[amsat-bb] mars express orbit

[Joe Steinmetz <joe_steinmetz@xxxxxxxxxxxxxxx>]

Hello All,

I am looking to better define the expected doppler for the mars express 
spacecraft. From the excellent article provided by James Miller at 
http://www.amsat-dl.org/p5a/reception_g3ruh.htm I have deduced the 
following:

3 major components of doppler shift.
    -gross motion of Mars
    -diurnal shift due to motion of Earth
    -motion of spacecraft around Mars

For the Mars Odyssey, the article indicated a "fairly static -375 kHz at 
present" for the gross motion of Mars. This seems to apply to Mars 
Express now that it is in orbit. But I would be interested in knowing 
when this changes and how to determine or calculate the value.

+-10 kHz for diurnal shift.

But what about motion of the spacecraft around Mars? Anyone know what 
type of orbit? Anyone know the orbital speed? Shall I just assume +-100 
kHz? Also looking to know what percentage of the time the spacecraft is 
blocked by Mars.

The reason I am trying to better characterize or "bound" the doppler is 
to narrow my search limits. With a 1.2m dish the signal level is fairly 
low (CNR of 16 dB/Hz) and it doesn't present itself as it did for 
Rosetta (i can hear Rosetta just fine) or as is does for those with 
larger dishes.

thanks,

Joe
k6sat






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