The trouble with GPS

GPS Unit Every year, thousands of GPS sets get purchased. In the guise of handheld units, car
 navigation systems, integrated yacht systems, chart plotters, mobile phones and
 much  more. We implicitly assume they will work. We pay no subscription, and merely
 assume  the right that GPS will be available for us to use.

 The American military GPS (Global Positioning System) has been with us in excess of
 30 years. It has not only revolutionised navigation at sea, but also in our daily lives. Most cars are fitted with ‘Tom-Tom’ type devices for land-based navigation. Emergency services all use GPS for quick location of casualties. Couriers and transport companies all use GPS to track shipments. Our smart phones use GPS to give us a whole host of information from local weather to our closest chandlery or Chinese restaurant.

GPS comes under the umbrella of a GNSS (Global Navigation Satellite System). GNSS also covers the Russian system (GLONASS), Chinese system (COMPASS) and European system (GALILEO), unfortunately, as things stand, GPS is the only available system that the public have access to, and as such we have the dubious situation of having all our eggs in one basket.

Our reliance of GPS is scary. Sadly, we humans are generally idle creatures, always looking for the easy option. GPS has made us lazy; every few months we hear amusing stories of people driving their cars into lakes or off cliffs, by diligently following their car navigation system. We hear of yachts driving straight into navigational buoys, because it was used as a waypoint. We hear of ship collisions and groundings through over reliance on electronic navigation. 

On the other hand, if GPS were to fail today, many navigators would struggle with even the simplest of manual navigational tasks. Can you put your hand on your heart and confidently say you could plot a 3-point fix, an estimated position or a course to steer without your faithful electronic friend?

But why worry? GPS is incredibly reliable. In all the years I’ve had it on-board it has never let me down, never so much as a hiccup, so why should GPS let us down now?

Life of the GPS system

GPS is now over 30 years old. The original constellation only had a lifespan of 5 years, though this was far exceeded. The oldest GPS satellites currently up there and operating are upwards of 20 years old, which is certainly a long operating time for a satellite. They're getting old. They've functioned beautifully during their lifetime, but time is taking its toll. No matter how well something is built, long-term wear and tear in the harsh environment of the upper atmosphere (GPS satellites are in a low orbit) will strain any system, and they are starting to feel it.

Progressively, new satellites have been added to the constellation as old one were decommissioned, however, it would appear that financial and technical issues have delayed the replacement of these satellites and it is expected that we may lose some of the 24 satellites required to run a full service. At present there are 24 satellites available, some sources suggest that unless new satellites are put into place, the GPS system may be severely depleted by 2015. Now 24 satellites may seem a lot, but remember they are orbiting the entire earth, so at any given moment, your receiver will only see a fraction of these. We need 3 satellite for a basic 2D fix, and 4 for a 3D fix. The more satellites available, the more accurate our position. If we lose satellites, positions could be significantly degraded.


We know that Piracy is on the increase, and that the pirates are using more and more sophisticated methods to capture vessels. Just a quick trawl on the Internet and you will find a whole host of GPS jammers for sale at very cheap prices. These jammers transmit a signal on the same frequency used by GPS. This causes the GPS transmissions to be overridden and the receiver to lose contact with the satellites and hence loss of position.

The problem lies within the strength of the GPS signal, it is very weak. Those of you who regularly use hand held devices know of their shortcomings when moving inside a building or a heavily wooded area. This makes the jamming and corruption of the GPS signal very easy. 

The best-case scenario is if the jammer interrupt the signal completely. In this case the GPS unit gives up, reporting no positional information. The worst case is when the jammer is able to modify the signal to give false information. Most jammers only work up to a range in the order of 10 or 20 metres, however with increased power you can imagine the possibility that the unwary crew of a vessel will now believe they are somewhere where they are not. This would be a gift for the pirates, able to lure vessels straight into their welcoming arms.

 In 2008 Trinity House did some trials on the jamming of GPS off the east coast of the UK. They reported that GPS positions reported unfeasible speeds, courses and positions. Also, significantly subtle errors were seen; errors where the vessel’s reported position differed slightly from the true location and wandered slowly. These differences showed that the impact of GPS jamming would be different for each vessel and depended on the model, installation and configuration of the onboard systems. It would need a very vigilant crew to pick up these changes.

Solar Activity

The sun goes through cycles of high and low solar activity. In high activity, huge flares are blown out into space. These flares throw out a geomagnetic storm that can disrupt the electronics found on most satellites.  We are now approaching a period of high activity (2012/2013). In the past, this high activity has had the ability to either temporarily or permanently disrupt satellite communication. At present, there are concerns that GPS signals could well be degraded to such an extent that the reliability of position fixing is severely reduced. The last major eruption in 1859 caused a major breakdown of the telegraph network in both Europe and the USA. Cables caught fire and some telegraph operators were injured! Consider the crudeness of that technology compared to our incredible delicate electronics in use today. Not only would GPS be vulnerable, but every piece of equipment using a microchip. A very scary scenario when you consider that even your lowly toaster, kettle or washing machine relies on this electronic brain to function. 

Other Options

So what are our other options? Predecessors of GPS, systems like Decca and Loran C have been slowly phased out, and at present are inadequate for reliable navigation. There is some on-going development in eLoran, a modern version of the old Loran C system, this may fill the gap, and appears more robust than GPS, the signal being harder to disrupt. Current studies indicate an accuracy of +/-8m, so well within the tolerance of current GPS.

Within the umbrella of other GNSS’s, we have the Russian’s GLONASS and the Chinese COMPASS. GLONASS is primarily a military system, however it had recently been made available for civilian use. Unfortunately, few manufacturers of receivers are GLONASS compliant. Our own European system GALILEO is still delayed. It was due to go live in 2008, but current estimates are closer to 2014. 


In the meantime, we rely solely on the elderly American military GPS. It’s a great system, but how much longer can we rely on it? The problem is not just about navigational position fixing, but other marine safety systems, consider VHF/DSC, AIS and RADAR, these all use GPS data to operate effectively.

The RYA still teach traditional navigational techniques as well as the new electronics, and I am a great believer in this ethos. Only by understanding the basic foundation of navigation, can we appreciate the short comings and fragility of our over reliance on electronic navigation.

My advice, get out those old dusty notes from when you studied your RYA Dayskipper / Yachtmaster theory and refresh yourself on traditional navigation. Sharpen your pencil, update your paper charts and clean the mirrors on your sextant! You never know, you might actually enjoy the satisfaction of finding your way without reliance of all those electronics!


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