Abstract: An apparatus computes first locations of a satellite for several points in time based on a first set of parameters values broadcast by the satellite for a first validity period and second locations of the satellite for these points in time based on a second set of parameter values with associated second validity period. The first or second validity period is extended by an equation of motion, which includes forces acting on the satellite. The apparatus computes a value of an error component for points in time by comparing first with second locations and fits parameter values of a model to the values of the error component to obtain a model of a time-evolution of values of the error component. The apparatus provides the model of the time-evolution as a basis for a correction of locations of the satellite that are computed based on the first set of parameter values.

Abstract: An apparatus computes first locations of a satellite for several points in time based on a first set of parameters values broadcast by the satellite for a first validity period and second locations of the satellite for these points in time based on a second set of parameter values with associated second validity period. The first or second validity period is extended by an equation of motion, which includes forces acting on the satellite. The apparatus computes a value of an error component for points in time by comparing first with second locations and fits parameter values of a model to the values of the error component to obtain a model of a time-evolution of values of the error component. The apparatus provides the model of the time-evolution as a basis for a correction of locations of the satellite that are computed based on the first set of parameter values.

Abstract: A method and corresponding apparatus and system for determining the position of a satellite at any instant of time between two sampling instants, based on information in at least one ephemeris message provided by the satellite, the information allowing the computation of the satellite positions at the two sampling instants. The method includes the steps of: computing the satellite positions at two sampling instants using parameters provided in one or more ephemeris messages with suitable times of ephemeris; and for each of the three dimensions of motion, constructing a polynomial of at least third degree by choosing the coefficients of the polynomial so that it interpolates the satellite position at each of the two sampling instants.