Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v11_2/v11_284.txt

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Subject: SPACE Digest V11 #284

SPACE Digest                                     Volume 11 : Issue 284

Today's Topics:
            Buran (was: Re: Space news...)
          Re: Pegasus launch from Valkyrie  (or ...
           Re: Questions about the Voyagers
          Re: Earthbound Asteroid.....trying again!
             voyager images on cd
       Re: Drake Equation (was Re: Interstellar travel)
----------------------------------------------------------------------

Date: Wed, 18 Apr 90 09:20:23 PDT
From: [e-mail]
X-Vmsmail-To: UTADNX::UTSPAN::AMES::"[e-mail]"
Subject: Buran (was: Re: Space news...)


In SPACE Digest V11 #280, att!cbnewsh![e-mail]
(maurice.r.baker) writes:
>In article <[e-mail]>, [e-mail]
>(Henry Spencer) writes:
>> Soviets say that the first Buran orbiter probably will not fly again,
>> since it is too far behind what is now considered full flight standard
>> in electronics and life support.
>
>Does anyone know how many orbiters there are in the USSR shuttle "fleet"?
>Is this really saying that there is a new orbiter design under construction
>now, or that the one-and-only (presumably) flight of the Buran is the last
>'shuttle' flight we'll see from USSR ?
>
>M. Baker
>homxc!jj1028

    In an interview with Oleg Moroz of the _Literary Gazette_, head
of Glavkosmos Alexander Dunayev said they would spend 1.3 billion rubles
on Energia/Buran this year.  When asked what they would use it for, he
said "...[we] have 581 proposals to other industries, related to new
materials, technologies and engineering developed during the program."
As to when this would happen, he only said before the year 2000.
    I posted the interview to SPACE_Digest a couple of weeks ago, but
I don't know how many people saw it since some reorganizations were going
on out there in netland.  I'll post it again if anybody's interested.

_____________
Dale M. Greer, whose opinions are not to be confused with those of the
Center for Space Sciences, U.T. at Dallas, UTSPAN::UTADNX::UTDSSA::GREER
      While the Bill of Rights burns, Congress fiddles. -- anonymous

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

Date: 18 Apr 90 07:53:39 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: Pegasus launch from Valkyrie  (or ...

I'd like to point out that nobody is "bugging" Mary Shafer about
anything.  People are properly posting articles addressing the *issue* --
not any specific person -- and Mary chooses to contribute because of
her interest in the subject.
--
"Of course, this is a, this is a Hunt, you   |*==|  Tom Neff
will -- that will uncover a lot of things.   |===|  [e-mail]
You open that scab, there's a hell of a lot
of things... This involves these Cubans, Hunt, and a lot of hanky-panky
that we have nothing to do with ourselves." -- RN 6/23/72

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

Date:     Wed, 18 Apr 1990 10:03 EDT
From: SIMMONS DONALD F  <[e-mail]>
Subject:  Re: Questions about the Voyagers
To: <[e-mail]>


ogicse!cs.uoregon.edu!spencer.cs.uoregon.edu![e-mail]  (David
Solana) asked

>Could someone out there please answer these questions about the Voyagers?

>   * Why didn't they visit Pluto? I read in Sky & Telescopes that
>     this decade would be ideal for sending a probe to Pluto.
>         Are there any plans to build such a probe?

     From what I read in Sky and Telescope (Jan 1990 I think), the ideal
time to launch a Pluto probe will be 2001, with the probe arriving in 2011.
There are two proposals for the mission. In the first, the probe would fly
directly to Pluto. The second is the so-called 'Fire and Ice' mission, where
the probe would fly to Jupiter, and during a gravity assist, divide into two
parts. One flies on the Pluto, and the other drops straight into the Sun.
Nifty idea, IMHO.

     I am not 100% sure about the Voyagers, but I think that Pluto was in the
wrong position to be included in the Grand Tour of the outer planets, unless
they skipped a few of them. Remember, they were only designed to positively
work as far out as Saturn, the Uranus and Neptune encounters of Voyager 2
being additional extras if all went well.

Donald Simmons   27000@AECLCR
Disclaimer - No one listens to me anyway

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

Date: 18 Apr 90 10:53:35 GMT
From: zaphod.mps.ohio-state.edu!samsung!munnari.oz.au!uhccux![e-mail]  (David Tholen)
Subject: Re: Earthbound Asteroid.....trying again!

