Longitudinal Control Of Unpowered Approach And Landings For Reusable Launch Vehicles With Different Configurations

Unpowered approach and landings is the last phase in reentry return process of Reusable Launch Vehicles(RLVs), which is the key phase for mission completion. Adaptability between longitudinal control system and configuration is the key issue for unpowered approach and landings of RLVs with different configurations, for which the longitudinal control technology is researched to provide autolanding solutions in this thesis.First, the altitude profile-based trajectory design method is studies, a generic, fast and reliable trajectory design toolbox is developed, and a design principle with "fixing attack angle in steep glideslope phase, changing initial pressure" is proposed. Utilizing such a toolbox and principle, RLV trajectories are designed and simulated. Simulation results show that the designed trajectories have strong adaptability.Then, the system stability is analyzed for a pitch-rate damper under both static stability and static instability conditions. As such damper cannot guarantee system stability when the degree of static instability is large, pitch-rate control augmentation system(PRCAS) is designed, and two control schemes(with and without an angle of attack feedback) of such PRCAS are further analyzed. The PRCAS ensures system stability when the degree of static instability is large, and the addition of an angle of attack feedback can improve system robust stability. Moreover, a μ-toobox with strong engineering applicability is exploited, which can quickly and efficiently evaluate system robustness for RLVs with different control schemes and different static stabilities.Finally, since the mass of RLVs influences autolanding most, and a larger mass will bring adverse effect such as a bigger landing velocity and a bigger angle of attack, an estimation algorithm is proposed to estimate the upper boundary of RLV mass, and such upper boundary is estimated for three different cases including without elevon deflection, with elevon deflection and when in an atmospheric environment with low temperatures. Combining with a nonlinear simulation, multiple upper boundary estimations are given and evaluated. The results show that with the estimated upper mass the landing reached a critical state; the boundary is small without high lift device; the boundary will increase 20% with elevon high lift; and the boundary will increase 45% when in an atmospheric environment with low temperatures, which verifies the effectiveness of the proposed estimation algorithm.