Active disturbance rejection control for load relief of launch vehicles considering elastic effects

The load relief control of launch vehicles reduces aerodynamic loads by decreasing the angle of attack. However, existing Active Disturbance Rejection Control (ADRC) methods for load relief do not fully consider elastic effects, which may lead to reduced disturbance estimation accuracy and even compromise system stability. To address this, this paper analyzes the impact of elastic vibration on disturbance estimation and observer gain, and proposes an improvement to suppress elastic vibration. By isolating elastic motion from rigid-body motion, the measured input of the Extended State Observer (ESO) is made to match the observation model, thereby reducing the influence of elasticity on disturbance estimation. Based on this, an open-loop transfer function of the ADRC system for load relief is derived considering elastic vibration, and a set of parameter tuning rules is provided. By properly configuring the bandwidths of the load relief feedback control and the ESO, the tuning process is simplified, while ensuring sufficient stability margins. Simulation and experimental results demonstrate that this method proposed can enhance system stability, while achieving effective disturbance suppression and load relief. Feasibility of the algorithm is validated through hardware-in-the-loop simulations and flight tests on a rocket.