Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_6/V13_638.TXT

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Subject: SPACE Digest V13 #638

SPACE Digest                                     Volume 13 : Issue 638

Today's Topics:
          Re: Extra Terrestrial Intelligence
                Re: Amputation
          Re: Extra Terrestrial Intelligence
              Re: Colonizing the galaxy
            Re: Fred Betting Pool?
           Re: Rational next station design process
        Expedition to the stars (hypothetical)
           Re: Rational next station design process
              Re: Colonizing the galaxy
              The Drake Equation

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

Date: 25 May 91 20:09:13 GMT
From: rochester![e-mail]  (Paul Dietz)
Subject: Re: Extra Terrestrial Intelligence

In article <[e-mail]> [e-mail] (Frank Crary) writes:
>In article <[e-mail]> [e-mail] writes:
>>(2) Why wasn't the entire galaxy colonized thousands of millions of
>>years ago? The time for a colonization wave to travel across the galaxy,
>>even with spacecraft traveling well below the speed of light, is only
>>a fraction of the age of the universe.
...

>I have two big problems with this logic: First of all, the age of the universe
>is not the correct time scale. Before any intelligent life could begin to
>colonize the galaxy: The first generation of star formation must progress
>to the point of supernovae.

However, the time to colonize the galaxy is << the age of the universe
(and << the time it has take for intelligence to evolve on earth).
And, not all parts of the galaxy metallize at the same time; stars
closer to the center of the galaxy have more metals, I understand.
It would be an amazing coincidence indeed if intelligent life
were common in the galaxy, but it arose near-simultaneously
in different places.

> My second objection is the speed at which a civilization is assumed to
> expand.  While the actual exploration crafts could have spread all
> over the galaxy, even at 0.001c and in only 500 million years, what
> the colonies would do is a totally different issue. At the speed I
> guessed at, travel between stars would take roughly 5000 years (at
> approximately 5 light years between stars.) But how long would it take
> a new colony to settle an entire new world, grow to the point where
> people want to leave it (and form a new colony) and have developed the
> industrial base to support an interstellar colonization effort?

The galaxy is about 100,000 light years in diameter, so spreading
at .001 c the travel time from one side to the other is only 100 megayears,
not 500 MY.  There will be some slowdown due to paths not being
entirely straight, but steps larger than 5 lyr and speeds of .01
c or greater are also feasible, given a sufficiently large industrial
base to separate the nuclear fuel (if that is the propulsion
technology chosen).

At a growth rate of 1%/year, 5000 years is more than 50 doubling times,
enough time for a population of 1000 to increase to 10^18.  I suspect
much shorter doubling times would be "selected" for, as the colonies
that bred faster would seed new stars more quickly.

>few thousand years. In fact, however, these colonists might easily get
>distracted. If they suffered a civil war/interstellar war/collapse of
>government the above process could be set back a great deal. In short, I feel
>the "colonization wave" would propogate at a much slower rate than suggested,

However, these distractions would have to occur at most of the
colonies most of the time for the wave to slow down; holes in the wave
would be filled in from the sides.  Significant intercolony rivalry
might very well speed up the wave, by giving strong incentive to grab
new star systems first.

>Finally, I don't like this model of a "wave of colonization" A difussion
>process (or a random walk) seems to me a better model. There will be empty
>worlds to be settled TOWARD as well as away from the home world of our
>hypothetical extraterrestrials.

You are in distinguished company in making this mistake!  Sagan wrote
a paper in which just such a diffusion model was applied to
interstellar colonization.  The error was that diffusion models only
apply when the population gradient at any point is small (in a sense
that can be made mathematically precise).  In galactic colonization,
where the wave spreads out like a detonation, the population density
going from zero to saturated in a short distance, and gradients are
large.

Ultimately, of course, one has to assume that aliens would actually
*want* to colonize the galaxy.  That's impossible to know a
priori, even in principle, so SETI still makes sense.  The
colonization idea does hint that we should look for emissions from
galactic megacivilizations at cosmological distances, under the
assumption that intergalactic colonization will not occur or has not
yet had time to get here.

