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| Problems Affects Global Positioning System |
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| Wednesday, 31 March 1999 00:00 | ||||||||
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Source: Computimes, The New Straits Times (page 34) Remember Die Hard II where Bruce Willis was fighting terrorists who took over an airport and interfered with navigational software? He was unable to stop an aeroplane crash when its software told it that the runway lies 300 feet under the ground. The scenario is not as far fetched as you would think.In 1978, the US developed a Global Positioning System (GPS) which allowed their military aircraft to pinpoint their exact location within a meter anywhere on the earth and its atmosphere. How does this work? Over a period of years over two dozen NavStar satellites were launched. Moving in orbit around the earth at an altitude of about 12,500 miles (20,200 kilometers), these satellites transmit signals on a time schedule precisely controlled by atomic clocks. GPS receivers automatically select the three satellites most favourably located and relay their signals into a computer, which calculates the position of the receivers by solving three simultaneous algebraic equations. The result is provided in the form of geographic position - longitude and latitude. Most consumer receivers are accurate to within 100 meters while military receivers are accurate to within a meter. In addition to displaying longitude and latitude, every receiver are accurate, every receiver may have a display screen that shows a map. Using software, your position can be shown superimposed on the map. For aeroplanes, balloons and so forth, a fourth satellite position is received. With four simultaneous algebraic equations, altitude as well as the geographic position is calculated and plotted. (This is the bit Bruce Willis' terrorists hacked.) Additional software calculates your speed and direction giving you estimated times of arrival to specified destinations. In other words, the GPS means no more getting lost in the dark or in fogs, storms, deserts and oceans. Initially, the US military keep tight control of the entire GPS. This changed when the Soviet Union shot down a Korean civilian aircraft. Apparently commercial flight KAL 007 was slightly off an established airline route and drifted into Soviet airspace. The Russian military mistook it for a hostile intruder and destroyed it with a missile killing everyone on board. This incident prompted the US military to distribute use of a significant part of the GPS worldwide - reserving some of the fancier function for itself to maintain military advantage of course. Who use GPS? Almost everybody. If you've been watching Discovery Channel recently, you will be aware that scientists are using the GPS to help them map underwater archaeological sites like Cleopatra's Palace. In addition, the GPS is used to help measure the movement of the arctic ice sheets, the Earth's tectonic plates, and volcanic activity. The GPS also helps us predict volcanic eruptions allowing us to minimise loss of life and damage. GPS receivers are also widely used by hikers, cross-country drivers and skiers, balloonists, sailors and other outdoor enthusiasts. With a laptop or palmtop, user can quickly find their true location and cross-reference this with traffic and weather information. This is especially useful for those engaged in dangerous sport such as desert racing. Not to be outdone, security firms use the GPS to trace stolen cars. This is not always an advantage. Remember Cindy Crawford and William Baldwin in Fair Game? Crawford and Baldwin are being chased by a renegade KGB team. When they race away in Baldwin's car, the bad guys find them using the electronic tracking system installed to help police recover the vehicle in case of theft. Renegade KGB teams notwithstanding, the GPS is a great boon to most people. There's just one small problem: The GPS has a similar to the Year 2000 (Y2K) all of its own. And it's set to go off 132 days before the dreaded Jan 1, 2000. This is due to a coding problem very much like the Y2K issue. The GPS measures time in weekly blocks of seconds starting from Jan 6, 1980. So at midday on Tuesday, Sept 17, 1996, the system indicates week 868 and 302,400 seconds. However, the satellite clocks are configured to deal with 1,024 weeks. This limitation means that when week 1,025 starts, some GPS receivers may think the system that it is Jan 6, 1980 (i.e. week 0000). Week 1,025 starts on 22 August 1999. Although the GPS broadcasts contain sufficient data to ensure that navigation need not be affected by the roll-over, there are widespread reports that not all receiver will function completely. Various people are to blame. Some manufacturers see this as Somebody Else's Problem, others hope that warranties will have expired leaving consumers in the cold but profit intact and still others are trying to solve the problem but are experiencing logistics problems. How widespread this problem is, is hotly debated. Y2K analyst Jack K. Horner reported that after examining just 10 per cent of the GPS ground station code, he found there were two major problems: one result from the omission of the "19" in the calendar year letting the computer think that year 200 is 1900. The other involves arithmetic that implicitly assumed no dates later that Dec 31, 1999, are possible. Worse, he suspected there were many hidden errors which can not be detected using tools. Testing GPS for roll-over problems is not as easy as it seems. As his report stated, "In GPS, it is not possible to construct good test cases to see what will happen at the millennium start, because of the future (time-) states of the system depend on physical values (orbital element, pole wander, Jovian gravitational force) that can be determined with sufficient accuracy only from the actual operation of the system within about three months of the time of interest. "Approximately one per cent of the total GPS code is affected by this class of problems, or affected it." Most Y2K specialists agree that technically speaking, solving the roll-over problem should be quite simple. GPS equipment has permanent parts called firmware. This ROM will have to be replaced in all older units. This is not difficult but the logistics of finding and replacing each part will take years. Manufacturers reported some time ago that the time required to evaluate all the necessary program code and replace the necessary ROMs is longer that that left until August 22, 1999. What effect will this have? If you rely on the GPS to state your true position you will be in trouble. This means that planes, trains, ships, cars, tractor, snowplows, earthmovers and mining equipment, etc, will not be where they think they are. Nor will hiker, explorers and car owner rich enough to afford the latest models. Aircraft operators have been warned not to rely exclusively on the GPS. They will have to use additional radio equipment to double-check data. Still, in my opinion, August is not the optimum time to travel, visit an automated underground mine or go for a hike in the desert with just a palmtop. In some places even bus services may be disrupted. The Washington Post reported in March 1995 that Montgomery County, Maryland, was going to use GPS to keep buses on time, by giving technicians the power to change traffic signals to green an tardy buses approach an intersection. Scarier is the fact that a lot of military equipment relies on the GPS. For example, some nuclear warheads developed for Trident use the GPS for terminal guidance. One can only hope that the military are telling the truth when they say the problem has been anticipated and fixed, but then again, why haven't we heard lots of crowing after the US military tested their equipment for the GPS problems on Feb 20 this year, in anticipation of the roll-over time? Finally a little personal horror scenario, or idea for Die Hard IV. What if there is a nuclear warhead failsafe system in place somewhere which is programmed to assume global thermonuclear war has begun when it loses communication with the outside world for more than a few minutes? Let's hope Bruce Willis will be efficient in seeing it doesn't launch its missile in the hope of a Pyrrhic victory. Gary North's Y2K Links and Forums: http://www.garynorth.com/y2k/search.cfm#Choices Risks Forum: GPS Problems Reported: http://catless.ncl.ac.uk/Risks/14.13.html#subj3.1 Re: Risks Associated with the Year 2000 Problem (Jack K. Horner): http://catless.ncl.ac.uk/Risks/18.96.html#subj9.1 US Coastguard Navigation FAQ: http://www.navcen.uscg.mil/ NavStar GPS Joint Project: http://gps.laafb.af.mil/ Keeping buses on time plus a little eavesdropping: http://catless.ncl.ac.uk/Risks/16.93.html#subj3.1 Or search newsgroups for keywords "GPS Y2K" or go directly to sci.geo.satellite-nav, sci.engr.surveying, rec.aviation.products, comp.software.year-2000 and geoinfonet.gis-gps for detailed information.
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