Marrying asteroid defense and asteroid mining

sorry for double posting. not fully awake

--- In spacesettlers@yahoogroups.com, "ANTIcarrot"
wrote:
>
> > From: Robert
>
> As a point of note here: If we're going to send a big heavy 'bruce
willis'
> style space ship to 'save the world' I say do the job properly and
use a few
> hundred well placed nukes. In fact use nukes anyway. They're much
more fun
> than mirrors.
>
the rest of this part was that the regolith would be vaporized and
would act as a very large explosion to push the asteroid from the
path. the questions is would one be enough.
>
> > 1) [the mirror's orbital path] would be extremely complex.
> > 2) all but the smaller asteroids would have a gravity of their own
>
> Very true. However a big enough mirror to do the job woudl be a
functional
> solar sail; and would have to constantly manouver against it's own
thrust
> anyway. An asteroid small enough that we have even a hope of moving
(in a
> dooms day scenario) will probably not impose significantly worse
problems on
> the solar mirror/sail's 'skipper' than everything else. I think.
>

the problem with a single large mirror is trying to keep it's focal
point on the hot-spot. a thousand small mirrors (1 meter by 1 meter),
each constantly and independently aimed would have a lot better
chance of vaporizing the surface that a single 1000 square meter due
to inertia and complexity. there was a test in Arizona many years
ago, where they melted a one inch thick steel plate using mirrors.
they had a large number of one meter squared mirrors focusing on the
steel plate.

the problem with a lot of small mirrors is that they would have to
have a steady frame of reference to be able to constantly be
refocusing.

>
> Not what I wrote.
>

nuff said

>
> I can see no point in the frame, other than as a psychological
crutch of
> some kind. Or possibly a cash-cow for whoever had to build it. The
kind of
> mini-mirror I described was deliberately independent of all the
others
> specifically so that no single failure of a component would bring
down the
> entire system. And because we could design and build such systems
today. In
> fact several proposed space telescopes use such frame-less
techniques. If it
> works for spotting planets I see no reason for a frame in this case.
>

I'm not formula with any space telescopes that have no frame what so
ever, so i cant really comment on that. on the other hand, they don't
likely have to make several adjustments per second and be accurate
to within a cm a large part of a mile away, if not farther. the
constant adjustments without a frame would require that they be using
large amount of fuel. if the mirrors are in close proximity to each
other, that spent fuel is going to be interfering with the others,
and with their receiving sunlight.

>
> That's a problem for any mirror based approach.
>

that depends on how small the hot-spot is and how hot is is. the
ideal would be that it would be hot enough to vaporize the rock
before any could dissipate, but that's not realistic. the best
approach would be for it to vaporize the rock before very much could
dissipate, which would require that the first heating of the material
to be very close to the point of vaporization.

>
> I remain rather skeptical that any kind of mirror could produce
very large
> or useful ISPs. Without a rocket bell to shape it, the expanding
gasses
> would mostly go sideways rather than 'upwards'.
>

that is part of the point of stopping the rotation. the initial
vaporizing would occur the same, but as the material vaporized it
would dig the hole deeper, forming a bell shaped 'rocket' engine. one
problem with this is that the gas would take large part of a second
to clear out. that's why I'm thinking a pulse laser system with a
rotating mirror, that would have several point of impacts in a close
vicinity, each recieveing a few pulses per second

>
> Depends on how long they last VS how long you need them for. For a
few
> months thrusting (existing applications) it's pointless. For more
than that
> (like a trip to mars say) you'd need replacement gratings, as
they're the
> part that wears out first.
>

since we are talking about something that will only be used for a few
months, replacing them would not likely be needed. on the other
hand, if it is, and you have to wait to send it from earth, that
might be a little bit too long of a wait.

>
> Yep. You'll also find water up there. I wouldn't recomend drinking
it or
> using it to fill up the radiator on your space-car though.
>

why not, all it would take is a little bit of refining. someone was
estimating that one of the comets has more water on it that earth.

>
> As others have pointed out, mass drivers eat anything. Ion engines
are a lot
> more fussy.
>
i think they are a little bit more fussy that you realise. how are
you going to accelerate the material. most of the designs i have seen
used a steel pad or aluminum ion gas behind the payload. that means
that the mass driver would need special material too.