Real time position correction to ground generated spacecraft ephemeris

An apparatus for accurately determining the orbital parameters of a spacecraft using reference trajectory data and position information, the apparatus comprising:

• a position information management module, for providing a measured spacecraft position corresponding to a first time;
• a reference trajectory management module, for obtaining a reference trajectory for the spacecraft from a source external to the spacecraft;
• a parameter calculation module, in communication with the reference trajectory management module, for determining the position of the spacecraft along the reference trajectory which corresponds to the first time;
• and
• an error estimation module, in communication with the position information management module, the reference trajectory management module, and the parameter calculation module, for comparing the measured position and the calculated position corresponding to the first time, determining a position error as the difference between the measured position and the calculated position corresponding to the first time, determining an in-track component of the position error as a portion of the position error that is parallel to the reference trajectory, providing time correction terms based upon the in-track component of the position error, and for calculating corrected orbital parameters based on the time correction terms.

A system for on-board accurate determination of orbital parameters of a spacecraft using reference trajectory data and position information, the system comprising:

• a communications unit, for obtaining a reference trajectory for the spacecraft from a source external to the spacecraft;
• a position information receiver, for receiving position information including a measured position of the spacecraft which corresponds to a first time;
• a memory, in communication with the communications unit and the position information receiver, for storing the reference trajectory and the position of the spacecraft which corresponds to the first time;
• and
• a central processing unit connected to the memory for determining a position of the spacecraft along the reference trajectory which corresponds to the first time, comparing the measured position and the determined position which correspond to the first time, wherein the comparison includes determining a position error as the difference between the measured position and the determined position corresponding to the first time, determining an in-track component of the position error as a portion of the position error that is parallel to the reference trajectory. and determining corrected orbital parameters based upon the comparison and the determined in-track component of the position error.