From: jfindley@cinci.nospam.rr.com   
      
   In article <3zeSH.68193$xa.35702@fx47.iad>,   
   jfmezei.spamnot@vaxination.ca says...   
   >   
   > A few days ago, I was reading about the LEM, and found out that they   
   > were "disposed" of in different ways.   
   >   
   > Some were left in orbit around the moon but eventyally crashed in   
   > unknown locations.   
   >   
   > I beleive one was sent to some heliocentric orbit and would still be there.   
   >   
   > And the last ones were deliberately crashed onto the moon.   
   >   
   > So some questions:   
   >   
   > What are the parameters that would cause an orbiting LEM to end up   
   > crashing on the moon? Is there a thin atmosphere around the moon that   
   > would slow down an orbiting ship over time?  Orbital precedence that   
   > would eventually result in some elliptical orbit that becomes more and   
   > more elliptical till perigy hits the ground?   
      
   The same thing that makes almost all lunar orbits unstable.  The moon's   
   gravity field isn't uniform.  It's got mascons (mass concentrations).   
      
   https://en.wikipedia.org/wiki/Lunar_orbit#Perturbation_effects   
      
   Jeff   
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