Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V15_4/V15NO404.TXT

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Date: Tue, 10 Nov 92 05:09:28
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #404
To: Space Digest Readers
Precedence: bulk


Space Digest                Tue, 10 Nov 92       Volume 15 : Issue 404

Today's Topics:
                      Asteroid impact simulation
            Automated space station construction (2 msgs)
              Coverup - gravity doesn't exist? (2 msgs)
                        Early life discussions
                       Hubble's mirror (2 msgs)
                            Ice hardness
                                imdisp
                 Looking for FTP site to get pictures
                Lunar "colony" reality check (2 msgs)
                         Man in space ... )
                             Metric again
                            reality check
                           Robotic surgery
              role of meteoroids in continental rifting
                           Sounding Rockets
         Ten embarrassed questions about the moon (very long)

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Date: Mon, 9 Nov 92 21:54:45 EST
From: John Roberts <[e-mail]>
Subject: Asteroid impact simulation

-From: [e-mail] (Doug Mohney)
-Subject: Re: "Earth Gains a Retinue of Mini-Asteroids"
-Date: 9 Nov 92 18:05:25 GMT
-Organization: Computer Aided Design Lab, U. of Maryland College Park

-In article <[e-mail]>, [e-mail] writes:

->With objects sized on the order of Barringer I can well imagine the
->mushroom cloud occuring: the energy is released very rapidly and in a
->very small area. Although at a certain size the explosion simply
->blows a hole in the atmosphere, ie it is a circular curtain rather
->than a mushroom cloud.

-I wonder how much trouble it would be to try to recreate one of those events
-under controlled and monitoried conditions.

-All we need is an asteroid, a vacant plot of land, and a lot of confidence
-in our aiming.

One of the episodes of "Space Age" showed an early V-2 launch where the
rocket was allowed to land ballistically. I believe the crater it made
was 80 feet across and 40 feet deep, with virtually none of the rocket
remaining recognizable. (Thus the incentive to develop in-flight radio
contact for collection of scientific data. :-)

John Roberts
[e-mail]

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

Date: Mon, 9 Nov 1992 22:18:03 GMT
From: "Carlos G. Niederstrasser" <phoenix.Princeton.EDU![e-mail]>
Subject: Automated space station construction
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Richard
A. Schumacher) writes:
> In <[e-mail]> ssi![e-mail] ("Louis F. Adornato")
writes:
>
> >communities in this country have, IMHO, paid for those programs.  If
> >you want to think that the NASA bias toward crewed programs is based on
> >funding, I'm certainly not going to change your mind.  However, there
> >are an awful lot of people who just don't think that firing toys into
> >the solar system is as awe inspiring as having _people_ out there,
> >regardless of the volume of raw data rerturned.
>
> Well, NASA's current (shuttle) and planned (Fred) manned programs manage
> to spend awe-inspiring amounts of money and keep awe-inspiring numbers
> of people employed in proportion to the amount of work done and
> data returned, but I can't seem to find these particulars in NASA's
> charter. I thought that exploring space was the whole idea? Yet Fred
> has consumed eight billion dollars so far without one piece of flight
> hardware being bolted to another, while Magellan is about to be turned
> off in the middle of collecting new and unique data on the structure of
> Venus for want of a miserable $20 million.
>
> If NASA can't get out of the astronaut, aerospace worker and bureaucrat
> welfare business it's liable to find its plug unceremoniously pulled one
> day.

The only problem, unfortunately, is that if NASA _does_ pull out of the
"welfare business" its plug will most definitely get pulled out.  In the past
election a Clinton basically stated that Freedom was a good idea mainly because
it creates jobs.  I'm not giving this example to agree with or criticize
Clinton, but rather to show that this is the general feeling in DC.  NASA has
found out, like many other government agencies, that the only way to get money
is to be spectacular, and to employ tons of people.

Because of this I think that by and large it is not NASA that needs to be
changed, but rather the whole pork-barrelling congress/administration as well.

