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.
Thanks
David G0MRF
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