In article <[e-mail]>, [e-mail] (Srinivas Bettadpur) writes:

> In article <[e-mail]> [e-mail] (Brian E. Alber) writes:

> >
> >I had heard that sometime last year or the year before that a large asteroid
> >or some other LARGE (I mean really BIG) object nearly hit the Earth.  It
> >    1.) Is there any truth to this?
> >    2.) When did this happen (where is it documented)?
>      Yes, this would sometime near the end of Spring semester 1989
> and the reports in most newspapers.

Close approach was March 23.  See my previous followup for more details.

> >    3.) How large was it?
> If I remember correctly, it was either 2 km or 20 km dia.

Not quite that large.  20 km exceeds the largest of the known Earth-
approaching variety.  1989 FC was in the 150 to 500 meter ballpark,
depending on its (unknown) surface reflectivity.

> >    4.) What would have happened if it hit?
>   It was not large enough to throw earth off the orbit on a fly-by
> or to crush it to dust on impact, but large enough to cause
> interesting tidal waves or dust clouds.
> >    5.) Why didn't we see it coming?
> I thought we *did* see it coming.  Actually there is not much we can
> do except *duck* :-)
> >    6.) How often do things this big come our way?
> Sorry, cannot help you there.

The recent discovery rate of Aten-Apollo-Amor asteroids has been around a
dozen per year.  Not all of these come close enough to the Earth to
create the kind of press coverage that 1989 FC and 1989 PB did.  So far
this year we've witnessed the discoveries of 1990 BA, 1990 BG, and 1990 DA.
There were five discoveries in about a one-week period around the beginning
of November 1989 (1989 UP, 1989 UQ, 1989 UR, 1989 VA, and 1989 VB).  None
of these have any near-term potential for running into the Earth, but after
gravitational perturbations accumulate for a few millions years, one or more
of them could possibly be put onto an Earth-intersecting (and potentially
an Earth-colliding) orbit.  Although we don't need to worry about these
guys, don't think that there's no immediate danger.  It's the ones we
haven't discovered that we have to worry about.  The goal, of course, is
to find them before they hit, thus giving us a chance to do something about
it before it is too late.  Please don't get carried away with the obvious
continuation:  just how might we go about destroying or altering the orbit
of an object that has been identified as a likely Earth-colliding object.
That discussion could go on and on...

Dave Tholen
Institute for Astronomy, University of Hawaii

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

Date: 18 Apr 90 20:37:07 GMT
From: zaphod.mps.ohio-state.edu!samsung!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!watserv1!ria!uwovax![e-mail]
Subject: voyager images on cd

In article <[e-mail]>, [e-mail] writes:
>
> I am interrested in obtaining the images from the Voyager Neptune flyby from
> last summer. Could somebody please let me know how I go about obtaining these?
> Also, does anybody know the format of the data files? I have a 386 AT with a
> VGA card and am wondering what sort of viewer I will need to write.
>
the images are available on CD and the IMDISP software works with VGA,
unfortunately it does not support super-vga or extended modes. I have
the address at home of where to write for the discs, the images are
also availave thru SPAN - email me if you still need the address, if
enough interest will post. Also, if anyone has modified or new version
of IMDISP with support for ATI VGA wonder pls let me know.
cheers

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

Date: 18 Apr 90 07:51:09 GMT
From: unmvax!nmtsun![e-mail]  (Daniel Briggs)
Subject: Re: Drake Equation (was Re: Interstellar travel)

I can't speak for any of the deliberate attempts at SETI that have
been made, but I think I can add a bit to the SNR on how radio astronomy
is "normally" practiced.

For those who don't care to read the whole thing here, the short
answer is that I agree with Forrest Gehrke.  We haven't heard anything
yet because for the most part we haven't been listening.

Dan Tilque writes:
>Forrest Gehrke writes:
>>Dan Tilque 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.  This seems to be better limiting data than the
>>> results of the Drake equation.
>>
>>Who is this "we" that has been listening?  And with what?  These
>>signals are not going to be picked up on a boombox with the
>>announcement the signal is from outer space.
>
>There's this obscure branch of science which you are probably unaware
>of.  It's called Radio Astronomy.  One of the things they're good at is
>aiming large radio antennae at the sky.

Reality check here.  It is *hard* to catch internal communications
over interstellar distances.  Here are a couple of rough numbers I
just pounded out.  You can assume that I've done the sums right, or
check them yourself.

