Research On Space Debris Environment Long-term Evolution Modeling And Its Safety Problem

The space debris environment consists of a large number of abandoned man-made objects moving in the near Earth orbit,which has been produced under effects of the launch traffic,the external forces,the mutual collision among objects,etc.,thus making it a complex space environment.Not only has the long-term evolution of the debris environment a great impact on the design and the life-cycle safety management of the spacecraft,but also it is a great challenge to the outer space sustainability.This thesis concentrates on the long-term evolution modeling of the debris environment.From the microscopic and macroscopic approaches,two kinds of model,i.e.the numerical evolution model and the state evolution model,are built respectively.Then,the long-term projection and the stability of the debris environment are studied,and the safety problems induced by the debris environment are evaluated.First and foremost,a long-term numerical evolution model is established by tracking the state of the space objects individually,which is aimed at stimulating the actual evolution process microscopically.External forces of the orbiting debris are determined in terms of the magnitude and computing complexity,and the effect on the distribution of the debris.For collisions among the objects,an efficient method for calculating the collision probability using the relative states of the two objects is developed,which has a linear computational complexity and can be applied to arbitrary near Earth orbiting objects.A long-term orbit propagation method is proposed,based on the mean equinoctial elements and the averaging theory.By omitting the short-periodic changes of the motion,the time step of the integration can be chosen by one day while reflects the long-term and long-periodic changes of the motion,which helps to improve the evolution efficiency greatly.By constructing a parallel computing framework,the numerical model can use a large number of CPU cores of the Tianhe-I supercomputer to carry on the long-term evolution.Secondly,utilizing the spatial density as the state variable of describing the distribution of the debris,the governing equations are deduced,and then the layered discrete evolution model is obtained.Mean equivalent effects of the air drag and mutual collisions among objects are included in the model.We get an analytic solution form the layered discrete model under the perturbation of air drag.Thus,the evolution tendency of the debris environment can be obtained with fewer computation,and the stability of the debris environment can be analyzed fundamentally.Next,with those evolution models,the low Earth orbit debris environment is projected for another 200 years.The distribution characteristics and the corresponding major effect factors of the debris environment are studied.Results show that the mutual collision among objects is the most important driver of the growth of the debris;even all the launch plans are canceled,the amount of the debris will increase continuously,which means the scale of low Earth orbit debris has developed beyond the critical level of stabilization;the launch traffic will worsen the stability of the debris environment,and will aggravate the chain reaction of “collision – breakup – collision”;when the spacecraft is maneuvered into the 25-year disposal orbit,the increase of the debris will slow down,but more strict regulations are required to change the debris environment into a stable state.Finally,safety problems caused by the debris environment are discussed.In terms of the debris cloud originated from the breakup of a space object,its evolution features are analyzed,and its collision risk on the satellite constellation is evaluated.Considering the debris collision risk on the large operational spacecraft,a collision probability calculation method is proposed,based the boundary crossing conditions.The method can be applied to evaluate the collision risk and its variations from different aspects,e.g.the risk distribution along orbit height,right ascension and declination.And the interaction of debris environment and the mega satellite constellation comprised of large number of small satellites is analyzed.Results show that if no disposal guidelines are adopted,the mega constellation will accelerate the growth of the debris environment apparently.Research of this thesis lays the theoretic foundation for studying the long-term evolution mechanism of the debris environment and provides an efficient analysis method,which are important supports for the life-cycle safety management of the spacecraft and the sustainable use of the outer space resources.