Two other examples: Advanced Solid Rocket Motors: NASA does not wanted Congress
gave them.  Super Conductor Super Collider: Bush pushed so much for it because
it is in Texas, a critical election state (which indeed he won)

I've purposely tried to avoid being partisan here, both Congress and the
administration are guilty.  NASA is only guilty of following the awful system
it is subjected to.
--
---------------------------------------------------------------------
| Carlos G. Niederstrasser        |   It is difficult to say what   |
| Princeton Planetary Society     | is impossible; for the dream of |
|                                 | yesterday, is the hope of today |
|                                 |   and the reality of tomorrow   |
| [e-mail]   |---------------------------------|
| [e-mail]     |    Ad Astra per Ardua Nostra    |
---------------------------------------------------------------------

--
---------------------------------------------------------------------
| Carlos G. Niederstrasser        |   It is difficult to say what   |
| Princeton Planetary Society     | is impossible; for the dream of |
|                                 | yesterday, is the hope of today |

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

Date: 9 Nov 92 22:06:20 GMT
From: Mark Benson 5-4228 <benson@gemed>
Subject: Automated space station construction
Newsgroups: sci.space

In article <[e-mail]> [e-mail]
(Frank Crary) writes:

>Is anyone looking into robots with very limited autonomy? That is,
>under direction from a human, but able to execute instructions on
>their own for periods of, say, ten seconds?

Yes, I believe so.  SSF had (and I believe still has) a program for the
Flight Telerobotic Servicer (FTS).  Under Phase B of the contract, various
options were studied, ranging from basically remote control to releatively
sophisticated, knowledge / rule based AI for functions ranging from task
planning and collision avoidance functions.  Among these possible levels was
a basic "learn and play" mode, where the operator would do the first one, and
then basically just monitor the subsequent 'n' executions of the activity.
I was working for Martin-Marietta at the time, and heard they won the
contract.  Haven't heard much since.

In fact, at the time, there was such a thing as the NASA / NBS Standard
Reference Model (NASREM), describing various levels of control over such
a system, from task planning and resource scheduling down to individual joint
motions and limit checks (kinematics).  At the time, we evaluated just what
it meant to take control at any given level of the architecture -i.e., tell
the beast to go change out a reaction wheel at a given location, vs. moving
the control stick while watching the end effector through strereo vision gear.

Now, this was in early '88.  By now there should be flight experminents
coming up in the next year or so to prove some of this out - I haven't
checked detailed shuttle manifests lately.

I also suspect there are several production lines that have robots going for
longer than 10 sec at a stretch without manual intervention.  One could argue
that lots of NC equipment meets this definition.

Mark Benson        [e-mail]
GE Medical Systems, Milwaukee, WI

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

From: Dave Jones <[e-mail]>
Subject: Coverup - gravity doesn't exist?
Newsgroups: sci.space

Date: 9 Nov 92 20:22:15 GMT
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John Roberts ([e-mail]) wrote:
>
> There's an apple tree on the NIST grounds that's a direct descendant of the
> tree Isaac Newton was sitting under when he thought up the laws of gravitation.

Hmmm.  After that fact was disclosed in your first-day orientation class,
were you sent out to fetch a can of striped paint ?

--
||Halloween Candy: the office snack    |
||from Nov. 1st onwards............... |Puff the Magic Dragon
||-------------------------------------|Lived by the sea
||Dave Jones ([e-mail])|Who knows what's in the autumn mists
||Eastman Kodak Co. Rochester, NY      |In the mind of Yadallee?

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

Date: Tue, 10 Nov 1992 01:36:57 GMT
From: david michelson <[e-mail]>
Subject: Coverup - gravity doesn't exist?
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Dave Jones) writes:
>John Roberts ([e-mail]) wrote:
>>
>> There's an apple tree on the NIST grounds that's a direct descendant of the
>> tree Isaac Newton was sitting under when he thought up the laws of gravitation.
>
>Hmmm.  After that fact was disclosed in your first-day orientation class,
>were you sent out to fetch a can of striped paint ?

