Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V16_9/V16NO897.TXT

Text File | 1993-07-20 | 26KB | 546 lines

Space Digest                Tue, 20 Jul 93       Volume 16 : Issue 897

Today's Topics:
                     Comet Mining -- An Overview
                                 DC-X
                      SETI information (2 msgs)

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Date: 20 Jul 93 05:17:24 GMT
From: Nick Szabo <[e-mail]>
Subject: Comet Mining -- An Overview
Newsgroups: sci.space,alt.sci.planetary

Comet Mining -- An Overview
Copyright 1993 by Nick Szabo
Permission to redistribute w/attribution granted

-- Introduction --

A relatively unexplored area of space development, comet mining, may
play a central role in cracking open the space frontier.  Volatile
extraction, considered by this author and others[1] to be an important
near-term catalyst for large-scale space industrialization, involves
the delivery and processing of volatile ice (water, methane, ammonia,
etc.) delivered via ice rocket from Jupiter-family comets,  which
have elliptical orbits between Earth and Jupiter.  A visual presentation
and marketing analysis were given in [2], technical presentations can be
found in [3-4], and various technical and marketing issues have been
discussed in [1].  Government [4,10] and commercial [9] organizations
are starting to sponsor research in this area.  This paper attempts to
unite this information into a comprehensive introduction to comet mining.

-- Comets, the Jupiter Family, and the Need for Volatiles --

The only hard and fast rule to distinguish between comets and
asteroids is that comets have been seen to outgas.
Several asteroids have recently been reclassified as comets
when outgassing was discovered, eg Charon.  The outgassing
indicates active sublimating volatiles.  Asteroids either
lack free volatiles or they never get warm enough to outgas.
Different volatiles (H2O, CO2, CH4, NH3, etc.) outgas
at different temperatures.  Objects in circular orbits
tend to reach an equilibrium temperature where outgassing
stops; all known comets are in elliptical or chaotic orbits
where temperatures change over the course of the orbit.

By far the largest proportion of materials used by most
processing industries are volatiles and organics.  This is true
for Earth industry -- oil for energy, wood for structure, plants
and animals for food, and vast amounts of water and air
for nearly industrial processes, which we often take for granted.  In
space, SSF expendables consist overwhelmingly of volatiles: air, water,
propellant, etc.  The most advanced theoretical technology,
worked out in detail by K. Eric Drexler[8] relies
primarily on volatile and organic materials, especially carbon.  The
most promising microgravity industry, pharmaceuticals, would be
dominated by volatiles and organics.  By far the greatest bulk
of near-raw materials launched from Earth into space are volatile
propellants.  Even metals extraction and refining industries rely on
much larger amounts of air and water than they produce in metal product,
and it is quite a leap to assume we can eliminate this dependency
without costly R&D efforts and while maintaining reasonable levels
of efficiency and thruput.

That's bad news, given that practically all native
materials work today has, for historical and political
reasons, focused on the dry Moon, and to a lesser extent
dry asteroids.  The good news is that volatile
extraction from ice is much easier than trying to
split oxidized metals into oxygen and metal (not to
mention trying to capture solar wind particles for
hydrogen, carbon, nitrogen, etc.).  Comet ice, full of
a rich diversity of water, nitrogen, and organic compounds,
is readily available.

The best currently known targets for volatile extraction
are the Jupiter-family comets.  These have been tossed into
the inner solar system by Jupiter, into highly elliptical orbits,
with perihelions as low as Mercury's orbit (0.4 AU) and aphelions
near Jupiter's.  Influenced by the inner planets, the orbits slowly
circularize.  Most of the perihelions are near 1 AU, although
to some extent that's observational selection; we're less
likely to see objects with perihelions at 2 AU, and ice there
sublimates much more slowly.

The comets live very short active lives on a geological timescale,
100,000's to millions of years, but Jupiter's gravity well
is quite hungry and continually replenishes the supply when
comets wander its way from the Kuiper Belt or Oort Cloud.
Some of these visitors get a rought welcome; we recently saw a
comet calve into dozens of pieces as it swung in too close to
Jupiter.  Caught in orbit around Jupiter, these pieces, the
largest c. 10 km diameter, are projected to collide with the gas
giant (on the far side, alas) in 1994[7].

