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AO-40 Orbital Stability

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

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