Back off, Dave Jones! ;-)  John Roberts is not *totally* out to lunch.

There are (were?) a couple of "Newtonian" apple trees planted
outside the Triumf Meson Facility (world's largest cyclotrom) at the
University of British Columbia in Vancouver, too.  I gather that Cambridge
University makes apple tree seeds which are direct descendants of the
trees from the orchard where Newton pondered available to deserving
institutions....

--

Dave Michelson
[e-mail]

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

Date: 10 Nov 92 00:24:44 GMT
From: Paul Dietz <[e-mail]>
Subject: Early life discussions
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:

>There was another spate of discussion on early life recently, some of
>which mentionied clay substrates. I thought this reference might be
>of interest to those debaters:
>
>    Oligomerization of Ribonucleotides on Montmorillonite:
>    Reaction of the 5'- Phosphorimidazolide of Adenosine
>        James P. Ferris and Gozen Ertem
>    Science, 4-Sep-92, V257, p1387-1389


Now, tell us all about the experiments that made pure
5'-Phosphorimidazolide of Adenosine with a spark from CO2, nitrogen
and water.

It's a fine tradition in origin-of-life research to assume away
your starting materials.  Rather a waste of time, IMO.

    Paul F. Dietz
    [e-mail]

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

Date: 9 Nov 92 22:41:08 GMT
From: "William H. Jefferys" <[e-mail]>
Subject: Hubble's mirror
Newsgroups: sci.astro,sci.space

In article <[e-mail]> [e-mail] (Claudio Egalon) writes:
#Henry Spencer is right. Although it was sometime ago that I read an
#article in Physics Today- which explained very nicely the real messed
#up-, I still recall that there was three diferent instruments that were
#used to measure the curvature of the primary mirror. Two of them
#used refraction principle and one of them used the reflection
#principle (don't remember the details so I may commit some
#mistakes. If so, I apologize). The results of the other two instruments
#that used the refraction principle to measure the mirror curvature
#matched up but... the measurements produced by the one that used
#reflection, reflective null corrector, was different and, since it was
#thought to be superior to the other two,  no one bottered about
#finding out why the discrepancy between the measurements... of
#course untill they found out that there was something wrong with
#Hubble.
#
#*However* as  I recall (and I may be wrong) the error in the RNC
#came along because the WRONG surface in the instrument was
#providing the reflection and not that because the instrument was
#built improperly. Aparently there was an scratch in a surface that was

No, the reflective null was built improperly. Here's what
happened: The field lens was supposed to be aligned to the
cell by using a precisely machined Invar rod, whose length
was traceable to NBS standards. A laser was used to align
the end of the bar to the cell. In order to guarantee that
the laser was reading just the end of the bar (which was
rounded), an end cap with a small hole was placed over the
end of the bar. The end cap extended 1.3 mm further than
the end of the bar, and was painted black so that there
would be no return to the laser from the end cap. Unfortunately,
as it turned out, a fleck of the black paint got scraped off,
and a significant return from the end of the bar was obtained.
Thus, the bar was positioned too far away from the laser, and
the other end of the bar (which was positioned against the
field lens) was 1.3 mm from where it should have been.

In order to misposition the field lens, they people who did
this _had to shim out the lens cell with washers_!!! The
cell had been properly built, but when the lens didn't fit
where they thought it should (in the wrong position), they
kludged it to _make_ it fit.

You are right that the refractive null and the inverse null
agreed with each other, but not with the reflective null. Why
the engineers didn't see the red flag waving by 2 out of
3 vote, and the fact that they had to shim out the lens position
in the cell, is beyond me.

