From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: japanese moon landing?
Organization: U of Toronto Zoology
Lines: 21

In article <1qnb9tINN7ff@rave.larc.nasa.gov> C.O.EGALON@LARC.NASA.GOV (CLAUDIO OLIVEIRA EGALON) writes:
>> there is no such thing as a stable lunar orbit
>
>Is it right??? That is new stuff for me. So it means that  you just can 
>not put a sattellite around around the Moon for too long because its 
>orbit will be unstable??? If so, what is the reason??? Is that because 
>the combined gravitacional atraction of the Sun,Moon and Earth 
>that does not provide a stable  orbit around the Moon???

Any lunar satellite needs fuel to do regular orbit corrections, and when
its fuel runs out it will crash within months.  The orbits of the Apollo
motherships changed noticeably during lunar missions lasting only a few
days.  It is *possible* that there are stable orbits here and there --
the Moon's gravitational field is poorly mapped -- but we know of none.

Perturbations from Sun and Earth are relatively minor issues at low
altitudes.  The big problem is that the Moon's own gravitational field
is quite lumpy due to the irregular distribution of mass within the Moon.
-- 
All work is one man's work.             | Henry Spencer @ U of Toronto Zoology
                    - Kipling           |  henry@zoo.toronto.edu  utzoo!henry
