Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V15_3/V15NO359.TXT

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Date: Sat, 31 Oct 92 05:00:05
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #359
To: Space Digest Readers
Precedence: bulk


Space Digest                Sat, 31 Oct 92       Volume 15 : Issue 359

Today's Topics:
        active planetary probes; should someone update the FAQ
                  Buck Rogers Plasmoid Launch Cannon
                       Comet Collision (3 msgs)
                              esa symbol
                      Galileo High Gain Antenna
                       GPS orbital information
                     How can the commit be seen?
                             HRMS for ETI
                     Planets, moons gifs, jpegs.
                   Please don't nuke the asteroids
                      Query Re: pluto direct/ o
          Re:Swift-Tuttle Comet a threat to earth? (2 msgs)
               Scenario of comet hitting Earth (2 msgs)
            Swift-Tuttle Comet a threat to earth? (2 msgs)
                        UN Space/Moon Treaty?

    Welcome to the Space Digest!!  Please send your messages to
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----------------------------------------------------------------------

Date: Fri, 30 Oct 1992 14:55:28 GMT
From: "J. I. Blackshear Jr." <[e-mail]>
Subject: active planetary probes; should someone update the FAQ
Newsgroups: sci.space

In article <3c=[e-mail]>, [e-mail] (Michael V. Kent) writes:
|> In article <[e-mail]> [e-mail] writes:
|> >There is also DSPSE (Deep Space Project Science Experiment) to be launched
|> >in Jan 94...it will do 2.5 phasing loops about the Earth and enter Lunar
|> >orbit on or about 21 Feb 94.
|>
|> Cool.  Is this a funded mission, or just a proposed one?  Where will it launch
|> from and what launcher will be used?

It is a currently funded mission and will launch from the WTR (Vandenberg)
on a Titan IIG on 24 Jan 94.

|>
|> Mike
|>
|> --
|> Michael Kent                                   [e-mail]
|> McDonnell Douglas                              Rensselaer Polytechnic Institute
|>
|> Tute Screwed Aero Class of '92                              Apple II Forever !!

--


                                             Jim Blackshear
                                             [e-mail]

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

Date: Fri, 30 Oct 1992 07:54:28 GMT
From: Jonathan Burns <[e-mail]>
Subject: Buck Rogers Plasmoid Launch Cannon
Newsgroups: sci.space

Just a short one. (Research time? Me :-?)

From time to time, I hear about "plasmoids". These are rarefied blots
of plasma, laced with magnetic flux. The plasma diffuses slowly across
the flux, while the flux attempts to eliminate loops, but can do so only
by doing work on the plasma. Researchers, some 20 years back, were
surprised at how long plasmoids took to dissipate.

As I understand it, Paul Koloc of Prometheus II has a serious scenario
for producing self-constricting structures like this, such that an inner
layer might be compressed to a fusion regime, but that's another story.

Question. What is the status these days of research, esp. into long-
lived plasmoids?

Application. Station a plasmoid cannon on a large rock, such as the
Moon or Deimos. Fire a stream into the maw of a Zubrin (didn't Alfven
come up with these first?) magsail, transferring momentum. Much more
effective, surely, than catching the solar wind.

The crucial number, I'd think, is the velocity of the particles after
dissipation. Would the remaining plasma spread out rapidly to many
times the sail collection area?

A nice inspiration, perhaps, to solar wind and flare research.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jonathan Burns        |  They say you can go to the pits a thousand times
[e-mail]|  and see nothing like the jaguar and the Black Knight.
Computer Science Dept |  I don't know 'bout that either. But I'm going back
La Trobe University   |  just in case I get lucky.
                      |      Lucius Shepard, _Life During Wartime_
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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

Date: Fri, 30 Oct 92 12:57:58 GMT
From: [e-mail]
Subject: Comet Collision

> Maybe this is all too much "pie in the sky" (no pun intended :-),
130 years is
> much too short to evolve technologies to do this sort of stuff,
witness  what
> could be viewed as comparativly slow progress in maned spaceflight
in the last
> 20 years (still that's probably a function of the spending). So
this sort of
> stuff is more like 500 years off in the future.

>


You are guilty of the classic fallacies of extrapolation. The first
fallacy is an overestimate of short term advance. The second is the
underestimate of the long term. Both are due, in part, to linear
thinking, straight line extrapolation. Technological capabilities and
knowledge are accumulating exponententially. If you make a linear
extrapolation in a particular field, you will tend to "draw a line"
of some slope that seems "reasonable". But the problems invariably
turn out to be more difficult in your field than you actually
believed.  So the exponential will for some period of time grow
slower (lesser slope) than your line, but when it finally does cross
it...

