Model for long term orbit prediction

Currently, Galileo Systems require that the operational Galileo ephemeri, which contain information about the position of the satellite, with respect to time, are to be refreshed every 100 minutes.

This refresh update was considered to be sufficient for standard applications and to meet performance requirements at the time of design. But, having the capability of uploading accurate long-term ephemeris predictions to the Galileo satellites would not only increase the overall Galileo system robustness, it would enhance the GNSS user performances in terms of reducing the Time to First Fix (TTFF). TTFF is a measure of the time required for a GPS navigation device to acquire satellite signals and navigation data.  

It would improve this by initialising the receiver using pre-stored ephemeris information, this could be obtained through an assistance channel, similarly to how GPS chips embedded in smartphones work.

An activity with TDE and GMV Aerospace and Defence in Spain has modelled all possible non-gravitational forces for the Galileo satellites, with the aim of improving their long-term predictions and testing this improvement, not only by comparing the predicted and estimated ephemeris, but also by testing their impact on the end users by means of mass-market receivers.

The principal objectives of this activity were threefold: Develop a revolutionary set of force models dealing comprehensively with those forces induced by electro-magnetic radiation either incident on, or emitted by, the Galileo satellites; Apply these force models for orbit determination and prediction of the Galileo satellites and; Study the impact of this new prediction capability on mass market user positioning. 

The final model is the 3rd generation of the model and has been enhanced with a special thermal model for the navigation antenna. This final model outperforms all the evaluated models for most of the criteria. Although this model gives the best overall results, there are still some relatively large uncertainties and imperfections.

Next, the activity plans to further improve the model using information on the the thermal household of the satellites. For even more improvements, further investigation is needed into the steady state of the energy flow through the satellites from the electrical current as well as from solar and terrestrial radiation. All these unknowns lead to an uncertainty in the scale of the orbit and the periodic forces, which could affect the model.

TDE activity T606-405ET closed in March 2020.