Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V11_3/V11_304.TXT

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Subject: SPACE Digest V11 #304

SPACE Digest                                     Volume 11 : Issue 304

Today's Topics:
      'Soviet Space' exhibit at Boston Museum of Science
       Re: Drake Equation (was Re: Interstellar travel)
         Re: Pegasus launchers, space-going DUCT TAPE
          Re: Radar (was Re: Drake Equation
       Re: Drake Equation (was Re: Interstellar travel)
              Re: Drake Equation
              power frequencies
               equation of time needed
       Re: Drake Equation (was Re: Interstellar travel)
                Dyson spheres?
              Re: Fatal voltages
           Pegasus launchers, space-going DUCT TAPE
----------------------------------------------------------------------

From: [e-mail]
Date: Sun, 22 Apr 90 18:10:51 EST
To: [e-mail], [e-mail]
Subject: 'Soviet Space' exhibit at Boston Museum of Science
Source-Info:  From (or Sender) name not authenticated.



     From June 1 to September 23, 1990 the Museum of Science in Boston will
be sponsoring a special exhibition entitled 'Soviet Space.'  Some of the
items in the exhibit are full-scale models of Sputnik 1 (the first man-made
satellite) and Lunakhod 2 (a moon rover); components of Luna 24 (the last
unmanned probe to the moon) and the Vega probe (which explored Venus in 1984
and Comet Halley).  Also featured will be a five meter model of the MIR
orbiter.  The exhibit will also include space suits, tools, and food from the
Soviet space program.  Technical experts from the Soviet Union will also be on
hand throughout the exhibit for lectures, questions, etc.

Please note:  I do not know what effect, if any, the situation in Lithuania
              will have on the exhibit.

For more information:  Museum of Science
                       Science Park
                       Boston, MA  02114-1099
                       [phone]

P.S. The exhibit 'Space Spinoffs,' focusing on technology that developed as a
     result of space research, ends this Tuesday, April 24.

                                           David R. Brierley
                                           Northeastern University

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

Date: 23 Apr 90 02:13:25 GMT
From: calvin.spp.cornell.edu![e-mail]  (John Sahr)
Subject: Re: Drake Equation (was Re: Interstellar travel)

In article <[e-mail]> [e-mail] (Paul Dietz) writes:
>In article <[e-mail]> [e-mail] (John Sahr) writes:
[]
>>1) 60 Hz is much lower than the "plasma frequency" of the ionosphere
>>(greater than about 1 MHz everywhere on the Earth).
>
>The plasma frequency of a plasma with electron density N (in units of
>eletrons per cubic meter) is 56.35 N^{1/2} Hz.

The formula above yields the radian-frequency.  The plasma frequency
in Hz is

                       9 sqrt(N)  Hz

(The "9" is approximate, should be 8.977297....)

Radian frequencies should be marked as 1/sec or sec^-1, which is not
the same as Hz.  For a nice intro to plasma physics, see the text
"Introduction to Plasma Physics and Controlled Fusion" by Francis
Chen (2nd edition is MKS, 1st edition is cgs).




--
John Sahr,                   | Electrical Engineering - Space Plasma Physics
[e-mail] | Cornell University,         Ithaca, NY  14853

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

Date: 23 Apr 90 00:12:00 GMT
From: crdgw1!sixhub![e-mail]  (Wm E. Davidsen Jr)
Subject: Re: Pegasus launchers, space-going DUCT TAPE

In article <[e-mail]> [e-mail] ("HENRY S. COBB, 1LT.") writes:

| Does the Space Shuttle carry duct tape?  You better believe it.  The
| In-Flight  Maintenance (IFM) kit contains a whole bunch of
| hardware-hacker stuff, including  voltmeters, breakout boxes, patch
| cords, black electrical tape, and "grey tape",  the official NASA term
| for space-qualified duct tape.

  I hope it includes "ductile soft iron fastening materials" (bailing
wire), too. That might be particularly useful in low G, since it has a
useful rigidity in addition to strength in tension. Good for holding
something "right there."
--
bill davidsen - [e-mail] (uunet!crdgw1!sixhub!davidsen)
    sysop *IX BBS and Public Access UNIX
    moderator of comp.binaries.ibm.pc and 80386 mailing list
"Stupidity, like virtue, is its own reward" -me

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

Date: 23 Apr 90 00:46:25 GMT
From: mailrus!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Radar (was Re: Drake Equation

In article <[e-mail]> [e-mail] (John Sahr) writes:
>>In order to detect ICBMs, these radars would have to have ranges of
>>about 2 or 3 times that of regular radars...
>
>...Even for the DEW-line radars, it may be pointless to increase the
>power.  Consider that the "E-region horizon" is only 1100 km away (you
>can see a 100 km tall mountain from 1100 km), and ICBM trajectories
>are fairly low...

