Autonomous orbit propagation system and method

Abstract

A method of predicting a location of a satellite is provided wherein the GPS device, based on previously received information about the position of a satellite, such as an ephemeris, generates a correction acceleration of the satellite that can be used to predict the position of the satellite outside of the time frame in which the previously received information was valid. The calculations can be performed entirely on the GPS device, and do not require assistance from a server. However, if assistance from a server is available to the GPS device, the assistance information can be used to increase the accuracy of the predicted position.

1 .- 20 . (canceled) 
     
     
         21 . A method of predicting an orbit of a satellite, comprising:
 receiving, at an RF antenna of a GNSS device, position data and a velocity associated with a satellite, the position data and the velocity valid for an effective time period, the GNSS device having previously received at the RF antenna at least one other position data and velocity associated with the satellite;   the GNSS device calculating, at a time during the effective time period, optimized force model coefficients for input to an orbit propagation modeller stored on the GNSS device, the optimized force model coefficients for improving position determining capabilities of the GNSS device by reducing radial and along-track errors between predicted position data and a predicted velocity of the satellite and the position data and the velocity of the satellite, the predicted position data and the predicted velocity being determined using a previously calculated orbit state vector stored in memory of the GNSS device, the previously calculated orbit state vector having been determined by calculation of force model coefficients to best match the at least one other position data and velocity to predicted satellite orbit positions and velocities determinable by the orbit propagation modeller; and   the GNSS device calculating a current orbit state vector using the optimized force model coefficients and storing the current orbit state vector in the memory, the current orbit state vector being used as initial state for propagating the orbit of the satellite within a predicted time period, at least a portion of the predicted time period occurring after the effective time period.   
     
     
         22 . The method of  claim 21 , wherein GNSS device determines the location of the satellite using the orbit. 
     
     
         23 . The method of  claim 21 , wherein the GNSS device is a GPS device. 
     
     
         24 . The method of  claim 23 , wherein when the effective time period has expired, the GPS device determines the location of the satellite using the propagated orbit. 
     
     
         25 . The method of  claim 23 , wherein during the effective time period, the GPS device determines the location of the satellite using the position data and velocity. 
     
     
         26 . The method of  claim 23 , wherein the position data and the velocity are received within an ephemeris. 
     
     
         27 . The method of  claim 26 , wherein the ephemeris is a broadcast ephemeris. 
     
     
         28 . The method of  claim 23 , wherein the current orbit state vector is stored in the memory as a polynomial. 
     
     
         29 . The method of  claim 28 , wherein the polynomial is converted into a synthetic ephemeris by the GPS device in order to determine the location of the satellite. 
     
     
         30 . The method of  claim 23 , wherein when a network interface of the GPS device is in communication with an AGPS server, the AGPS server providing a synthetic ephemeris to the GPS device when the effective time period has expired. 
     
     
         31 . The method of  claim 23 , wherein the force model coefficients are calculated iteratively. 
     
     
         32 . The method of  claim 22 , wherein the position data and velocity associated with the satellite is mapped to a WGS84 reference coordinate system prior to calculation of the optimized force model coefficients, and the predicted position and the predicted velocity are mapped from the WGS84 reference coordinate system back to the reference coordinate system of the GNSS satellite. 
     
     
         33 . The method of  claim 32 , wherein the satellite is a GLONASS satellite and the position data and velocity associated with the satellite are mapped from the PZ90 coordinate system to the WGS84 reference coordinate system. 
     
     
         34 . The method of  claim 33 , wherein the position data and velocity of the satellite are mapped to the WGS84 coordinate system reference using a Helmert transformation. 
     
     
         35 . A GNSS device comprising:
 an RF receiver for receiving position data and a velocity associated with a satellite, the position data and the velocity valid for an effective time period;   a processor for calculating, at a time during the effective time period, optimized force model coefficients for input to an orbit propagation modeller stored on the GNSS device, the optimized force model coefficients for improving position determining capabilities of the GNSS device by reducing radial and along-track errors between predicted position data and a predicted velocity of the satellite and the position data and the velocity of the satellite, the predicted position data and the predicted velocity being determined using a previously calculated orbit state vector stored in memory of the GNSS device, the previously calculated orbit state vector having been determined by calculation of force model coefficients to best match at least one other position data and velocity received by the RF receiver with predicted satellite orbit positions and velocities determinable by the orbit propagation modeller, and the processor for calculating a current orbit state vector using the optimized force model coefficients; and   a memory for storing the orbit propagation modeller and the current orbit state vector;   wherein the current orbit state vector is for propagating an orbit of the satellite within a predicted time period, at least a portion of the predicted time period occurring after the effective time period.   
     
     
         36 . A method of predicting a location of a satellite, comprising:
 receiving, at an RF antenna of a GNSS device, an ephemeris associated with a satellite, the ephemeris valid for an effective time period the GNSS device having previously received at the RF antenna at least one other ephemeris associated with the satellite;   using the ephemeris, the GNSS device calculating position data and velocities of the satellite for a plurality of time intervals over the effective time period;   the GNSS device calculating, at a time during the effective time period, optimized force model coefficients for input to an orbit propagation modeller stored on the GNSS device, the optimized force model coefficients for improving position determining capabilities of the GNSS device by reducing radial and along-track errors between predicted position data and predicted velocities of the satellite and ephemeris-derived position data and velocities of the satellite at each of the plurality of time intervals over the effective time period, the predicted position data and predicted velocities being determined using a plurality of previously calculated orbit state vectors stored in memory of the GNSS device, the previously calculated orbit state vector having been determined by calculation of force model coefficients to best match ephemeris-derived position data and velocities of the at least one other ephemeris to predicted satellite orbit positions and velocities determinable by the orbit propagation modeller;   the GNSS device calculating a current orbit state vector using the optimized force model coefficients and storing the current orbit state vector in the memory, the current orbit state vector being used as initial state for propagating an orbit of the satellite within a predicted time period, at least a portion of the predicted time period occurring after the effective time period; and   the GNSS device determining the location of the satellite using the orbit.   
     
     
         37 . The method of  claim 36 , wherein the GNSS device is a GPS device. 
     
     
         38 . The method of  claim 37 , wherein when the effective time period has expired, the GPS device determines the location of the satellite using the propagated orbit. 
     
     
         39 . The method of  claim 37 , wherein during the effective time period, the GPS device determines the location of the satellite using the position data and velocity. 
     
     
         40 . The method of  claim 36 , wherein the ephemeris is a broadcast ephemeris.