confussed

[chrismmm]

I have had a search on the web for info on gps but few sites seem to answer my quaestions.
1 I thought that gp sattelites were geo stationary apparently not - why not ? would it not be more sensible to have them fixed, there must be a good reason not too.

2 Do these satelites stay in the same orbit path on every lapse of the earth?

3 If they are following the same path in orbit is any correction made manually ie from intervention from an earth station or do they just stay in the same path naturally?
hope somebody can point me in the right direction or enlighten me.

chrismmm

[Pocketgps]

Hello chrismmm

Have a look at this link

http://www.garmin.com/aboutGPS/

[Skippy]

The quick answers are:

1. The GPS satelites orbit the earth every 12 hours. The DGPS (WAAS/EGNOS etc) satelites are geostationary. I'm not sure why they aren't all fixed.

2. Yes.

3. The satelites keep a track of any variation in their orbit and they transmit this to the receiver as part of the Ephemeris data. This is what your GPS receiver is waiting for when it "locks on" to a satelite. This data is repeated every 30 seconds.

If you are really interested in how GPS works, there is an excellent tutorial on Trimble's website. There's more information than you ever wanted to know but it's presented in simple terms.

http://www.trimble.com/gps/

Enjoy!
_________________
Gone fishing!

[chrismmm]

Thanks for the links that explains it in nice simple terms, still no idea why they are not geostationary though.

chrismmm

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