🚀 go-pugleaf

>From OTA@S1-A Mon Dec 14 03:45:58 1981

SPACE Digest                                      Volume 2 : Issue 59

Today's Topics:
		     Costs of laser launch facilities
			 hammering the dinosaurs
	       Beam weapons, comments from Access to Energy
			    Ultimate strengths
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Date: 13 Dec 1981 0916-PST
Sender: LEAVITT at USC-ISI
Subject: Costs of laser launch facilities
From:  Mike Leavitt <LEAVITT at USC-ISI>
To: VaughnW at HI-MULTICS
Cc: SPACE at MC
Message-ID: <[USC-ISI]13-Dec-81 09:16:59.LEAVITT>

        Actually, you must worry about interest costs in building
these big facilities only if you are a "public" utility or a
government.  Utilities finance captial projects through bonds
much more often than through new stock issues, and everything new
that the government funds must be considered to be funded from
the proceeds of a loan at the going short-term T-bill rate.

        If, instead, you are an entrepreneur, you have the option
of substituting equity growth for interest as the inducement to
get new capital.  This is the way most new enterprises get their
capital if they can avoid the venture capitalists for long
enough.


        Mike <Leavitt at USC-ISI>

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Date: 13 December 1981 12:49-EST
From: Ron L. Levin <LEVIN at MIT-MC>
To: SPACE at MIT-MC

	Thank you for all the replies about project Orion.  These are listed
 in MC:USERS5;LEVIN ORION.  Two people mentioned McPhee and his book "On the
 Curve of Binding Energy."  The consensus is that it probably works, and that
 it may be possible to reach 10% of the speed of light in a year.  A model
 with "equivalent" TNT explosives was tried.  The advantage of Project Orion
 over other nuclear powered systems, is the rapidity with which nuclear fuel
 can be consumed.  The project was terminated with the nuclear test ban treaty.
 

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Date: 13 Dec 1981 1648-PST
From: Stuart McLure Cracraft <McLure at SRI-AI>
Subject: hammering the dinosaurs
To: space at MIT-MC

!a266  1741  12 Dec 81
AM-Dinosaur Deaths,480
Theory Blames Dust, Darkness for End of Dinosaurs
By ROBERT LOCKE
AP Science Writer
    SAN FRANCISCO (AP) - For perhaps two months, the Earth was wrapped
in a cloud of dust so thick that the sun was obscured and temperatures
over land everywhere fell below zero.
    Within six months, according to the new verion of a 2-year-old
theory, the landscape was littered with carcasses. Species after
species became extinct. Plants stopped growing and dinosaurs couldn't
find enough food and died.
    The idea that a giant asteroid or comet, crashing to Earth and
kicking up huge clouds of dust 65 million years ago, ended the
140-million-year reign of the dinosaurs was described at a meeting of
the American Geophysical Union by atmospheric scientist Owen B. Toon.
    Toon, of the National Aeronautics and Space Administration's Ames
Research Center at Mountain View, Calif., said theories of the end of
the dinosaurs continue to stir considerable interest.
    ''It's one of the longest-standing mysteries in science,'' he said
in an interview Friday. ''If it could happen to them, it could happen
to us. They were the kings of the earth.''
    The extinction of the giant reptiles launched the age of mammals,
which survived, Toon theorizes, because they were small enough to
burrow underground for warmth ''and could probably stumble across
enough food,'' including dead dinosaurs.
    ''All the mammals were mostly mice and little things like that and
that's how we survived ... But if you're a big guy like a dinosaur,
you've got to find an awful lot of food,'' Toon said. ''Plus, you can
imagine how dangerous it would be for a dinosaur to stumble around in
the dark.''
    He said cold and the inability to find food probably killed off any
creature that weighed more than 75 pounds.
    The idea of a dust-producing collision was proposed in 1980 by a
team of scientists led by Walter Alvarez of the University of
California's Lawrence Berkeley Laboratory.
    They based the theory on geologic evidence that, about 65 million
years ago, a thin layer of debris was deposited around the Earth. The
concentration of certain metals in this layer is much different from
that found in the Earth's crust, but about right for an asteroid.
    The group concluded that a meteorite, perhaps 8 miles across, caused
a dust cloud that darkened the Earth for several years.
    Toon, with colleagues at Ames, R&D Associates of Marina del Rey, the
University of Colorado and Informatics, Inc., of Palo Alto, used
computer simulations designed to study volcanic ash and the
atmospheres of other planets to better determine the effects of such a
collision.
    The team presents a different picture, with shorter but more
dramatic impacts.
    ''The duration was less than six months and possibly less than three
months,'' Toon said.
    The crash, possibly in the ocean, would have had 10 million times
the energy of the Mount St. Helens volcanic explosion last year, he
said.
    
ap-ny-12-12 2041EST
**********
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Date: 14 December 1981 02:06-EST
From: Gene Salamin <ES at MIT-MC>
Subject: Beam weapons, comments from Access to Energy
To: SPACE at MIT-MC, ARMS-D at MIT-MC

     The December 1981 issue of Access to Energy deals with beam weapons.
It may or may not turn out to be practical, but you don't know until you
try.  The following is a quote from AtE.

