VERY-LOW ORBIT SPACECRAFT DYNAMICS MODEL AND VALIDATION UNDER ATMOSPHERIC EFFECTS

Very-low Earth orbit (VLEO) spacecraft experience significant atmospheric drag with strong temporal and spatial fluctuations during orbital flight, and the magnitude of the drag is closely related to the spacecraft's configuration, materials, and atmospheric environment. Atmospheric drag is associated with the atmospheric parameters at the spacecraft's location and orbit time, including density, temperature, and composition, and is directly influenced by orbital motion. At the same time, it is also related to the spacecraft's characteristics, such as surface materials and configuration, and is affected by attitude motion. Due to the difficulty in accurately providing multiple parameters through simplified models, the simulation calculation of atmospheric drag through these models (such as USSA-76 atmosphere model) on spacecraft models often has considerable errors. This study used the more precise NRLMSIS-2.0 atmospheric model and molecular dynamics model to simulate the atmospheric drag on VLEO spacecraft considering orbital and attitude dynamics, and analyzed the significant impact of the wall adaptation coefficient of materials on aerodynamic drag. To determine the mission window for VLEO flight, the correlation between atmospheric drag and environmental parameters was analyzed. The results showed that the drag fluctuated by 37% and 15% with F10.7 and day of year (DoY), respectively, while the changes with Ap and the right ascension of the ascending node (RAAN) of the orbit were less than 5% and 0.15%, respectively. Using the orbital and spacecraft configuration data from existing VLEO missions (Tianxing-1 and Qiankun-1 upper stage), the wall adaptation coefficient in the drag calculation model was fitted and analyzed in combination with the atmospheric model. The results were consistent with the actual surface material characteristics of the spacecraft.