An open-source camera-based trifilar pendulum setup for measuring mass moment of inertia of small satellites

Given the growing use of CubeSats and other small satellites, direct measurement of mass properties such as the mass moment of inertia (MoI) has become increasingly important for attitude-control applications. Although CAD and finite-element models are widely used to estimate spacecraft mass properties, their accuracy depends on model fidelity and may omit practical assembly details. This paper presents an open-source, camera-based trifilar pendulum for measuring the MoI of CubeSat-scale hardware and other compact rigid bodies. The system comprises an additively manufactured platform, a camera, and custom analysis software, with a hardware cost of approximately €55. Depending on the required accuracy and budget, either a low-cost webcam or a GoPro camera may be used in combination with steel or Dyneema suspension lines. The accompanying software provides optical tracking, automated MoI calculation, centre-of-mass offset compensation, uncertainty estimation, and a graphical user interface. Validation using calibration masses with known theoretical inertias and a representative CubeSat-like test article showed measurement errors below 5% for MoI values above $0.003\mathrm{kg}{m}^2$ and a 7.2% deviation from an independently generated CAD model. All hardware designs, software, and assembly documentation are openly available to support reproduction and further development.