A Global Navigation Satellite Systems "GNSS" receiver onboard a satellite, comprising: an antenna for generating analog Global Positioning System "GPS" signal data in response to detection of analog GPS signals; front-end circuitry connected to receive said analog GPS signal data from said antenna, said front-end circuitry comprising an analog-to digital converter which converts analog GPS signal data to digital GPS signal data; and a computer processor programmed to perform the following steps: (a) buffering digital GPS signal data outputted by said front-end circuitry over a time interval that is greater than the duration of a bit of a navigation message; (b) calculating a respective set of parameters based in part on the digital GPS signal data remaining after navigation data wipe-out for each data point in a search array; (c) calculating time-domain averaged I and Q signal components as a function of said respective set of parameters for each data point in said search array; (d) calculating respective correlation magnitudes based on said time-domain averaged I and Q signal components for each data point in said search array using a kalman filter; and (e) determining an orbit state correction based in part on said correlation magnitudes, wherein said computer processor is further programmed to perform the steps of: using a periodic function corresponding to a periodic thermal profile of said satellite to model clock errors, and said respective set of parameters are calculated in step (b) based in part on said modeled clock errors; and estimating corrections for the clock error model and a thruster error model; and wherein the kalman filter feeds back the determined orbit state correction to an orbit propagator, the clock error model and the thruster error model. an antenna for generating analog Global Positioning System "GPS" signal data in response to detection of analog GPS signals; front-end circuitry connected to receive said analog GPS signal data from said antenna, said front-end circuitry comprising an analog-to digital converter which converts analog GPS signal data to digital GPS signal data; and a computer processor programmed to perform the following steps: (a) buffering digital GPS signal data outputted by said front-end circuitry over a time interval that is greater than the duration of a bit of a navigation message; (b) calculating a respective set of parameters based in part on the digital GPS signal data remaining after navigation data wipe-out for each data point in a search array; (c) calculating time-domain averaged I and Q signal components as a function of said respective set of parameters for each data point in said search array; (d) calculating respective correlation magnitudes based on said time-domain averaged I and Q signal components for each data point in said search array using a kalman filter; and (e) determining an orbit state correction based in part on said correlation magnitudes, wherein said computer processor is further programmed to perform the steps of: (a) buffering digital GPS signal data outputted by said front-end circuitry over a time interval that is greater than the duration of a bit of a navigation message; (b) calculating a respective set of parameters based in part on the digital GPS signal data remaining after navigation data wipe-out for each data point in a search array; (c) calculating time-domain averaged I and Q signal components as a function of said respective set of parameters for each data point in said search array; (d) calculating respective correlation magnitudes based on said time-domain averaged I and Q signal components for each data point in said search array using a kalman filter; and (e) determining an orbit state correction based in part on said correlation magnitudes, wherein said computer processor is further programmed to perform the steps of: using a periodic function corresponding to a periodic thermal profile of said satellite to model clock errors, and said respective set of parameters are calculated in step (b) based in part on said modeled clock errors; and estimating corrections for the clock error model and a thruster error model; and wherein the kalman filter feeds back the determined orbit state correction to an orbit propagator, the clock error model and the thruster error model.