Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v08/v8_332.txt

Internet Message Format | 1991-07-08 | 17KB

Return-path: <[e-mail]>
X-Andrew-Authenticated-as: 0;andrew.cmu.edu;Network-Mail
Received: from po5.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr1/ota/space/[e-mail] (->+dist+/afs/andrew.cmu.edu/usr1/ota/space/space.dl) (->ota+space.digests)
          ID </afs/andrew.cmu.edu/usr1/ota/Mailbox/po5.andrew.cmu.edu.1252.0.0>;
          Sun, 21 Aug 88 04:09:19 -0400 (EDT)
Received: from andrew.cmu.edu via qmail
          ID </afs/andrew.cmu.edu/service/mailqs/q004/QF.andrew.cmu.edu.230e8478.1b5281>;
          Sun, 21 Aug 88 04:06:20 -0400 (EDT)
Received: by andrew.cmu.edu (5.54/3.15) id <AA00636> for +dist+/afs/andrew.cmu.edu/usr1/ota/space/space.dl; Sun, 21 Aug 88 04:05:18 EDT
Received: by angband.s1.gov id AA07176; Sun, 21 Aug 88 01:05:31 PDT
    id AA07176; Sun, 21 Aug 88 01:05:31 PDT
Date: Sun, 21 Aug 88 01:05:31 PDT
From: Ted Anderson <[e-mail]>
Message-Id: <[e-mail]>
To: [e-mail]
Reply-To: [e-mail]
Subject: SPACE Digest V8 #332

SPACE Digest                                      Volume 8 : Issue 332

Today's Topics:
            Re: 95% vs. 99.9% reliability
              exotic propulsion methods
       Re: SETI (was Re: Time dilation affecting SETI)
             death of Anatoly Lewtschenko
                   Re: SETI
               Re: SPACE Digest V8 #320
            Re: 95% vs. 99.9% reliability
            Re: 95% vs. 99.9% reliability
            Re: 95% vs. 99.9% reliability
         Re: Most distant galaxy detected (Forwarded)
          Re: Re: ET phone home? (SETI)   RESPONSES
----------------------------------------------------------------------

Date: 10 Aug 88 20:58:31 GMT
From: jpl-devvax![e-mail]  (Larry Wall)
Subject: Re: 95% vs. 99.9% reliability

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
: In article <[e-mail]> [e-mail] (Jay Wooten) writes:
: >You can bet the Soviets would have hardly missed a beat in sending up
: >another one (something they've proved several times in the past).
:
: As somebody wrote in Aviation Week a few months afterward (roughly, from
: memory):  "If the same thing had happened to the Soviets, they would have
: swept the debris off the launch pad, hoisted the next launcher onto the
: pad, and started the countdown.  Anyone who objected would have been told
: where to go, or sent there."

You guys are comparing Apples and Orchids.

The Soviets aren't hazarding a gigabuck each time they launch.

I think they must study different economics textbooks than we do.    :-)

Larry Wall
[e-mail]

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

Date: Wed, 10 Aug 88 20:37:01 EDT
From: John Roberts <[e-mail]>
Subject: exotic propulsion methods



>From: [e-mail] (Allen C. Kistler)

>>From: b.gp.cs.cmu.edu![e-mail]  (Ralf Brown)
>>In article <[e-mail]> [e-mail] (B Gray) writes:
>>}TSS-1 will deploy a satellite at the end of a 20km conducting
>>}wire with an insulating coating, upwards from the shuttle....

>In _Journal_of_Geophysical_Research_, vol. 70, p.p. 3131-3145, (1 July 1965)
>...
>The neat thing is that if you apply a big enough
>voltage of your own across the satellite to MAKE the current go the OTHER way,
>then you get a little bit of boost out of it, rather than drag.  This will
>never be more than 50% efficient since you'll still be sending some of the
>energy away as plasma waves.  I don't know of any satellites that have ever
>actually used this method propulsion, so it may not be an especially practical
>method.  Anyone else?

