[amsat-bb] Re: Asymetric doppler curves?

Miguel EA1BCU ea1bcu at amsat.org
Sun Jun 10 02:28:19 PDT 2012

HI David,

Maybe you can find here an interesting answer to your question.


Miguel Menéndez
IN73an. Spain

 De: "g0mrf at aol.com" <g0mrf at aol.com>
Para: amsat-bb at amsat.org 
Enviado: Domingo 10 de junio de 2012 1:20
Asunto: [amsat-bb] Asymetric doppler curves?
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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