Dear Domenico, Dave, Miguel Trevor and Ivo.
Thank you all for your thoughts and references. James Miller's Plan 13
etc is an excellent resource as, I discovered is Ivo's thesis.
I have reached the conclusion that extracting more information from
Doppler measurements in the limited time available may be considered a
little tenuous. A reasonable approximation of satellite velocity and
altitude should be straightforward. However I think trying to measure
the Earths rotational speed suffers from one major source of error and
that is the stability / calibration of the satellite transmitter and
the groundstation receiver. To accurately measure the difference or
asymmetry in Doppler between AOS and LOS (e.g. AOS may be fc +10,000Hz
while LOS could be fc - 10,200) depends entirely on knowing the exact
center frequency of transmission. Without that, the valid data becomes
lost within the errors. However, hopefully some of the students will
find it an inspiring addition to their study of gravitational fields.
Regards and thanks
David
-----Original Message-----
From: i8cvs <domenico.i8...@tin.it>
To: Amsat - BBs <amsat-bb@amsat.org>; G0MRF <g0...@aol.com>
Sent: Sun, 10 Jun 2012 3:25
Subject: Re: [amsat-bb] Asymetric doppler curves?
Hi David, G0MRF
If you read the old issues of OSCAR-News from AMSAT-UK you
will realize that a serious traking program like PLAN-10 written
by James Miller G3RUH take into calculation all perturbations due
to inclination and velocity of the satellite due to Earths rotational
speed added / subtracted at either end of the pass and so doppler.
73" de
i8CVS Domenico
----- Original Message -----
From: <g0...@aol.com>
To: <amsat-bb@amsat.org>
Sent: Sunday, June 10, 2012 1:20 AM
Subject: [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.
Thanks
David G0MRF
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