Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V15_3/V15NO362.TXT

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Date: Sat, 31 Oct 92 05:03:58
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #362
To: Space Digest Readers
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Space Digest                Sat, 31 Oct 92       Volume 15 : Issue 362

Today's Topics:
                   Galileo High Gain Antenna Update
                 Gore Blames George Bush for Big Bang
              Re: Swift-Tuttle Comet a threat to earth?
                           re HRMS for ETI
                Smith-Tuttle Comet a threat to earth?

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Date: 31 Oct 92 06:48:38 GMT
From: Cameron Newham <[e-mail]>
Subject: Galileo High Gain Antenna Update
Newsgroups: sci.space

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

 >
 > I've had a question and I don't know who to ask, so I'll do it here.
 > This question really doesn't require an answer to me, I'm just
 > wondering if the High Gain Antenna problem could be helped...
 >
 > So the question 1) does HST have the capability of imaging Galileo
 > when it gets close to earth?  and 2) would this help the engineers at
 > all?
 >

I don't think HST has the ability to slew fast enough to image Galileo.

-cameron.

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

Date: 30 Oct 92 21:12:24 GMT
From: Tim Stevens <[e-mail]>
Subject: Gore Blames George Bush for Big Bang
Newsgroups: talk.politics.space,sci.space

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


|> >       The Florida Institute of Technology is the first school in the
|> > country to offer a degree in space technology.  Many of its graduates
|> > go on to work at NASA, Grumman, Lockheed, and Martin Marietta.  The
|> > school is located about 25 miles south of Cape Canaveral.  Gore
|> > echoed his remarks in Florida during a visit later in the day to the
|> > U.S. Space and Rocket Center in Huntsville, Alabama.
|>
|> There was a large contingent from the University of Alabama in Huntsville at
|> this little party carrying Bush/Quayle posters. Too bad it did not get on TV.
|> Sorry Gore baby but it was the University of South Dakota that did it first.
                                                ^^^^^
Sorry Dennis baby but it was the University of *North* Dakota that 'did it first.'
                                                -----
David Webb started the 'Space Studies' program  ~'87 (not sure of the exact year.)
BTW it's an excellent program.

|> David Webb has also put the program in place at Emery Riddle University in
|> Florida.  The University of Alabama in Huntsville continues in its efforts
|> to train the real space professionals of the twentyfirst century. These
|> students can read write and see propaganda when it is put out. Your
|> talk is just talk.
|>
|> The Clinton/Gore Campaign is like a man trying to bed a beautiful virgin. They
|> promise anything that they think can woo her to bed. What usually happens is
|> that after the conquest the virgin is discarded as trash. Let this not happen
|> to our nation.
|>
|> Dennis, University of Alabama in Huntsville

--
Tim Stevens, (formerly of) University of North Dakota at Grand Forks
[Always a NoDak]

------
Tim Stevens                              [e-mail]
Control Data Systems Inc.                [phone]

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

Date: Sat, 31 Oct 1992 06:26:10 GMT
From: Dave Tholen <[e-mail]>
Subject: Re: Swift-Tuttle Comet a threat to earth?
Newsgroups: sci.astro,sci.space

Thorsten Altenkirch writes:

> I understand that it is pretty unlikely that Swift-Tuttle will hit
> earth in 2126. However, I would like to know what would happen in the
> case such a big object would collide with our planet? I am not sure
> whether my memory is right but in the discussion about the
> disappearance of the dinosaurs an object of a size like 200m was
> mentioned. Now, Swift-Tuttle is supposed to be much bigger (10 km?)...

Your memory is partly in error.  The disappearance of the dinosaurs involved
an object about 10 km in diameter.  200 m would produce only local, not
global, effects.

But yes, if P/Swift-Tuttle shares the low albedo of other comets like
P/Halley, then it could be 10 km in diameter as well.

A direct hit on Earth would not be good news.

