[amsat-bb] Asymetric doppler curves?

g0mrf at aol.com g0mrf at aol.com
Sat Jun 9 16:20:23 PDT 2012

Hi all.

I'm doing a small demonstration for a physics class using Doppler 
measurements on the HO-68 beacon.

Hopefully we'll be able to calculate spacecraft velocity and from that 
result,  go on to calculate orbit altitude.  However, in thinking about 
this I realised that there is a potential source of error.   We are not 
stationary !!   - OK, it's obvious really, but I've never seen this 
mentioned in topics like Doppler correction programs and I've not seen 
it visually in displayed Doppler curves.

The issue is that while a spacecraft with zero eccentricity will have a 
constant velocity, the speed relative to an observer on Earth at AOS 
and LOS will be different for each half of the pass depending on the 
observers latitude and the inclination of the satellite.

The worse case would be something travelling East to West or West to 
East as the velocity of the satellite would have the Earths rotational 
speed added / subtracted at either end of the pass.

Has anyone seen this effect? Perhaps on the ISS?    I think it could be 
as much as 7% which may be measurable. - But not on HO-68 which is 
polar orbiting....

Just want to make the most of my 45 minutes.


David  G0MRF

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