I think the effect is due to the tendency to analyze technology in
terms of a single field rather than that of the whole of human
knowledge. There is an exponential because of the unpredictable
interactions between areas of knowledge. A discovery in surface
chemistry leads to a new chip that allows an instrument that lets
physicists study an effect that leads to a new instrument that lets
biologists unravel new secrets of the mind... and so on.

The capabilities of 130 years from now are really and truly outside
the realm of science fiction. We can't extrapolate that far ahead at
the current rate of advance. The exponential is rising so fast now
that knowledgeable projection and hard science fiction are almost
indistinquishable and cover the same time frame: no more than 30-50
years in the future. My own feelings are that 2020 is about the limit
at which things start getting very strange: the exponential will be
essentially vertical with respect to human perceptions of time. Note
that as Arel Lucas pointed out in a recent article in Cryonics, the
size of a computer memory cell can be projected to be at the level of
a couple atoms by that time at the latest, And that is based on a
curve that is essentially unchanged since 1900.


In 2126 we'll be able to do just about anything we care to do with
that oversized snowball. As to what that might be, I fear my crystal
ball is bit cloudy today.

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

Date: Fri, 30 Oct 1992 15:40:56 GMT
From: Nick Haines <[e-mail]>
Subject: Comet Collision
Newsgroups: sci.space

In article <[e-mail]> [e-mail]
writes some stuff about extrapolating exponential progress. I agree
with some of it and disagree with some of the rest, and I think the
briefest way of getting my point across is by replying to this
snippet:

            My own feelings are that 2020 is about the limit
   at which things start getting very strange: the exponential will be
   essentially vertical with respect to human perceptions of time.

Technological development is an aspect of human activity. This will
remain true until such time as we have strong AI (where this can be
defined as computers which can `do' technology on their own). We don't
have that now, we're not particularly close, and I don't believe we
will have it before 2020. Until that time, there is a maximum slope to
the technological graph, determined by things like how fast are
results disseminated, how fast can experiments be set up, and (most
limitingly?) how quickly any given researcher can think of a new idea.
Thus until we have strong AI, the exponential _cannot_ become
`essentially vertical'. Sure, it'll get steeper, but not indefinitely.

A separate point is that a lot of people don't like the
faster-and-faster aspect of modern life. This portion of the
population will grow (IMO) as the slope steepens, and may well be able
to apply brakes at some point. Speaking for myself, I don't want to
have a newer, better, faster car every day (or even every year). Every
five or ten years is fine by me.

Nick Haines [e-mail]

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

Date: Fri, 30 Oct 1992 16:40:31 GMT
From: "Scott D. Young" <[e-mail]>
Subject: Comet Collision
Newsgroups: sci.space,alt.sci.planetary

In <[e-mail]> [e-mail] (John Black) writes:

>Maybe a near comet approach could be a good thing. I did a rough calculation
>and estimated that there must be something of the order of 10 to the power 11
>metric tonnes of water. Maybe in 130 years time somewhere on the Earth could do
>with some water, eg the interior of large continents affected by drought. I
>know that one of the effects of the greenhouse effect is to make sea levels
>rise, but that is salt water, no good for crops, and still would be hundreds of
>miles from a continental desert region. The comet presumably is almost pure
>water and therefore would be ideal for crops, drinking etc.
   When they say comets are made of "ices", they don't necessarily mean H2O.
   There's lots of methane, ammonia, etc. and the even detected Cynanide in
   Halley's in 1910. Not fit for easy consumtion.

   Scott Young
   [e-mail]

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

Date: 30 Oct 92 11:15:53 EST
From: donald simmons <[e-mail]>
Subject: esa symbol
Newsgroups: sci.space

      Recently in a space magazine I saw the logo for the European Space
Agency, and I wondered what it was suposed it mean. It consists of a
blue circle with a lowercase 'e' inside it on the right hand side, and a
small white dot on the left. My best guess is that the 'e' stands for
Europe, and also represents the Earth, while the white dot is supposed
to be the Moon. Anyone know for certain?

