Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

GPS System "Close to Breakdown"

Discussion in 'The Pub' started by Stueh, May 21, 2009.

  1. I'm a bit scepticle, but interesting nontheless:

    Source: http://www.guardian.co.uk/technology/2009/may/19/gps-close-to-breakdown

  2. [​IMG]
    Don't throw it out !!..
  3. People who can't get around without satellites deserve to get sent via Geelong.
  4. Yeah, I sorta find it hard to believe, and this boosts that too.

    It's one of the comments at the bottom of the article by "CautiousOptimist":

  5. I don't have an in depth technical knowledge of how GPS systems work at the electrical level, but I've often wondered my entire life how there can only be X-number of satellites and yet the end users (aircraft, boats, satnav's, phones etc etc) seems to grow exponentially.

    Some further reading is required.

    Interesting stuff... I'm suprise they don't "prioritise" the units, so military use and emergency beacons get right of way over satnav's and phones...
  6. So Galileo isn't such a bad idea after all???
  7. It doesn't work like that... The GPS satelites orbit over the same spot on the earth constantly (dunno what thats call, geo-orbit??) and transmit a wide signal stating its lat/long position... your GPS unit needs 3 or more of these to work out where you are by triangulating the signal based on which signal it picks up at which time. Ie, if you're closer to one satellite, it 'hears' its signal first and then the other two (or more) and is able to work out where you are in a lat/long scale and then your GPS software puts your blip on a map.

    So no matter how many users there are it'll always work, its not a point to point system, its sort of like yelling, everyone can hear you and tell where you are...
  8. I get that bit except the distance bit. In order to triangulate including heights, a distance between the user and satellite would need to be determined. So it either goes off signal strength or some other means of which I'm yet to research up on this part (when I get bored of work, prob this arvo).

    In order for the satellites not to be jammed up with the more and more devices coming online everyday, the communication between the satellite and user would have to be one way; satellite -> user device. This is the bit I don't get yet at the electrical technical level. As mentioned, I need to read up on it more...
  9. Does a radio station get jammed up if it has too many listeners? ;)
  10. does your car tell you how far away from the radio tower you are?
  11. All Hail Wiki...

    something to do with timing of pulses / beeps from the satellites...
  12. Jah, timecoded signals.
  13. Geosynchronous would be the word you are after.
    Basically a GPS device works out how far it is from a minimum number of satellites. I think 4 may be the magic number.
  14. Yup yup, Geosynchronous. It orbits at a speed and height so that it's orbit matches the earths rotation, and stays above a certain point, yup yup!

    While 4 is the normal minimum, if you have another sort of "manual" input, eg. your height from an altometer (or if you're at a constant height, even better) then this will be input into the GPS and you only need three satellite connections.
  15. Nothing to do with signal strength. Your gps reciever measures its distance from each satellite based on the time taken to recieve incoming transmissions from each satellite. Beeps. ITs very easy to measure distance with radio frequencies. Aircraft have been doing it for a long time. Well before GPS came about. NDBs and Radar are an example of this. (radar slightly different but same principal.) GPS requires a minimum of 3 satellite locks to give position but the more satellites, the more accurate the system is. And as long as they can keep making recievers, more and more people can use the system without any degradation whatsoever.
  16. Temporary land based transmitters are also setup all the time for large scale construction projects.
  17. This isn't going to happen, what a joke of an article.

    GPS is worth a fortune to industry, the free market wouldn't let it fail.
  18. But the "free market" doesn't own the satelites...
  19. I don't care, I can read a map and use a compass.
  20. All good discussion above. It is too useful a system to let fail so it won't funding will be found.

    Just one correction the satellites are not in Geosynchronous orbit they are in Medium Earth Orbit (MEO) at about 22 thousand km. Geosynch is about 44 thousand km. This means that you get different satellites in the same location at different times of the day. Generally about 6 at once. This lower orbit also makes them cheaper to launch you don't need all that extra fuel to get up to a Geosynch orbit.