Research on the Fitting Algorithms of Almanac Parameters for Navigation Satellites

The problem on the navigation satellites’ almanac is synthetically studied and in combination with the analytic solution of the J2 term two sets of new fitting methods of almanac parameters and the user algorithms are proposed. What is different from the normal algorithm lies in that in the 8-parameter almanac fitting algorithm the almanac parameter Ω1 is directly replaced by the recessiveness . In the user algorithm for the MEO and high altitude orbit satellites ωk = ω0 − ω1 · (Δt/2 − tk) and ωk = ω0 − ω1 ·(Δt/2−tk)/2 are respectively used to modify the almanac parameter ωk, where . In the 9-parameter almanac fitting algorithm on the basis of the 8 parameters an almanac parameter is added and in the user algorithm ωk = ω0 − ω1 · (Δt/2 − tk) and are respectively utilized to modify ωk and Mk. The results of the almanac fitting experiment of many groups of simulation orbits and IGS precise orbits show that the new 8-parameter almanac fitting method has the merits such as few parameters, fast speed of iteration and convergence and high fitting accuracy for MEO satellites and that the new 9-parameter almanac fitting algorithm is superior to other algorithms in fitting accuracy, with fast iteration and convergence.