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starship-design: LINAC efficiency

Well, I shoulda known. The optimal stationing of laser power stations on
Mercury has solar collection stations at the Not East Pole and the Not West
Pole too. Shucks, I was hoping to get out of working at those hellacious
places. Before you even get there, you have to have cooling tubes laid
halfway around the planet, exactly, to meet you there. Such a project
obviously involves construction in phases; you have first the (true) polar
stations, which can see dark sky in the nadir direction, so they're coolable
places. The second phase is building a quadrant tube around 1/4 of the
planet from each pole, on brightside, to each hotspot, total of four
planetary quadrant tubes, plus one between the hot spots for safety
redundancy. As you build tubes in, you must spread out heatpipes (from the
rotational poles) for veins in a leaflike growth of carbon plates, to glow
dark red in the dark black and cool your living environment when they're in
the dark, but with heat conduction shut down when they're sunlit. When your
tubes all meet, you establish two planetary isotherms, which are the heat
rejection channels for the energy system and life environment, with
avoidance of coupling. These planetary heat pipes are single fault tolerant,
for catastrophe at no one place can cause systems failure, and are the only
way to keep your cool on Mercury's hot side. That's the only way you can
build those fancy liquid lead boilers and stuff at the Not Hot Poles.

Sure we can ship heat to the Cool Poles, and we do, in the Industrial Heat
Tubes, but mainly we ship power, because in lossless helical mode waveguide
tubes, it's a lot more portable than heat. Most of that power feeds the big
starship pushers at the Cool Poles, large free-electron lasers. The planet's
mostly iron, but nobody bothers to say "One lump or two?" any more. The
mines are big borings at the poles, all the way through the crust to the
planet's core. They have big mountains of slag all around their pits, with
tracks tunneled through them for mass launchers to throw slugs of iron into
a point in Lunar orbit. Mercury iron is usually uncompetitive with asteroid
stainless, so it keeps piling up in those silver sparks, but Mercury has
surplus energy, and keeps high hopes for a project someday that'll need lots
of iron, and keeps building those big ring batteries for starships and
asteroid pushers.

The 1 g acceleration parameter isn't a "why" question, it's a "how"
question. "Any way you have to" is the "how" answer. The "why" is because
it's the only we can get there feeling comfortable with ourselves, which is
not only the way we'd rather feel, but pretty darn close to a requirement
for our health, and a starship with a sick crew is a bad sign rather than an
economic savings. We don't go there. The people in that can are the most
expensive people we got, and they have good credit with us. If we can, and
if it's a matter of cost, we will send them to that planetary system of a
remote star and bring them back in good health and relative comfort, just to
prove we're a civilized species who will flagrantly expend resources for the
few lucky enough to do our learning for us, so they will come back to us in
good health and report at the best possible speed, what wonders they have
seen. You must face the prospect that decades will lapse in many cases, to
eventuate to centuries, between times Earth sees members of a ship's crew,
even though spacers see seven years between journeys every time. These
people have really, really, really good credit.

Let me give a figure: one hundred atoms per cubic centimeter. There, now the
estimates for space gas density quoted in this newsgroup this week span
eight orders of magnitude! (Or so.) No, that's just the figure I have seen
for typical cloud density. (An opposing view, from instruments on the same
Ulysses, I found after my post on gas density: Gary P. Zank of the Bartol
Research Institute at the University of Delaware -- who doesn't think we're
in a cloud right now, thinks it might make us dead. "Currently, Zank says,
the solar system is in a region of space containing between 3 and 4
particles per cubic inch.")
http://www.sciencedaily.com/releases/1998/06/980602080449.htm but note that
Landgraf published December 17, 1999 in Science, after Zank, and thinks
we're in a cloud, and has seen the characteristic silicate dusts known to
accompany gas clouds of 100 atoms/cc. That's a ramscoop of a different
color. Local to us means everywhere we're likely to go soon, and the
evidence suggests to me this space is permeated by such a relatively high
density of gas. I'll not hesitate to declare the ramscoop revived, since
within a year or two the Voyagers will be crossing theough the 100 AU
heliopause, where the solar wind shocks against the interstellar wind, and
we ought to be able to find out for sure, how soupy it is in our

What I think would be a good magnet ring, would be a double annular
aluminized polymer torus. Inside the inside ring would be a weblike pattern
printed with thick-layer cuprate superconductor. A thin continuous stream of
liquid helium flows over part of this pattern, the vapor pressure from which
keeps the inner ring inflated. The outer ring enveloping it is held in place
just because it's there, and because tiny columns of silica aerogel at
intervals provide spacers separating it from its contained torus. The outer
torus isn't inflated with anything if we can help it, for it provides the
outer wall of the Dewar vessel to keep stray heat away from the inner tube
inside it, and pushes on it to make it go forward. So the magnet ring is as
light as we can get away with. After all, the things do wear out in a few
months as their helium goes away, if nothing else happens to them first,
like a vagrant dust speck that just wouldn't be repelled, and they have to
be replaced. So we grow them from the front of the ship, and graduate them
forward as they get larger, extruded from the little growbots around their
rim, which we feed with neutral beams from the ship. Growbots spin with
their rings, or they couldn't extrude right, and in fact we use them to help
spin their rings.

Just for sport, we shoot bullets out of the bow of our spaceship, and then
push on the bullets with lasers, until those poor bullets are all worn out
with erosion. Nobody really expects rocks to pop up out of empty space, but
just in case anything ever did materialize, we would want it to have the bad
luck to be met by an almost relativistic bullet, and not us. A flash in
front would be bad news, because it would be real bright, in rays that
aren't good for our health. It might crisp some leading rings, but that
would be a better grade of bad news than if it got closer to flash. We don't
even allow solids to get anywhere close to our bows. But since that never
happens, this is just a useless precaution, except that any energy we beam
forward ionizes the medium, and we use our ionic winds to stir up the atomic
winds, which bring us our clear sailing.

Johnny Thunderbird