Marrying asteroid defense and asteroid mining

From: spacesettlers@yahoogroups.com
[mailto:spacesettlers@yahoogroups.com] On Behalf Of Robert

> i was initially assuming that the mirror would be attached to
> the asteroid. the advantage of this are:
>
> 1) its closer, therefore the beam is more focused.

I don't see that making a difference. A detached mirror could be
brought very close (just short of touching, I suppose), or an attached
mirror could be mounted quite a ways away if the struts are very long.

At what distance the beam was brought to a focus would depend on the
curvature of the mirror. A smaller curvature would result in the focus
being further from the mirror. (That might be advantageous, due to a
point coming up later.)

> 2) the spot is in the same place all the time.

It's in the same place all the time on the asteroid surface, but the
point I was trying to make was that with a solar concentrating mirror
one might have the hotspot be consistently on /the same side of the
asteroid/ (relative to the rest of the universe), even while the
asteroid rotates under the beam and that hotspot describes a complete
circle around on the surface. For moving an asteroid, what's needed is
continuous thrust along the same vector. If we've halted the rotation
of the asteroid, that vector is consistent with regard to the surface.
But if we seek to avoid the complication of de-spinning the asteroid,
the vector needed is constantly turning relative to the surface of the
body. (For example, MADMEN addresses this by landing a large number of
small thrusters which are fired sequentially.)

> 3) all the energy is used, instead of some of it being put into
> part of the asteroid that moves out of the beam before it
> melts/vaporized.

That might be a significant concern. Still, I'd say given sufficient
area of the concentrator, the material under the focused light ought to
explode to vapor in a second or less, I would think.

> 4) no need to worry about the odd shape of the asteroid affecting
>the point of the focus.

Now that would be a major concern.

> 5) with the mirror mounted on the asteroid, a glass could rotate
> in front of the mirror, then away to be cleaned of the splatter.

As with your first point, I don't see a difference here. Such a disk of
glass could rotate in front of an unattached mirror as easily as an
attached one. The only difference is the requirement for RCS on both
the mirror and the disk of glass.

And I'm not so sure it would be all that easy to clean the glass.
Depending on the temperature we're assuming, what we'd be doing is
essentially vacuum vapor deposition, like what puts the silvering on the
back of a mirror. It wouldn't be like mud splattering on a surface.

> what about the fact that the asteroid would not be spherical,
> nor is its course going to be a stead one, due to the action
> of the asteroid reacting to the action of the spraying material.
> it would be extremely difficult to keep the mirror focused on the
> surface.

I would rate the non-sphericality of the asteroid as a bigger challenge
to maintaining focus than the course change, which would be a change
occurring only very gradually over long periods of time, relative to the
rotation period of the asteroid. But yes, there are challenges to be
overcome here.

> there are easy ways to take care of that, space would quickly cool
> the spatter so that by the time it hits a transparent shield, it
> would be fairly cooled and not to more than coat the sheild. it could
> be quickly scape away.

Maybe. If we depend on cooling of the vaporized material, that would
suggest keeping the mirror as distant from the hotspot as possible. To
me, that makes it more likely to be free-flying than attached.

> my persoally favority method is the multi stage ion engine, but so
> far no one listens to me about that.

I think my reason for favoring mass driver over ion engine is that the
mass driver can use literally anything for fuel (reaction mass, really),
while ion engines require specialized fuel. It would be advantageous to
not have to launch the system to the asteroid with the reaction mass
needed.

Regards,

Mike Combs