Watch the GPS launch
15 May sees the latest GPS launch during the window 2138-2156 UTC - it can be watched on the web.
The Atlas 5 rocket was rolled out to the pad on 14 May. Forecasters predict an 80% chance of favourable conditions for the launch.
The Atlas 5, Centaur upper stage and nose cone housing GPS IIF-4 are an impressive 189 ft (57.6 m) high.
Details of the positioning of the satellite can be found under 'Previous News' below - and the launch can be viewed at the Spaceflight Now or United Launch Alliance links below . .