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*Subject*: R: R: [amsat-bb] Re: AO40 orbit drifting south, then north?*From*: "i8cvs" <domenico.i8cvs@xxxxxx>*Date*: Wed, 27 Mar 2002 15:47:17 +0100

----- 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 > _______________________________________________________________________ > > ---- > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org > ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**References**:**Re: AO40 orbit drifting south, then north?***From:*Stacey E. Mills

**Re: R: Re: AO40 orbit drifting south, then north?***From:*Stacey E. Mills

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