Orbit Evolution Analysis And Collision Risk Assessment For LEO Satellite Constellation

Low-orbit large satellite constellation is a research hotspot in recent years,and its application value in the field of communication and remote sensing has been gradually discovered.Relevant constellation operators have applied for constellation deployment plans containing thousands to tens of thousands of satellites.A large number of small satellite launch plans will lead to a sharp increase in the number of space objects in some important orbital areas,a decrease in the sustainable use of orbit and frequency resources,and a significant increase in the collision probability of space objects.Although some satellites add automatic collision avoidance function and active derailment link at the end of the mission in the design process,the collision risk in operation may cause these functions to fail.Therefore,in order to better simulate and measure the impact of constellation introduction on the space environment,on the basis of accurate prediction of the satellite constellation orbit,the reasonable risk assessment parameters and the changes of space environment parameters within a certain period of time after collision are given.This paper takes the rapid deployment of the Starlink constellation as the research object,makes a slight improvement on the orbit prediction method of the constellation,gives the overall collision risk assessment parameters and maneuver avoidance strategy selection of the single satellite constellation,evaluates the consequences of the satellite collision,the short-term and long-term impact on the space environment,and gives the impact of the satellite post-mission disposal success rate on the environment.The main research contents of the text are as follows:The model affected by the perturbation force during the operation of the spacecraft and the necessary coordinate transformation are introduced,which makes a good preparation for the follow-up modeling and calculation.The launch data of Starlink constellation are screened,and the stable and regular launch batch inversion satellite climbing thrust is obtained.the relationship between thrust and release mode is analyzed,and the average thrust and the thrust of real data evolution are compared to ensure the reliability and effectiveness of the data.Based on the tangential thrust perturbation model,the prediction time of 6 hours is selected,and the Runge Kutta numerical method is used to simulate the position and velocity prediction error and accuracy improvement under the two-body model and the introduction of thrust model.the possible causes of errors and the direction of improvement are analyzed.The calculation methods of collision probability and flux of space objects are given.4425 satellites deployed in the initial stage of the Starlink constellation are selected as the overall analysis object,and the object size threshold causing catastrophic collision is calculated with the mass-energy ratio as the reference standard.The mission phase of the whole life cycle of a single satellite is divided,the orbit change and the corresponding time parameters are obtained,and the overall satellite collision probability and object flux under different orbit parameters are calculated respectively.According to the set acceptable collision level,the overall collision avoidance times of a single satellite and the optimized orbital satellite and the corresponding risk reduction index are analyzed.When selecting the avoidance execution mode,the velocity increment required for maneuver and the corresponding propellant mass fraction are given.The number,velocity increment and area-to-mass ratio of debris produced by Starlink satellite after collision are simulated under different collision intensities.The falling time of debris at different orbital height is calculated,and the effects of orbital parameters and collision intensity on collision disintegration events are obtained.The density change of the space environment is obtained by generating all the orbital parameters of the Starlink constellation,and the Monte Carlo method is used to simulate the evolution of the number of space cataloged objects without introducing the constellation and inserting the real satellite constellation launch data.The growth trend of the number of space objects with success rate after different missions is simulated,the growth ratio is obtained,and the potential impact of constellation on the space environment is analyzed.Based on the improved collision early warning system and the real data of in-orbit satellites,the prediction results of collision rendezvous within3 days after a given epoch time are calculated.different acceptable collision levels are selected to give the dangerous rendezvous information between the satellite and the catalogued object and with the satellite in the constellation.The configuration and distribution of constellations may increase the probability of close contact and collision,which need to be selected according to the specific situation.Collision risk assessment is conducted for manned spacecraft and satellite constellations to measure the potential impact of constellations on manned missions.Based on the improvement of orbit prediction,the collision risk analysis of satellite constellations,and the risk analysis of satellite constellations and space environment,the possible interaction forms between large Leo satellite constellations and space environment,the shortcomings of current early warning technology and the improvement direction and focus of future research are summarized.