When Colin and I set sail from Halifax, Nova Scotia, in late July 1973 there was only one safe way to navigate a small boat across the ocean – you had to use a sextant to measure the heights of the sun and stars above the horizon. You also needed a chronometer to determine the exact time of each sextant sight. With these two bits of information you could plot your position anywhere on the surface of the earth – and if you were skilful and the conditions were favourable the fix might be accurate to within a mile or two. This was exactly the way Captain Cook navigated back in the 1770s.
By coincidence it was also in 1973 that the US Air Force began developing the satellite navigation system we now know as GPS. It wasn’t the first such system but it represented a major step forward in terms of accuracy and sophistication. And it was a really amazing technical achievement. At its heart is a network of satellites in precisely determined orbits each carrying its own atomic clock. GPS receivers pick up the faint signals from these satellites and use them to fix their positions in three dimensions.
Of course Colin and I knew nothing of these developments. I suppose we may have been dimly aware that the US military were already using some kind of satellite navigation – as indeed they were – but the Cold War was still very much in progress and such technology was highly sensitive. That was to change when the Iron Curtain was lifted in 1989 and the Soviet Union fell apart. GPS was already publicly available in the 1990s and in 2000 the last controls were lifted so that the public had access to the best positional information. Anyone who could buy a GPS receiver could now fix his or her position to within a few meters. It was quite incredible until it became so routine and familiar.
Since 2000, as the price (and size) of GPS receivers has dropped, this astonishing navigational technology has swept the board. It’s everywhere: in our mobile phones, our cars, in planes and of course in boats. We are even being told that we can put GPS transponders in our valuables or on our children so that we can keep track of where they are! GPS has made life much easier and, in many ways, much safer. But it has its shortcomings. First of all, it’s very vulnerable to interference and can easily be jammed. Secondly, it’s quite easy to ‘spoof’ the GPS signals and persuade a receiver that it’s somewhere where it’s not. There are other risks too – charged particles entering the atmosphere from outer space can potentially fry the circuitry in the GPS satellites. For all these reasons – and others – robust backup systems are now being developed. One possibility is to revive and improve LORAN – a radio-based navigation system developed in World War II.
Of course the most robust alternative to GPS is the good old sextant. It doesn’t even need electricity! But to navigate reliably with a sextant requires practice – and lots of it. It’s a real skill, and a deeply rewarding one. And the saddest thing about the dominance of GPS is that so few people are now acquiring it.