Failure Modes, Effects and Criticality Analysis of the Langmuir Probe Instrument for the ROMEO satellite in Radiation Environment

Sammanfattning

Small satellites are revolutionising space exploration, offering cost-effective solutions for research and communication. However, operating in space presents significant challenges, particularly due to interactions with the plasma environment and exposure to radiation, which can affect satellite performance and reliability. This study therefore investigates the reliability of the Langmuir Probe, an instrument that provides information on electron density for plasma diagnostics. This thesis presents a Failure Modes, Effects, and Criticality Analysis (FMECA) performed for the Langmuir Probe developed for the ROMEO satellite. Based on the results of this analysis, a mitigation and redundancy plan was developed to minimise the impact of critical failures. The success of the ROMEO mission depends on reliable measurements of electron density and temperature. Failures in the probe or its interfaces could degrade scientific return and compromise satellite operations. The main objectives of this work are to identify all failure modes for the probe hardware and electronics, assess their effects and probabilities to produce ranked criticalities, validate the most critical failure mechanisms experimentally or analytically, and define design changes, test requirements, and operational mitigations to reduce residual risk to acceptable levels. A systematic FMECA workflow was applied to the entire instrument. Functional decomposition divided the system into different circuits to obtain more precise results. Using theoretical handbooks, a FMECA was carried out to identify risks in the electronic components based on theoretical models and component-level reliability predictions. Radiation was integrated into the FMECA as a key environmental factor influencing component degradation and failure modes such as single-event effects and total ionizing dose damage. The analysis results directly informed the component selection process, ensuring that only radiation-tolerant parts were chosen for critical circuits. In this way, the relationship between radiation exposure, FMECA findings, and component selection established a robust design approach that improves the reliability of the Langmuir Probe in the harsh environment. For each element, failure modes, causes, and effects on measurement quality and spacecraft safety were documented; severity and occurrence scores were assigned, and priority numbers were calculated. Critical failure candidates were further investigated and mitigation strategies were developed to improve overall reliability. Moreover, component selection was also performed according to the mission’s budget constraints and radiation tolerance requirements. Although radiation is a key factor in the Medium Earth Orbit (MEO) environment, the short mission duration and existing shielding significantly reduce its impact. Finally,the effect of redundancy on overall system reliability was analyzed to demonstrate that a reliabilityassessment and robust design can substantially improve the performance and resilience of small satellitemissions.