wrote in message
...
On Sat, 10 Nov 2007 03:00:58 GMT, Brian Thorn
wrote:

Lunar orbits are unstable over long-ish durations. They crashed, some
deliberately... to provide seismic data.

Thanks to the wikipedia links 2 others provided, it appears Apollo 11
and 16 LM were left in lunar orbit and eventually crashed into the
moon. My questions:
1. forgetting mascons for the moment, wouldn't the effects of the
earth and sun on a lunar orbit tend, over time, to pull the LM into a
higher orbit around the moon?
2. considering mascons as well as outside gravity effects, wouldn't
the effect of these be only to alter the orbit, but not cause a crash
onto the moon? My limited background suggest to me that the LM would
have to lose a lot of energy in order to lower it's orbit enough to
crash. What would be the process that causes this?

The orbit becomes eccentric enough until it crashes into the Moon.

Note the orbits were fairly low to begin with.

On one of the later Apollo missions, the CSM drifter low enough overnight as
to cause alarm at Mission Control when they realized they missed a mountain
by a lot lower margin than they wanted. (It was still 5 miles or more I
believe but still a bit alarming.)


Thanks to all for the help. Stan