Newsgroups: sci.space.policy,sci.astro,sci.misc
From: henry@spsystems.net (Henry Spencer)
Subject: Re: (Liquefying the sand into slag) Re: Yours, Mine or Ours...
Date: Sun, 13 Feb 2000 20:23:07 GMT

In article <Pine.GHP.4.21.0002121756090.3406-100000@leo.et.byu.edu>,
Jonathan A Goff  <jongoff@et.byu.edu> wrote:
>> Which frequency will liberate Oxygen from a typical bucket
>> of lunar sand?  How long does it take to liberate 90% of
>> the oxygen contained in the sand?
>
>I was under the impression that most of the lunar Oxygen
>is tied up in oxides.

Correct.  You won't get oxygen out by direct heating, unless you reach
very high temperatures indeed (which has been suggested, but has a number
of problems).

The idea of heating specific types of atoms, by the way, falls down rather
badly because they proceed to bounce off their neighbors, spreading the
heat around.

>...However, by liberating
>hydrogen, you can take it with regolith, and heat it up
>a bit with the microwave, and have it strip the oxygen
>out yielding Iron, Water and Rutile.  The water can be
>broken down and used again.

See previous comments about problems with microwave heating.  Also, such
chemical processing has many unknowns, and some known difficulties.  For
example, there is some sulfur in lunar regolith, and that means that the
hydrogen process also ends up producing sulfuric acid, which will not be
kind to the equipment...
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.policy,sci.astro,misc.survivalism,sci.misc,us.misc
From: henry@spsystems.net (Henry Spencer)
Subject: Re: (Liquefying the sand into slag) Re: Yours, Mine or Ours: Who Owns, 
	the Moon?
Date: Sun, 13 Feb 2000 20:31:17 GMT

In article <Pine.SUN.3.96.1000212231003.13061D-100000@compass.oregonvos.net>,
Matthew Montchalin  <mmontcha@OregonVOS.net> wrote:
>But we know that oxygen is also bound into the sand, and so far,
>we've only removed the volatiles?  So what we have to do at this
>point, is increase the average temperature of the sand to the point
>that the stuff melts?  Will this be enough to allow the oxygen to
>separate from the taffy-like liquefied sand?

No.  In general, the oxygen starts to separate only after temperatures are
high enough to vaporize the regolith.  (By the way, regolith has a fairly
low silica content and shouldn't be thought of as sand.  Wrong model.)
There have been proposals -- the buzzphrase is "vapor-phase pyrolysis" --
to extract oxygen that way, but the energy demands are very high and the
separation processes are heavy on handwaving and light on specifics.

A more promising method, by the way, is electrolysis of molten regolith.
That actually seems to work fairly well.  The main difficulty, aside from
the need for large amounts of electricity, is that it's terribly hard on
the electrodes and the container.  Making long-lived equipment for this
will be a challenge.

It's just plain *difficult* to get oxygen out of regolith in quantity.
If there really is ice, or permafrost, or whatever at the poles, mining
that and electrolyzing the water would probably be easier.
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.policy,sci.astro,misc.survivalism,sci.misc,us.misc
From: henry@spsystems.net (Henry Spencer)
Subject: Re: (Liquefying the sand into slag) Re: Yours, Mine or Ours...
Date: Sun, 13 Feb 2000 20:18:03 GMT

In article <Pine.GHP.4.21.0002120845560.2786-100000@leo.et.byu.edu>,
Jonathan A Goff  <jongoff@et.byu.edu> wrote:
>> It'll take a *lot* of energy to heat that much regolith.
>
>Use microwaves...

Unfortunately, if I recall correctly -- don't have time to go digging for
the references right now -- experiments with microwave heating of lunar
soil generally have not worked very well.  There is a positive-feedback
effect which makes hot spots more effective absorbers, and the result is
very uneven heating, with localized hot spots and little bulk absorption.
(Remember that lunar soil is an *excellent* thermal insulator; its heat
conductivity is very low.)
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)

From: Bruce Dunn <bpdunn@home.com>
Newsgroups: sci.space.tech
Subject: Re: regolith to rocket fuel?
Date: Fri, 22 Sep 2000 21:51:21 GMT

Hiram Berry wrote:

 A conventional solid fuel grain of Mg/Al
> or an alloy thereof would get very hot throughout very quickly, probably to
> the point of the metal melting and ineffectually splattering off into the
> exhaust stream

Some spectroscopic studies have suggested deposits of sulfur on the
lunar surface.
Sulfur may be a useful binder for metal particles in a hybrid rocket
using LOX and metals derived from lunar regolith.

