说明：  二体问题求解程序 包含两个文件： 1.orbit_solver.m 初始化程序，数值计算并画图输出。 在此设置卫星的初始位置坐标r0和速度v0，设置仿真起止时间t0和tf，然后可以直接运行即可。 2.dif_orbit_dynamic.m 轨道动力学函数，包括无摄动力学和J2摄动下的动力学方程，具体采取何种动力学需要在此程序中进行设置。
(Two body problem solving program There are two files: 1.orbit_ Solver. M initialization program, numerical calculation and drawing output. Set the initial position coordinate R0 and speed V0 of the satellite, set the start and end time t0 and TF of the simulation, and then it can run directly. 2.dif_ orbit_ Dynamic. M orbit dynamics function, including the unperturbed dynamics and the dynamics equation under J2 perturbation, which dynamics should be set in this program.)