#suposed to be black, for absorbing incoming radiation, and it was this
#scratch that worked as the WRONG reflecting surface. So,  that how
#the wrong prescription came about. Another reference for the
#investigation on the problem of the mirror was the report put out by
#Lew Allen's review board (I guess I have a copy of it at home and I
#am confindent that you people can get one from NASA but I do not
#know whether they  will charge you or not). Maybe, not oddly
#enough, there were other complaints about the handling of the
#project  like people did not like to be bothered with criticism (read
#peer review)... So aparently, the problem was both technical and
#arrogance.
#
#Claudio O. Egalon

Bill

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

Date: Mon,  9 Nov 92 19:25:01 PST
From: Brian Stuart Thorn <[e-mail]>
Subject: Hubble's mirror
Newsgroups: sci.astro,sci.space

If there is a perfect mirror presumably sitting at Kodak, why doesn't NASA
simply return Hubble to Earth and replace the faulty mirror?

I know, I've read many times that returning Hubble to Earth is *not* an
option, but I can't figure out WHY. At 24,000 lbs, Hubble is well within
the Shuttle's landing cargo capacity, and since the only part of Hubble
likely to suffer damage during a 3g return is primary mirror (which
will be replace anyway) I don't understand why NASA doesn't simply swap
mirrors. NASA has already spent a fortune building COSTAR and ESA is
building replacement (no wobble) solar panels. With three spacewalks, the
Shuttle crew will be hard pressed to get all the work done.

Doesn't bringing Hubble home for repairs make more sense than jerry-rigging
and dangerous EVAs on orbit?

-Brian

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

Date: Tue, 10 Nov 1992 02:15:43 +0000
From: Andrew Haveland-Robinson <[e-mail]>
Subject: Ice hardness
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:

>-From: [e-mail] (John F. Woods)
>-Subject: Re: Swift-Tuttle Comet a threat to earth?
>-Date: 2 Nov 92 17:28:43 GMT
>
>[e-mail] (Robert Sheaffer) writes:
>->I should think that, given that a comet consists largely of ice and
>->other volatiles, even one good-sized H-bomb placed directly into the
>->nucleus would pretty much eliminate any "threat to earth". Seems it
>->would be mostly vaporized and scattered.
>
>-The thermal mass of a several-km-diameter comet is quite a bit larger than
>-you think.  Furthermore, most of it is "ice" at just a few Kelvin (depending
>-on how far out its orbit takes it, and how long it spends there), which means
>-that "ice" is going to be every bit as hard as the formerly-molten silicate
>-you're standing on...
>
>A number of science fiction writers seem to assume that water ice at
>cryogenic temperatures would be many times stronger than ice at slightly
>below freezing. Is there any indication that this is true?
>
>John Roberts
>[e-mail]

"Air temperatures down to -50'C make the near surface ice a thousand times
stiffer than the basal ice, which geothermal heat from the underlying rock
can bring to near melting point"

                                    Richard Frolick, Brit Antarctic Survey
                                            Physics World Vol5/11 p21, IOP

I would assume that this is an indication that cryogenic ice is pretty
hard stuff...

Andy.

+-----------------------------------------------------------------------+
| Haveland-Robinson Associates   | Email: [e-mail]         |
| 54 Greenfield Road, London     |        [e-mail] |
| N15 5EP England. 081-800 1708  | Also:  0621-88756 081-802 4502       |
+-----------------------------------------------------------------------+
>>>> Those that can, use applications. Those that can't, write them! <<<<

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

Date: Tue, 10 Nov 1992 02:04:41 GMT
From: Earl W Phillips <[e-mail]>
Subject: imdisp
Newsgroups: sci.space,sci.astro

Does anyone know what images are used for the imdisp
software, and where to get 'em?

*****************************************************************
*                                    | ====@====      ///////// *
* [e-mail]|     ``________//         *
*                                    |       `------'           *
*                 -JR-               | Space;........the final  *
*                                    | frontier...............  *
*****************************************************************

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

Date: 9 Nov 92 19:00:05 CST
From: [e-mail]
Subject: Looking for FTP site to get pictures
Newsgroups: sci.space

I'm looking for an FTP site that accepts ANONYMOUS logins.

I'd like to get space images... telescope images, etc.  I
have heard that NASA has such public access sites.

Email replies preferred.

