Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V11_2/V11_295.TXT

Internet Message Format | 1991-07-08 | 18KB

Return-path: <[e-mail]>
X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/[e-mail] (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests)
          ID </afs/andrew.cmu.edu/usr1/ota/Mailbox/sa=zLBq00VcJME2E5M>;
          Sat, 21 Apr 90 01:55:26 -0400 (EDT)
Message-ID: <Aa=[e-mail]>
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Sat, 21 Apr 90 01:54:56 -0400 (EDT)
Subject: SPACE Digest V11 #295

SPACE Digest                                     Volume 11 : Issue 295

Today's Topics:
        Re: What happened with the Barium drop
       Re: Drake Equation (was Re: Interstellar travel)
       Re: Drake Equation (was Re: Interstellar travel)
                   Re: SETI
              Re: Decompression and 2001
              Re: Decompression and 2001
              Re: Drake Equation
              Re: Fermi Paradox
              Re: Ariane Launch Failure
            Re: 2001 Decompression
----------------------------------------------------------------------

Date: 20 Apr 90 21:24:59 GMT
From: ogicse!plains![e-mail]  (Glen Overby)
Subject: Re: What happened with the Barium drop

In article <[e-mail]> [e-mail] (Jack Vinson) writes:
>What happened with the barium canister that was to be released from
>PegSat Sunday morning?  I haven't seen anything in the local newspaper
>or any quick blurbs here.  Did I miss it when skipping one of the long
>Headline postings?

I haven't seen any follow-up reports on the results of this drop.  I was
hoping there would be.

I, myself, stepped away from my monitor to watch for the drop, but I'm not
sure I ever saw it.  From the sites listed (MA, TX, CA), I expected to be
able to see the drop from where I am (46 52 N / 96 48 W city -- North of TX,
and about halfway between MA and CA [the center of North America is in ND]),
but I'm not sure I did.  From the house where I live, I do not have a very
clear view of the east and north horizons, so about 10 minutes after the
scheduled drop, I moved north where I had an "ok" view of the north horizon,
and I saw what I would normally consider to be Aurora.  Not very exciting.

I can see the MilkyWay from in town on a good night, so I didn't figure I'd
have to get out of town.

Anybody see the drop?  How long did each color phase last?
--
        Glen Overby    <[e-mail]>
    uunet!plains!overby (UUCP)  overby@plains (Bitnet)

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

Date: 20 Apr 90 17:24:39 GMT
From: att!cbnewsl!moss![e-mail]  (Forrest Gehrke,2C-119,7239,ATTBL)
Subject: Re: Drake Equation (was Re: Interstellar travel)

In article <[e-mail]>, [e-mail] (Daniel Briggs) writes:
> And one more followup to my own article.
>
> It turns out that 60 Hz loses, guys, because of galactic background
> radiation.  There are a lot of natural things out there that are putting
> out a fair bit of energy at those frequencies.  It seems that as far as
>  [   ]
> I looked in _Radio Astronomy_, 2nd Ed.  by John Kraus, and he has a small
> interoduction to SETI.  It's only about 5 pages long, but convers the basic
> mechanics of an interstellar communications link.
>   I'd say that if you're interested in the subject, this would be a
>   darned good place to start looking.


John Kraus is also a well-known antenna expert, especially in the
field of arrays.  A study of his book "Antennas" (not real positive
of the title) will help to explain why much of the MW being radiated
by TV stations is NOT being wasted on space.

The W8JK rotatable array, famed among radio amateurs and a forerunner
of the Yagi array, is attributable to John Kraus.

Hi Power pulsed microwave radars are the best source today for a
signal that might be detected at +LY distances.  Unfortunately,
these do not operate continuously and when they are operating they
seldom stay on one path for very long.  In any military
operation it's downright dangerous to do so for more than a few pulses.