    Paul F. Dietz
    [e-mail]

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

Date: 25 May 91 21:52:58 GMT
From: news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Amputation

In article <[e-mail]> [e-mail] (Doug Mohney) writes:
>>2) was damaged because by insisting on everything flying on Shuttle,
>>JSC ensured Galileo would have to take a trajectory it was never
>>designed for -- one which damaged it,
>
>You are implying that Galileo's antenna deployment problems are a direct
>result of the trajectory. or that flying it on Shuttle damaged it. Could you
>please produce some direct evidence of this? ...

One major speculation is that the antenna problem is due to something that
happened in the Venus-encounter leg of the mission, when Galileo was closer
to the Sun than it had been designed for.  The sunshades kept things under
control, but it's still possible that some parts got warmer than planned.

However, the original comment is total nonsense.  There was no available
booster that could have launched Galileo on a more direct trajectory.
(I'm not sure even Titan IV plus Centaur could have done it, and that
combination was not available without substantial added delay.)  It was
JPL, not JSC, that ensured Galileo would have to take a trajectory it
was never designed for, by permitting weight growth to the point that
the only launcher that could carry it was a very costly one with practically
no other customers, i.e. one that was very vulnerable to cancellation.
It's not the first time that JPL has made this mistake, either, as witness
what happened to the original Voyager program after it got too big for a
Saturn IB.
--
"We're thinking about upgrading from    | Henry Spencer @ U of Toronto Zoology
SunOS 4.1.1 to SunOS 3.5."              |  [e-mail]  utzoo!henry

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

Date: 26 May 91 03:09:00 GMT
From: jarthur!nntp-server.caltech.edu![e-mail]  (Steinn Sigurdsson)
Subject: Re: Extra Terrestrial Intelligence

In article <[e-mail]>, fcrary@lightning (Frank Crary) writes:
>In article <[e-mail]> [e-mail] writes:
>>(2) Why wasn't the entire galaxy colonized thousands of millions of
>>years ago? The time for a colonization wave to travel across the galaxy,
>>even with spacecraft traveling well below the speed of light, is only
>>a fraction of the age of the universe. Our solar system has apparently
>
>I have two big problems with this logic: First of all, the age of the universe
>is not the correct time scale. Before any intelligent life could begin to
>colonize the galaxy: The first generation of star formation must progress
>to the point of supernovae. This is necessary since these early stars were
>"metal poor" meaning lacking in materials other than hydrogen and helium. Many
>stars must have become supernovae before the intersteller medium had sufficient
>carbon, nitrogen, oxygen and other heavier elements for life to be possible.
>Once this occured, stars (and planets) must then have formed and life evolved
>on these planets. This whole process would take a considerable ammount of time.
 ..deleted
>My second objection is the speed at which a civilization is assumed to expand.
>While the actual exploration crafts could have spread all over the galaxy, even
>at 0.001c and in only 500 million years, what the colonies would do is a
>totally different issue. At the speed I guessed at, travel between stars would
>take roughly 5000 years (at approximately 5 light years between stars.) But
>how long would it take a new colony to settle an entire new world, grow to the
>point where people want to leave it (and form a new colony) and have developed
>the industrial base to support an interstellar colonization effort? Even if
>they worked as hard as they could at it, I suspect it would take at least a
>few thousand years.

It only took 300 years to get North America to its current point, that
without pre-existing technology. Major limitation would be birthrate,
I would guess < 1000 years to get a newly settled planet to the point
where it would consider building its own spacships. That is assuming
_no_ radical changes in AI, robotics, genetic engineering or
artificial wombs.

> In fact, however, these colonists might easily get
>distracted. If they suffered a civil war/interstellar war/collapse of
>government the above process could be set back a great deal. In short, I feel

Even if 90% of the colonies failed like that the argument is still
valid, it only takes a few waves or individual groups going through
rapid expansion to set up embarrassingly many colonies.