Michael McGinnis                Internet: [e-mail]
Computer Center                   Bitnet: mcginnis@ukanvax
University of Kansas               Voice: [phone]
Lawrence, KS  66045                  FAX: [phone]

Rust never sleeps.

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

Date: Mon, 9 Nov 1992 23:09:01 GMT
From: Louis Giglio <[e-mail]>
Subject: Lunar "colony" reality check
Newsgroups: sci.space,alt.sci.planetary

In article <[e-mail]>, [e-mail] (Allen W.
Sherzer) writes:

|> >* A livable atmosphere is mostly nitrogen, not oxygen.
|>
|> Which comes as a rude suprise to the astronaust who lived
|> weeks on end on pure oxygen.
                   ^^^^ ^^^^^^

I'm not agreeing or disagreeing with either party, but I want to point
out that
this can't possibly be correct.  The oxygen had to be diluted with
something.
They would have died otherwise.



Louis Giglio
Severe Storms Branch
NASA/GSFC

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

Date: Tue, 10 Nov 1992 01:50:30 GMT
From: david michelson <[e-mail]>
Subject: Lunar "colony" reality check
Newsgroups: sci.space,alt.sci.planetary

In article <[e-mail]> [e-mail] (Louis Giglio) writes:
>In article <[e-mail]>, [e-mail] (Allen W.
>Sherzer) writes:
>
>|> >* A livable atmosphere is mostly nitrogen, not oxygen.
>|>
>|> Which comes as a rude suprise to the astronaust who lived
>|> weeks on end on pure oxygen.
>                   ^^^^ ^^^^^^
>
>I'm not agreeing or disagreeing with either party, but I want to point
>out that
>this can't possibly be correct.  The oxygen had to be diluted with
>something.
>They would have died otherwise.
>
>Louis Giglio
>Severe Storms Branch
>NASA/GSFC


Suffice it to say that Mercury, Gemini, and Apollo astronauts worked in a
5 psi pure O2 environment.  This simplified the environmental control system
and eliminated the need to purge N2 prior to EVA.

Didn't Skylab add a small amount of nitrogen to the mixture in an effort to
reduce the fire hazard and improve the acoustics?  Perhaps someone can fill
in the details.

--

Dave Michelson
[e-mail]

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

Date: Tue, 10 Nov 1992 01:58:23 +0000
From: Andrew Haveland-Robinson <[e-mail]>
Subject: Man in space ... )
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:

>>>>>   What will happen if the space suite of an austronaut gets ripped in> space> ?
>>>>
>>>Ever put your hand up against the nozzle of vacuum cleaner? Your skin
>>>will hold about 1 atmosphere pressure nicely.
>>>
>>>Astronauts might wear spacesuits without gloves for delicate work!
>>
>> Ah well... I stand corrected...  Thanks for the explanation, it still

> Anyone who thinks you get 15psi of `suck' from a vacuum cleaner is
> seriously in error.  A typical reduction in pressure (nozzle to atmosphere)
> is about 2--4 inches of water: remember that one atmosphere is 32 feet of
> water approximately.  You need a much larger diameter, and a much larger
> rotation speed, to get a bigger pressure difference from a centrifugal
> pump for air, as the density is so low. To get a decent vacuum from
> something of a similar size you need a displacement-type pump (i.e. one
> with valves, such as a diaphragm or rotary vane pump).
>
> You can certainly plug up a hole about 1/4" diameter with your finger for at
> least a minute -- I've done it (got a leak rate of about 10^-8 mb l/s) ,
> but I wouldn't advise trying a larger area for a long time as the skin
> isn't sufficiently rigid.  I do remember a story of someone trying --
> he was in hospital for a long time.
>
>Tim Kingsmill-Vellacott
>Atmospheric, Oceanic and Planetary Physics
>University of Oxford, UK.
>[e-mail]  preferred


It's a little more than 2--4 inches of water!

I have a VAX, (no not the DEC thingy!)... and thought I'd actually do this
experiment with a rigid pipe 7ft in length.