I think you're a little confused.  First, DEW-line radars, ICBM-warning
radars, and OTH radars are three entirely different systems.  The DEW
line is an old bomber-warning network.  Second, both DEW and the BMEWS
ICBM-warning radars are ordinary microwave line-of-sight radars that
largely ignore the ionosphere.  Third, ICBM trajectories are quite high
in most cases, as "depressed trajectory" paths reduce payload (although
they are considered in defense planning because they also reduce warning
time).
--
If OSI is the answer, what on |     Henry Spencer at U of Toronto Zoology
Earth could be the question?? | uunet!attcan!utzoo!henry [e-mail]

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

Date: 22 Apr 90 15:49:23 GMT
From: rochester![e-mail]  (Paul Dietz)
Subject: Re: Drake Equation (was Re: Interstellar travel)

In article <[e-mail]> [e-mail] (PUT YOUR NAME HERE) writes:

>To the extent possible, the power grids are "in phase" across the USA.
>However, 60 Hz probably isn't such a great place to go looking for
>radio sources.
>
>1) 60 Hz is much lower than the "plasma frequency" of the ionosphere
>(greater than about 1 MHz everywhere on the Earth).

The plasma frequency of a plasma with electron density N (in units of
eletrons per cubic meter) is 56.35 N^{1/2} Hz.

The electron density of the solar wind is roughly around 10^6 m^-3; of
interstellar space, perhaps 10^4-10^-6 m^-3.

Looking for low frequency leakage from alien power grids is,
therefore, futile -- space is opaque at those frequencies.

    Paul F. Dietz
    [e-mail]

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

Date: 21 Apr 90 23:45:32 GMT
From: unhd![e-mail]  (Robert M. Kenney)
Subject: Re: Drake Equation

In article <[e-mail]> [e-mail] (Lou Adornato) writes:
>>The point that people are forgetting is the impracticality of advanced
>>civilisations using radio signals, especially if they're technologically
>>advanced enough to have colonised other worlds and thereby need to keep in
>>contact. We are acting like American Indians a couple of hundred years ago
>                             Native Americans
>>looking for smoke signals from a neighboring tribe to indicate they're
>>presense when they're using CB radios.
>
>
>I'm certainly willing to conceede that there are things in the universe
>that we don't understand. However, I'm not sure I can accept that
>there's an information medium that can travel through a vacuum at (or
>faster) than light over long distances, of which we are completely
>ignorant.


    How about gravity waves?  As far as I'm concerned, we're not too
   far(couple of centuries, at most) from having G-wave communications
   ourselves.  Just a consequence of finishing the GUT, which could be
   any day now.

--
-----------------------------------------------------------------------
Robert M. Kenney                uucp:    uunet!unhd!rmk
USNH Computer Services                Nearnet: [e-mail]
Kingsbury Hall, UNH                BITNET:  R_KENNEY@UNHH

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

Date: 23 Apr 90 00:54:17 GMT
From: mailrus!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: power frequencies

In article <[e-mail]> [e-mail] (Steve Nuchia) writes:
>To include a shred of space relevance, which power distibution
>scheme is currently in vogue for the space station?  ...

DC.  For a while they were planning an insane 20kHz system, which would
have meant custom-building everything from wiring to lightbulbs.  When
they abandoned that as a cost-cutting measure, I guess it would have been
humiliating to admit the mistake, so they went straight to DC instead of
using the aviation standard of 400Hz AC.
--
If OSI is the answer, what on |     Henry Spencer at U of Toronto Zoology
Earth could be the question?? | uunet!attcan!utzoo!henry [e-mail]

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

Date: 22 Apr 90 17:23:30 GMT
From: bbn.com![e-mail]  (Martin Grossman)
Subject: equation of time needed


I'm looking for the equations (or tables) of time that will give me
how many minutes and seconds the sun is fast/slow during the year.

This is going to be used on a microprocessor (8031) hooked upto a sundial.

PS Do the equations take into effect height ?
PS Do the equations take into effect latitude ?
PS Do the equations take into effect logitude (ie how far away I am from the
   centerline of the eastern time zone) ?


Please send reply via email to
    [e-mail]

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

Date: 22 Apr 90 18:11:29 GMT
From: nuchat![e-mail]  (Steve Nuchia)
Subject: Re: Drake Equation (was Re: Interstellar travel)

In article <[e-mail]> [e-mail] (Dan Tilque) writes:
>[e-mail] (Steve Nuchia) writes:
>>spectral lines are at 50 and 60 Hz (remember, not all the
...
>>choosing the optimally fatal frequency than we did).

>Is this a figure of speach or is some low frequency actually fatal?

One thing about power grids -- they reach into homes, where they
occasionally come into contact with children, pets, electricians,
whatnot.  Different frequencies of AC, in contact with the body,
differ in probability of serious injury.  60 Hz is just above
the saddle in the 50% fatal voltage level curve, 50 Hz is closer.
The fact that they also use twice the voltage we do for standard
residential service is probably a more important factor in the
different electrocution statistics, which I don't have handy
(and which are skewed by the fact that the Europeans *know*
getting shocked is more dangerous than we do.)

