Date: Mon, 07 Feb 2000 07:11:40 -0800
From: Doug Jones <random@qnet.com>
Newsgroups: soc.history.what-if,sci.misc,sci.astro,sci.space.policy,us.misc
Subject: Re: (Oxygen to spare) Re: Yours, Mine or Ours: Who , Owns   , theMoon?

Conrad Hodson wrote:
>
> On Sun, 6 Feb 2000, Matthew Montchalin wrote:
> > |You would need about 20-30 km of ring coils, spaced 10-20 yds apart.
> > |How heavy each is depends on your materials. High temp superconductors
> > |would be light, ferrous magnets would be heavy.
> >
> > Is it possible to *decelerate* something using the same sort of
> > arrangement?
>
> Theoretically yes.  But _very_ scary.

Not too scary at all, *if* you abandon the idea of threading through the
eye of a needle. The decelerator track can be just that- a flat planar
track, made of rather dumb iron plates.  The vehicle has a maglev magnet
array on its side, with many poles to achieve *poor* maglev L/D. While the
magnets are attracted to the iron track, the maglev current induction
repels from the track, and the flying height is stable.  Very large eddy
currents are induced in the track, causing strong deceleration.  Note that
the vehicle kinetic energy is turned into heat in the track, and no
regeneration is possible.

Like the Loftstrom launch loop, the magnet array and track interaction is
entirely passive, requiring no active control systems- the overall field
strength and number of poles determines the braking force, which remains
constant down to the point where the magnetic attraction overwhelms the
maglev- at which point the vehicle touches down on wheels but continues to
decelerate.

Guidance must still achieve cross-axis accuracy of less than a meter, but
the abort mode is much more benign- a propulsive pull-up of just a few
meters allows the vehicle to overfly the track without deceleration.

[This concept is not original with me, I read about it somewhere (most
likely an SSI publication) years ago.  I haven't had much luck finding
references on the web.]

--
Doug Jones
Rocket Plumber, XCOR Aerospace
http://www.xcor-aerospace.com

Date: Mon, 07 Feb 2000 21:26:55 -0800
From: Doug Jones <random@qnet.com>
Newsgroups: soc.history.what-if,sci.misc,sci.astro,sci.space.policy,us.misc
Subject: Re: (Oxygen to spare) Re: Yours, Mine or Ours: Who , Owns   , theMoon?

"Robert G. Shimmin" wrote:
> Why should the heat be deposited in the track and not the payload?  As far
> as I a can see, the deceleration requires currents in both, both of which
> will be resisted, depositing heat in both.

No, currents flow only in the track- this is simply eddy current braking,
which has been routinely used in large variable speed variable torque
electric motors for decades- see
http://www.dynamatic.com/ec-principles.html  Since the vehicle doesn't see
any changing fields (the induced fields in the track move at vehicle
speed), there are no eddy currents in, and no heating of, the vehicle.
Consider a ferrite magnet flying along an aluminum track- the magnet is not
electrically conductive, but the track is conductive, and currents are
induced in the track whick produce a "mirror image" of the ferrite magnet.
Only the track has currents, only the track has I^2R losses. Even a
conductive cobalt magnet would not have currents induced, and would not see
heating.

*All* the kinetic energy goes into heating the track, and only the low
temperature thermal radiation from the hot track can heat the vehicle.  The
magnets on the vehicle can be simple neodymium-iron-boron permanent
magnets, no need for superconductors.

> Not that this isn't insurmountable (it wouldn't have to be too much more
> heat than is generated on an atmospheric reentry) but on reentry, the heat
> is deposited in the outer skin only, and has the nearby air to help carry
> it away.  In the rail decelerator, the heat would be deposited in any
> conductor and in vacuum, radiation is the only convenient cooling
> mechanism.