Grains for hybrid rockets would be cast from molten sulfur and metal
particles, and burned with LOX.  The sulfur would oxidize to SO2, a
working gas which has a higher MW than O2, but which is generated in an
energy releasing reaction.  Oxidation of metals would heat the working
gas to higher temperatures than would be generated by oxidizing the
sulfur alone.  Density of the grain would be excellent, being around
2000 kg/m^2 for the sulphur, and 2700 kg/m^3 for aluminum particles.

From: Bruce Dunn <bpdunn@home.com>
Newsgroups: sci.space.tech
Subject: Re: regolith to rocket fuel?
Date: Mon, 25 Sep 2000 07:21:49 GMT

Hiram Berry wrote:

> Might you possibly know which mission gathered that data?  Was it elemental
> sulfur or a sulfide bearing ore?

I only have second-hand information, as related in the Handbook of
Chemistry and Physics ( see for example
http://www.speclab.com/elements/sulfur.htm ).  The statement in the
writeup on sulfur in the handbook appears to be derived from ground
based astronomy, and to refer to elemental sulphur (as is found in
terrestrial volcanic areas):

" A dark area near the crater Aristarchus on the moon has been studied
by R. W.
Wood with ultraviolet light. This study suggests strongly that it is a
sulfur deposit."

As an alternative to a hybrid grain, I has occurred to me that one could
make a liquid rocket fuel with molten sulfur, and metal particles
consisting of an alloy of magnesium and aluminum tailored to have a
density identical to the sulfur (the density of magnesium is lower than
that of sulfur, while that of aluminum is higher).  With a density
identical to that of the liquid, the solid particles would not settle.
Molten sulfur is commonly piped in industrial situations, with only
modest insulation of the pipes needed (molten sulfur is roughly at the
same temperature as industrial steam).

I appreciate your concerns about the possible reactivity of metals with
sulphur.  I don't know about the reactivity of magnesium, but I have
melted sulfur in an aluminum foil cup without having had it react.

From: Bruce Dunn <bpdunn@home.com>
Newsgroups: sci.space.tech
Subject: Re: regolith to rocket fuel?
Date: Mon, 25 Sep 2000 07:35:34 GMT

Hiram Berry wrote:

>
> I don't know about that fabrication technique; molten sulfur reacts with a
> lot of metals.

The Encyclopedia Britannica states:

"at temperatures up to red heat, aluminum is inert to sulfur."


http://www.britannica.com/bcom/eb/article/printable/6/0,5722,6036,00.html

From: Doug Jones <random@qnet.com>
Newsgroups: sci.space.tech
Subject: Re: regolith to rocket fuel?
Date: Sun, 24 Sep 2000 15:05:53 -0700

Hiram Berry wrote:
>

> A conventional solid fuel grain of Mg/Al
> or an alloy thereof would get very hot throughout very quickly, probably to
> the point of the metal melting and ineffectually splattering off into the
> exhaust stream (both elements have low melting points, and their eutectic is
> less than either). Maybe you could modify this behavior by the use of foamed
> metals to decrease the bulk coefficient of thermal conductivity.

IIRC LOX/aluminum and water/aluminum hybrids have been built and tested
by various experimenters, using tightly wrapped foil as the fuel grain.
This tends to delaminate and shear off layer by layer, promoting even
wear and combustion.  The inherent oxide layer prevents layers welding
together, and the poor thermal contact between layers prevents premature
bulk melting.  For larger engines it may be necessary to deliberately
increase the oxide thickness to serve as a thermal barrier, but thicker
foils may also be possible.  Sulfur might be usable as a glue between
layers.

The brute force approach would be to use a steel tank and molten
aluminum fuel, with a regeneratively LOX cooled chamber.  This would
have the advantage of being hypergolic, no igniter required (ignition is
not a simple task for an Al/LOX hybrid). Having some parts of the
vehicle at 90 K and others at 1000 K would be a bit challenging- and
keeping the feul from freezing in the injector head without overheating
the oxidizer galleries and igniting the injector would be even more so.

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