Donald Simmons
--
Canada Remote Systems  - Toronto, Ontario
World's Largest PCBOARD System - 416-629-7000/629-7044

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

Date: 30 Oct 92 09:54:34 GMT
From: Bill Higgins-- Beam Jockey <[e-mail]>
Subject: Galileo High Gain Antenna
Newsgroups: sci.space,sci.astro

In article <[e-mail]>, [e-mail] writes:
> In article <[e-mail]>, [e-mail] (Jim Klavetter) writes:
>>
>>  So the question 1) does HST have the capability of imaging Galileo
>>  when it gets close to earth?
>
> No.  If Galileo were close enough to resolve (remember one arcsecond is
> about one meter at 200 km distance), the relative velocities would be
> MUCH too high.

Plus, it would conflict with Ben Zellner's request for HST time to
observe Toutatis on the same day!  (-:

     O~~*           /_) ' / /   /_/ '  ,   ,  ' ,_  _           \|/
   - ~ -~~~~~~~~~~~/_) / / /   / / / (_) (_) / / / _\~~~~~~~~~~~zap!
 /       \                          (_) (_)                    / | \
 |       |     Bill Higgins   Fermi National Accelerator Laboratory
 \       /     Bitnet:     [e-mail]
   -   -       Internet:  [e-mail]
     ~         SPAN/Hepnet:      43011::HIGGINS

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

Date: Fri, 30 Oct 92 15:56:00 GMT
From: Shane Gustafson <[e-mail]>
Subject: GPS orbital information
Newsgroups: sci.space,sci.physics

Hello,

    I am looking for an algorithm that while generate the orbital positions
of  a GPS satellite.  I am trying to generate an ephemeris file.  I have one
algorithm but I can't not get the output data to match the values distributed by
the U.S. Coast Guard.  The information I have is as follows:
the Epoch, the semi-major axis, the eccentricity, the right ascension, the
argument of perigee, and the mean anomaly.

The algorithm I am using is coming from the book ""Satellite
Communications" byTimothy Pratt and Charles Bostian  copyright 1986 John
Wiley and Sons.

1. calculate the angular_velc
    angular_velc = 1/semi-major_axis *
    sqrt(MU/semi_major_axis)*Radians_to_Degrees.
    MU = 398601.352

2. find the time of perigee
    time_of_perigee = Epoch_date_converted_to_seconds -
    mean_anomaly/angular_velc

3. find the mean anomaly at the analysis date.
    mean_anomaly = angular_velc*(analysis_date - time_of_perigee)

4. find E - eccentric anomaly
    mean_anomaly = E - sin(E);
    solved in an iterative approach and is around mean_anomaly + or - 1

5. find r0 - radius from the origin of the coor-system to the satellite.
    r0 = semi-major_axis*(1.0 - eccentricity*cos(E))

6. find the true_anomaly
    I solved this equation for the true_anomaly

    temp = ((semi-major_axis)/(r0*eccentricity))*(1.0 -
    eccentricity*eccentricity)) - 1.0/eccentricity

    true_anomaly = acos(temp)

7. find the x0 and y0 values.  There is no z component because the equations
are derived in the z plane
    x0 = r0*cos(phi)
    y0 = r0*sin(phi)

the last part solves for the xi,yi,zi triplet.  This is the triplet I am using to
compare my results from the program called GSS.  I am getting x and z values
to be very close to the output from the program and I am not getting the y
values close at all.  The next part is complex because I had to solve the matrix
to get the equations.  I am going to use some shorthand to simplify the
equations.
    a = cos(right_ascension)    b = sin(right_ascension)
    c = cos(arg_of_perigee)    d = sin(arg_of_perigee)
    e = cos(inclination)    f = sin(inclination)

    a11 = a*c - b*e*d
    b11 = -a*d - b*e*c            the matrix
    c11 = -b*d + b*e*c    |xi|    | a11    b11    na | |x0    |
    d11 = a*d + b*e*c    |yi|  =    | c11    d11    na | |y0    |
    e11 = d*f        |zi|    | e11    f11    na | |z0 = 0|
    f11 = c*f

    xi = a11*xo + b11*y0
    yi = c11*xo + d11*y0
    zi = e11*x0 + f11*y0

after implementing the algorithm I ran the program I was getting out data that
looked like the following
    x0 = 15254.499(km)    y0 = -21551.16(km)
    xi = -17367.91923    yi = -829.09        zi = 15610.593
From the GSS program
    xi = -17207.79        yi = 12394.955        zi = 15732.192
I have compared this results with the  U.S. Coast Guard and they seem close, so
I can assume my algorithm has the problem.