Forrest Gehrke [e-mail]  k2bt

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

Date: 21 Apr 90 02:00:05 GMT
From: uvaarpa!murdoch!astsun8.astro.Virginia.EDU![e-mail]  (Robert W. Spiker)
Subject: Re: Drake Equation (was Re: Interstellar travel)

In article <[e-mail]> [e-mail] (Jim Meritt) writes:
>
>Why use radio waves?  You have a very powerful emitter centrally located
>already.  Why not just dump a mass into the central star of something
>that clearly does not belong there?  A line for technium in the
                                        ^^^^^^^^^^^^^^^^^
>spectroscopic examination of a star should be a REAL indicator of
>a technological civilization nearby.
>
>Any ideas on how much of what could be used?
>
Actually technetium is an element which has been *observed* in stellar
atmospheres of certain supergiant stars, known as S stars.  Technetium
(which has a half-life of oh, 100,000 years) is produced by the
s-process in the star's atmosphere.  The s-process forms elements
heavier than iron by slow capture of free neutrons onto iron and similar
elements.  It's something we know a good bit about, without having to
resort to ETs to explain it.

(There's also something called the r-process which is a little bit
trickier, but hey, no one's got all the answers.)
Robert W. Spiker, UVa Dept. of Astronomy
--------------------------------+ It is truly written that a man has five
[e-mail] | times as many fingers as ears, but only
  or @bessel.acc.virginia.edu   | twice as many ears as noses.

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

Date: 20 Apr 90 06:26:23 GMT
From: news-server.csri.toronto.edu!qucdn![e-mail]  (Arnold G. Gill)
Subject: Re: SETI

In article <[e-mail]>, [e-mail]
(John Roberts) says:
>
>I know that modern radio telescopes are amazingly sensitive, but I don't know
>the exact magnitude of their abilities. With their current transmitters and
>receivers, how far across space could Goldstone or Arecibo communicate with
>comparable devices?
     This is all from memory, but I had read that with Arecibo size dishes,
Galaxy wide communication could be achieved with current technolgy or a factor
10 improvement.  Not impossible by any means.
-------
 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
|  Arnold Gill                        |                                     |
|  Queen's University at Kingston     |     If I hadn't wanted it heard,    |
|  BITNET   : gilla@qucdn             |       I wouldn't have said it.      |
|  X-400    : [e-mail]  |                                     |
|  INTERNET : [e-mail]  |                                     |
 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

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

Date: 20 Apr 90 19:11:53 GMT
From: groucho![e-mail]  (Steve Emmerson)
Subject: Re: Decompression and 2001

[e-mail] (Henry Spencer) writes:

>As any scuba diver will tell you, holding your breath during decompression
>is a thoroughly bad idea.  The alveoli don't object to low pressures much
>(remember 3psi of pure oxygen in pre-shuttle US spacecraft), but they are
>not mechanically strong and it's easy to damage them if there is more
>pressure inside than out.

Quite correct.  The technical term is "air embolism" in which the lungs
rupture, releasing gas into the body.  This has happened in as little as
six feet of water from taking a deep breath and ascending to the surface.

The pressure differential between the surface and six feet is much
less that between one atmosphere and vacuumm.

I wouldn't hold a deep breath.

Steve Emmerson        [e-mail]        ...!ncar!unidata!steve

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

Date: 20 Apr 90 16:58:14 GMT
From: hplabsb![e-mail]  (David Smith)
Subject: Re: Decompression and 2001

In article <[e-mail]> [e-mail] (Andrew Bennett) writes:
>I have read (from multiple sources) that an individual should be able to
>survive about 30 sec. in a vacuum (give or take, depending on the individual).