>the "colonization wave" would propogate at a much slower rate than suggested,
>and that this rate would be dominated by social, rather than
>technical, issues

Possible, in particular cultural introversion or decadence might be a
major setback, but you still only need to break out of that pattern
once to get an apparently irreversible expansion going

>Finally, I don't like this model of a "wave of colonization" A difussion
>process (or a random walk) seems to me a better model. There will be empty
>worlds to be settled TOWARD as well as away from the home world of our
>hypothetical extraterrestrials. New collonies are as likley to "fill in the
>blanks" missed by earlier settelers as go out into new and uncharted space.
>Also, they might preferentially settle stars totally unlike out sun. For
>example, a planet in an open star cluster would be an ideal place for a
>colony. There would be many planetary systems, all within a few light years.
>If these were setteled first, it might be quite a while before anyone bothered
>with a single star system.

Open clusters would be fairly bad for a civilization with a long term
view, too violent and too short lived. If the halo population has
planets it would be the best bet, although the stars may be too red
and dim. In either case there are plenty of second generation G
dwarfs, and we _know_ they can suffice.

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

Date: 26 May 91 05:01:29 GMT
From: sdd.hp.com!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!unixhub!slacvm![e-mail]  (Jon J Thaler)
Subject: Re: Colonizing the galaxy

Regarding interstellar travel:
There is an interesting discussion of the relativistic kinematics and
the background hydrogen problem in a book by Taylor and Wheeler:
   "Spacetime Physics"
This book requires only a knowledge of high school algebra and geometry,
but it is the most lucid explanation of SR that I have found.

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

Date: 25 May 91 23:55:36 GMT
From: agate!lightning.Berkeley.EDU![e-mail]  (Frank Crary)
Subject: Re: Fred Betting Pool?

In article <[e-mail]> [e-mail] (Jim Bowery) writes:
>> 2. Killing Freedom will not transfer its money to space science.
>
>Whoa!  When you have a political set up where you axe either
>Fred or space science, I think it is safe to say a zero-sum
>game is going on.

In fact, it is not a zero-sum game. This week's aviation week states that
NASA's TOTAL budget was cut by roughly 2 billion dollars, while 800 million
dollars were ADDED to "housing, veteran and environmental programs." While,
for all that agencies budgeted by the House of Representitives' HUD, VA and
Independent Agencies subcommitte, it may very well be a zero-sum game, (since
they were forced to cut a total of 1.2 billion dollars,) but for NASA alone
this is not the case.

                 Frank Crary

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

Date: 25 May 91 18:20:53 GMT
From: agate!lightning.Berkeley.EDU![e-mail]  (Frank Crary)
Subject: Re: Rational next station design process

In article <[e-mail]> [e-mail] (Nick Janow) writes:
>[e-mail] (George William Herbert) writes:
>> The government in its infinite (cough) wisdom already funds similar
>> missions/needs, so presumably that's where it will come from.
>
>It sounds like you're again saying, "This is the way they do things, so it must
>be okay."

No, the way it sounds to me is: "This is the way they do things, lets try to do
SOMETHING, rather than fight with the government over administrative/legal
details." While I'm not sure I agree, there is often a lot to be said not not
banging your head against a brick wall.

                      Frank Crary

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

Date: 26 May 91 04:53:08 GMT
From: agate!bionet!raven.alaska.edu!raven![e-mail]  (Eric Olson)
Subject: Expedition to the stars (hypothetical)

If a team of explorers were to hop a ship to a nearby star, what
should they take and why?

I'm interested in forming as comprehensive a list as possible, and I'd
appreciate any input.  Anything is valid---their goals once they get
there aren't presupposed, but they should be ready to do anything.
Net mass and volume and so forth of what should be taken isn't
important; you can cart the whole Earth there if you want to, but it
seems a little unnecessary.

