Risk-based space system design: A novel probabilistic approach to design risk for small satellites

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Spacecraft are complex systems that involve different subsystems and multiple relationships among them. The design of a spacecraft is an evolutionary process that starts from requirements and evolves across different design phases. During this process, a lot of changes can happen and affect mass and power at component level, at subsystem level, and even at system level. Each spacecraft has to respect overall constraints in terms of mass and power: for this reason, it's important to be sure that the design does not exceed these limitations. Current practice in system modeling primarily deals with this problem allocating margins. However, a statistical characterization of the fluctuations in mass and power in the early design phases is missing. This lack of statistical characterization would result either in a risky spacecraft design that might not fit the mission constraints and requirements, or in a conservative design that might not fully utilize the available resources. The authors have previously developed a mathematical approach ( [1] [2] [3] [4]) to quantify the likelihood that the major design drivers of mass and power of a space communication system would meet the spacecraft and mission requirements and constraints through the mission design lifecycle. The methodology uses a combination of statistics based on data and probabilities assessed by experts in the field. Additionally, the methodology is innovative in the approach developed to elicit experts' opinions [5] which allows the analyst to identify biases or mis-calibrations which can affect the final estimation. The work presented in this paper extends the approach developed to the entire spacecraft design, focusing on small spacecraft (less than 50 Kg mass) due to the recent interest in the space community in such platforms. The spacecraft is analyzed in its subsystems and related components. A database is constructed to compute data statistics. An interview process to elicit expert opinions in all the areas of spacecraft design is developed and the results are presented. A test case made of a small satellite mission (CASTOR) is presented and the results are described.