spr postings not getting through.

[J. J. Lodder]

J. J. Lodder <nos...@de-ster.demon.nl> wrote:

> Chalky <chalk...@bleachboys.co.uk> wrote:
>
> > It is well known that projectiles (eg spacecraft) can have their
> > trajectories substantially altered via gravitational slingshot effects.
> > It thus strikes me as possible, via sufficiently accurate planning and
> > timing (or blind chance), to arrange for such a projectile to have its
> > direction reversed via multiple such slingshot effects. It is, of
> > course, even better known, that planets and comets achieve 2 such
> > direction reversals per orbit, as a matter of course. However, in this
> > latter case, such projectiles are gravitationally bound to the body
> > around which they orbit, by definition. Consequently, my question is as
> > follows:
> >
> > Would it be possible, in principle, to fire a projectile from
> > interstellar space, such that it is returned from whence it came, via
> > multiple gravitational slingshot effects?
>
> In general, no.
> Coming in from an arbitrary direction you will not meet any planets,
>
> Jan
>
> [Moderator's note: I think the response is based on a misunderstanding.

Sorry, my posting was in the first place a test.
(hence the one-liner)
Server problems have made posting to spr imposible for me,
so I wanted to know if these problems have cured themselves.
(yes, apparently)

> Note above "sufficiently accurate planning and timing (or blind
> chance)"; in other words, the original poster was imagining this to be
> an exception, not the rule.

That's not how I read it.

> The question is whether it is possible at
> all, not whether it is possible coming in from an arbitrary direction.
> -P.H.]

It is obviously possible in very special cases. (at modest velocities)
Start in the Jovian plane, swing past the sun in a narrow hyperbola,
and time it so that Jupiter is in the right place
to bend the orbit by the right amount to let it go back
in the original direction.

Jan