I had read the same figure before "2001" came out.  But the keyword here is
"survive."  The same sources had said that the time of useful consciousness
is about 8 seconds.  Dave went longer than that before he pulled the lever.
--
    David R. Smith, HP Labs    | "It is said that St. Patrick drove the
    [e-mail]    | snakes out of Ireland.  They were last seen
    [phone]        | selling junk bonds."  -- Johnny Carson

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

Date: 18 Apr 90 22:19:48 GMT
From: zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!nic.MR.NET!timbuk![e-mail]  (Lou Adornato)
Subject: Re: Drake Equation

>From article <[e-mail]>, by [e-mail] (Dan Tilque):
> [e-mail] writes:
...
> Since we've been listening to the sky at radio frequencies for > 40
> years now and haven't discovered any alien generated signals, it's
> probably safe to say that there are no civilizations like ours within
> that 50 ly radius.

The reason we're obvious 50ly out is that we started generating major
league radio noise ourselves 50 years ago (clue - how far does a radio
wave travel in 50 years?).  ONLY if you postualate that ALL
civilizations in this galaxy started broadcasting at the same time
(which is a real strecth except for the trivial case) does the lack of
received signals imply a minimum distance between us and any
neighbors.

One thing to keep in mind about the Fermi paradox is that the sky is
_big_, and there's a lot of radio spectrum to cover.  Not only that,
but how large a sample is necessary to isolate an artificially
generated signal from natural radio noise (remember when pulsars where
thought to be artificial constructs?).  There's an all sky/all freqs.
survey going on right now.  I haven't heard any news from it for a
while, but I'm pretty sure the work isn't finished yet.

>The point that people are forgetting is the impracticality of advanced
>civilisations using radio signals, especially if they're technologically
>advanced enough to have colonised other worlds and thereby need to keep in
>contact. We are acting like American Indians a couple of hundred years ago
                             Native Americans
>looking for smoke signals from a neighboring tribe to indicate they're
>presense when they're using CB radios.

>If they are +100
>years in relation to us they are probably sending heaps of stuff but it is
>unlikely to be radio signals
>...
>Think just how small a unit of 100 years is in relation to the entire history
>of life on Earth (in billions of years).

What you're saying is that there is a narrow window during which a
civilization can be detected, and it's narrow enough in relation to the
length of time between the evolution of intelligent specieces, that
it's practically zero.  Nice idea, but for perhaps the wrong
reasons...

I'm certainly willing to conceede that there are things in the universe
that we don't understand. However, I'm not sure I can accept that
there's an information medium that can travel through a vacuum at (or
faster) than light over long distances, of which we are completely
ignorant.  The physicists have pretty well mapped out the forms of
energy in the universe.  Even if there is such a medium, radio waves
are pretty handy, and will probably be used pretty extensively by any
advanced civilization.  You have to accept some basic assumptions, even
in this field, if you're going to do _anything_ useful.

One possible limit to your window is data compression.  If I can be
allowed to postulate that a civilization much advanced from ours is
going to have even more spectrum crowding than we are presently
experiencing, then there's probably some pretty advanced data
compression algorithms thrown on top of an alien language different
from anything we've ever seen (unless _Star Trek_ is right and all
aliens speak American English).  It may well be that our information
technology isn't able to identify these signals as artificial.  Picture
one of our scientists in 1940 trying to figure out a predictively
encoded PCM voice signal, or even the data stream from a 9600 baud
modem.

Another possible limiting factor is creeping conservatism.  The idea is
that beings with very long lifespans (postulating that advanced
civilisation == longer (indefinite?) lifespans) is going to become very
cautious.  This is based primarily on observations of humans and
extrapolations, but the process is pretty logical; taking a risk only
makes mathematical sense if you're not risking much.  Immortality
makes "slow and cautious" look really good, and anything else is
long odds.  So, it could well be that any civilization that acheives
sufficiently long lifespans will take extrordinary measures to conceal
it's presence.

>The only real way to find out is to go take a look.

It's a mighty big universe, it would be nice if we could narrow it down
just a little.  Especially when you're talking about hundreds (or
thousands, or, if you're Carl Sagan, BILLions and BILLions) of years
between launching a probe and getting the results.

