Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v11_2/v11_288.txt

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Subject: SPACE Digest V11 #288

SPACE Digest                                     Volume 11 : Issue 288

Today's Topics:
            Re: Abundance of stars
              Re: Decompression and 2001
               Re: Interstellar travel
       Re: Drake Equation (was Re: Interstellar travel)
          Re: Quick launches ( was: Intelsat
        Re: releasing data / digitized images
           Payload Status for 04/19/90 (Forwarded)
                 SETI
              Aerobrake Vehicles
      Re: Listening to the Star (was RE: Drake Equation)
----------------------------------------------------------------------

Date: 19 Apr 90 16:50:01 GMT
From: clyde.concordia.ca!news-server.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca![e-mail]  (Christopher Neufeld)
Subject: Re: Abundance of stars

In article <[e-mail]> [e-mail] (Dan Tilque) writes:
>[e-mail] (Daniel Briggs) writes:
>
>>I don't happen to know the exact numbers, but we
>>are probably talking tens of thousands of eligible suns within that
>>[50 ly] radius.
>
>There are about 50 star systems containing about 70 stars within 16 ly
>of Earth.  If this is a representative sample (a reasonable assumption)
>that gives about 1500 star systems in that 50 ly radius.
>
   Well, by an odd coincidence I was at the planetarium yesterday. There
is a very interesting scale model of the stars within 50 light years.
The recorded voice claims that "all 787 stars within 50 ly are present"
in the spherical model. Beacuse many stars are doubled or tripled up,
this gives considerably fewer than 1500 star systems.

>Dan Tilque    --    [e-mail]


--
 Christopher Neufeld....Just a graduate student  | "Like most
 [e-mail]              | intellectuals he is
 [e-mail]          Ad astra! | intensely stupid."
 "Don't edit reality for the sake of simplicity" |  Marquise de Merteuil

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

Date: 19 Apr 90 23:47:31 GMT
From: swrinde!zaphod.mps.ohio-state.edu!rpi!uwm.edu!ogicse!zephyr.ens.tek.com!wrgate!mrloog![e-mail]  (Dan Tilque)
Subject: Re: Decompression and 2001

[e-mail] writes:
>
>I have often wondered about this as well, and recall reading a sci-fi story
>or two where humans moved between two craft in open space without suits
>(supposedly the decompression problems were solved by hyperventilating, then
>expelling all air from the lungs and leaving your breathing passages open
>8-O ?).

By a not so amazing coincidence, this was also a Clarke story.  It was
written back in the 50's, I think.  Unfortunately, I can't remember the
name but the plot goes like this:

They're building a wheel type space station with modular ring sections.
During a sleep period, one module of the station breaks off and three guys
are in it.  They chase it down but there are complications: the module is
slowly losing air and there isn't time to tow it back to the station.
Also there are no suits in the module.  In order to be rescued, they must
breath vacuum for a minute or so.

I think that leaving the mouth open came from the fact (? assumption)
that a closed mouth wouldn't be able to retain 1 atmosphere of pressure
anyway so it's best just to let the air escape freely (less stress on
the body).  I don't know if this is realistic or not.

---
Dan Tilque    --    [e-mail]

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

Date: 19 Apr 90 03:36:30 GMT
From: mnetor!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Interstellar travel

In article <ca=[e-mail]> [e-mail] writes:
> As one of the people who intermittently "trumpets interstellar ramjets
> as an obvious fallacy" I would be interested in specific references to
> the "ramjet literature" you allude to.

Much of what I'm aware of has been in the "Interstellar Studies" issues
of JBIS over the years.

The "obvious fallacy" part is when somebody discovers the "speed limit"
supposedly imposed when exhaust velocity equals intake velocity.  A quick
look at the literature reveals that this was noticed, and circumvented,
long ago:  it's a problem only if the kinetic energy of the incoming gases
is lost (e.g. in heating them) rather than stored (e.g. by decelerating
the protons against an electric field, so the exhaust can be re-accelerated
as an "afterburner").

There *is* a problem with the fuel, as you point out.  Unless some devious
way can be devised to make an ordinary-hydrogen fusion reaction burn much
more quickly than the natural ones, ramjets don't work well.  Devious ways
are not impossible, as are complete departures from fusion, like monopole-
catalyzed annihilation reactions.  They just aren't at the stage where we
can definitely say they're possible.  (For example, monopole-catalyzed
annihilation works only if monopoles exist, really do catalyze annihilation,
and have a useful catalysis cross-section... and there is indirect evidence
that at least one of these requirements probably isn't met.)

> The only variant that seems barely plausible is bringing along your own
> energy (anti-matter is the only thing with enough energy density) and
> using the scooped hydrogen as reaction mass.  And still this only buys
> you slightly more than a factor of two in propellent mass...