If it works as described, the <50% efficiency is no problem, and it could be
a useful method. In low Earth orbit, energy is available in large quantities
via solar cells, but reaction mass is hard to come by. It sounds as though
none of the mass of the craft is used (unless the wire is evaporating).

                                  John Roberts
                                  [e-mail]

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

Date: 10 Aug 88 22:14:29 GMT
From: thumper![e-mail]  (Phil R. Karn)
Subject: Re: SETI (was Re: Time dilation affecting SETI)

> Does anyone have a proof
> that all encrypted messages that can be statistically distinguished
> from noise?

The reverse is instead true. Randomness is an important concept in
cryptography. It is easy to show that "apparent" randomness (to the
eavesdropper) is an essential feature of any good cipher system.

A few "random" comments on SETI:

The important issue with regards to frequency selection for SETI, which
hasn't really been discussed here fully yet, is the dependence of the
background noise level on frequency. The combined effects of galactic
synchrotron radiation, absorption by the interstellar medium, quantum
effects and the like are such that the optimum frequency window for
interstellar communication within our galaxy is between 1 and 10
gigahertz. Any other intelligent civilizations within our galaxy
studying the same problem would almost certainly come to the same
conclusions.

There is nothing particularly magic about the "water hole" band used for
the initial SETI experiments. It was picked more or less whimsically,
probably with intent to fire up people's imaginations, but also because
it was as good a place as any to start. A *true* SETI search would cover
far more spectrum than the water hole, but unfortunately large parts of
it are already in use by humans.

The conventional wisdom in SETI has long been to search for coherent
signals, like carriers.  Yes, civilizations could be using more complex
signals (e.g., spread spectrum) but even for simple signals, the search
space (direction, bandwidth, frequency, signal level) is enormous. This
point merits emphasis: SETI has only just begun, and all of the searches
to date have only barely scratched the surface of the search space, even
if only simple coherent signals are considered. I think we should rule
out the simple cases before spending much effort on the more complex
possibilities.

The comment about TV transmitters being the most conspicuous evidence of
life on earth is true. But this applies only to detecting a TV signal,
not demodulating it. Much of the power in a TV transmission is in the
narrowband carrier, and this is far easier to detect than the sidebands
that are spread out over several megahertz.

Also making the earth extremely "bright" at radio frequencies are the
various deep space tracking radars. These are probably not as effective
as TV transmitters because they aren't as numerous, don't operate full
time and are inherently broadband (they don't put most of their energy
into a single, coherent, narrowband carrier).

Phil

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

Date: 10 Aug 88 08:38:49 GMT
From: mcvax!unido!ecrcvax![e-mail]  (Bruno Poterie)
Subject: death of Anatoly Lewtschenko

The soviet cosmonaut Anatoly Lewtschenko died last Saturday,
of a "big desease" (no more precision). He came back from Mir
on 29th of December 87, together with Romanenko (326 days stay)
and Alexandrow, few days also after starting his planned stay.

It is not sure that this is to relate directly to weightless,
or to the starting chock, or if this could have arrived after
i.e. a routine fly on a jet. The list of space victims is getting
longer by one, but let's hope that studying the reasons will
help shorten it for the future.

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

Date: 10 Aug 88 19:12:18 GMT
From: vrdxhq!daitc!csed-1![e-mail]  (Jonathan Zweig)
Subject: Re: SETI

Isn't it pretty ridiculous to envision a species that is (a) nasty enough
to want to exploit other civilizations, (b) has the capability for
interstellar travel and the weaponry to actually get away with it and (c)
can't sniff out intelligent life forms unless they are broadcasting?

Come off it! If we want to shield our planet from obeservation, fine -- I
think there is just about enough conducting material in the solar system to
build a pretty nice faraday cage around the earth -- oops! We have to put
it in place without using radio communications so the BGM (Big Green Men)
don't come and zap us.