Most such comets are whipped into heliocentric orbit (ie orbit
around the sun), with aphelion at Jupiter and perihelion
in the inner solar system.  Over the comet's lifetime this orbit continues
to circularize until one of the following happens: (1) all the
volatiles exposed to the sun bake out, and the comet turns into an
asteroid, or (2) perihelion increases, and volatiles
remain frozen during the entire orbit, again turning the
comet into an asteroid.  For this, reason, many scientists
believe that many earth-crossing asteroids, especially types
C and D, may be old Jupiter-family comets, and some may still
contain frozen volatiles.  We know that many earth-crossing
asteroids contain water, and perhaps ammonia, locked to the regolith by
hydration.  This is harder to extract.  We should consider
these closer objects as alternate targets for volatile extraction,
comparing the tradeoff in transport and equipment costs.

Thousands of earth-crossing asteroids are believed to exist
with round-trip delta-v's from Earth orbit lower than the
lunar surface.   Jupiter-family comets take somewhat more energy
to get to; escape + 8 km/s one way for good windows, shaving off
a few km/s on the way there and/or the way back if we
can use Venus, Earth, or Mars for gravity assist [1,3,5].
With a slightly more sophisticated mission we can manufacture
aerobrakes by sintering comet dust, eliminating most of the
return delta-v [6].  A speculative method called
"cometary aerobraking" has also been proposed [1].

-- Ice Rockets --

The industrial flexibility of volatiles makes its first
and most dramatic impact in deep space transportation technology.
We can combine easily extracted native thermal propellants with a tankless
rocket design, eliminating the need to launch either propellant,
tanks, or heavy electric powerplants from Earth.  The specific transport
technology that embodies this principle has been dubbed the "ice
rocket" [1].  The ice rocket design [1,2,3] consists of a long cylinder
about the same size and shape as a Space Shuttle's solid rocket booster,
but made out of ice and coated with a thin insulating paint.  To
this is attached a tiny thermal rocket, about the size of a fist,
and a  tiny nuclear reactor, or few square meters of mirror,
which concentrates sunlight on the rocket engine. The engine
slowly eats the ice, converting it into a high-velocity vapor
exhaust. The rocket engine is designed for minitiarization and
simplicity, so that dozens of them can be built and launched
on a small, commercial budget at launch costs not much
lower than today's.   A larger nuclear-powered design is
presented in [4].

To mass-produce the ice rockets we melt cometary ice and
purify it with a centrifuge, in some designs combined with
an inflatable still.  We form the ice cylinder in two
steps. First we freeze a thin shell by wetting a large, cold
cylindrical form.  As this ice gets thicker, it freezes further
layers more slowly, so we start squirting small spheres
across a shaded vacuum.  These spheres freeze on the
outside, then accumulate on the inside of the cylinder.  Soon
the cylinder is filled with partly frozen water, which will
continue to freeze over several years while the rocket travels
towards its destination.

The icemaking equipment is the most important part of the
system.  It must  produce a very high ratio of  ice mass to
equipment mass (aka mass thruput ratio (MTR): output product
per year divided by equipment mass launched from Earth).
It must be automated and reliable; think of a tiny auto-maintained
sewage treatment plant. Other parts of the comet (organics, dirt,
etc.)  can be gathered and attached as payload.   The cylinder is
then attached to the small rocket engine, whose tiny thrust over the
course of two or three years delivers the payload to a variety of
destinations: orbits around the Earth, Jupiter, or Mars, the surface
of Earth's Moon, or to asteroids. To get to high Earth orbit we must
exhaust about 90% of the ice, or 80% if we take a  couple
extra years to use a gravity assist. (See [5] for patched-conic
math to compute such trajectories, and [6] for safety issues
involved in using Earth for gravity assist and aerobraking
of various varieties and sizes of payloads).  We might also find hidden
in some Earth-crossing asteroids, in Martian moons, or at the
lunar poles, in which case more than 10% can be obtained.

If the output of the icemaking equipment is high, even 10% of
the original mass can be orders of magnitude cheaper than
launching stuff from Earth.  This allows bootstrapping: the
cheap ice can be used to propel more equipment out to the
comets, which can return more ice to Earth orbit, etc.  Today
the cost of propellant in Clarke orbit, the most important
commercial orbit, is fifty thousand dollars per kilogram.  The
first native ice mission might reduce this to a hundred dollars,
and to a few cents after two or three bootstrapping cycles.

