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*Subject*: Re: [amsat-bb] AO-40 Orbital Stability*From*: "Stacey E. Mills, M.D." <w4sm@xxxxxxxxxx>*Date*: Mon, 25 Dec 2000 12:27:12 -0500*In-Reply-To*: <000901c06e6f$c1c03bc0$0300000a@win1>

At 07:39 AM 2000-12-25 -0500, MCGWIER ROBERT wrote: >Stacey: > >Your pictures bear out WHY it is important to have >a burn of the 400 N motor. The instability (perigee >bouncing around) is a real problem when your >perigee is 360 km. Perigees in highly elliptical orbits ALWAYS bounce around. That, by itself is not a sign of orbital decay or "instability". If you look at the 10 year chart that I posted, it's less "busy" and you can see the scales on the left better. As mentioned in my earlier e-mail, the perigee's fluctuate from about 270 km to about 700 km. Remember, however, that in a highly elliptical orbit, the time at perigee is minimal. If you look at the total energy of the orbit, as reflected by mean motion, there is no net loss even after 40 years. In fact, there is a slight increase in energy (decreased mean motion). In other words, gravitational forces pump more energy into the orbit than the perigee drag removes. >The graphs are so busy that >I can't make out the units. What are the maxima >and minima of the perigee heights AND what >was the apogee of the spacecraft. It was not >clear that your graphs assumed the current >conditions. The graphs do not plot apogees, but they can be derived from the graph since eccentricity is plotted. The orbit does not significantly circularize. To do so requires a LARGE amount of perigee drag. These graphs ARE based on the latest NORAD elements. I realize that everyone is "perigee shy" after AO-13, but the height at perigee is not the only factor, it's the nature of the perigee fluctuation that is critical. For AO-13, it was a combination of high inclination, along with disadvantageous RAAN and ArgP that conspired to have the moon and sun pull the perigee into the earth. Drag was really not a factor until near the end of its life when the orbit began to slowly circularize and the drag heating eventually destroyed the S/C. In its current low inclination orbit AO-40 does not suffer from these problems and it will be around for far longer than any of us.....even if we don't change the current orbit. -- _______________________________________________________________________ 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

**Follow-Ups**:**Re: AO-40 Orbital Stability***From:*MCGWIER ROBERT

**References**:**Re: AO-40 Orbital Stability***From:*Jon Ogden

**Re: AO-40 Orbital Stability***From:*MCGWIER ROBERT

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