Sheesh. I thought a pretty sensible assumption with SETI is that it simply
isn't feasible for *any* of the parties involved to travel (else they would
be here now, etc. etc.) and that's why we use gigawatt radio beacons. I'll
take my chances -- who knows, maybe if we make enough noise the Galactic
Police would come to investigate at the same time as the Space Pirates come
to get us. ;-)

Johnny Z

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

Sender: "chaz_heritage.WGC1RX"@xerox.com
Date: 11 Aug 88 02:34:39 PDT (Thursday)
Subject: Re: SPACE Digest V8 #320
From: "chaz_heritage.WGC1RX"@xerox.com

In his 3 Aug 88 02:14:51 GMT Jay Maynard writes:

>Main power on the space station is specified as 220 VAC at 20 kHz.

This, of course, makes power supplies efficient (since, in essence,
they're giving you the front half of a switching power supply), but can
indeed generate AC across a lithium battery in the manner described.<

I stand corrected.

The explosions were held to be due to blocking diode failures. Perhaps those in
charge of such things will ensure that circuitry rated for the Space Station is
designed to preclude any possibility of diode failure causing application of
high-frequency AC to lithium cells.

Then again, perhaps they won't.

Regards,

Chaz

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

Date: 11 Aug 88 13:33:25 GMT
From: jumbo![e-mail]  (Jorge Stolfi)
Subject: Re: 95% vs. 99.9% reliability

Keith Rogers wrote:
>
>   Sure the O ring thing had to be fixed, but did it have to kill
>   the entire U.S.  space program in the meantime?

Jay Wooten wrote:
>
>   You can bet the Soviets would have hardly missed a beat in
>   sending up another one (something they've proved several times
>   in the past).

When, precisely?

In April 67, while the Moon race was heating up, Soyuz 1 crashed and
the the Russians lost their first cosmonaut (Komarov).  A full eighteen
months elapsed before their next manned launch.  This delay was only
three months less than the US delay after the Apollo fire.

There was another long hiatus in Russian manned launches after three
cosmonauts died in the reentry of Soyuz 11 (June 1971).

Those gaps may have been due to other causes, but the point is that
there is no obvious evidence that the Russians are or were less
bothered than the US by fatal accidents in their manned space program.

Besides, a 2.5 year gap in the US manned space program is nothing
compared to the 10 year hole in the unmanned planetary exploration
program...

                Jorge Stolfi @ DEC Systems Research Center
                [e-mail], ...!decwrl!stolfi


    The hazards involved were greatly increased by the notorious
    nonchalance of American cannoneers; during the civil war, they had
    actually loaded their guns with cigars in their mouths.
        --Verne, _From the Earth to the Moon_ (1865)

DISCLAIMER: The above opinions are not the sort of stuff my employer,
my teachers, my friends, or my mother would like to be associated with.

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

Date: 11 Aug 88 02:00:38 GMT
From: bsu-cs![e-mail]  (Brad Majors)
Subject: Re: 95% vs. 99.9% reliability

In article <[e-mail]>, [e-mail]
> >a certain temperature, they should have continued launching >above that
> >temperature<, while working on a better engineering solution.
>
>
>     I couldn't agree more.  This has been my attitude ever since the
> Challenger disaster.  I just don't see
                        ^^^^^^^^^^^^^^^^

FLAME ON *******

Impatience caused the Challenger to explode.

FLAME OFF***********


The Improved O rings are just one of many features that were changed
on the shuttle. Don't you keep up on your readings?  Many faulty parts
were found in the investigation sparked by the challenger tragety.

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

Date: 11 Aug 88 17:48:29 GMT
From: [e-mail]  (Eugene Miya)
Subject: Re: 95% vs. 99.9% reliability

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (Jay Wooten) writes:
>>You can bet the Soviets would have hardly missed a beat in sending up
>>another one (something they've proved several times in the past).
>
>As somebody wrote in Aviation Week a few months afterward (roughly, from
>memory):  "If the same thing had happened to the Soviets, they would have
>swept the debris off the launch pad, hoisted the next launcher onto the
>pad, and started the countdown.  Anyone who objected would have been told
>where to go, or sent there."

