[amsat-bb] Re: Contribution
clivew at zetnet.co.uk
Fri Oct 10 05:10:34 PDT 2008
Rob Redmon wrote -
> I realize that accurate positioning is detrimental. I've been retrieving
>TLEs for two weeks now and in that window, VO-52 has had 2 updates with
>a 10 day cadence. Is ~10 days the usual tracking priority for such
>satellites? Are there already "good enough" techniques for filling the
>orbital element gaps? Are there more sophisticated public domain orbit
>propagation algorithms just waiting to be tried out? The dawn of a new
>solar cycle (24) is upon us. How does will already employed prediction
>techniques stand up to the next solar max?
The tracking algorithms for satellites have been developed over the
years and AFAIK they are adequate, certainly for amateur use. The
orbital elements contain a drag factor (orbital decay) which compensates
the tracking for the gradual orbital decay.
IMHO updating elements every 10 days is adequate for most satellites.
If you use manual tracking the time interval between updates can be
increased. I tracked OSCAR-11 (UO-11) manually for many years, and
usually, only needed to change the Keplers about four times a year, when
the predicted time error exceeded more than a minute or so.
Satellites in very low orbits have a greater rate of decay, and it helps
to update the Keps frequently, especially those nearing the end of their
orbital life. The manned space stations have a high rate of orbital
decay. Their orbital height is corrected by firing their thrusters, so
frequent updating of Keps is needed.
Regarding solar max, this will increase the decay rate, but in most
cases this will be corrected by the increased drag factor in the Keps.
> As part of my graduate curriculum, I am enrolled in an astrodynmics
> course. The course >requires a course project.
Three possible projects -
Firstly, when satellites decay and burn-up in the earth's atmosphere,
there is always an interest in predicting when this will happen, say a
month before. In the past we have had several so called 'Chicken Little'
competitions for the best prediction. I did a lot of work on this 20
years ago, but never finished the project. It was based on a
statistical analysis of how the drag factor varied with height, the
exosphere and solar flux. As a project you could reasearch any work on
this topic, or try to produce a procedure for predicting satellite
Secondly, you could investigate tracking errors caused by changes of
solar flux. The effect of these errors, and how often Keps should be
Lastly, there are at least two, possibly more different algorithms for
tracking calculations. You could explore the differences, between them
for amateur satellite aplications.
If you are interested, I may be able to help. Please e-mail me direct
g3cwv at amsat.org ( replace the ' at ' by @).
Hitchin, North Hertfordshire, UK.
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