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Eutelsat Hotbird

Peter Benney <tugboat@...>
 

Ian/Douglas,

Here are some interesting views and movies of the Hotbirds in orbit from John Locker.

http://www.satcom.freeserve.co.uk/geos.htm

He reports one of them them shows a tendency to drift more than he would expect and has
sent copies of his findings to Eutelsat , and is at this moment he is waiting to hear from their control centre.

He tells me, "The bird moving rather more than the rest has been labelled HB3 , however ,
there is little to support this at present...it could well be HB6....this is
what I need to iron out with Eutelsat".

Regards,

Peter

Ian S Deans <ian@...>
 

Peter,

Thanks for your mail and interesting link. I saw a program on TV less than a
year ago about SES ( Astra ) and it also showed how they had to adjust the
drift of the various satellites from time to time at their 19.2 degree
slot -- extremely interesting. However I am getting off topic -- I can
sense a mail from David !!

Thanks again

Regards

Ian

Alan Sewards <alan.sewards@...>
 

Peter,
The reference you quoted is a little naive on motion of geostationary
satellites in orbit. It is also misleading to say that the rate of drift
tends to increase as the satellite gets older. When a geostationary
satellite is placed in orbit there is normally a small residual error in the
velocity vector from that intended for a perfect geo orbit. This manifests
itself by a figure-of-eight motion of the satellite about its orbital point
above the equator, every 24 hours. The amount of the motion can be
controlled by firing the satellite's thrusters, but as this uses up fuel
propellant it is done as sparingly as possible. Normally stationkeeping (as
it is called) is done periodically say every month or a number of weeks.
When the satellite has used up all its expendable fuel, it can no longer do
stationkeeping and the amplitude of the figure-of-eight begins to increase,
and will eventually take the satellite out of the beam of the ground
antennas for part of the day. Normally, well before that situation arises,
the bird has been taken out of service and replaced by another, and the last
bit of fuel propellant is used to push it out of geostationary orbit. If you
have a program such as WinTrak or the various alternatives, you can put in
the Celestrak 2-line orbital data sets for the various geostationary
satellites and it will show the amount of movement - the figure-of-eight
pattern is clearly visible.
I don't think satellite stationkeeping has anything to do with our
Eumetcast problems!

Best regards - Alan

----- Original Message -----
From: "Peter Benney" <tugboat@...>
To: <MSG-1@...>
Sent: Monday, October 27, 2003 5:00 PM
Subject: Re: [MSG-1] Eutelsat Hotbird


Ian/Douglas,

Here are some interesting views and movies of the Hotbirds in orbit from
John Locker.

http://www.satcom.freeserve.co.uk/geos.htm

He reports one of them them shows a tendency to drift more than he would
expect and has
sent copies of his findings to Eutelsat , and is at this moment he is
waiting to hear from their control centre.

He tells me, "The bird moving rather more than the rest has been labelled
HB3 , however ,
there is little to support this at present...it could well be HB6....this
is
what I need to iron out with Eutelsat".

Regards,

Peter



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