Sure about that?  With a ramjet, you don't optimize for maximum exhaust
velocity any more -- you get maximum momentum transfer out of a given
supply of antimatter by using it to accelerate lots of reaction mass,
since the reaction mass is free.  That's how it looks to me at first
mathematical glance, anyway... it's not an area I'm really up on.
--
With features like this,      |     Henry Spencer at U of Toronto Zoology
who needs bugs?               | uunet!attcan!utzoo!henry [e-mail]

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

Date: 19 Apr 90 14:46:45 GMT
From: unmvax!nmtsun![e-mail]  (Daniel Briggs)
Subject: Re: Drake Equation (was Re: Interstellar travel)

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
trying to send an intelligible signal is concerned, you are best off
choosing a wavelength between a few millimeters and maybe 30 centimeters.
The rest will get swamped by the natural stuff.  (This is, after all, why
we built radio telescopes in the first place.)

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.  (He assumes a density of
.01/lyr^3.  Which gives about 5000 stars within 50 lyr.)  He also points out
that there was a 1985 IAU Symposium #112 entirely devoted to SETI.  I'd say
that if you're interested in the subject, this would be a darned good place
to start looking.

-----
This is a shared guest account, please send replies to
[e-mail] (Internet)
Dan Briggs / NRAO / P.O. Box O / Socorro, NM / 87801  (U.S. Snail)

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

Date: 18 Apr 90 21:00:56 GMT
From: usc!zaphod.mps.ohio-state.edu!sdd.hp.com!ncr-sd!ncrlnk!ncrwic!encad!ensub![e-mail]  (Mark Johnson)
Subject: Re: Quick launches ( was: Intelsat

I have a vague recollection of reading an article on Minuteman I operational
tests in the 1960's. These were apparently conducted by drawing a missile
squadron out of a hat, and transporting the crewmen and one of their missiles
to Vandenburg for an operational test firing. This was viewed as quite an
honor to be selected thusly. Although the actual missile firing might not
have been successful, the article, as I recall, has at least one photo of
a Minuteman leaving the silo.

There were also some tests with cut-down first stages and inert upper stages
from silos in North Dakota. These performed as intended, with impact about
3 miles from the silo. As far as I know, these reduced-power firings were
the ONLY times an operational Minuteman was ever launched from a 'real'
silo.

I will double-check my old files and see if I can find the reference to
all this; I will either post a confirmation or retraction in a day or two.
--
Mark Johnson      WB9QLR/0      NCR Peripheral Products Division
[e-mail]    3718 N. Rock Rd.
[phone]                  Wichita, KS  67226

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

Date: 19 Apr 90 19:26:56 GMT
From: ubc-cs!alberta!arcsun.arc.ab.ca!calgary!cpsc![e-mail]  (Darik Datta)
Subject: Re: releasing data / digitized images

In article <[e-mail]> [e-mail] (Ted Fabian) writes:
>data is made available to the world at large through the networks.. it's
>then grabbed from a server somewhere by foreign groups or individuals with
>whom the United States does not currently have exchange agreements.. those
>people research that data, and turn it around into something that could be
>used against the United States...
>
>now that scenerio may not apply here for digitized space images, but the
>idea is the same.. if someone does not have the "need to know" or the
>"need to access data" that data should not be released...
>
>it would be like my asking you personally to post you income tax returns
>and copies of all your receipts to the nets... you'ld undoubtedly respond
>that it's "none of my business"... it's the same thing here.. while some folks
>may be justified in needing the images, it's not necessarily the best vehicle
>to release those images over the net... some control needs to be present..
>yet the same goal exists in my asking you for your tax info.. it would
>provide me knowledge... again, your control of that info stops me..
>
>
>think about it..

  But, think about this... Many images are published in newspapers, magazines,
etc., and many more are available in film or print form.  This information
is not exactly classified or sensitive.  I wouldn't care if you wanted my
tax info if I had already published it.

  Later,
    Darik Datta

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

Date: 19 Apr 90 18:27:21 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: Payload Status for 04/19/90 (Forwarded)


    Daily Status/KSC Payload Management and Operations 04-19-90.


    - STS-31R HST (at pad-B) -

    HST battery charging continues.


    - STS-35 ASTRO-1 (at OPF) -

    Support for VAB operations continues.


    - STS-40 SLS-1 (at O&C) -

    Module leak checks, rack and floor installation into the
    module, and preps for experiment train interface test will
    continue today.


    - STS-42 IML-1 (at O&C) -

    On Wednesday module pyrell foam replacement, floor staging,
    and racks 4 and 7 staging operations were performed.  Pyrell
    foam replacement and floor staging will continue today along
    with racks 4, 6, 7, 8, 9, and 11 staging.


    - STS-45 (Atlas-1)-

    Cold plate support were installed Wednesday.  Bonding straps
    will be installed today.


    - STS-55 SL-D2 (at O&C) -

    No activity is scheduled for today.


    - HST M&R (at O&C) -

    ORUC interface testing continues.