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

Date: Sat, 31 Oct 1992 01:57:53 GMT
From: Alan McGowen <[e-mail]>
Subject: re HRMS for ETI
Newsgroups: sci.space

Some speculations (what else is this thread, anyway?):


P(life | suitable planet)
    ~ 1              (Check out recent evidence for multiple origins
                of coding. The person who said the "organic
                soup" theory was dead because of improbability
                should learn about the theory, due to Manfred
                Eigen, of the origin of coding by heterocyclic
                catalysis. Generating the negentropy is not
                a severe theoretical problem, and if coding
                actually had multiple origins it must have
                been a cakewalk for nature, however badly
                we might explain it.)

P(multicellular life | life)
    ~ 0.5             (Within the lifespan of a biosphere.
                It might be lower. The estimate is based
                on nothing more than the fact that
                multicellularity appeared roughly midway
                through the main sequence lifespan of the
                sun.)


P(smart life | multicellular life)
    ~ 0.01                 (Smart life means e.g. birds and mammals.
                Check out Bonner's book _The Evolution
                of Complexity_, which might put this at ~1.
                That may be a major overestimate, however:
                there may be just one fundamental adaptation
                -- vertebrate sociality -- which drives the
                entire phyletic trend towards increasing
                "smartness" (encephalization). If that basic
                adaptation itself has a very low prior
                probability, this one is an overestimate. No
                similar phyletic trend apparently occurs
                outside the vertebrates.

                The justification for the number is that it
                is roughly the inverse of the number of
                animal phyla, only one of which exhibits
                encephalization.)

P(symbolic intelligence | smart life)
        "1 e-12"               (Specifically human intelligence is no more
(really just some very small   likely than is the specific adaptation
 number)               pattern of any other species. The fact that it
                   may open a new adaptive zone *if reached*
                   is not relevant to its conditional
                   probability, which has to do with how easy it
                   is to arrive at an adaptation (preadaptation),
                   not with how good it is to have it once it
                   has been arrived at (fitness).  By contrast
                   to symbolic intelligence consider, e.g. eyes,
                   which have evolved independently many different
                   times. So has flight.

                   There is also the Saganistic possibility
                   that symbolic intelligence does *not* prove
                   to be adaptive for very long: the evidence
                   of its mounting effect on the biosphere
                   makes this a more than abstruse possibility.)

It interests me that many physical scientists seem to think either that

Sagan: P(life) ~ 1 & P(radio telescopes | life) ~ 1 --> many civilizations

or that

Tipler: P(life) ~ 0 & P(radio telescopes | life) ~ 1 --> sparse civilizations

while virtually all evolutionary biologists seem to think that

Simpson: P(life) ~ 1 & P(radio telescopes | life) ~ 0 --> sparse civilizations.

See Stephan Gould's essay about this in _Bully for Bronotosaurus_, and also
see his book _Wonderful Life_ (which I understand has not been a favorite
of the Seti crowd). [Some of the strange Cambrian critters Gould discusses
in that book have recently been held to be fossilization artifacts
-- hodgepodges of bits of other organisms -- or to be assignable to known
groups after all.]

------------
Alan McGowen

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

Date: Sat, 31 Oct 1992 07:09:30 GMT
From: Dave Tholen <[e-mail]>
Subject: Smith-Tuttle Comet a threat to earth?
Newsgroups: sci.space

Jack Romachek writes:

> Strange.  I did a calculation using the orbital elements from IAU
> Circular 5636 and had the comet returning to perihelion on 17 Dec. 2127,
> when according to the circular should happen 11 July 2126.  That
> is approximately the same time difference encountered above.  Will including
> planetary perturbations cause the comet to arrive 17 months earlier than
> a strictly two-body (comet+sun) calculation?

Yes.  That and whatever non-gravitational terms Marsden assumed for his
extrapolation to the next perihelion passage.

