> For what I've understood, the GPS doesn't need a constant feeding of data from ground stations - it's ""simply"" a bunch of satellites sending out the current time from their on-board atomic clocks.
When you get a GPS fix the very first thing your handset does is download the ephemeris data. This is broadcast at regular intervals along with the location signals. This data tells you the orbital parameters of each satellite, without it you couldn't get a precise location fix because you wouldn't know where the satellites you were getting signals from were.
The GPS satellites are incapable of calculating their own ephemeris data, it needs to be uploaded from the ground. The system cannot simply reuse the same data forever because the orbits of the satellites change over time, and because the system is sensitive to very small changes a lot of higher order effects (such as radiation pressure, the non-sphericity of the Earth's geoid, and so on) come into play which are not easily calculable. Over short periods the future ephemeris are predictable within reasonable bounds of precision, so the USAF uploads 30 days worth of ephemeris data to the GPS satellites on a regular basis.
If it were no longer possible to upload that data the system would eventually become either non-functional (depending on how the satellites and individual handsets are designed) or increasingly inaccurate until no longer useful.
> If it were no longer possible to upload that data the system
> would eventually become either non-functional (depending on how
> the satellites and individual handsets are designed) or
> increasingly inaccurate until no longer useful.
If that were to happen you could just augment GPS
receivers to use more accurate ephemeris data provided from other
sources.
It is, after all, now computed on the ground and uploaded to the GPS
constellation, having it be provided by the satellites is just a
convenience, not a necessity.
When you get a GPS fix the very first thing your handset does is download the ephemeris data. This is broadcast at regular intervals along with the location signals. This data tells you the orbital parameters of each satellite, without it you couldn't get a precise location fix because you wouldn't know where the satellites you were getting signals from were.
The GPS satellites are incapable of calculating their own ephemeris data, it needs to be uploaded from the ground. The system cannot simply reuse the same data forever because the orbits of the satellites change over time, and because the system is sensitive to very small changes a lot of higher order effects (such as radiation pressure, the non-sphericity of the Earth's geoid, and so on) come into play which are not easily calculable. Over short periods the future ephemeris are predictable within reasonable bounds of precision, so the USAF uploads 30 days worth of ephemeris data to the GPS satellites on a regular basis.
If it were no longer possible to upload that data the system would eventually become either non-functional (depending on how the satellites and individual handsets are designed) or increasingly inaccurate until no longer useful.