kenrw

I was basing accuracy on the public view using satellite navigation. It is true that ALL satellites require ground stations to perform adjustments in the background so that users get their preset accuracy whether it be civilian or military use. To quote from Gallileo website which most likely be the same for all the systems. "The orbits of the satellites can be slightly nudged by the gravitational tug of Earth’s slight equatorial bulge and by the Moon and Sun. Even the slight but continuous push of sunlight itself can affect satellites in their orbital paths. The quality of signals received on the ground can be affected by their transit through the ever-changing ionosphere, the electrically active outer layer of Earth’s atmosphere. Galileo sensor stations, with small omnidirectional receiving antennas around just 50 cm high, are on place around the globe to check the accuracy and signal quality of individual satellites in real time, and work together to pinpoint the current satellite orbits. These measurements are transmitted via secure satellite communications to Fucino, where they serve as the basis of a set of corrections – accounting for timing or orbital slips – to be uplinked to the satellites via a network of 3 m-diameter uplink stations for rebroadcast within navigation messages to users, currently updated every 50 minutes."

Withi GNSS there is GPS, GLONASS an Galileo satellite positioning systems. GPS American owned with accuracy to 5m radius, GLONASS Russian owned with accuracy to 2.8m radius and the EU Galileo is 1m radius. However even though the UK has put billions into the EU Galileo system following Brexit we'll not have location access to it. There business GPS systems that can access licenced GPS access to closer radius though not as tight accuracy available to the military.