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


Newsgroups: sci.astro,sci.space
Subject: Re: Collision with Comet P/Swift-Tuttle
Message-Id: <[e-mail]>
From: "lewis.h.mammel..jr" <[e-mail]>
Date: Sat, 31 Oct 1992 04:36:14 GMT
Followup-To: sci.astro
References: <[e-mail]>
Organization: AT&T
Summary: orbit calculations, questions
Lines: 84
Sender: [e-mail]
Source-Info:  Sender is really [e-mail]

In article <[e-mail]>, [e-mail] (<A.C.Beresford>) writes:
>                                                Circular No. 5636
> Central Bureau for Astronomical Telegrams
> INTERNATIONAL ASTRONOMICAL UNION
> Postal Address: Central Bureau for Astronomical Telegrams
> Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
>
> PERIODIC COMET SWIFT-TUTTLE (1992t)
>      Orbital computations by the undersigned, and also by S. Nakano,
> Sumoto, Japan, have so far failed to link all the observations, even
> when allowance is made for nongravitational forces.  Although a
> reasonable fit can be made to the 1862 (except October) and 1992
> observations, the resulting transverse nongravitational component is
> so large that the resulting eighteenth-century perihelion time is 15
> months too late.  Alternatively, although the three perihelion times
> can be well represented without any consideration of nongravitational
> forces at all, there are strong systematic errors, amounting to more
> than 1', in 1862 and 1992.  The gravitational orbital elements below
> satisfy the observations in 1992 and in Oct. 1862 very well, and they
> also represent the presumed 1737 perihelion time within 1 day.

1862 - 1737 = 125
1992 - 1862 = 130
2126 - 1992 = 134

By Kepler's law this corresponds to a continuing increase in the
semimajor axis, which dynamically means that the comet is gaining
energy ( per unit remaining mass ) on each orbit. Is this right?
( I don't see how it could be wrong. ) Is it unusual ?

> Backward computation of this solution reveals few candidates for
> earlier appearances of the comet, although the one of -68 fits within
> 1 year (there being 15 revolutions between then and 1862), and the
> comet of +60 may also belong.  Future extrapolation gives the next
> return to perihelion as 2126 July 11, although the problem with the
> computation of the nongravitational forces must introduce some
> uncertainty; a change by +15 days could cause the comet to hit the
> earth on 2126 Aug. 14.  It therefore seems prudent to attempt to
> follow P/Swift-Tuttle for as long as possible after the present
> perihelion passage, in the hope that an adequate independent orbit
> determination, uncontaminated by nongravitational effects, can be made
> from mid-1993 (at r = 3 AU and far to the south) to, say, 1998 (when r
> = 15 AU and an assumed nuclear absolute magnitude of 14 yields an
> apparent magnitude of 26).
>
>                     Epoch = 1992 Dec. 4.0 TT
>      T = 1992 Dec. 12.323 TT          Peri. = 153.013
>      e = 0.96359                      Node  = 139.456   2000.0
>      q = 0.95812 AU                   Incl. = 113.430
>        a = 26.31666 AU     n = 0.007301     P = 135.00 years

I don't understand why P is 135.00 NOW, given that it's been
increasing, and that it's due back in 134 years.

I fiddled with these numbers ( Thanks for posting them! ) and
I found that, as given, they bring the comet to 1.03156 AU at its
descending node at longitude 319.456. I calculate that the earth
is at 1.01317 at this longitude, so it seems that we're dealing
with a 2% variation to get a hit - that's about 230 earth diameters.
( Of course, the predicted perturbations may put it much closer. )

Now in 15 days, the earth moves about 3000 earth diameters,
so I can see why you might get an elongated "footprint", where
the major uncertainty is in arrival time.

You can take a "spherical horse" approach, and put the earth in
a target plane displaced from the bull's eye by 3000, 200.
Then assume that the standard deviation is about the same
along each axis as these displacements. Of course the earth has
an area of about 1 in these units, so I get a probability of one in:

    2*pi*e*3000*200 ~1e7

So I agree with whoever said 1 in 10,000 was way to pessimistic.
I wonder if Marsden did an essentially 1-d estimation ? I get a
one in 7300 chance that way ( 3000*sqrt(2*pi*e) ). Surely there
must be SOME uncertainty in the transverse direction ?

You know, a good unit of risk might be "decks",  meaning how
many shuffled decks you would have to cut simultaneously
to the Ace of Spades to get a death sentence. Marsden's got
us between 2 and 3 decks.

Lew Mammel, Jr.

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

End of Space Digest Volume 15 : Issue 362
------------------------------