How important is the dynamical information in determination of LEO orbits

Abstract

The interest in a precise orbit determination of Low Earth Orbiters (LEOs) using GNSS observations to recover of the Earth's gravity field has been grown rapidly. With the advent of precise orbit and clock products at centimeter level accuracy provided by the IGS analysis centers and the geometrical connections between GNSS satellites and LEOs, the orbit of LEOs can be estimated based on only a single GNSS receiver onboard LEOs. The determined LEO orbit is based on only geometrical configuration between GNSS and LEO. This procedure is known as Geometrical Precise Orbit Determination (GPOD). The ephemerides of point-wise LEO positions can be derived by this method at every observation epochs. Kinematical Precise Orbit Determination (KPOD) is another estimation procedure, which is based on the geometrical information too. Based on a new proposed method, the kinematical orbit is represented by a sufficient number of approximation parameters, including boundary values of the LEO arc. This kind of orbit representation not only allows to determine arbitrary functional (e.g. velocity and acceleration) of the satellite arc's, but it is also possible to use dynamical observations for the determination of orbit parameters. It should be mentioned that in the geometrical and kinematical orbit determination procedures, no dynamical (force) information is used at all. Because of the close relation of the estimated kinematical parameters with the force function model, the orbit determination can be designed as a pure kinematical orbit determination on the one hand, and a pure dynamical orbit determination on the other hand. In other words, this formulation of the orbit determination allows a smooth transition from a kinematical to dynamical orbit determination. At the one end, the orbit parameters are determined without any force (dynamical) information at all, and the other extreme end, all orbit representing parameters are functions of the force model. If only weak dynamical restrictions are introduced to the estimation procedure, then a reduced-kinematical orbit results. In this poster, the new proposed orbit determination concept will be introduced and the effect of the dynamical information in the orbit determination procedures will be presented for the GOCE mission as a case study based on the simulated data. The various possibilities with the corresponding results of GOCE based on GNSS observations will be presented.