New GPS sats to lack Selective Availability
Availability will still be selective though
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The US military announced yesterday that it will no longer procure Global Positioning System (GPS) satellites with the capability for worldwide civil sat nav degradation.
In a release dated yesterday, the Pentagon confirmed that "this capability, known as Selective Availability (SA), will no longer be present in the next generation of GPS satellites".
Until 2000, the accuracy of the GPS civil signal was reduced using SA, so that a normal sat nav receiver would be accurate to only 100 metres or so. There was and remains a separate military signal, encrypted so only those with appropriate keys - such as the US forces and their allies - can use it.
Despite SA, many civil users were able to achieve excellent accuracy using a technique known as Differential GPS, in which a ground station at a known location would calculate the SA error and transmit corrections to a mobile civil receiver in real time.
SA was switched off in 2000 on the orders of President Clinton, but it remained an option. In the years since, the US government has sought to assure civil GPS users that SA would never be used again, but its presence has remained a concern.
Now it has been confirmed that the next generation of satellites will not have SA built in. According to the Pentagon: "While this action will not materially improve the performance of the system, it does reflect the United States' strong commitment to users by reinforcing that this global utility can be counted on to support peaceful civil applications around the globe."
This announcement may reassure users somewhat, but the GPS civil signal still isn't a given. America will retain the option to degrade or deny it altogether over limited areas, and this was always much more likely to happen than the relatively blunt instrument of degrading performance worldwide.
The European Commission is just about to make its case for pushing ahead with the proposed new Galileo Euro sat nav constellation. One might speculate that the timing of this American announcement isn't a coincidence. ®
COMMENTS
RE: And another thing
"Apart from a declaration of war by US allies in Europe there is no chance of our allies losing access to GPS."
What if the US did declare war on Europe? If you don't control it, you can't trust that you'll always have access to it.
In response/addition to other comments: It's not necessarily an economical advantage that the US owns and controls the only GPS-like system, it's a strategic military advantage. Who cares about the US companies? It's all about control. If the US military controls it, it can mess with it all it wants. And if the US wanted the UK's military to stop using the "Military Channel", it could just disable their keys.
American Government are liars
The American Goverment doesnt have a good track record on things and they are especially good at backtracking and changing the rules at any moment when it suits them. So its quite possible the Bush administration might turn around and stop anyone it doesnt like from using the system and it could (in theory) even send out a wrong signal...
Given the reliance on SatNav these days it makes perfect sense to have more than one system. For one it means that if (in the unlikely event) the GPS system goes down (and it has done, albeit only once if memory serves) there is another system to use instead.
To the Americans:
The question is not that the “world” is not grateful for GPS, the question is that the world now relies on accurate positioning, and fears that should any “troubles” were to start, and US will decide to encrypt GPS signals, a European (and Russian, forgotten in these comments) systems would come in handy.
Strategically speaking, having accurate positional data is quite important, I am more than positive that US has a way of rendering GPS signals useless during war time. It is most probably classified, and I would not be at all surprised if US military receivers have hidden firmware settings to switch to a different frequency and protocol, if the main GPS signal goes dead.
What I have always wanted to know, however, is how the old ICBMs navigated, before satellite positioning...
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