Furthermore, we can deliver volatiles not just to Earth orbit,
but anywhere else in the inner solar system.  A volatile
dump around Mars can slice an order of magnitude off the
propellant needed to launch a large-scale mission to Mars.
Comet volatiles are synergistic with lunar operations, adding
the missing elements needed to make lunar exploration or
industry productive.

Once the volatiles and organics have been separated, they are
fed to a series of chemical microreactors and converted to
essential  nutrients and construction materials for
greenhouses.  Greenhouses can be made in a very simple,
automated fashion, for example by pumping air
into liquid polymer spheres which are then solidified and filled
with nutrients and trellises for the crop.  The crops grow not
only pharmaceuticals, but also fiber and resins to provide structural
strength for further greenhouses, and genetically engineered
enzymes are extracted and used in the chemical
microreactors.  The greenhouses contain a low pressure (c.
1/5 atm), CO2-rich atmosphere to facilitate the growth of
genetically modified fiber plants while keeping the engineering
task of building the pressure vessels minimal.

Methane, ethane, and several other hydrocarbons have been seen in
varying abundance (<1% to 5% for methane) in comets.  If you want
to get rich in 2020, design a system to extract the methane from
the water & ammonia ice and the gravel/muck of comets, perhaps
manipulating a large gas/plasma interface (cf. comet tail dynamics).

A refinement of the ice rocket manufacturing process
is a 3D printer to produce very large structures.  Shoots droplets of
several kinds of materials following a digital pattern.  For example a
high-temp-sublimating ice, a low-temp-sublimating ice, and a
ceramic slurry.  The target object forms on a very large, cold
radiator in the shade.  The goal is to have the particles mostly
freeze before they impact the target, but nevertheless stick to and
accumulate on precise points on the target (in 3-space, layer
by layer) without too much splatter.  If the target itself must
freeze the droplets we run into heat conduction problems pretty
soon, and the target object couldn't get very thick.   The
low-sublimating-point ice allows hidden surfaces to be "etched" by
sublimation when the structure is rewarmed, provided there are
escape holes.

-- Open Issues --

Many engineering tasks need to be undertaken to make comet
mining a reality:

* Simple processes to create 1/5 atm pressure vessels from cometary
    ice & tar, including greenhouse windows
* elaborate/refine 3d printer designs
* variable gravity bolo
* minimize processes requiring gravity
* Gas/plasma separation processes
* plant automation (maintenence, etc.) -- this may be the
primary technological bottleneck
* Nitrogenous fertilizer from ammonia
* Carbon -> CaC -> acetylene vs. syngas (CO + H2) -> hydrocarbons
    via Fischer-Tropsch
* Phenolic resins vs. urea-formaldehyde/fiberboard
* Polyethylene, alpha-olefins, polystyrene, PVC

Among cometary science to do:
* Cometary sources of phosphate, potassium, and halogens
* Detailed analysis of comet surfaces needed to optimize
choices and enable autonomous operations

Among biotechnology to do:
* Detailed design for "self-reproducing" greenhouses
* Fiber source that facilitates automated processing

Also of great interest are low pressure & plasma manufacturing processes,
especially those that can be greatly scaled up in space.
We would like to manufacture variety of products from
cometary and asteroidal material, including
but not limited to:

* paints (for spacecraft thermal control)
* polymer structures and coatings
* aluminization of polymer surfaces (very large reflectors/solar energy)
* Inconel or silicon carbide frit (for rocket motor)
* radiation shielding
* propellant: thermal, mono- and bipropellant chemical, and ion/MPD
* pressure vessels
* pipes
* single-isotope diamond & fullerenes (C12, C13, C14)
* solar wind isotope separation (eg He3)
* etc. (your ideas go here)

Greenhouse Bootstrapping

The known Jupiter-family comets with lowest-eccentricity may get above
0C at their surface long enough to create an extensive plant growth.
Don't need to move them.  Moving cometary materials to a warm circular
orbit via gravity assist and ice rocket is desirable for some
markets, but it's not necessary to start out the operation if we
have a sufficiently flexible biosystem that can
colonize the comet.  There's also the possibility of chemosynthetic
life to live off the energy frozen in the comet as free radicals,
in which case it doesn't matter how far from the sun we are, but
that's speculative so I'll skip it for now.

