Mike Comb's "catching" mass driver

I wonder if a pipeline would be more efficient in moving the water-
ice/slush over the long distance to the equator, rather than small
energy intensive mass driver shots. Lay it underground where the
thermal mass would moderate the temperature, have temperature
control stations and pumps along the route and you could move huge
volumes of water. What do you think?

--- In spacesettlers@y..., "Combs, Mike" wrote:
> From: victoriatangoman [mailto:tango_dancer@h...]
>
> Mike, I enjoyed your story and had a few questions about the
details
> of the catching process at Chaffee Base.
>
> Thanks.
>
> How do your forsee the process? Is it a violent touchdown? How
much
> room for positional error is allowed? Does it come down onto a
> track, through a guiding funnel, etc.
>
> The total deceleration process might well take place in less than
a second.
> I'm pretty sure the acceleration process does.
>
> I had visualized the entry end of the decelerating mass-driver as
having a
> funnel shaped mouth somewhat in the shape of a bugle flare. One
that might
> start out at 2 or 3 meters diameter, and then narrows down to more
like the
> dimensions O'Neill discussed for his lunar mass-driver (he
compared the
> diameter to a dinner plate, I believe).
>
> The earlier mass-driver models had a pull-push design. But later
models
> were pull-only. One advantage of this approach is that the pull
regime
> exerts a very strong centering force on payloads. In a
deceleration phase,
> for example, each coil is fired only as the bucket comes abreast,
and then
> pulls on the bucket coils as they continue on. So even if there
were minor
> aiming errors, these forces would work very strongly to bring the
bucket
> back to the very center of the mass-driver. I suppose there might
be some
> oscillation effects that would have to be damped out
electromagnetically.
> I'm fairly sure something could be worked out for that.
>
> Without any details I got to thinking, would it be possible to
have
> a funnel, a very large funnel because I'm assuming that there
would
> be posiional error if you're targeting from a quarter of the
> circumference of the moon away, and have huge magnetic forces
> slowing and guiding the package onto a track. Is this what you
> intended?
>
> Yes. And there are things we could do to keep the aiming errors
very low
> indeed. In the mass driver design, there was always a plan for
downrange
> correction of aiming errors. After exiting the mass-driver, and
before the
> payload has risen a significant distance above the lunar
landscape, it was
> proposed to have an electron gun which would spray the payloads
with a
> negative charge. Once charged, each payload would then pass
through a
> series of electrostatic deflection plates, which, in concert with
position
> and velocity sensing, would make whatever final minor tweaks to the
> trajectories needed. The process is similar to how the deflection
plates in
> a CRT change the path of an electron beam to paint an image on the
front of
> the tube.
>
> Here's an illustration of the deflection plate arrays:
>
> http://www.ssi.org/assets/images/astronaut_at_lunar_mass_driver.jpg
>

>
> I had envisioned such arrays at regular intervals (perhaps only
one every
> several dozen miles) making minute adjustments to trajectory just
to keep
> everything on track.
>
> Alternatively, if catching is taking place during lunar night,
would
> it be possible to have a "lake" of liquid (?) and the package
> splashes down in it, and now you've got less worry about
positional
> error, and you could extract the heat of friction from splashdown,
> from the "fluid". Is the gravity of the moon sufficient to hold a
> lake of some liquid, and can liquid oxygen, let's say, maintain
its
> state in a vacuum.
>
> If not a liquid, do you think the concept would work with another
> material.
>
> I doubt seriously if such a scheme would be practical. At these
kind of
> speeds, we'd probably better stick with electromagnetics. You
talked about
> energy recovery. Bear in mind that with this kind of EM system, a
> percentage of the energy could be recovered as useful electrical
current,
> rather than as diffuse heat.
>
> I'd love to pose the question to an artillery officer. How
accurate
> can you be when firing long distances. I don't know. Can you
foresee
> a package coming in right on target for a "catching" mass driver?
>
> Love to hear more of your thoughts.
>
> I think it could be done, if lunar mass-drivers can be made to
work at all.
> I suppose if there was some great difficulty with aim, one might
instead
> talk about a maglev running from a pole to an equatorial station.
As a
> minimum, it would at least need a curved, conductive trough
(aluminum would
> do) running the entire distance if working off of dynamic magnetic
> levitation via eddy currents. The velocity could be a substantial
fraction
> of lunar orbital velocity, which means the track would only have to
> magnetically support a fraction of the payload's weight. But I
decided on
> the method described in my story because it replaced a continuous
track with
> very widely spaced deflection plate arrays, and that struck me as
a much