Would any of the surveyors happen to know what the altitude of the GPS constellation is? ?ÿ
- I have a few references putting it at 12,500 miles above the earth
- One conversation with a tech putting it at 11,900 miles above earth (GLONASS)
- And one text putting it at 10,900 miles above the earth
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GPS and GLONASS have different orbital periods so, one being a function of the other, they naturally orbit at different heights. No surprise there.
According to Wikipedia GLONASS orbits at 19,130km (11,887 miles) and GPS at 20,180km (12,540 miles). Wikipedia is never wrong.
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This was interesting;
Wikipedia is cool
If they were not at different heights they would hit each other, so there has to be variations within each constellation
THe US NAVSTAR GPS satellites orbit the geocenter at a nominal value of 26,560,000 meters. This value?ÿis readily verified using values from a RINEX NAV message which shows in the fourth column of the second line after the SV identifier and date/time of observation the square root of the SV orbit radius.
For a sample NAV file and description as well as more details about orbits see:?ÿ http://geodesyattamucc.pbworks.com/f/Class_17_2k7.ppt
Obviously the distance from the surface is different. Look at the pseudo ranges in the RINEX OBS file.?ÿ
BTW, the US NGS is hiring ??Orbiteers ?? Unfortunately Keplerian theory is not enough.?ÿ
HTH,
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DMM
'If they were not at different heights they would hit each other, so there has to be variations within each constellation.'
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From a half dozen Navstar queries on the site linked above, the altitude can range from 12,200 - 13,200 miles in altitude.
It's hard to believe the buffer needs to be that large - not doubting the professionals - when a documentary on landing the rovers on the planet Mars explained that making the two come together from launch was like trying to thread a needle from fifteen miles away.
There is no such thing as a perfect orbit. As the satellites circumnavigate the sphere? called earth the satellites bob up and down because the gravity beneath them varies considerably. Beside varying the satellite altitude gravity also affects the satellites velocities. Precise orbit data gives every satellite position at 15 minute intervals. In that 15 minutes each satellite travels about 1080 miles through space.
Since correcting altitudes use fuel, all of which has to be in the satellite at launch and they are up there for 12 or more years, one has to allow for error in altitudes otherwise the constellation would turn into space junk.
Paul in PA
Having sourced two separate satellite tracking sites, and run through the list of current SVNs, it appears a rough mean between the apogees and perigrees averages out to roughly 12,500 miles in altitude.
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One thing that seemed odd, the SVNs 24 and 34 on both sites - one which might source the other - shows 34(last of the IIA) out of plane, when the USCG Nav center shows it being healthy as of today. The same sites show 24 in plane when it doesn't even appear on the constellation.
SVN 24?ÿis long out of service. Are you looking at a PRN number?
Paul in PA
SVN 24?ÿis long out of service. Are you looking at a PRN number?
Paul in PA
SVN 24?ÿis long out of service. Are you looking at a PRN number?
Paul in PA
Yeah. The site that I went to has log in and permission issues, if you wish to distribute any data or material.
Here's a clip from one site showing SVN 34, an apparently healthy satellite at an strange altitude compared to the rest.?ÿ
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SVN 24 was in a .csv list - on that other site - with an altitude of roughly 12,500 miles.?ÿ
That altitude is a bit high and I would assume SVN 34 was moved there?ÿ to keep it out of the way of the main constellation.?ÿ It will probably soon be out of fuel and out of service. Note that the higher elevation also results in a longer period (12.7 hrs.). It is in Slot 6, which does not regularly mean it is between 5 and 1.
BTW, where and how did you find the data box to the right.
Also I have used the Nav Center site for years and did not know you could change the sort arrangement. I have only seen it before with the default sort of Plane and Slot.?ÿ
If you are interested, open a RINEX file in a text editor and read the C1/P1 and C2/P2 observations. That is the distance in meters from the satellite to the observation antenna, typical range is 20,000,000-24,000,000, less your elevation above MSL.
Paul in PA