A bigger problem is maintaining sufficient internal pressure
to keep water above the triple point (otherwise it sublimates
straight to gas, like dry ice).  One way is to go back to
the bag, except use it as a greenhouse instead of a still.
(Or in addition to a still -- plants exhale pure O2 and
H2O which can be extracted).  A second way, with much higher
MTR (mass thruput ratio), is to have the plants grow their own pressure
vessel, some kind of strong cellulose fiber bound together with a resin
secretion.  It need only hold a CO2-rich atmosphere at < 1/4
atm.

This presents a chicken-and-egg (or more
properly plant-and-seed :-) problem, so we probably would use
bags for the first perihelion.  The mass thruput ration of
this scheme becomes astronomical (pardon the Saganism :-), reaching
millions/year by the second decade of operation, far outstripping the
time cost of money, and all that from just one rocket payload full of
plastic bags filled with seeds.  This makes it highly economically
attractive, even with only a minute fraction of the greenhouse products
being separated (eg by electrophoresis) into pharmaceuticals, etc. and
sent back groundside, or materials being processed and used as propellant,
shielding, structure, life support, etc. in interplanetary or Clarke
orbit, or on the Moon, etc.

Going from native comet goop to pure water, and resin/fiber
for the pressure vessel, is an interesting problem in metabolic
engineering, which combines genetic engineering with an in-depth
knowledge of plant metabolism, in order to optimize certain growth
features (in this case cellulose and resin output, and resistance
to vacuum conditions).  I'd probably started with a fast-growing fiber
plant like hemp or jute or kudzu, and throw in some genes from
deep-salt-lake creatures that maintain an active water gradient across
their outer membrane, which should also be pretty good for vacuuum
protection.  Extensive testing/breeding in groundside vacuum
chambers and micrograv testing in low Earth orbit would be in
order.

-- Conclusion --

Extraction and processing of volatiles from the Jupiter-family comets,
combined with the crude but effective technology of
ice rockets, present a wide variety of new possibilities along
the path from our current small scale space operations to large-scale
space industrialization.  Native volatiles can be processed to
supply current space operations, while making possible new
industries with low up-front investment.  Bootstrapping
of transporation with native ice rockets and industry with
chemical microreactors and self-reproducing greenhouses blazes a
wide path along fertile territory, leading to the technological
and economic resources for large-scale space industry and space
colonization.

References

[1] Szabo, various articles posted to sci.space on native volatile
extraction and processing, 1988-present.  See also articles
by Paul Dietz, Gary Coffman, Phil Fraering, and others.

[2] Szabo, "Comet Mining", a presentation to
Seattle Lunar Group, Feb. 1992 (visual
presentation & initial marketing analysis)

[3] Szabo, "Some Issues in Comet Mining", May 1992,
unpublished (technical overview)

[4] Zuppero, et. al., in _10th Symposium on Space Nuclear Power
and Propulsion (AIP Conf. Proc. 271, 1993)

[5] Sauer, "Optimization of Interplanetary Trajectories with
Unpowered Planetary Swingbys", AAS 87-424, pg. 253

[6] Szabo, "Safety of flyby & aerobraking for large payloads at Earth",
sci.space Message-ID: <[e-mail]>
Mon, 28 Sep 1992

[7] Baalke, "Comet Shoemaker-Levy, Possible Collision With Jupiter in 1994",
sci.astro Message-ID: <[e-mail]>,
and subsequent discussion.

[8] Drexler, _Nanosystems_, John Wiley & Sons 1992

[9] Brian Thill, Boeing Corporation, personal communications

[10] Anthony Zuppero, U.S. Department of Energy, personal communications


--
Nick Szabo                     [e-mail]

------------------------------

Date: Tue, 20 Jul 1993 06:06:18 GMT
From: stephen voss <[e-mail]>
Subject: DC-X
Newsgroups: sci.space

This is a public (repond with a post) question

1)Could DC-1 replace the space shuttle for all manned surface to orbit
needs at a much lower cost,if so how much lower

2)If DC-1 is going to be so much better than other programs then why
does Mcdonnel Douglas need govt backing at all . Im sure private
companies would be piling in to fund it or McDonnell Douglas could
issue stock

3) Why should we be funding space programs at all when we have (fill in
your favorite social cause) here at home

These questions need some answers
I already agree with you guys but I need some better answers to deal with
the public when I try to convince my fellow local politicians of the
merits of the space program

help me out here!

