Ionospheric model for GPS-based precise relative navigation of LEO spacecraft in formation flying

For the spaceborne interfeometric synthetic aperture radar (InSAR) system, the spacecraft in formation flying generally require cm-level accuracy of relative navigation. The ionospheric effect is regarded as the main factor determining the quality of relative navigation of low-altitude Earth orbit (LEO) spacecraft. From the common models of ionospheric delays for spaceborne applications, this paper proposes a new modified model, based on which the impact of ionospheric effects for relative navigation is analysed in detail. The analysis of the paper shows that altitude separation will cause the most significant ionospheric errors on differential observables. It is identified that the length of altitude separation between LEO spacecraft, rather than the baseline length, generally determines the accuracy of relative positioning using for L1-only carrier phase measurements.