I don't think the Soviets are as callous as one might make them out to be
in this series of notes.  Otherwise I think we would have seen more boosters
come out faster.  I think they would have spent some time trying to figure
out what "caused" the problem.  Our problem was that we had a series of
civilian and military losses (Delta [formerly Thors] and Titan]).  They
are back launching both of these now.  We are just a bit more hung up
on the sanctity of life than the Soviets, the Japanese, the Chinese, etc., etc.

Another gross generalization from

--eugene miya, NASA Ames Research Center, [e-mail]
  resident cynic at the Rock of Ages Home for Retired Hackers:
  "Mailers?! HA!", "If my mail does not reach you, please accept my apology."
  {uunet,hplabs,ncar,decwrl,allegra,tektronix}!ames!aurora!eugene
  "Send mail, avoid follow-ups.  If enough, I'll summarize."

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

Date: 10 Aug 88 18:45:15 GMT
From: hp-pcd!hplsla![e-mail]  ( Dean Payne)
Subject: Re: Most distant galaxy detected (Forwarded)

>MOST DISTANT GALAXY DETECTED

>     Called 4C41.17, the newly-discovered galaxy is located at an
>estimated distance of 15 billion light years -- more than 90
>percent of the distance to the visible limits of the universe.

>     Once the galaxy was identified optically, the researchers
>established its huge distance by taking an optical spectrum which
>uncovered emission lines in carbon and hydrogen produced by the
>elements within the galaxy.
>     The observations reveal that these lines are greatly shifted
>along the spectrum, or reddened, more than those of any galaxy
>previously observed.

Like many press releases, this article gives the disputable estimated
distance without giving the real meaningful data -- the observed red
shift value.

Some local papers often condense these releases, leaving out most of the
news and just printing part of the background information.  I wish I had
saved a classic from a few years back.  The banner said something about
'Astronomers announce major new discovery', followed by several
sentences of background.  There was no mention about what discovery had
been announced.

So, what is the measured red shift of this galaxy?  It will probably be
out-dated by the time S&T can publish it.

Dean Payne

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

Date: 9 Aug 88 18:01:33 GMT
From: hpda!hpcuhb!hp-sde!hpfcdc!hpfclm![e-mail]  (Bob Myers)
Subject: Re: Re: ET phone home? (SETI)   RESPONSES

>}    I was wondering if it is true, as I heard, that only the
>}    carrier wave from TV signals is able to reach beyond the
>}    atmosphere -- i.e., no aliens out there are examining TV
>}    pictures from Earth.
>}
>}I believe this is more or less correct.


>I believe that the "less" is more accurate than the "more".


Agreed.  To put it in slightly oversimplified form, the higher the frequency
of the signal, the less the signal is refracted (not, as some believe,
reflected) by the various layers of Earth's ionosphere.  VHF TV, and to a
greater extent UHF TV, are certainly at sufficiently high frequencies so that
there's an excellent chance of the signal making it through to space.

A very good example is the OSCAR series of amateur radio satellites; these
are routinely used by hams running no more than 100W ERP (effective radiated
power), at roughly the 145 MHz range - smack in the middle of the VHF TV
bands. (Channels 2-6 are below this band; 7-13 are above.)

By the by, I don't know how it would be possible that the carrier of a signal
would be able to reach "beyond the atmosphere", but the information carried
on that signal (the modulation of the carrier) would not.  Certainly it is
possible that the entire signal can be weakened to the point where it is
just detectable that the signal is there, but it's rather a neat trick to
somehow strip the modulation off and leave a nice healthy carrier behind.


Bob Myers  KC0EW                         |  Opinions expressed here are not
                                         |  those of my employer or any other
{the known universe}!hplabs!hpfcla!myers |  sentient life-form on this planet.

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

End of SPACE Digest V8 #332
*******************