A US government contract has gone to the Lockheed Martin to start building a new generation of global positioning satellites.

Lockheed beat Boeing to supply the first batch of satellites in the new Global Positioning System, known as GPS III.

GPS satellites, in one of six Earth orbits, circle the globe every 12 hours beaming precision navigation and timing signals that are used, among other things, for military mapping and weapons positioning.

The system is operated by the Air Force Space Command for the US Defence Department, which makes the signal available worldwide for free.