (MIL) and (ii) robustness validation using hardware in the loop (HIL). The architectural aspects of the proposed FEM framework support its instantiation to any communication channel of the CubeSat standard. As an example, FEM prototype was instantiated to I2C communication channel to support NanosatC-BR2 testing. NanosatC-BR2 is a Cubesat based scientific mission, under development and integration at Brazilian Institute for Space Research (INPE), which uses I2C communication channel for its payloads interactions with the On-Board Data Handling computer subsystem (OBC). FEM prototype was used to support OBC integration testing with each payload subsystem at MIL scenario aiming at anticipating the robustness requirement verification on the development lifecycle. Moreover, the FEM prototype was also validated at HIL scenario using Test Cases automatically generated. Results of these two scenarios executions are reported demonstrating in a case study the effectiveness of FEM framework in detecting the lack or noncompliance of robustness requirements by the interoperated subsystems under testing.