GPS Satellites' height

Hellow,

On most webpages I find that the speed of the GPS satellites is about
11000 km/h (some also say 12000 km/h).

But if I calculate the speed that a
satellite must have in order to stay in it's orbit at a height of 20240 km, I
find 13938 km/h as the result.

Here is the calculation:

v= sqrt(G* mA/(rA+h))

where v = velocity (speed)
G = 6.67*10^-11 (N*m²)/kg²
mA= the earth's mass =
59.8*10^23 kg
rA= the earth's radius = 6.37*10^6 m

after filling in these
numbers:

v = sqrt(3.99*10^14/(6.37*10^6+20,240*10^6))
v = 3871.61 m/s
v = 13938
km/s

why is the result so much off from the data on the websites? Am I doing
something wrong?

Thanks a lot!!


--
TiTaN_pi8

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YES

TiTaN_pi8 wrote:
km/h (some also say 12000 km/h).
it's orbit at a height of 20240 km, I find 13938 km/h as the result.
something wrong?

Take a look at the figure you are using for rA+h.

You can get the square root of the semimajor axis for each satellite
from the YUMA data
http://www.navcen.uscg.gov/ftp/GPS/almanacs/yuma/yuma341.txt
http://www.navcen.uscg.gov/ftp/GPS/almanacs/yuma/
http://www.navcen.uscg.gov/gps/almanacs.htm

Regards,
-Sam

TiTaN_pi8 wrote:
km/h (some also say 12000 km/h).
it's orbit at a height of 20240 km, I find 13938 km/h as the result.
something wrong?

I get

http://www.google.com/search?q=sqrt%28%28G *6*10%5E24+kg%29%2F%282.65596*10%5E7+m%29%29
based on the radius of a satellite from YUMA data.

Where did you read 11,000 km/hr for a GPS sat? Are you sure that is not
for GEO?

Phil

TiTaN_pi8 wrote:
km/h (some also say 12000 km/h).
it's orbit at a height of 20240 km, I find 13938 km/h as the result.
something wrong?