Xref: utzoo sci.astro:3327 sci.space:9203
Newsgroups: sci.astro,sci.space
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Finding Lagrange's Libration Points
Message-ID: <1989Jan20.180839.7800@utzoo.uucp>
Organization: U of Toronto Zoology
References: <1989Jan18.044744.18328@sq.uucp> <11854@dartvax.Dartmouth.EDU>
Date: Fri, 20 Jan 89 18:08:39 GMT

In article <11854@dartvax.Dartmouth.EDU> dalex@eleazar.dartmouth.edu (Dave Alexander) writes:
>So if L1, L2, and L3 are loci of unstable equilibrium, how can we expect
>an object to librate or oscillate about any of them?

You can't, and it won't, without help.  An object *precisely* at one of
those points, with *no* perturbations, would stay there, but in the real
world, that doesn't work.

There are trajectories near those points -- so-called "halo orbits" --
which are *almost* stable, requiring only very slight corrections to
maintain.  ISEE-3 was in a halo orbit around the Earth-Sun L1 point for
some years, to study the solar wind "upwind" of Earth.
-- 
Allegedly heard aboard Mir: "A |     Henry Spencer at U of Toronto Zoology
toast to comrade Van Allen!!"  | uunet!attcan!utzoo!henry henry@zoo.toronto.edu