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R: R: Re: AO40 orbit drifting south, then north?




----- Original Message -----
From: Stacey E. Mills <w4sm@cstone.net>
To: Amsat Bulletin Board <amsat-bb@AMSAT.Org>
Cc: i8cvs <domenico.i8cvs@tin.it>
Sent: Wednesday, March 27, 2002 6:08 AM
Subject: Re: R: [amsat-bb] Re: AO40 orbit drifting south, then north?


> At 05:27 AM 2002-03-27 +0100,  I8CVS wrote:
>
>
> >Hi  Stacey,
> >
> >The greater the inclination, the more the variability is not completely
> >correct.
> >If the inclination ( i ) is 63.34 degrees the line of the apsis  that
> >join the apogee with perigee do not rotate at all and so the rate of
> >change of the argument of perigee ( W ) is zero degrees and the satellite
> >subpoint SSP at apogee stay constant for ever.
>
> [snip]
>
>
> >If the inclination is less than 63.34 degrees the line of the apsis
rotate
> >in the same direction of the satellite motion along the orbit
>
> [snip]
>
> >If the inclination is greater than 63.34 degrees the line of the apsis
> >rotate in a direction wich is opposite to the satellite motion
>
> [snip]
>
> What you say is absolutely correct, well, except for the "forever".
That's
> a very long time.  The fixation of ArgP precession at inclination = 63.34
> degs is the definition of a Molniya orbit and what we were aiming for with
> AO-40.  However, I think you missed my point.  The discussion was about
> variation in subsatellite latitude.  I did not say that the higher the
> inclination the more (rate of) variation in ArgP.  This is, of course, not
> true.  As you have indicated, the rate of change in ArgP decreases as
> inclination increases towards 63.34 degs.  Above that, change in ArgP
> begins increasing in the opposite direction.   My point was that the
higher
> the inclination the more variability in SUBSATELLITE LATITUDE as ArgP
> changes.  Hence my reference to AO-13's much larger apogee shifts above
and
> below the equator.  The rate of change of ArgP was much lower for AO-13
> because of the higher inclination, but that wasn't my point.  I was only
> discussing the amount of variation in subsatellite latitude.
>
> I hope this clarifies things.
>
>
Hi  Stacey,

I aegree with you and infact the amount of variation in subsatellite
latitude is a funtion  of both orbit inclination ( i ) and  ArgP ( w )

The equation to compute the SSP latitude at perigee is the following:

Lat. perigee = arc sin ( sin i  x  sin  w )

Where:
i= orbit inclination
w= argument of perigee

To get the SSP latitude at the apogee change only the signe.

The higher is the inclination ( i ) and greater is the latitude of apogee
subpoint change for a given ArgP ( w ) variation.

The associated value of the ArgP (w ) is also very important and infact
for a given AO40 inclination i= 7.29 degrees,the apogee SSP latitude
changes by  1.015 degrees for an ArgP change of 10 degrees for example
from w=32  to w=42 degrees in about 31 days but it will change only by
0.111 degrees for the same  10 degrees change of ArgP from w=80 to w=90
about  148 days from now.

73" de i8CVS Domenico

> --
>   _______________________________________________________________________
>   Stacey E. Mills, W4SM    WWW:    http://www.cstone.net/~w4sm/ham1.html
>    Charlottesville, VA     PGP key: http://www.cstone.net/~w4sm/key
>   _______________________________________________________________________
>
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