Newsgroups: sci.space.policy
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: NEA and lava-tube surveys (was Re: lunar resources)
Date: Fri, 19 Jan 1996 18:57:57 GMT

In article <82587-821951990@mindlink.bc.ca> Nick_Janow@mindlink.bc.ca (Nick Janow) writes:
>> ...The cost of findng a lava tube will be less
>> than the cost of doing a survey of the NEA's.
>
>I assume that finding a suitable NEA would require a few inexpensive,
>lightweight probes (private built, using off the shelf parts, not NASA
>built). Slow data transfer (no video images) reduces operating expenses.
>It might be possible to select a few "best possibilities" using Earth-based
>observation.

Unfortunately, it's not that simple.  All the optical instruments in the
world, whether on a probe or on Earth, will tell you only what the outer
millimeter or so of the asteroid is like.  If you're going to be mining
the thing, you need to know about its interior, or at least about the
outermost few meters of regolith.  (We have no clear idea of how thick
the regolith is, or how this varies from asteroid to asteroid, never mind
its composition.)  Radar sounders and gamma-ray spectrometers will help,
but will give you only coarse data about composition, and won't tell you
much at all about consistency.  This kind of data might give us the basis
for a reasonable guess, *if* we understood asteroids fairly well.  Trouble
is, we don't -- there's no background of experience to base guesses on.

The sort of thorough going-over that's needed to pick a good mining
location will not be had from cheap lightweight probes, not at our current
level of ignorance.  The probe(s) will need to be able to land, excavate,
perhaps drill. 

>Maybe with the cold war over, the government would be willing to allow the
>use of some of the spysats (maybe not suitable, but it's a thought).

There is nothing about US spysats which is either cheap or lightweight!
And the spysat people haven't noticed that the Cold War is over.

>Delta-v to a NEA is low, and the mission could be timed for near approach,
>to minimize downlink costs (and allow teleoperation).

The approaches aren't that near, and a low-delta-V rendezvous mission will
not usually arrive at or near a time of close approach.

>Compare that with a seismic survey of parts of the moon, looking for the
>deep, large lava tubes that you are seeking.  If you want "a large amount
>of information about the structure of the moon", you're not talking about
>just searching a few "most likely" areas; you're talking about a full
>surface survey.  That would be very expensive.

Actually, one can *probably* find lava tubes with radar sounding rather
than surface surveys.  (The lunar regolith is so dry that radar penetrates
it rather well -- some experimental radar sounding was done by Apollo 17,
but there was never any followup.)
-- 
The Earth is our mother.                           |       Henry Spencer
Our nine months are up...                          |   henry@zoo.toronto.edu

From: dietz@interaccess.com (Paul F. Dietz)
Newsgroups: sci.space.policy
Subject: Re: I want to *GO!*
Date: Sat, 01 Feb 1997 06:30:20 GMT

om@ix.netcom.com ( om) wrote:

>....The point that a lot of people seem to miss about mining the
>asteroids is that a lot of the precious metals, compounds and dense
>crystalics are formed through millennia of geological processes found
>only within an active geosphere or similar environment.

But the asteroids (well, the differentiated ones) *are* the product
of millenia of geological processes: segregation of melts and
subsequent very slow crystallization as the entire asteroid cooled.]
This segregation took place 4+ billion years ago, granted, but it did
take place.

The metal fraction of LL chondrites is considerably richer in
platinum group metals than the richest such ores on earth (most of the
earth's PGMs are in the core.)  That they could be extracted
economically is not clear.

	Paul