Comprehensive Load Relief of Launch Vehicle with the Constraints of Legacy Stages

Abstract

Facing diversified launch needs, it is uneconomical to redevelop new rockets from scratch. The concept of combining legacy modules into a new launcher has become attractive. However, these mature modules may not adapt to new flight profiles due to differences in factors such as the propulsion system configuration, payloads, and trajectories. Thus, structural load relief measures play a key role in module integration. A comprehensive load relief strategy applied in the Long March 8 (LM-8) rocket is introduced, including the inflight load reduction by engine throttling, wind biasing trajectory, and onboard load relief control techniques. A unified analysis process for the elastic loads caused by gusts and fluctuating pressures was proposed, and an integral optimization problem for simultaneous planning with complicated constraints (such as the maximum dynamic pressure, wind biasing, and throttling level and time) is discussed. A real-time load relief technology based on an extended state observer, which predicts the angular acceleration caused by the wind, is proposed. Its efficiency, adaptability, influence on the stability and control accuracy, and application in the LM-8 maiden flight are studied. The proposed scheme expands the launch probability of LM-8 and provides a systematic solution for the load relief design and control of in-service rockets.