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Fwd: AO-40 Orbital Stability

>Following the ARCJET cold out-gassing to raise perigee in June 2001, the 
>orbit was modeled and, like AO-10,  it is stable for hundreds  and 
>hundreds of years.  I got tired of letting the orbital integrator 
>run!!   I had an amsat-bb post regarding this, but can't find it at the 
>moment.  The software used is the same software that correctly predicted 
>AO-13's re-entry to the DAY, using keps immediately after its second 
>orbital burn, just after launch.

Is this the post you were thinking of Stacey?  At least it's relevant...



>X-Sender: w4sm@cstone.net
>X-Mailer: QUALCOMM Windows Eudora Version 4.3.2
>Date: Sun, 24 Dec 2000 19:17:40 -0500
>To: amsat-bb@AMSAT.Org (Amsat Bulletin Board)
>From: "Stacey E. Mills, M.D." <w4sm@cstone.net>
>Subject: [amsat-bb] AO-40 Orbital Stability
>Sender: owner-AMSAT-BB@AMSAT.Org
>X-RCPT-TO: <hammond@surrealnet.net>
>At 04:30 PM 2000-12-24 -0600, you wrote:
>>One other question to be considered: Is the current orbit stable?  I know
>>next to nothing about orbital mechanics.  But AO-13 died a firey death
>>because of an orbital instability.  We wouldn't want the same thing to
>>happen to P3D.  But then again, it might be fine.
>I'll take a shot at this one.  The orbit is incredibly stable.  It's not 
>the eccentricity per se that creates instability.  It's the combination of 
>eccentricity and high inclination, along with RAAN and ArgP that has the 
>potential for instability due to solar/lunar forces.  The current low 
>inclination orbit is highly stable.  I've integrated the orbital elements, 
>accounting for drag, and the pull of the sun and moon for decades and the 
>orbit is quite stable.  Perigee height varies by several hundred km and 
>there is some very minor drag loss when the perigee is at its lowest 
>point, but there is also gravitational "pumping" of energy into the 
>orbit.  In fact, after 40 years, mean motion is 1.266, lower (ie. a higher 
>energy orbit) than it is today.  For a graph of the orbital elements over 
>the next approx. 10 years, 20 years and 40 years download:
>NOTE:  these graphs, particularly the 40 year graph are very "busy" and 
>difficult to read.  However, note that mean motion (in green) barely 
>changes and height at perigee (in black) shows a cyclic variation from a 
>low of about 270 km to a high of about 700 km.  If you look carefully, you 
>will also see the cyclic effects of the sun and the moon on the orbital 
>  _______________________________________________________________________
>  Stacey E. Mills, W4SM    WWW:    http://www.cstone.net/~w4sm/ham1.html
>   Charlottesville, VA     PGP key: http://www.cstone.net/~w4sm/key
>  _______________________________________________________________________

Mark L. Hammond  [N8MH]

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