I solved for the c11 and d11 coefficient and should be getting results for c11 to
be -.0057 and d11 to be-.57.  After doing some manipulation of changing the
equations the best I could do was to come up with a c11 = -.0047 and a d11 = -
.642 and this brought my yi to be 13764.811 still far away from the expected.  I
have run with different data at different time and still get the same type of
results.  The x and z are good but the y is wrong.

I need some help in figuring about a different algorithm that will work and give
me close data are find out what I am doing wrong in this algorithm.

Also,  in the Yuma file format I need to know how to convert the Right Ascen
at TOA which is from the GM(Greenwich meridian) to the right ascen from the
Vernal Equinox.  And how to convert the Mean anom in yuma format to the
almanac format.  In the case of the right ascension value it is 26.7 degrees
different from the almanac file I am using and the Mean anon is about 59.9
degrees different.  This causes a problem because the algorithms assume the
angles from the VE not the GM.

Any help these areas would be very useful.  I am starting to run into deadlines
and need all the help I can get.

If you post the response to the net for the others to gain information, please
email me also.  I don't get the time to read much news and would not like the
response to get lost.

thank you
shane gustafson

[e-mail]

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

Date: 30 Oct 92 18:12:49 GMT
From: [e-mail]
Subject: How can the commit be seen?
Newsgroups: sci.space

Considering that the commit on a probable colision course with earth
is about 5km in diameter and is about n*n*m (n, m very large) km
away from the earth, how can it be monitored acurately?

Who picked up the signal? and how?

I'm wondering if Halley's commit can be tracked for the whole 75 years?
It should be if you can pick up the newcomer?

By the way, what is the new commit called?

-Hans
--
testing my signature

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

Date: Fri, 30 Oct 1992 15:22:31 GMT
From: Nick Haines <[e-mail]>
Subject: HRMS for ETI
Newsgroups: sci.space,sci.bio

In article <[e-mail]> [e-mail] (Stanley Friesen) writes:

   In article <[e-mail]> [e-mail] (Paul Dietz) writes:

   [... conditions for life ...]

                            For example,
   |perhaps deposition of organic material from space is required.

   This last is an extremely unlikely requirement.  The basic upshot of the
   Urey experiment and its follow-ups is that organics form spontaneously
   under most non-oxidizing 'medium-energy' conditions.  The presence of
   organics in interstellar dust clouds just confirms this basic ubiquity.

OK, organics are everywhere, Paul Dietz's example is flawed.

   [...]

   Now, it is true that we do *not* know the exact range of
   temperatures and pressures under which the ubiquitous organics are
   able to generate life forms, but this is a much smaller level of
   uncertainty than you suggest.

But what we do know is that simply putting lots of organic chemicals,
amino acids, what-have-you together, even in planetary quantities for
billions of years, is not likely to `generate life forms'.  That was
my original point that started this discussion: that organic chemicals
do not seem to be prone to generating self-reproducing systems,
largely because in order to reproduce they must have very carefully
controlled conditions, and such conditions will not evolve when there
is no evolutionary pressure (it's a chicken-and-egg syndrome). The
current idea is that one starts with a self-reproducing system that
does not _need_ such a finely-controlled environment (such as a clay
mineral), that such a system can, over time, select to control more of
its environment (a `cell') and that this environment may be suitable
for the development of nucleic acids (or something similar). But it's
a very long and precarious chain to get from clays to algae (or even
to viroids). And clay minerals aren't going to be sending us any radio
signals.

Lest you misunderstand me, I fully support spending money on SETI:
it's not expensive, and it attempts to answer one of the really big
questions about the universe. But none of us really expect to find
high-tech civilizations everywhere (for the simple reason that we
haven't seen them yet) and I think the reason lies in that term of the
Drake equation. When we get out there, I don't expect to find
universal dumb life, I expect to find no life at all.

Nick Haines [e-mail]

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

Date: Wednesday, 28 Oct 1992 19:59:19 TUR
From: [e-mail]
Subject: Planets, moons gifs, jpegs.
Newsgroups: sci.space

      Try FTP ames.arc.nasa.gov
          CD /pub/SPACE/GIF

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

Date: Fri, 30 Oct 1992 15:10:13 GMT
From: [e-mail]
Subject: Please don't nuke the asteroids
Newsgroups: sci.space

I would rather be shot at with a .45 than a 12-gauge, wouldn't you?  At
least there would be only one bullet to duck.

