Friday, 1 July 2011

What if GPS went out?

A recent edition of the IET Magazine picked up some interesting issues with the GPS system.
In January 2007 the Commander of the US NAVCEN, reported the loss of GPS signals. Navigation equipment for general aviation stopped, cellular phone operations were disrupted, and the hospital's mobile paging system went down.
It took three days to pinpoint the source – a two-hour US Navy training exercise in communications jamming between two ships in the area. They stopped the exercise but didn't report the incident beyond their usual channels because the jamming was not meant to be in the GPS L-band.
A GPS jamming attack on the ship THV Galatea two years later off Newcastle-upon-Tyne showed some of the more subtle effects of jamming. Under low-power jamming, at about the same level as the real GPS signal, the ship's GPS-driven bridge instruments showed plausible but wrong positions and velocities.

Earlier this year in the New Scientist reported on a device that is illegal to use in the US, UK and many other countries. The low-tech devices can be bought on the internet for $30. Sellers claim they're for protecting privacy. Since they can block devices that record a vehicle's movements, they're popular with truck drivers who don't want an electronic spy in their cabs. They can also block GPS-based road tolls that are levied via an on-board receiver. Some criminals use them to beat trackers inside stolen cargo.

Power distribution networks, banking and financial trading systems, broadcasting and industrial-control networks all use GPS timing making them  vulnerable to unintentional or deliberate (the civilian equivalent of navigational warfare) interference.

There is available a backup.
The 100kHz terrestrial radio navigation system eLoran  is a strong contender in the UK and Europe as a systemic timing back-up, according to Dr Sally Basker, president of the International Loran Association. 'GPS is low-power, high-frequency, whereas eLoran is the reverse, which means you get very different failure mechanisms.

I was interested to read about the Loran system, as I wrote interfaces to use these systems many years ago. The Loran system was used alongside, Decca, and Omega systems. One small bit of coding I performed during the late 1970’s was to provide an “autofix” feature for the navigation system for a cable repair ship. The “autofix” would automatically reset the ships position to that given by the satellite system, as long as it was within a set distance of the currently calculated location.

America has just closed down its Loran-C network, which had been used for marine navigation, with no published plans to upgrade it to eLoran

In the closing of its article the IET E&T says - Of course, until there is a major GPS outage, we may not know the extent of our dependency on GPS. Space weather events such as sunspots and solar flares may do the job for us, says Bob Cockshott, location and timing programme director of the UK Technology Strategy Board's Digital Systems Knowledge Transfer Network. 'In 1859 a solar flare known as the Carrington Event electrified transmission cables and set fire to telegraph offices,' he explains. 'That was the limit of the technology then. We don't know enough to be able to predict such events or their effects now.'

There is nothing much to find out about “Hydroplot” on the web. There is an article that I have found:
Later this month Cable Ship Mercury arrives at Immingham dock to be fitted with a new navigation system, Hydroplot, that was developed for the Royal Navy's hydrographers. Widely recognised as one of the most accurate commercial systems available, Hydroplot uses an Elliot 905 computer and signals from US Navy space satellites to pinpoint the ship's position to within 300ft. The £100 000 system, supplied by Marconi Space Systems and International Marine Radio, integrates all the ship's other navigational aids and is able to produce an accurate plot of the route the cable is laid over. This will be a vital aid to any repair operations the cable may require.”

There is also a small mention of the Royal Navy Hydrographic ships here:

An awful lot of natter going on here, but it is interesting how the past may come and help with the present.

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