In flight characterization of a balloon-payload dynamic through a sensorised sounding balloon’s chain

• In-flight quantification of flight chain relative dynamics using synchronized dual IMUs. • Altitude-dependent dynamic coupling effects identified during atmospheric ascent. • Significant eastward drift observed due to strong stratospheric winds. • Comparison between ground-lab modal analysis and flight data. • Dual-IMU framework provides foundation for assessing dynamic related effect on payload performance. Minimalist design of the flight train highlighting the balloon and payload reference systems with representation of their relative movements. Understanding the in-flight relative dynamics between a balloon and its suspended payload is essential for stratospheric mission, as these interactions directly affect payload stability and scientific data quality. This work presents a flight data analysis characterization framework that links laboratory-based modal analysis of the flight chain to real operational conditions, focusing on the quantification of relative motion between balloon and payload. A stratospheric mission was launched from Livorno, Italy, using a sensored flight train with two inertial units, one attached to the balloon and the other attached to the payload, aimed at capture the evolution of relative oscillations. Furthermore, flight data analysis revealed the activation of relative motions as a function of altitude. Compared to estimates conducted in the laboratory, clear altitude-dependent deviations emerge due to vibration modes coupling and excitation within the flight chain. The analysis compared the dynamic behaviour resulting from laboratory tests with fly data to highlight the coupled movements due to the atmospheric disturbances. The resulting framework enables a validation of pre-launch models, the identification dynamic couplings, and provides actionable insights for improving payload connection strategies, stabilization approaches, and future mission design in scientific ballooning.