Millions of U.S. consumers have come to depend on GPS technology for a variety of daily activities, like avoiding traffic jams, finding the shortest route to a vacation destination, or for just finding the nearest movie theatre. Hopefully, those GPS-addicts haven't cleaned the maps out their glove compartments just yet -- according to a U.S. government report obtained by U.K. newspaper The Guardian, the nation's satellites used for GPS may be failing and could even begin to malfunction by 2010.
The Air Force maintains the satellites -- which have been in operation for approximately 20 years -- but hasn't replaced any of them. The first replacement, scheduled to launch in 2007, has yet to be sent into orbit. It's surprising that the Air Force allowed the system to get so bad, considering that the military relies heavily on GPS for mapping, reconnaissance work, navigation, and targeting.
Those articles in my opinion are way over-blown. They are filled with words like: could, might, perhaps, chance of, etc. Going by the numbers and not an emotional response, there is at worst an 80% chance that the system will maintain 24 satellites (necessary for a "full" constellation) over the next few years. And even if they don't maintain 24 (less than 20% chance), GPS will still work for our purposes.
Also keep in mind many of those reports are coming from Europe based news outlets. Nothing against Europe, but they are also working on building a network of navigation satellites to compete with the GPS system.
Joined: 05 Jun 2008 Posts: 2874 Location: New Jersey
Wed May 20, 2009 12:50 pm
Tim, I don't understand that chart. As I read it, there is a 0.8% (less than 1%) probability and not an 80% probability. Is that a typo on the chart or am I not interpreting it correctly?
Joined: 07 Mar 2009 Posts: 84 Location: West Chester PA (Nuvi 760 +MSN)
Wed May 20, 2009 5:18 pm
Tim, I agree with you that the whole thing is overblown. It reminds me of the doomsday everyone was predicting for Y2K. Yes I, along with millions of others, tested and redid code to smooth out any issues, but this is the same press that has to create a crisis to sell papers.
You're also correct in following the money. The Europeans are launching their own network of satellites and these are where those doom and gloom stories are being hyped the most.
Joined: 04 Apr 2009 Posts: 13 Location: River Grove, Illinois
Sat May 23, 2009 2:22 pm
There is an excess of military satellites for precision guided munitions, and for operating unmanned Predator drones in Afghanistan and Pakistan, and unmanned drug surveillance aircrafts in Latin America. The report said that the Pentagon has not launched any new satellites, which meant, when new military satellites with updated military technology are deployed, the presently operating will be decommissioned for commercial use. Since only 3 satellites are necessary for a GPS, even though more are better, the number of satellites now operational far exceed the minimum, and new launches in the next 10 years will always keep a surplus up there for us. This view is based on my prior military service.
Since only 3 satellites are necessary for a GPS, even though more are better, the number of satellites now operational far exceed the minimum
Actually four for dependable spotting, but that's quibbling. An array of 24 are required operational to ensure the minimum needed can be found at a specific location. At any one time, many/most are outside the horizon.
Joined: 04 Apr 2009 Posts: 13 Location: River Grove, Illinois
Sun May 24, 2009 12:42 pm
To Gatorguy:
I did not mean 3 Satellites need for GPS guidance globally - or over the horizon - as you said, but at any specific point, or location. The pinpoint location of GPS systems is calculated by "trilateration", the "tri" means 3 in Greek. For moving objects, cars, cruise missile, etc, more satellites increase the algorithmic azimuth precision [military term] of the guidance system as the moving GPS unit obtain better angles from aditional sattelites -IMO.
My point was that with 31 operational satellites in orbit currently, according to Wikipedia, there is a suplus of satellites available, and
the current scare about our GPS systems becoming relics is unwarranted.
3 locked sats give you only a rough 2D position fix. 3D requires a lock on 4 satellites.
EDIT: I want to expand for those that have a problem picturing the difference. Using a military scenario, say you want to fire an artillery round on an enemy located at the very peak of a mountain. With three sats locked, you now know roughly where the base of that mountain top would be if you drilled down from the peak. But that's not where you want to fire the round. At least one additional satellite is required to discern the altitude and thus the true position of the peak.
Joined: 04 Apr 2009 Posts: 13 Location: River Grove, Illinois
Sun May 24, 2009 2:52 pm
Artillery fire scenarios are not applicable to GPS devices. Artillery shells travel at bullet speed, and have no guidance systems (gyroscopic fins) to change direction at mid course. The artillery target is determined by crossing its distance and its azimuth trajectory points. That is how the 155mm artillery works [personal experience], and it is the standard for self-propelled artillery as well. Precision guided munitions are rocket-propelled, slow, and they can scan the terrain and make adjustments [cruise missiles], but from air fired missiles, the target is illuminated, and the guidance system locks on until target is hit. The 2D or 3D is probably part of the cruise missiles, but my knowledge is limited on them. However, since Geometric Trilateration is used for GPS positioning, which in Greek means "Geometric Intersection of "three converging points into
one spot" (think about the "Where am I"), I still believe 3 satellites are enough for regional navigation.
Joined: 04 Apr 2009 Posts: 13 Location: River Grove, Illinois
Sun May 24, 2009 5:49 pm
You are correct, Gatorguy, that 4 Satellites are necessary for GPS units to function. Even though the GPS position is obtained by "triangulation" [from three angles), the GPS system is built on 4 satellites constellations (groups) to keep the system functioning if ionospheric static in the radio (Shortwave) signal of one sat is delayed. Quibbling? No. I did not know that even though the system needs 3 sats to pinpoint a location, it is built to work on 4 as a safety feature against atmospheric interruptions, and constancy if one sat signal was delayed or failed momentarilty. Thank you.
Artillery fire scenarios are not applicable to GPS devices. Artillery shells travel at bullet speed, and have no guidance systems (gyroscopic fins) to change direction at mid course.
You sure about that? And what are gyroscopic fins? Did you mean movable aerodynamic flight control surfaces?
The Excalibur GPS precision guided artillery round was used in Iraq in 2007.
Joined: 13 Feb 2008 Posts: 162 Location: Northern Va, US
Mon May 25, 2009 10:36 pm
Nick wrote:
You are correct, Gatorguy, that 4 Satellites are necessary for GPS units to function. Even though the GPS position is obtained by "triangulation" [from three angles), the GPS system is built on 4 satellites constellations (groups) to keep the system functioning if ionospheric static in the radio (Shortwave) signal of one sat is delayed. Quibbling? No. I did not know that even though the system needs 3 sats to pinpoint a location, it is built to work on 4 as a safety feature against atmospheric interruptions, and constancy if one sat signal was delayed or failed momentarilty. Thank you.
Actually, I think I remember reading someplace the 4th satellite is required by the GPS to provide some type of relative time offset against the other 3, so that the clocks can all be syncronized. I must confess I don't understand the science here, but apparantly failure to do this could throw the GPS way off.
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