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Satellites...how Many Etc....


The Blind Acorn
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There are (were?) 32 "block 1" Sats. Do to their orbits, only a certain number are visible from your location.

 

I've had days where only about 8 were even "possible" from my location.

 

I don't know how many "block 2" sats are up. (These are the ones with WAAS frequencies integrated.)

 

All of this is from fuzzy memory. If you REALLY want to know check out Joe & Jacks GPS site. Just search for that and it will come up. It's like www.gpsinfo.com or something similar.

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There were only 11 block I satellites. The WAAS satellites are not part of the GPS constellation, but are seperate geostationary satellites above the equator. The GPS constellation of satellites are in about a 60 degree inclination orbit and therefore do not go directly over the poles. The closer you are to the equator, the more satellites you are likely to have in view at one time. At 39 degrees North latitude where I am, I have seen 11 once but usually see somewhere between 6-9.

Edited by Poindexter
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According to the United States Naval Observatory website at http://tycho.usno.navy.mil/gps.html "The current GPS constellation consists of 30 Block II/IIA/IIR satellites. All the Block I's have been decommissioned.

 

Another page in their website, at ftp://tycho.usno.navy.mil/pub/gps/gpsb2.txt , they describe the different types of GPS "birds" and if gives you a history of EACH GPS "bird" ever launched (or almost-launched, one didn't make it).

 

You can even go to http://science.nasa.gov/Realtime/JTrack/3D/JTrack3D.html (over at NASA) and scroll to see the current positions of the GPS "birds". On the menu of the 3-D image go to "Satellite" and click on "Select" then, on the pull-down menu labeled "Types" choose "Navigation". When the menu resets itself, pull-down the menu under "Navigation" and find the satellites labeled (obviously) GPS BIIsomething.

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You can even go to http://science.nasa.gov/Realtime/JTrack/3D/JTrack3D.html (over at NASA) and scroll to see the current positions of the GPS "birds". On the menu of the 3-D image go to "Satellite" and click on "Select" then, on the pull-down menu labeled "Types" choose "Navigation". When the menu resets itself, pull-down the menu under "Navigation" and find the satellites labeled (obviously) GPS BIIsomething.

OK, not quite as useful as the Trible page, but I've gotta say that is really cool!

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I'm not talking about how many you get lock with, but how many will the unit search for...

In reference to your "True that there are 24 available" question in the subject - Yes. A Full pattern is considered 24 active at any one time, in 6 (?) different orbits. There's also one 'spare' satellite in each orbit to take over should one of the 4 active ones fail at any time, or go down due to maintenince.

 

It's impossible to see all 24 at any one time, and very rare to see the full 12 that most GPSrs are capable of locking to.

 

As at Tue Jan 11 17:55:15 UTC 2005, There is only one of the 30 unusable, and there's scheduled maintenance on another set to occur from 18 Jan 1830 UT to 19 Jan 0630 UT. (Repositioning)

 

Here's another bit snipped from a text file - "The U.S. Air Force Space Command (AFSC) formally declared the GPS satellite constellation as having met the requirement for full operational capability (FOC) as of April 27, 1995. Requirements include: 24 operational satellites (Block II/IIA/IIR) functioning in their assigned orbits and successful testing completed for operational military functionality."

 

Bionico - Those tycho.usno.etc.etc pages are good info!

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