  Only two years ago one could find articles explaining why atmospheric
  absorption would preclude particle beams.  These forecasts (as near as
  we can tell from the open literature) have proved wrong; not because
  any physical laws have been broken, but for lack of experience with
  an energy threshold where other factors come into play.

  There have been such cases where just a little experimental physics,
  or the lack of it, considerably affected warfare.

  The secret invention of radar was not only decisive in the Battle of
  Britain (the entire tiny RAF fighter force always intercepted the
  Luftwaffe squadrons wherever they chose to approach), but it also
  revealed to the British that very short radio waves will propagate
  well beyond the horizon, rudely overruling contemporary physics and
  engineering textbooks.  Again, no physical laws were broken, but the
  texts had failed to take account of a tiny, but decisive (refractive)
  effect of the atmosphere.  The British used this effect in 1941 to
  bomb Berlin at night, through clouds, for unknown to the Germans,
  Berlin (and Western Europe) was covered by a navigational net spun
  from signals emitted by radio beacons in Britain.  They were received
  on board British aircraft by the grandfather of today's electronic
  navigation, the "G-box", tuned to the then stunningly high frequency
  of 50 MHz (the band of today's commercial TV channels).

  The G-boxes had a detonator to destroy their most secret ingredients
  on impact, but it failed to explode on one of the planes shot down,
  and the Germans appointed a commission to top experts to investigate
  the puzzle.

  "We couldn't make head or tail of it", one of its members told this
  writer some years after the war.  "But we unanimously concluded that
  it was something for training purposes only, because it was easy
  enough to determine the frequency to which the receiver was tuned,
  and we all 'knew' that such short waves could not possibly propagate
  beyond the transmitter's horizon."

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Date: 14 Dec 1981 0217-EST
From: HPM at CMU-20C
Subject: Ultimate strengths
To: foner at MIT-AI, space at MIT-MC
cc: hm60 at CMU-10A

Actually there are several "ultimate" limits.  I was talking about
normal, earth surface, conditions where all the interaction
between atoms happens amongst the outer electrons.  The characteristic
energies are a few electron volts per atom.  These few evs are
the inter-atomic glue in materials, and what is liberated in
energetic reactions.  If you messed with the inner electrons, that
would jump to tens of ev,  nuclear energies are in the millions of ev,
and total conversion of mass to energy gets you billions to tens of
billions of ev per atom.

With normal chemistry and materials science you get to tap only the
one or two evs, the rest of the atom is essentially dead weight.
As it happens, it takes tens of ev to lift even light atoms out
of earths potential well, and this is what makes high mass ratios
in rockets and cables or towers necessary: It takes the energy of tens
of atoms to get just one to escape.  It much easier on the moon, where
a few ev per atom suffices, and much harder on the bigger planets.  It
takes hundred of ev to get an atom off jupiter, and a simple chemical
rocket would have to have an astronomical mass ratio (but nuclear
could work).

	Back to earth-normal:  the ultimate strength of normal substances
can be calculated by looking at the in-lattice bond strength between
adjacent atoms, and dividing by the atom's mass.  A real chunk of matter
would achieve this strength only if all the atoms in it were so bonded
in the direction of the stress, and if the stress were perfectly uniformly
distributed over all the bonds.  Normal engineering materials blow it
on both counts. Grain boundaries and other lattice defects create both
some inferior bonds, and cause stress to be concentrated unevenly.
The overstressed regions break long before the rest of the material
reaches its limits, but then the load is passed to what's left, and
it all breaks. Perfect single crystals with smooth surfaces can exhibit
nearly the theoretical strengths, however, and a lot of this is retained
in bulk materials when single crystals are bonded together in a soft
matrix (often metal) which distributes the stress among them pretty
evenly.

	A nice intuitive way to express the strength to weight ratio
of a material is called "characteristic length".  It is the length
of material fashioned into a constant cross-section rope that can
just support itself when hung from one end in a uniform one earth
gravity field. (The formula is  tensile-strength/(density*1g)).
Graphite, with its strong covalent carbon-carbon bonds is the best
actually existing material. Its theoretical characteristic length
is several thousand km.  A metastable metallic version of hydrogen
that can exist at room temperature might be quite a bit better
because hydrogen has much less dead weight, but its existence is
only conjectured.

	Later editions of the CRC handbook have a NASA originated
table labelled "Mechanical and Physical Properties of Whiskers".
The indicated whiskers are actual laboratory grown, millimeter
length, single crystal rods of various substances, whose strength
and density can be measured.  The measured properties give the
following characteristic lengths:

	Graphite whiskers	961 km
	Al2O3 whiskers		527 km
	Iron whiskers		162 km
	Si3N4 whiskers		455 km
	SiC whiskers		704 km
	Si whiskers		337 km

These numbers are about 1/5 to 1/10 of the theoretical limits for the
substances.

By comparison we have todays engineering materials:

	Bulk aluminum		  10 km
        Bulk iron		  11 km
	Bulk steel		  40 km
	Nylon			  88 km
	Fiberglass		  98 km
	Kevlar			 195 km

As stated in my previous message, a strength five times that of Kevlar
would make earth elevator cables of varoius varieties possible. This
means a characteristic length of about 1000 km; a bulk material with
the graphite whisker strength above would do fine.
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End of SPACE Digest
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