Assume a 1 GW transmitter 50 lyr away.  Since this is supposedly an
evesdropping situation, we had better assume that this is radiating
isotropically.  If you want to assume a beamed transmitter, you can.
That will raise the power of the beam by whatever geometric factor you
assume, and also cut down the chance we will see it by the same
factor.  If you want to stay inside of 50 lyr, you are talking modest
number statistics.  I don't happen to know the exact numbers, but we
are probably talking tens of thousands of eligible suns within that
radius.  If you start assuming a geometric beaming factor of tens or
hundreds, then you are reducing the number of "eligible" suns by that
factor --- the rest of them we won't see.  We wouldn't consider the
fact that we didn't detect life in a sample of 10 suns a definitive
result that there is no life within 50 lyr.  A sample of 10000 suns,
and the assumption that the XTs use a moderately directional
communications beam, reduces to the same case.  (But the beam itself
is much easier to detect.)

Enough digression.  Assume that we can only evesdrop on the
extraterrestrial Lawrence Welk Show if we can detect the isotropic
transmission.  I have no good idea of what to assume for a transmitter
power.  I think that 1 GW is pretty damned big by today's standards.
(Correct me if I am badly off here, BTW. I may be.)

    1 GW spread over a sphere of 50 lyr is 3.6*(10)^-2 (10^-26 W/m^2)

The reason for the funny choice of units is that radio astronomers
like to talk about Janskys.  1 Jy = 10^-26 W/m^2/Hz.  To make it
easier to detect, we will assume that the aliens are using a
monochromatic transmitter.  In this case, to go from the above power
flux to Jy, we divide by the bandwidth we observe at.  *For a
monochromatic source*, the smaller bandwidth you use, the better.  For
the the case where you have power spread all over the spectrum, more
bandwidth is better.  Anyway,

    Our transmitter looks like

    3.6*(10)^-2
    ----------- = 7.1*(10)^-4  microJy     (the normal continuum case)
    50(10)6 Hz

       and also like

    3.6*(10)^-2
    ----------- = .2 microJy               (the most extreme spectral line
    .20(10)6 Hz                             case that we can observe at the
                                            VLA)

To give you some feeling as to what we can actually detect, twelve
hours of observation at 1.4 GHz (the 21 cm line that you have heard so
much about), will get us down to an RMS noise of 15 microJy in the
continuum case, and down to 240 microJy in the spectral line case.)
Assume that we need at least 5 times the noise level to get anyone's
attention, and we find that the ratio of detectable signal to actual
signal is about 100,000 in the continuum case, and 6,000 in the
spectral line case.  This is staring straight at it with one of the
most sensitive instruments in the world!  To get a serendipitous
discovery, you generally need a signal that is a good deal more
powerful than that.

>Also there have been
>some programs to listen to a number of nearby stars for unusual
>signals.

Quite true.  If you streched Arecibo to the limit, you might be able
to get this sort of signal from some of the very nearest stars.
That's about the only antenna on earth that could, though.  (Not
excepting us, BTW).  If you are really streched to the limit like
this, it means that you don't get a very large sample, though.  I
think that many of the SETI experiments have to assume that the other
guys are deliberately sending stuff, and then guess where to look, and
what a deliberate signal might look like.  This is to dodge the
problem that isotropic radiation is so damned hard to pick up.  When
you get into this sort of guessing game, then you have to sample an
enormous paramter space.  That's what these million channel receivers
are all about.  Normal radio astronomers aren't interested in this:
you don't use a SETI specialized receiver by accident!  I should
probably shut up about SETI, since I don't really know that much about
it.  Anyone care to enlighten us with SETI details?

>>It is also a daunting problem to discriminate against
>>the signals being caused to be transmitted by ourselves.
>
>One of the steps in processing radio astronomical signals is to filter
>out locally generated signals.

Sorry Dan, but I have to agree with Forrest here too.  At the lower
frequencies, interference is a hell of a problem.  You don't just
"filter it out".  Generally you do your best to observe where it
isn't, but this is really tough.  At the low frequencies (say less
that a GHz or two) where ordinary civilian electronics can contribute
significant stuff, it's terrible.  (Not just transmission equipment,
but anything electronic or electromechanical.  Cars, computers, &
microwave ovens are all detectable!)  At the middle frequencies, (say
a few GHz to a few tens of GHz), we only have to fight with civilian
radar and the military.  This isn't as bad, since there isn't as much
of it.  Also, it is usually fairly narrow band and directional.  From
several 10s of GHz to maybe a hundred or so there is not a whole lot
other than military projects and space projects.  Above a hundred GHz
we pretty well have the spectrum all to ourselves.  (Or at least so it
appears to us.  I know that the spectrum has been allocated by the FCC
well past this point.  Most of the high end stuff seems to be labeled
"space" or "mobile communications".  I just haven't personally run
into any of this as a problem.  It's a fact, though, that it is much
harder to build receivers at these kind of frequencies.  This too will
change....)

-----
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)

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

End of SPACE Digest V11 #284
*******************