In my wandering in old publications, I got the sept/oct 1961 issue of
"Coelum" an astronomy magazine published in Italy by the Bologna
astronomical observatory.
I found an article in which was suggested to time the eclipse of the
satellite caused by the shadow of the Earth.
To take in account the movement of about 1 deg/day of the umbral cone of
the earth, for satellite with a period of about 2 hours and moving in
direct mode, the suggestion is to subtract 2 sec per evolution.
The timing over 1 year gives for Echo sat the period decreasing from
118.28 min (31 aug 1960) to 116.9 min (15 aug 1961).
What do you think about this kind of observation ?
So crude as the one made with the dipleidoscope ?
A big advantage is that you have not to build any instrument - need only
a binoculars.
From observing satellite vanishing in the earth shadow, I guess you can
time the swicth-off-time with an approximantion of some seconds, the
observation program on a single satellite must be run for, say, 1 year
at least.
I have found also a formula for the time of ascending node:
T = D + AN + BN^2 + CN^3
where D is the epoch date, A the period, N the number of revolutions, B
and C the drag terms.
With the data obtained in 1 year of observation I could try to find B
and C with a min-square fit of the data with a 3rd order parabola ...
Greetings
Paolo Morini
Michael Waterman wrote:
>As has been pointed out, determining the orbit period of a
>satellite from timing when it crosses the meridian (= the
>line South to North) is not accurate. Over 1 orbit the error
>is between 5 and 10%, over a day the error is about 1%.
>
>If however you time when a satellite crosses the East to
>West line the effect of the rotation of the earth is eliminated.
>The error over 1 orbit is about 1%, and 0.1% over a day.
>
>Obviously this can only be done if the inclination of the
>orbit is more (say at least 20 degrees) more than your latitude.
>
>Mike Waterman mike.waterman@marconi.com
>Site Yateley = COSPAR 2115 = 51.3286N 0.7950W 75m (reference OSGB36).
>
>
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