------------------------------

Date: 20 Jul 93 04:25:50 GMT
From: Remi Cabanac <[e-mail]>
Subject: SETI information
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Russ Renaud) writes:
>
>I'm rather new to this newsgroup, so I'm not sure if this topic has
>been discussed.
>
>Where on the Internet could one get some information
>re: the SETI project?  I'm looking for some basic info,
>as well as perhaps some technical details, such as what is
>the smallest discernible signal that the SETI radio telescope
>are capable of detecting?  How are they processing the
>myriad of signals they must be receiving.
>
>I saw in a past posting of SPACENEWS that some 160-odd signals have
>been detected that warrant further investigation.  What form
>do these signals take?
>
>Any info would be appreciated.
>
>[e-mail]
>
>--

I've just heard a lecture from Franck Drake and Billingham on the SETI project,
at ISU in UAH few minutes ago.  Basically, the SETI receivers are built to
detect the equivalent of earth emission from 5000 light years, which
corresponds roughly to 10-23 W/m2/Hz (I'm not sure of the units).
But it depends on the radio-telescope used (these data are for Arecibo).
The emission are processed by an MSCA able to manage 6 million channels at once.
Each emission is filtered with rigorous criteria such as periodicity, intensity
regularity, etc...
Until now, 38 signals are interesting and cannot be explained by radio
terrestrial interference (yet).  But none are periodic.

Remi Cabanac.

------------------------------

Date: 20 Jul 1993 08:30:39 GMT
From: Tad Perry <[e-mail]>
Subject: SETI information
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Remi Cabanac) writes:
>In article <[e-mail]> [e-mail] (Russ Renaud) writes:
>>
>>Where on the Internet could one get some information
>>re: the SETI project?  I'm looking for some basic info,
>>as well as perhaps some technical details, such as what is
>>the smallest discernible signal that the SETI radio telescope
>>are capable of detecting?  How are they processing the
>>myriad of signals they must be receiving.
>>
>>I saw in a past posting of SPACENEWS that some 160-odd signals have
>>been detected that warrant further investigation.  What form
>>do these signals take?
>

[fixed your margins; they're too long for quoting]

> I've just heard a lecture from Franck Drake and Billingham on the
> SETI project, at ISU in UAH few minutes ago.  Basically, the SETI
> receivers are built to detect the equivalent of earth emission from
> 5000 light years, which corresponds roughly to 10-23 W/m2/Hz (I'm not
> sure of the units).  But it depends on the radio-telescope used (these
> data are for Arecibo).  The emission are processed by an MSCA able to
> manage 6 million channels at once.  Each emission is filtered with
> rigorous criteria such as periodicity, intensity regularity, etc...
> Until now, 38 signals are interesting and cannot be explained by radio
> terrestrial interference (yet).  But none are periodic.

May I take it that Arecibo is the main data gatherer in the SETI
project?  Actually I'm getting rather interested in SETI too. Just
like with my question about HST I'm beginning to wonder about it's
organization. Like major data collection points, where that data is
forwarded and just exactly who (which organization/people) look at the
data. The above does tell me what they look for once they get it
but does anyone know the rest?

------------------------------------------------------------------------
Tad Perry      Internet:    [e-mail]
               CompuServe:  70402,3020
               NIFTY-Serve: GBG01266

------------------------------


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JL>Organization: The University of North Carolina at Chapel Hill
JL>From: [e-mail] (Jon Leech)
JL>Message-ID: <[e-mail]>
JL>Newsgroups: sci.space
JL>
JL>In article <[e-mail]>,
JL>[e-mail] writes:
JL>|> However, for all intents and purposes, the U.S. lunar program was
JL>killed
JL>|> by Congress, yet again, in the last go-around.
JL>


Lunar Scout, a lunar polar orbiter, had been included as part of Clinton's
'new technologies' program. However, although much of the mission was
pretty far along, Scout disappeared from the appropriations bill passed by
the House in early July.
>

___ WinQwk 2.0b#0

--- Maximus 2.01wb

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End of Space Digest Volume 16 : Issue 897
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