GPS is now recognised as being vulnerable to jamming either by accident or by design and despite a lot of talk from politicians there is no back up if the system goes down through jamming or spoofing.
A solution to this vulnerability now exists in the form of Satellite Time and Location (STL) signals. “STL signals provide the safest, strongest, most dependable backup to our GPS infrastructure and they originate from the Iridium satellites, whose beams are high-powered, location-specific, and incredibly difficult to jam.” commented American company Satelles who have developed the system. Their time and positioning system that uses the powerful Iridium signals as a means of propagating enhanced GPS information which is claimed to be much more reliable and powerful than the original GPS signals alone.
The Iridium satellites are a constellation of low orbit satellites that have been put into orbit to provide a telephone and data connection for mobile units anywhere in the World. There are 66 Iridium satellites and each satellite uses a network of powerful spot beams to send and receive signals to and from the earth’s surface.
By using these Iridium signals as the carrier for the enhanced GPS signals the user on the ground or at sea receives a much more powerful signal. The stand alone GPS signals are so weak that they have been compared with looking at a 100 watt electric light bulb from a distance of 100 miles. The signals from the Satelles system are considered to be up to 1000 times more powerful. This means that they are much more difficult to jam by sending out a transmission on of near to the same frequency that is more powerful than the GPS signal but the nature of the new transmitted signal also means that it is very difficult to spoof, meaning to send out false signals.
In their present state the position accuracy from the Satelles system cannot match that of the stand alone GPS signals but for many uses it has an adequate accuracy. At present this may be in the range of 20 to 50 metres and in many cases it can as good as 10 metres which may be fine for general positioning but is probably not accurate enough to position fixed structures. At present the system is being developed primarily as a more resilient source of accurate time which is used for many communications and infrastructure requirements. French Company Orolia which is the parent company of McMurdo, is developing the system in Europe.