It's been a while since I did the calculations, but a very small delta
velocity can make the difference between a planet hit or not, if that
velocity has decades or centuries to act.  Maybe someone would compute
the necessary energy for representative cases, and compare that, for
example, to the kinetic energy of a Shuttle in orbit.  The point is to
identify the hazardous objects early enough.

Along those lines, Tom Gehrels is hosting a symposium entitled "Danger
of Near-Earth Asteroids" in Tucson the first week of January.  There is
intense interest from scientists, engineers, and the press.  We have to
watch out for the "giggle factor" from the press and possibly a few nuke-
happy engineers, but the latter will get no sympathy from Gehrels.

As to the terrestial effect of mega-explosions:  I think a big difference
is that the largest volcanic or nuclear explosions are still confined to
the atmosphere and thus subject to ordinary aerodynamic forces, whereas
something like the fireball from the K-T impact would break entirely out
of the atmosphere.  A lot of the debris would go ballistic, and thus blanket
the whole earth rather uniformly.  You would get total, worldwide darkness
for months or years, with all the implications for biology.

As to radioactivity, breaking up the earth's crust into little pieces always
releases radioactivity, I think mainly trapped radon.  People have noted
that coal mining has put a lot more radioactivity into the atmosphere than
all of nuclear power.

Ben

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

Date: Fri, 30 Oct 1992 16:33:02 GMT
From: Ian Taylor <[e-mail]>
Subject: Query Re: pluto direct/ o
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Tomas Svitek) writes:
>HS>>Aerobrake?
>
>HS>In what? :-)  Pluto does have an atmosphere of sorts at the moment, but
>HS>I'd guess it's too thin to do much aerobraking in, even if we knew its
>HS>properties well enough to plan an aerobraking mission, which we don't.
>HS>And we'd have to kill a lot of velocity; Pluto is roughly 150 km/s-years
>HS>away (how's that for strange units? :-)), so for a reasonable trip time
>HS>we're talking about killing maybe 20 km/s, which is high.
>
>Actually, there is a fairly serious proposal (albeit very tentative)
>from GE Reentry Systems regarding aerobraking at Pluto.

How about aerobraking at Neptune first?

While I'm here, anyone know if a gravity assist trajectory can be used to
*reduce* speed?


+-- I -------- fax [phone] --------------------- voice [phone] --+
| T a y l o r  Alcatel-ELIN Research, 1-7 Ruthnergasse, Vienna A-1210 Austria  |
+-- n ---- [e-mail] --- PSI%023226191002::SE_TAYLOR --- 20731::ian -----+

             ...but officer, I was only doing 20km a second...

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

Date: Fri, 30 Oct 1992 14:13:20 GMT
From: "David B. Snyder" <[e-mail]>
Subject: Re:Swift-Tuttle Comet a threat to earth?
Newsgroups: sci.astro,sci.space

In article <[e-mail]> [e-mail] (James Davis Nicoll) writes:
>    I was noodling around with impact energy estimates for S-T, and
>got a value of about 30 million megatons. *IF* the energy were distributed
>like a nuke's (Which it wouldn't be,  but maybe it's good enough for my
>purposes), you could expect buildings to be  seriously damaged over
>an area about 4200 km wide, and windows to be shattered over an area
>12,000+ km wide. Fires should extend out to the horizon,whatever
>that is in this case. While fallout would be non-radioactive, there'll
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>be gigatons  of the crap blocking sunlight.

I am under the impression that the Mt. St Hellen's volcano released a
detectable amount of radio-active fallout, dosages much more than
Three Mile Island, and over a much larger area.  No, I don't have
numbers to support the conclusion.  I would expect that much of the
fallout would be from the earth's crust (and at 25km deep) the mantle.
Is this component significantly radioactive or not?

>    The crater should be very impressive: ~50 km wide and 25km
>deep, although I expect  it wouldn't stay that way  for long.

>                            James Nicoll

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

Date: 30 Oct 92 17:12:30 GMT
From: James Davis Nicoll <[e-mail]>
Subject: Re:Swift-Tuttle Comet a threat to earth?
Newsgroups: sci.astro,sci.space

In article <[e-mail]> [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.

    If by  'good-sized' you mean something around 50 megatons, then
I suggest you check to see:

    1: How massive S-T is.
    2: How many degrees 2x10**17 Joules will raise the temperature
        of that  much ice. I get guesstimates of between 20 to
        200 J/kg, off the top of my head (My HP has gone catatonic
        on me). I strongly doubt that is sufficient. Bear in
        mind transporting the energy from the detonation site
        to all of the comet may be tricky.