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

Date: 19 Apr 90 16:28:58 GMT
From: mcsun!ukc!newcastle.ac.uk!turing![e-mail]  (J.D. Taylor)
Subject: SETI


   All this talking about the Arecibo message and communicating over vast
interstellar distances made me think about one pretty big problem. How do we
know that a totally alien culture could even distinguish and interperet
anything we send to them anyway? Take the Arecibo message as an example. They
have to be listening to the EM spectrum at the frequency which hydrogen
resonates (I think thats right) and have just 27 seconds (or so) to pick up the
message. They then have the problem of decoding it. We hope that these aliens
can order the message as an m by n array of binary digits, look at it and say

"Oh look, there is a nice picture of their solar system and thats what one of
them looks like and yes, that looks like a parabolic dish, probably the one
they used to send the message...."

   Lots of chance of this happening eh? We are basically assuming an alien
culture which thinks along the lines we do. They may not. Even if they study
the signal for years and years and arrange it into all possible formats their
culture may well omit a format which we find totally natural. They may be
looking for a particular kind of message ("We come in peace") and might dismiss
the Arecibo message as some sort of unexplainable noise when they cannot decode
it.

   Don't get me wrong, I'm all for SETI, space travel and all the rest of it,
but I just think that the whole thing is too full of problems which we may
never be able to overcome. But I still hope I am wrong ;-)




John D. Taylor, Dept. of   | "I'm the one who's got to die when its time for me
Elec Eng, Newcastle univ.  |  to die, so let me live MY life, the way I WANT to"
[e-mail] |                             - Jimi Hendrix.

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

Date: 19 Apr 90 20:09:40 GMT
From: ccncsu!longs.LANCE.ColoState.EDU![e-mail]  (Jay Lewis Nestle)
Subject: Aerobrake Vehicles

I am interested in doing possible graduate work on aerobrake
and reentry vehicle design, test, and simulation.  Currently I am looking
into and testing primitive vehicle design types in a fluid dynamics class
and considering making this my senior project.  I am also writing two
computer simulations;  Using E&S 390 computer I plan to simulate the dynamics
involved in an Earth -> Mars transit.  I am also working on a high resolution
ray traced simulation that could eventually be used to help train astronauts
for such a trip.

    Has anyone done any reentry vehicle modelling or analysis in wind
tunnels of this type?  If so which design criteria (i.e. Reynolds,
Froude, etc.)
did you use and why?  Also if the Reynolds criteria was used how did you take
care of the high model velocities required upon reentry for aerobraking?

    Any help concerning this sort of thing will be greatly appreciated!
Also if there is any information out there concerning other schools or
companies
that do this sort of research work please let me know.  Thanks in
advance!  Jay.

(M.A.A.R.S. Project: Martian Aerobrake & Atmospheric Reentry Simulation)

[e-mail]
       ...ncar!boulder!ccncsu!longs.lance.colostate.edu!jn190068

  ^  ^
  |/\|
  |  |  "Save the earth, develop space."  -  Bumper Sticker
  /  \
  ----
  |  |

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

Date: 20 Apr 90 00:55:22 GMT
From: sun-barr!newstop!jethro!norge.Sun.COM![e-mail]  (John McKernan)
Subject: Re: Listening to the Star (was RE: Drake Equation)

In article <[e-mail]> [e-mail] (Tom Neff) writes:
>The point is that civilization tends to add new media, not eliminate old
>ones.  We will surely still be emitting RF of identifiably sentient
>origin many centuries from now.

I don't think there's any reason to assume that another technological
civilization would use RF for communication, there are a lot of other
other ways which are probably better. If your favorite music station
transmitted neutrinos, you could tune it in in China as easily as in
the US. While a civilization's hardware probably would emit some RF,
that kind of hardware noise would probably not be very intense, and/or
easy to separate from natural noise.

The Fermi Paradox does not seem very paradoxical to me. It seems very
likely that we can't detect any technological civilizations yet. All we
know is that there is a reasonable chance that: (a) there are lots of
planets, (b) the chemical reactions that are "life" will occur, (c)
life will become intelligent (note that there are lots of reasonably
intelligent life forms on the Earth), (d) some of these intelligent
life forms will want to modify their environment (ie. technology).
Given that we have pathetically little information about anything not
on Earth, it's no surprise that we haven't seen signs of alien
civilizations.  There's an infinite number of reasons as to why "they"
haven't colonized Earth (there are a LOT of other places to live, they
prefer to live in space, etc ad infinitum). As to "one hundred light
year wide engineering projects", why would "they" bother, and if 1 out
of a million did we wouldn't be able to see it (it's obscured in the
galactic center, you can't see a Dyson sphere anyway, etc ad nauseum).

John L. McKernan.                                                  [e-mail]
Disclaimer: These are my opinions but, shockingly enough, not necessarily Sun's
-------------------------------------------------------------------------------
"There is no such thing as Cyberpunk, but there are alot of imitations."
               - William Gibson

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

End of SPACE Digest V11 #288
*******************