It was struggling, some water was getting through because I could feel it
it the flexible section...  I then tilted the straight bit, and the water
flowed when the apex was about 6ft above the surface of the water.

Pressure difference = 14.7*6/32 = 2.76 psi

Doesn't sound a lot really, and it's quite a powerful vacuum cleaner (1kW)
Puts a real vacuum into perspective!  Based on this I certainly wouldn't
like to wear a gloveless space suit if the internal pressure is 5 psi...
2.76 psi would be bad enough.

                 /\ 7ft
       _       /  |
     +---+   /    |
     |VAX|_/      |
     |||||        |
    ~~~~~~~       |
                  |
                  |
                  |
                  |
                | | |
                |~|~|
                ~~~~~

Andy.

+-----------------------------------------------------------------------+
| Haveland-Robinson Associates   | Email: [e-mail]         |
| 54 Greenfield Road, London     |        [e-mail] |
| N15 5EP England. 081-800 1708  | Also:  0621-88756 081-802 4502       |
+-----------------------------------------------------------------------+
> Some dream of doing great things, while others stay awake and do them <

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

Date: Mon, 9 Nov 92 22:10:03 EST
From: John Roberts <[e-mail]>
Subject: Metric again

-From: [e-mail] (Bruce Dunn)
-Subject: Metric again
-Date: 8 Nov 92 17:03:22 GMT
-Organization: MIND LINK! - British Columbia, Canada

-> John Roberts writes:
->
-> By the way, I think you'll be much happier in the long run if you do your
-> calculations in SI (metric) units. I often do simple calculations in
-> standard
-> units, but the tough problems are much more easily handled using SI.

-        I am delighted to find that NASA seem finally to be moving toward
-metric, not just in theory but in reality.

-        Does anyone know if NASA uses degrees C for reporting things like the
-Shuttle cabin temperature and the temperature of experiments?

The US officially became "metric" on October 1, I think. I'm pretty sure
what this means is that government publications are required to include
the SI units (but not forbidden to also include the "standard" units). I
don't know of plans to change highway mile markers and speed limits any time
soon. (Note: these are my own impressions - that's not the part of NIST I
work for.)

There are risks associated with changing the working units of a working
system - if the Shuttle launch people have given up on feet elevation and
nautical miles downrange, I'm not aware of it. I don't know what effect this
recent policy decision will have on SSF - it *was* planned to use standard
units.

I'm pretty sure the furnaces, etc. have been using SI units all along.

John Roberts
[e-mail]

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

Date: Mon, 9 Nov 92 23:52:38 EST
From: John Roberts <[e-mail]>
Subject: reality check

-From: [e-mail] (Josh 'K' Hopkins)
-Subject: Re: Lunar "colony" reality check
-Date: 8 Nov 92 22:27:41 GMT
-Organization: University of Illinois at Urbana

[e-mail] (Nick Szabo) writes:
->* Because of transportation costs for recycling equipment,
->  recycling on the moon is far more expensive than recycling on
->  earth.  Even on earth the best attempt at building a livable,
->  working biosphere masses hundreds of thousands of tons and leaks
->  over tens of tons of air per year.

-This Biosphere was of course designed for Earth conditions.  A lunar station
-won't have plate glass windows or it's own rainforest.  Besides, using current
-launch costs only proves that Moon bases aren't economical now -- something I
-won't debate you on.  Assuimg that none of the current attempts to lower launch
-costs will succeed is as ludicrous as auuming they all will.

Biosphere II was in the news again last week. They had trouble a while back
with excess production of carbon dioxide. Now the problem is decreasing
oxygen levels. Apparently some of the team members are breathing supplementary
oxygen.

->* Hydrogen is extremely innefficient to transport from
->  earth.

-So get it from comets.  If we don't colonize the moon, just what do you think
-will be the market for your comet resources?

So ship it in the form of nylon. Plenty of hydrogen, nitrogen, and carbon,
and able to withstand high impact velocity, which should save considerably
on delta-v to land it on the moon.