                            James Nicoll

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

Date: Fri, 30 Oct 92 12:31:46 GMT
From: [e-mail]
Subject: Scenario of comet hitting Earth

> (This is one of the SDI falacies of 'shooting down' ballistic
missles.

> They be coming down no matter what.  Like the SCUDs - hitting a
missle

> ain't enough.)

>


Hmmm. Take your pick:

A) A pile of junk hits your city at terminal velocity, and some of it
is radiocative.

B) A functioning 500kt warhead explodes at 1000 meters over the city
centre.

Your statement about the comet is correct, because it's damage is
entirely due to kinetic energy. The best approach is to change the
orbital plane enough get rid of the crossing at Earth orbit. If you
were to simply blow it up, you'd better get the debris down to the
size of Frankian snowballs.

Robert Zubrin figured he could move an outer system asteroid to Mars
impact with 5 Nerva class engines over 10 years. An environmentalist
friend of mine (the head of a Rain Forest Action Coalition group in
an american city) suggested maybe we could kill two birds with one
stone: make it hit Mars instead. Save one biosphere, get one free :-)

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

Date: 30 Oct 92 15:11:20 GMT
From: "James G. Acker" <[e-mail]>
Subject: Scenario of comet hitting Earth
Newsgroups: alt.sci.planetary,sci.astro,sci.space,talk.origins

Steve Linton ([e-mail]) wrote:

: On diverting it:
:
:In their book, possibly called `comet' or maybe not, Greg Benford & David Brin
: discuss two methods of steering a comet:


    "Heart of the Comet".  Great book.  Has a lot to say about
opportunistic colonization by organisms under the right conditions, and the
possibility that there is a LOT of life out there.

    Jim Acker
    [e-mail]

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

Date: 30 Oct 92 16:50:26 GMT
From: "Scott D. Young" <[e-mail]>
Subject: Swift-Tuttle Comet a threat to earth?
Newsgroups: sci.astro,sci.space

In <[e-mail]> [e-mail] (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?)...

>--

> Thorsten Altenkirch             And there's a hand, my trusty fiere,
> Laboratory for Foundations         And gie's a hand o' thine,
> of Computer Science               And we'll tak a right guid-willie waught
> University of Edinburgh            For auld lang syne!

   According to the data I have seen (I will try and find the reference),
   a comet 1 mile in diameter moving at an averge orbital velocity (what
   ever tht means) would cause a crater 40 miles diameter, and destroy
   everything for 100 miles. 400 million cubic *miles* of dirt would be
   thrown up into the tmosphere, nd stay there for up to 1000 years,
   blocking 98% of solar radition. As someone else put it, "You die, I
   die, everybody dies".

   The best estimte for S-T is 8km diameter, moving at 60-70km/s when
   it reaches us (or if). If it hits the ocean, you get  *lot* of water
   vapor in the air (105% humidity for centuries). An all-out nuclear war
   is easier to survive, and has shorter-ranging effects, than a large
   cometary impact.

   Scott Young
   [e-mail]

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

Date: 30 Oct 92 16:56:36 GMT
From: "Scott D. Young" <[e-mail]>
Subject: Swift-Tuttle Comet a threat to earth?
Newsgroups: sci.astro,sci.space

In <[e-mail]> [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.

   All the pieces would still be moving in the same orbit, and the chance
   of one or many hitting earth would go up dramtically. You have to alter
   the orbit, not blow it up. Also consider that the Giotti probe was aimed
   right at the nucleus of comet Gregg-Skjellerup (sp?) and missed by
   several kilometers.

   Since the comet's inclination is 130 degrees, it will be coming down on
   us from above.  Even if it is smaller thaan expected, if it vaporizes
   the polar ice cap, everyone just goes away. Floods, solid clouds all
   century, all the good Biblical stuff.

   However, seeing the Perseids that night might make it worthwhile  :).

   Scott Young
   [e-mail]

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

Date: Fri, 30 Oct 1992 15:30:43 GMT
From: Robert Nychka <[e-mail]>
Subject: UN Space/Moon Treaty?
Newsgroups: sci.space

In article [e-mail], [e-mail] (Marc A.
Boschma) writes:
>Robert,
>    Your mail address [e-mail] bounces, do you have another ?
>(X.400 perhaps, though internet prefered).


I don't have official E-Mail access, I'm limited to public posts.  Is there
any way you can just post the info to this group?

ROb Nychka

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End of Space Digest Volume 15 : Issue 359
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