If we had it to do over again, 400 Hz would have been a much better choice.
At the time though, the extra complexity in the rotating machinery
placed a low upper bound on the frequency.  Today's utility generators
are plenty complex; wouldn't be a big deal.  Changing over would.

Nothing about low frequency *radiation* is particularly hazardous.

To include a shred of space relevance, which power distibution
scheme is currently in vogue for the space station?  I wonder
if shock hazard is one of the things they are considering in
making the choice?  The RF they were proposing is (somewhat)
less hazardous in direct contact, but it is a lot more likely
to find a leakage path to the case, than DC or 400 Hz.  I don't
know which is the best choice, but I suspect it's 400 Hz.

Given that the human specimens selected for space duty are in
superb condition, and that they are isolated from communicable
diseases once on station, electrocution has to rank pretty high
on the list of mission-critical medical contingencies.  Contamination
of the air supply, eg by a small fire, and burns from experiments
or fires are about the only other things that are likely (ignoring
EVA for the moment).  Minimizing electrocution risk would seem to be
worth a few kilograms mass.

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

Date: 22 Apr 90 18:46:42 GMT
From: sun.udel.edu![e-mail]  (Andrew Salamon)
Subject: Dyson spheres?

So whats a dyson sphere?

Magic in my Mind                     |   /Andrew/
Music in my Heart                    |   soi-disant Bleydion op Rhys
Laughter in my Soul                  |   [e-mail]
And...A Sword in my Fist (sigh)      |

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

Date: 22 Apr 90 20:01:26 GMT
From: usc!cs.utexas.edu!news-server.csri.toronto.edu!qucdn![e-mail]  (Arnold G. Gill)
Subject: Re: Fatal voltages

In article <[e-mail]>, [e-mail] (Steve Nuchia) says:
>
>whatnot.  Different frequencies of AC, in contact with the body,
>differ in probability of serious injury.  60 Hz is just above
>the saddle in the 50% fatal voltage level curve, 50 Hz is closer.
     You are going to have to explain this one to me a little bit better.  I
guess I was always under the mistaken impression that the dangers of
electricity have a lot more to do with voltage and the amount of current that
that voltage can pump through a person (0.1A is supposedly the fatal current
level).  What effect can frequency have?
-------
 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
|  Arnold Gill                        |                                     |
|  Queen's University at Kingston     |     If I hadn't wanted it heard,    |
|  BITNET   : gilla@qucdn             |       I wouldn't have said it.      |
|  X-400    : [e-mail]  |                                     |
|  INTERNET : [e-mail]  |                                     |
 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

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

Date: 22 Apr 90 14:01:00 PDT
From: "HENRY S. COBB, 1LT." <[e-mail]>
Subject: Pegasus launchers, space-going DUCT TAPE
To: "space" <[e-mail]>


                  I N T E R O F F I C E   M E M O R A N D U M

                                        Date:     22-Apr-1990 13:38 PDT
                                        From:     HENRY S COBB, 1LT
                                                  COBBHS
                                        Dept:     CLFP
                                        Tel No:   643-2504

TO:  _MAILER!                             ( _DDN[[e-mail]] )


Subject: Pegasus launchers, space-going "duct tape"

In all this discussion of possible launch aircraft for Pegasus, I haven't seen
anyone mention OSC's _actual_ plan:  they are accepting bids for a (used)
passenger airliner, jumbo-jet class.  OSC expects to wind up with a Lockheed
L-1011.  The airlines don't like them any more, because they are relatively rare
and therefore comparatively expensive to support.  This makes them cheap to
acquire; I heard rumors that OSC thought they could get one for some $3-5
million, an order of magnitude less than the price new.

The "launch-a-rocket-from-a-dirigible" idea was tried as far back as the late
'50's.  Look it up under the name "rockoon" (from rocket-baloon).  In the
rockoon concept, the baloon was expendable, but high-altitude baloons aren't all
that expensive (under $1 million per shot, if memory serves).

And now to duct tape:  Yes, Apollo 13 was saved by duct tape (among other
things).  Why did they have duct tape when they needed it?  Probably for the
same reason Mary Shaefer's tool crib stocks it -- the stuff has a million uses,
and can save your bacon if you're smart enough to improvise.  Nobody ever said
NASA was dumb.

Does the Space Shuttle carry duct tape?  You better believe it.  The In-Flight
Maintenance (IFM) kit contains a whole bunch of hardware-hacker stuff, including
voltmeters, breakout boxes, patch cords, black electrical tape, and "grey tape",
the official NASA term for space-qualified duct tape.

Cheers... --Stu
Round up the usual disclaimers ...
(COBBHS @ AFSC-SSD.AF.MIL)

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

End of SPACE Digest V11 #304
*******************