John Roberts
[e-mail]

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

Date: Tue, 10 Nov 92 00:19:53 EST
From: John Roberts <[e-mail]>
Subject: Robotic surgery

Some weeks ago, Allen challenged somebody (Nick, I think) to undergo
surgery by robot. Well, now's his chance. In the news today, a robot has
just been used to perform a significant part of a hip operation.

The function of the robot was to act as a precision milling machine - it
cut away the interior of the bone in a shape to exactly fit an implant,
with much greater precision than a human surgeon could have done it.
The bone was clamped rigidly in place, and the dimensions of the cut were
specified ahead of time, so it wasn't a situation calling for extreme
robotic intelligence, but still it's an important first step. (There was
also no lightspeed delay to worry about. :-)

There was speculation that the technique could eventually be extended to
soft tissues - perhaps even the brain. The robot would never do the whole
job itself - there will continue to be human attendants and a supervising
surgeon present.

John Roberts
[e-mail]

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

Date: 9 Nov 92 22:55:41 GMT
From: Joe Cain <[e-mail]>
Subject: role of meteoroids in continental rifting
Newsgroups: sci.astro,sci.space,sci.geo.geology,alt.sci.planetary

In article <[e-mail]> [e-mail] (Dave Jones) writes:
>keith farmer;S10000 ([e-mail]) wrote:

>> In article <pad.720924805@probitas> [e-mail]
(Paul A Daniels) writes:
>> If I remember correctly, Pangaea and Gwandonaland are two names fro
the super-continent...

This thread has been perking along in sci.astro for about a week now
starting with the worry over the August 14, 2126 "end of the world."

Non-geologists appear to be confused by the time scale of events about
which such events have occurred. All geologic reconstructions of the
continents have been done for the Phanerozoic Eon (570 My ago to
present), and mostly late in this eon, whereas meteoroid
bombardment, based on lunar evidence, decreased to its present
level some 1000 My ago. Thus although one cannot rule out a meteoroid
hit having something to do with initiating such a rifting, the only
evidence is for "normal as seen today" rifting from tectonic
processes involving thinning of crust mainly from internal heating.

The really big hits that Earth must have taken were of course in the
Hadean (4.6-3.8 Gigayears ago) decreasing in size and intensity as on
the Moon during the Archean when the continents being formed must have
been relatively small, and possibly being significant only in the early
Proterozoic (2.6 - 0.6 Gy) when the continents began to increase in
size as the Earth continued to cool (ca 100 deg K per Gy).

Many of us would be interested in evidence to the contrary on these points.
The biggest hit of all, that whose debris is theorized to have
produced the Moon, must have occured very early. Has anyone seen
discussions on its epoch?




Joseph Cain        [e-mail]
[e-mail]        scri::cain

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

Date: Tue, 10 Nov 1992 00:40:30 GMT
From: John Urbanski <[e-mail]>
Subject: Sounding Rockets
Newsgroups: sci.space

Anyone have / know where I can get data
on sounding rockets.

Thanks for any info you can send me .


john



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

Date: Tue, 10 Nov 1992 02:24:09 GMT
From: "robert.f.casey" <[e-mail]>
Subject: Ten embarrassed questions about the moon (very long)
Newsgroups: sci.space

>In article <[e-mail]>, [e-mail] (Henry Spencer) writes...
>>Finally, there is a well-known and well-understood
>>human tendency to remember the unusual and forget the mundane.  Yes, odd
>>things sometimes happen at the full moon... but to draw any meaningful
>>conclusions from this, you have to figure in the times when odd things
>>happened without a full moon, or the times when nothing noteworthy happened
>>during a full moon.  Coincidences do happen; to establish correlation, you
>>have to look at the non-coincidences too.
>>--
One of my Chinese friends told me that the crescent Moon is their time for
strange events and such.  Which means that people don't agree on the
same phase of the Moon.  Which pretty much negates the Moon related
strangeness connection.

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End of Space Digest Volume 15 : Issue 404
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