[ExI] pentagon wants orbiting solar power stations

Jeff Davis jrd1415 at gmail.com
Wed Oct 17 01:57:50 UTC 2007

I've found this thread quite fascinating as, it seems, have many.  So
I would like pose two questions related to asteroid mining.

Ion drives provide impressive gains in performance over chemical
propulsion, and seem particularly suited to operation in vacuum and
out of an atmosphere-blanketed gravity well.

I asked sometime back about using other substances than Xenon for the
reaction mass, with an eye to using native asteroid material. Sadly
the responses were disappointingly uncreative, emphasizing for example
the way bulk iron doesn't present itself as individual atoms but comes
all clumped together.  Well, duh!  Whether you grind it up, oxidize
it, or vaporized it, it all boils down to the same thing, you're going
to have to work the bulk material into a form suitable for use as
reaction mass.  That may take equipment and energy, but I doubt it
will turn out to be technically daunting.  If you're on earth with
availability and cost what they are hereabouts, then Xenon is
terrific.  It's good to go in its native form.  But out in the 'roid

Anything with mass that can be ionized and propelled out the back can
be used as reaction mass. Xenon is probably not all that abundant out
in the vicinity of the asteroid belt, so what do you do?. You find
something else.  Put your thinking caps on folks and help me out here.
 There's lots of mass out there so some way needs to be found to make
it into "fuel".  Iron's plentiful, why not use it?  Or something else,
then.  C'mon.

Which brings me to my real question.  Your ion tug has hooked onto a
particularly juicy asteroid fragment, and has set it on course toward
earth.  Since you're moving "down" the solar gravity well, the ion tug
will have to slow you down gradually as you spiral in, or, if your
taking a more direct route, you're going to have to find another way
to decelerate when you reach your destination.  How could you do this?
 If you had a processing plant on the moon, you could just slam right
on in.  Could you keep the relative velocity low enough to keep your
goods from vaporizing  or keep from causing excess environmental
damage to the moon?  Or perhaps you aim for the earth, grazing the
atmosphere but of course avoiding actually grazing the surface.  I
suspect that some of the folks on earth my look askance at such a
method, but hey, we're just talkin' her, right?

Anyway, your thoughts on the matter?

Oh, one other little question.  Does being on moderation mean I'm
banned from posting, or just subject to oversight, or ,...what?

I guess I'll find out.

Best, Jeff Davis

   "Everything's hard till you know how to do it."
                           Ray Charles

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