Ephemeris Closed-Loop Tracking of LEO Satellites with Pseudorange and Doppler Measurements

A framework for refining the ephemerides of low Earth orbit (LEO) space vehicles (SVs) is presented. This framework is based on a known receiver that tracks the LEO SVs using pseudorange and Doppler measurements extracted from the LEO SVs' signals. A procedure to determine the process noise covariance for the LEO SVs' motion is developed. Monte Carlo simulations are performed to demonstrate the improvements in the tracked LEO SVs' ephemerides over open-loop SGP4-propagated ephemerides for three measurement scenarios: (i) pseudorange, (ii) Doppler, and (iii) pseudorange and Doppler. The improved ephemerides are subsequently utilized to localize an unknown receiver drawing pseudorange measurements on LEO SVs, and the resulting positioning error is compared for the true, open-loop, and closed-loop SV ephemerides. Experimental results are presented showing (i) a refinement of two Orbcomm LEO SVs' ephemerides with reductions of 879.3 m and 817.7 m in their estimated position errors over SGP4 predictions and (ii) a 53.65% reduction in the two-dimensional (2-D) localization error of an unknown stationary receiver by using the tracked ephemerides instead of SGP4-propagated ephemerides.