Mostly what I'm looking for are things you might look for on a planet
you found at that star; for example, you could take some "spy"
satellites to assist in mapping it, surveying equipment to look for
valuable resources and determine the general structure, and so forth.

Any suggestions?

Eric Olson <[e-mail]> Gryphon Gang Fairbanks AK 99775

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

Date: 25 May 91 18:48:46 GMT
From: agate!lightning.Berkeley.EDU![e-mail]  (Frank Crary)
Subject: Re: Rational next station design process

In article <[e-mail]> [e-mail] writes:
>This requires looking at alternate needs and designs, rather than
>remaining glued on the narrow concept of a "space station" and the
>narrow set of needs it might meet.

In fact, I way talking about the value of missions which could ONLY be
done by a space station, or which would be grealty simplified by a space
station. As a result, the concepts would all, most likely, be space stations.
The question posed by assessing the value of the missions is, as I phrased it,
"Is it worth the costs to build a space station?" While you seem to want to
study the question, "What would the best way to satisfy these missions?"
While your question is more generally useful, mine is more practicle. By
limiting the scope of the problem, I make it easier to answer. Only space
station designs need to be considered. There are far fewer station designs
than "alternate" designs.

                       Frank Crary

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

Date: 25 May 91 21:06:29 GMT
From: usc!wuarchive!uwm.edu!csd4.csd.uwm.edu![e-mail]  (Mark William Hopkins)
Subject: Re: Colonizing the galaxy

In article <[e-mail]> [e-mail] (Mark William Hopkins) writes:
>   A trip at constant 1G acceleration/deceleration to a star 5 light years
>away only takes 3 or 4 years ship time.  A trip across the galaxy with 1G
>acceleration/deceleration only takes 20 years ship time.
...

>The diffusion theory, on that count, is dead wrong.  A better theory would
>liken the spread of aliens to a metasthesizing cancer...

Yes, I know 20 years ship time still means 100,000 years from the frame of
reference of the stars in the galaxy.  The point is that the galaxy time is
irrelevant to WHERE the destination colony is to be: destination can be
ANYWHERE.  The ship time is what's relevant.  Thus: the analogy to a cancer
that envolopes the entire body in an instant (100,000 years).  The spur of
colonization will hit everywhere in that time frame.

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

Date: 25 May 91 19:27:29 GMT
From: deccrl!news.crl.dec.com!nntpd.lkg.dec.com!rburns.enet.dec.com![e-mail]  (Larry Klaes)
Subject: The Drake Equation


        The following formula, known as the Drake Equation, as it was
    created by Frank Drake (and Carl Sagan) in the 1960s, is set up thusly:

                              N = R*fgfpneflfifaL

          N - The number of advanced technological civilizations in the
              Milky Way Galaxy.

         R* - The mean birth rate of stars in the Milky Way Galaxy.

         fg - The fraction of stars resembling the Sun (Sol) which are
              not members of binary or multiple star systems.

         fp - The fraction of such stars with planetary systems.

         ne - The number of Earth-like planets in each system orbiting
              within the life-supporting zones of their stars.

         fl - The fraction of these planets where life has arisen.

         fi - The fraction of life-bearing planets on which life has
              developed intelligence.

         fa - The fraction of intelligent civilizations which have
              developed an advanced technology.

          L - The average lifetime of civilizations with advanced
              technology.

        Needless to say, this formula is comprised mostly of currently
    unknown factors; depending on various estimates, there may be as many
    as one million advanced civilization in our galaxy or as few as one.
    This equation also does not take into account intelligent races which
    may have developed in environments other than Earth-like worlds and do
    not possess and/or use technologies recognizable to humans.

        Larry Klaes  [e-mail]
             or - ...!decwrl!rburns.enet.dec.com!klaes
                 or - [e-mail]
                     or - [e-mail]

             "All the Universe, or nothing!" - H. G. Wells

        EJASA Editor, Astronomical Society of the Atlantic

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

End of SPACE Digest V13 #638
*******************