Bad form to reply to your own post, but here's an afterthought anyway.

I attended the ICDERS 19 meeting (International Colloquium on
the Dynamics of Explosions and Reacting Systems) in Hakone,
Japan, this year, where one of the presentations related to research
on implosion-tube launchers -- the idea of lining a long tube with
high explosives and detonating them (but smoothly, smoothly!) behind
the projectile, with a mediating gas between the leading wave of
implosion and the projectile, so that you don't simply vaporize
the sabot and its payload.  The presenter was a graduate student
under the supervision of Andrew Higgins at McGill University,
operating out of the lab once operated by the notorious but
(IMHO) underappreciated Gerald Bull.  (Bull, you might remember,
came to grief before his Iraq Supergun could go into operation.
This installation was dismantled by the U.N. in the early
90s.)  Andrew Higgins is very expert in direct launch proposals,
and did quite a lot of research on the ram accelerator concept
at University of Washington.  He's still interested in pushing
ram accelerators through their current slump in funding, but is
also clearly hedging his bets.

If the problems of controlling the rate that the implosion
travels can be solved, an idea mentioned here by Jack Reeve --
using standard oil drilling equipment to make a long tube
through hard rock -- could considerably reduce the cost
of labor and facilities.  You'd need special equipment to line
the tube with explosives, but it's astonishing what the oil
prospecting industry is doing with downhole robotics these
days.  There may even be equipment available now that
could do the job with minor modifications.  Exploratory
wells have been drilled at costs in the order of hundreds
of thousands of dollars, reaching depths that are adequate
for high-G launch.  30-inch drill bits have seen production
use, and treating the bore with liner and explosive wouldn't
reduce the diameter very much.  Drilling for oil and gas
at angles appropriate for direct launch has a long history.
In papers proposing ram accelerator designs, you can
find estimates that a mere 500 m/s delta V is required to
prevent the projectile from reentering the atmosphere
at the opposite side of the Earth. So a kick motor stage
need not be a huge contributor to costs or a serious
reduction in mass payload ration.  Can a rocket, especially
a liquid fueled one, survive gun launch?  Probably --
Bull proposed immersing it in water, inside the sabot,
to equalize the pressure on the fuel tank walls.

Getting a bit optimistic, and guessing that you could loft
500 lbs for $500,000 yields a quite appealing $1,000 / lb
-- from the first shot. Having drilled in one place, it's
somewhat cheaper to drill again nearby -- you need to
move the rig, but you'd better do that anyway, if you're
launching something at 8 km/s out of the hole.  And this
doesn't address the scenario in which boreholes are
reusable -- if you can make one borehole fire 10 shots,
truly impressive economies might appear.  The whole
operation could be substantially automated -- you might
have a few dozen people on site, once it's in production,
launching every few days, rather than the thousands
that attend to a single typical satellite launch.

Now, there's still something wrong with this picture; I
didn't mention Gerald Bull just for colorful historical
background.  To spell it out: any way to put stuff into
space relatively cheaply (or, even more cheaply, to
drop it into the atmosphere on the other side of the Earth,
if not closer) will be cheap not only for The Good Guys
(that's us, right?) but also for anybody else.  An
illegitimate launch complex that can be so easily
camouflaged as nothing more than a oil/gas prospecting
activity raises even more questions.  In short, for the
prospects of cheap launch in the near term, if there is
anything that has cast a longer shadow than the collapse
of the telecom bubble (with its high rocket launch rates),
it's a day whose second anniversary is almost upon us.

-michael turner

----- Original Message -----
From: "Michael Turner" <[EMAIL PROTECTED]>
Sent: Sunday, September 07, 2003 1:19 PM
Subject: mass drivers for earth-to-orbit cargo lift (was Re: SPACE: Loss of
the Saturn V)

> Robert (or maybe Larry) writes:
> > I suspect I'd lean towards a mass-driver + small rocket combination
> > before I'd go with a space elevator.  The nice thing about
> > robotic missions is that they can be hurled off a mass-driver
> > at much higher velocity (due to higher G-force acceleration)
> > than can be done with human missions.....
> > I've never seen to date any estimates for what it would take in
> > terms of a mass driver that could launch 100 tons with the velocity
> > of a Saturn V 1st stage but I would like to know.  Apparently
> > the Saturn V 1st stage puts out enough power to power NYC for several
> > minutes so one would probably need several nuclear reactors to power
> > the mass driver.
> A rocket launcher has very high short-term energy expenditure in
> part because it's mostly lifting its own fuel for most of the burn.
> A terrestrial mass driver is pushing little more than the payload
> itself, which makes a huge difference in the energy requirements.
> One of the more elegant (but, it turns out, somewhat persnickety)
> gun-type launch systems I've looked into, the ram accelerator,
> stores all its fuel in the launch tube itself.  It's a fair amount of
> fuel (various mixtures at pressures on the order of 40 atmospheres)
> in a long launch tube, but the total energy requirement is quite modest.
> Energy isn't really a cost issue for launch -- it's said that the Shuttle
> could power a medium-size town for the minutes that it's burning
> rocket fuel.  That sounds impressive, but if you do the math,
> you come up with a dollar amount that would cover the
> costs of an only-mildly-lavish wedding reception.  This is not
> how all that money is being burned.  If there's a serious
> energy cost component in the Shuttle program, it's more in the
> gasoline used to fuel the cars of its employees, and the
> industrial fuels that make western-style affluence possible.
> Engineering a mass driver to push 100 tons to orbit is rather
> pointless, actually -- the chief advantage of mass drivers is
> the potential for massive throughput, not high payload mass.
> If you can launch 200 lbs to orbit at $200/lb, every few
> days, many problems simply go away.  On-orbit construction
> of 100-ton packages is mainly held back by the cost of putting
> construction equipment, teleoperators, and people into orbit.
> Putting people up will always be expensive (until gizmos
> like the Space Elevator come along, anyway), but when
> you look at how much of a human being's space-survival
> infrastructure outweighs the person, and think about how
> it might be redesigned to survive very high accelerations,
> the arguments for going multimodal in space transportation
> (if other, much cheaper, non-man-rated modes can be
> made to work), appear very compelling.
> Also, with mass drivers and space elevators, it's not an
> either-or proposition.  Mass drivers, used to get
> a bootstrap quantity of carbon nanotube ribbon up
> geosynch orbit, may in fact end up being a prerequisite
> technology more than a competing one.
> In any case, the capital requirements are daunting, and
> there's the question of market.  There are lots of ideas
> for how to make space transportation much cheaper,
> in some very long run -- "take my plan and add $50 billion."
> As Gerard O'Neill pointed out, until you squeeze all the
> technical risk out of these proposals, it hardly matters that
> you might ultimately be able to produce clean power from
> space more cheaply than any energy technology on Earth.
> The Panama Canal was just a big digging project;
> the main technological breakthrough that made it
> possible was the discovery of quinine as a treatment
> for malaria.  Space transportation faces much more
> serious challenges, in both technological and market
> terms.
> -michael turner
> ==
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