see url:
https://www.theregister.co.uk/2017/07/31/gps_iii_ocx_satellite_gps_project_delays/
UK dependent on US systems, could cost UK government 1 billion a year if
it doesn't start working in time. Luckily (or unluckily for some) the
EU, Russian and China have built and are improving their own GPS
systems, just in case of an accidental or inadvertent switch off.
Apparently, the biggest problem is securing the command and control
system from being hacked by script kiddies...:-)
ATB
Dougie.
P.S. A comprehensive article on the US GPS system is available at:
http://www.gps.gov/systems/gps/space/#generations