Yes, radiation is the only workable cooling method- and the track can take
several minutes to cool down after the vehicle goes by.  That is a strength
of the concept- and the track can be made from lunar resources, since it is
essentially an overgrown playground slide.  Actually the track would be an
array of several thousand overlapping plates, each anchored at the uprange
end and free to move at the downrange end. The loads on the track sections
would be almost entirely in tension, puling downrange from each anchor.

--
Doug Jones
Rocket Plumber, XCOR Aerospace
http://www.xcor-aerospace.com

Date: Tue, 08 Feb 2000 08:42:01 -0800
From: Doug Jones <random@qnet.com>
Newsgroups: soc.history.what-if,sci.misc,sci.astro,sci.space.policy,us.misc
Subject: Re: (Oxygen to spare) Re: Yours, Mine or Ours: Who , Owns   , theMoon?

Conrad Hodson wrote:
>
> On Mon, 7 Feb 2000, Doug Jones wrote:
> >
> > Not too scary at all, *if* you abandon the idea of threading through the
> > eye of a needle. The decelerator track can be just that- a flat planar
> > track, made of rather dumb iron plates.  The vehicle has a maglev magnet
> > array on its side, with many poles to achieve *poor* maglev L/D. While the
> > magnets are attracted to the iron track, the maglev current induction
> > repels from the track, and the flying height is stable.  Very large eddy
> > currents are induced in the track, causing strong deceleration.  Note that
> > the vehicle kinetic energy is turned into heat in the track, and no
> > regeneration is possible.
> >
>
> This sounds like it could be useful--not much to break down, and easy to
> imagine as a product of fairly early lunar industry.  Do you know if any
> working-model or prototyping has been done?

I doubt if anyone has demonstrated the technique at high velocities,
although I imagine a small projectile could be fired from a cannon into a
vacuum test range, using existing apparatus at a ballistics range like the
US Army Aberdeen test center.

A neat desktop demo to show the concept is at
http://www.eskimo.com/~billb/neodemo.html#fall

> > Guidance must still achieve cross-axis accuracy of less than a meter, but
> > the abort mode is much more benign- a propulsive pull-up of just a few
> > meters allows the vehicle to overfly the track without deceleration.
> >
>
> "Houston, we still have a problem."  This benign abort mode is certainly
> more benign than hitting a rock or launch structure at 3 kps.  However,
> the alternative is _missing the whole moon_ by those same few meters.  Are
> we talking about backup rockets on each load?  Some kind of tugs on
> standby?  Just writing off all the loads that miss, and letting them go
> off in their ballistic way to escape or crash somewhere?

If the landing track is positioned properly on the moon (basically in the
center of the farside), it will be at the perilune of a free-return
trajectory, or very close to it.  Unmanned vehicles would do a contingency
burn of perhaps less than 100 m/s, continue into an elliptical Earth orbit,
and try again a month later.  If you're nuts enough to put people on the
thing, it should have enough delta-v to decelerate into lunar orbit, only
about 800 m/s needed.  Then you could try again two hours later.  Unused
fuel would be tapped after landing and put into the tank farm.

Alternately, you could use the track only for the last 1600 m/s, and plan
to always enter lunar orbit propulsively- this would allow a phasing orbit
or two to set up for the landing, and multiple opportunities if an approach
must be waved off.  The position of the track on the lunar surface is also
much less constrained, but still should be close to or on the equator to
remove orbit plane considerations.

> Or have I got it wrong somewhere?  I'm just doing quick
> back-of-the-envelope guesswork here--yours is the first I've heard of this
> particular version of magnetic capture.

Hey, if you think this is whacked, you'd love the track decelerator former
NASA administrator Tom Paine was pushing years ago... a well-graded dirt
road, basically.  The lander has skis and a gadget that looks like an ice
ax, which scoops the regolith up into a glorious rooster tail.  Serious
lithobraking.

At a mile per second.  Yee friggin hah.

--
Doug Jones
Rocket Plumber, XCOR Aerospace
http://www.xcor-aerospace.com