I think a lot of the delta-vee necessary to bring asteroid material to
near-earth space is to get rid of the relative velocity between it and
earth. In other words, just getting an intersecting trajectory is (I
think) a lot cheaper. So it would be good if you could do some
equivalent of aerobraking.

I propose such an equivalent: launch stuff from a coil gun on the moon,
and have it hit the approaching asteroid. You could have the
projectiles be ultra-cheap spacecraft with limited maneuverability,
powered by metal-air batteries and having one in twenty be expected to
fail.

This is interesting. I wonder, would the projectiles have to be
"spacecraft" at all? Would balls of dust, whacking the approaching
payload with impacts too small to shatter it, but many thousands of
them, work just as well?

I imagine some ball of dust that expands as it approaches the target.
The asteroid chunk isn't hit with a 10 Km/sec baseball (and then
another, and then another...), but with several hundred thousand 10
Km/sec dust specks over a millisecond or so (and then, a second or two
later, several hundred thousand more, then several...).

For a ten thousand ton chunk of asteroid, this could add a hundred
tons or so of Lunar material to the payload, but that's not a bad
thing. Moon fans and asteroid fans unite!

From: sailor.barsoom

> This is interesting. I wonder, would the projectiles have to be
> "spacecraft" at all? Would balls of dust, whacking the approaching
> payload with impacts too small to shatter it, but many thousands of
> them, work just as well?

That would certainly be a lot cheaper. Would take some careful aiming,
though.

Regards,

Mike Combs

On Apr 28, 2008, at 12:37 PM, sailor.barsoom wrote:
> This is interesting. I wonder, would the projectiles have to be
> "spacecraft" at all? Would balls of dust, whacking the approaching
> payload with impacts too small to shatter it, but many thousands of
> them, work just as well?
>

It should -- momentum transfer is momentum transfer.

Best,
- Joe

2008/4/28 sailor.barsoom :
> I imagine some ball of dust that expands as it approaches the target.
> The asteroid chunk isn't hit with a 10 Km/sec baseball (and then
> another, and then another...), but with several hundred thousand 10
> Km/sec dust specks over a millisecond or so (and then, a second or two
> later, several hundred thousand more, then several...).

Basically it's a form aerobraking I suppose- you vapourise the dust
against the asteroid and use the vapour to slow it down. You would
have to be careful that the asteroid can't fragment and potentially
impact the Earth and also that the dust was used well above the Earths
magnetosphere so that the Suns solar wind should carry any fragments
away from cis-lunar space (you don't want to generate lots of space
debris).

--
-Ian Woollard

We live in an imperfectly imperfect world. If we lived in a perfectly
imperfect world things would be a lot better.