Lou Adornato    |  Statements herein do not represent the opinions or
Cray Research   |  attitudes of Cray Research, Inc. or its subsidiaries.
[e-mail]    |       (...yet)

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

Date: 20 Apr 90 16:22:18 GMT
From: swrinde!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Fermi Paradox

In article <[e-mail]> [e-mail] (Lou Adornato) writes:
>There are only 2 elements that are capable of being the basis of
>creating long, complex molecules, and those are carbon and silicon...

Actually, silicon makes a lousy carbon substitute.  It's just different
enough chemically that it prefers to clump up in rings and the like
rather than forming long chains.  The only way you get long silicon chains
is to alternate silicon and oxygen -- that's what silicone (note the E)
compounds are.  Silicones are much too stable to be useful for life at
normal temperatures, although they might perhaps be useful in some
high-temperature solvent like molten sulfur (!).
--
With features like this,      |     Henry Spencer at U of Toronto Zoology
who needs bugs?               | uunet!attcan!utzoo!henry [e-mail]

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

Date: 20 Apr 90 16:28:59 GMT
From: idacrd![e-mail]  (Robert McGwier)
Subject: Re: Ariane Launch Failure

From article <[e-mail]>, by [e-mail]:
> Some more news from the ESA Information Retrieval System:
>
>  ARIANE 44L booster exploded Feb. 22 because a piece of cloth lodged in a
>  water pipe, an Arianespace accident inquiry board reported.
>
>  CLOTH LODGED IN WATER LINE BLAMED FOR ARIANE EXPLOSION
>


As a frequent flyer on Ariane (and they don't give us a DISCOUNT, hey
how do you discount zero ;-)  AMSAT folks were pleased as punch to hear
that the launch vehicle was vindicated.  We are negotiating a ride on
the first Ariane 5 and these little incidents really slow down the
rides when they are the fault of the launcher technology and not a very
human mistake.

Bob

--
____________________________________________________________________________
    My opinions are my own no matter    |    Robert W. McGwier, N4HY
    who I work for! ;-)            |    CCR, AMSAT, etc.
----------------------------------------------------------------------------

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

Date:         Fri, 20 Apr 90 16:13:29 CDT
From: John Nordlie <[e-mail]>
Subject:      Re: 2001 Decompression



>I have read (from multiple sources) that an individual should be able to
>survive about 30 sec. in a vacuum (give or take, depending on the individual).
>Your ear drums would probably rupture, you'd get a bloody nose and you'd have
>a sinus headache not to be believed.  Your eyes and tear ducts will not fare
>well, either (some bleeding from the ducts).

>The most serious problem(s) are damage to your lungs (the avolii(sp?) don't
>like low pressures) and the 'bends' (nitrogen nucleation in the body).  So
>holding your breath is a good idea, for your lungs' sake.


You got the part about the bends right, but as for holding your breath,
well, that would be a very bad idea.  When I took up SCUBA diving,
the one thing my instructor kept drilling into us was KEEP BREATHING.
If you take in a breath and hold it while swiming toward the surface,
you stand a very good chance of blowing a lung.  The pressure generated
by the water at depth compresses the air in your lungs, so you need
to take in air at greater pressure (compared to sea level) than normal
to fill them.  When you ascend, the pressure from the water drops,
the air in your lungs expands, and POP!

I too have heard that you can survive about 30 seconds in a hard
vacuum, but don't hold your breath (ruptured lungs cause internal
bleeding and eventually you will drown in your own blood).  This
value was determined in the '50s (I think), when goats were placed
in chambers and exposed to a hard vacuum.  The animals expanded to
about twice their normal size (blood at body temp in a hard vacuum
boils quite vigorously).  The animals were hurt, but survived exposure
times of up to about 30 seconds.  I didn't see Dave swell up like
a balloon in 2001, but the scenes from 'Outland' where more realistic
(I think, anyway).

--------------------------------------------------------------------
" I compute, therefore I am. "              JC Nordlie
--------------------------------------------------------------------

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

End of SPACE Digest V11 #295
*******************