Autonomous orbit propagation system and method
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. A method of predicting a location of a satellite, comprising:
receiving, at an RF antenna of a GNSS device, position data and a velocity associated with a satellite, said position data and velocity valid for an effective time period;
the GNSS device calculating, at a time during the effective time period, a correction for reducing error 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 GNSS device calculating a current orbit state vector using force model coefficients adjusted based on the correction 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 said satellite using the orbit.
2. 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 calculating, at a time during the effective time period, a correction for reducing error 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; and
the GNSS device calculating a current orbit state vector using force model coefficients adjusted based on the correction 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.
3. A method as claimed in claim 2 , wherein the GNSS device is a GPS device.
4. A method as claimed in claim 3 , wherein when the effective time period has expired, the GPS device determines the location of the satellite using the propagated orbit.
5. A method as claimed in claim 3 , wherein during the effective time period, the GPS device determines the location of the satellite using the position data and velocity.
6. A method as claimed in claim 3 , wherein the position data and the velocity are received within an ephemeris.
7. A method as claimed in claim 6 , wherein the ephemeris is a broadcast ephemeris.
8. A method as claimed in claim 3 , wherein the error between the predicted position data and the predicted velocity of the satellite and the position data and the velocity of the satellite comprises radial errors and along track errors.
9. A method as claimed in claim 3 , wherein the current orbit state vector is stored in the memory as a polynomial.
10. A method as claimed in claim 9 , wherein the polynomial is converted into a synthetic ephemeris by the GPS device in order to determine the location of the satellite.
11. A method as claimed in claim 3 , 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.
12. A method as claimed in claim 3 , wherein the force model coefficients are calculated iteratively.
13. A method of predicting a location of a satellite, comprising:
a GNSS device propagating an orbit of the satellite using an orbit state vector calculated using a force model, coefficients of the force model being calculated at a time during an effective time period of a broadcast ephemeris received by an RF antenna of the GNSS device, the coefficients being calculated to reduce an error between position data and a velocity received in the broadcast ephemeris and predicted position data and a predicted velocity for a same time calculated using a previously calculated orbit state vector; and
when the effective time period has expired, determining the location of the satellite using the orbit.
14. A method as claimed in claim 13 , wherein the GNSS device is a GPS device.
15. A method as claimed in claim 14 , wherein the error comprises radial errors and along track errors.
16. A GPS 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, a correction for reducing error 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 GPS device, and the processor for calculating a current orbit state vector using force model coefficients adjusted based on the correction; and
a memory for storing 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.
17. A GPS device as claimed in claim 16 , wherein the error between the predicted position data and the predicted velocity of the satellite and the position data and the velocity of the satellite comprises radial errors and along track errors.