Abstract:

CubeSats always choose two-line element (TLE) in conjunction with the SGP4 model to determine the orbit, or as a backup method. To settle the problem that the propagation error accumulates over time, the source and distribution of the errors are analyzed and two improved approaches are proposed by using Doppler shifts. One is to directly correct the drag coefficient and results show a significantly decrease in intrack orientation error. The position difference is improved to 4 km in 10 days. The other approach is to update the TLE epoch time to the pass time firstly, and then correct the argument of the latitude. Simulation results indicate that the position error can be almost removed in a short time but the long time performance is worse than the first method. The conclusion is also verified by actual measurements from the in-orbit CubeSats.