How satnav works

Your satnav receiver needs a minimum of four satellites in the sky, their onboard clocks synchronised and orbital positions monitored by global ground segments. It picks up signals from each satellite, which each incorporate a precise time stamp.

 By calculating the length of time it takes for each signal to reach your receiver, the receiver builds up a three-dimensional picture of your position – longitude, latitude and altitude – relative to the satellites. Future receivers will be able to track Galileo satellites in addition to US and Russian navigation satellites, providing metre-scale positioning accuracy almost anywhere on or even off Earth: satnav is also heavily used by satellites.