Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_6/V13_677.TXT

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Subject: SPACE Digest V13 #677

SPACE Digest                                     Volume 13 : Issue 677

Today's Topics:
            Re: Asteroid Hazard Avoidance
     Re: Female Cosmonauts (Was Re: The Reasons for a Station? )
              Beanstalk analysis reprise
      Re: Fred vs. Exploration: head-to-head competition
                The Long Term

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Date: 27 May 91 15:09:22 GMT
From: mcsun!inesc!unl!unl![e-mail]  (Jose Pina Coelho)
Subject: Re: Asteroid Hazard Avoidance


In article <[e-mail]> [e-mail] (James C Krok)
writes:
> [...]
> I recall reading somewhere that if such a large asteroid were again found to
> be on a collision course with the Earth, it would be easier to move the Earth
> out of the way with nuclear charges (at the poles?) than to intercept the
> asteroid with said charges and deflect it.  I believe the article was in
> Scientific American, September or November of 1990.

I wouldn't call this ridiculous.  I would call it hilarious.


1 - Any asteroid that is smaller that the earth would be easier to
displace than the earth.
  - Blow the bombs there, where they don't cause polution.

<< Move the earth out of the way >>
With what ?  Star Treck's warp drive ??

To the general public information, the only law we can apply is
action/reaction.  An atom bomb doesn't get much mass out of the
atmosphere.  And the little mass that might get out doesn't go very
fast, just little above escape velocity.


2 - The energy necessary to get earth off the way is, if applied as
bombs, enough to break the crust (how are your magma-swiming abilities
 ? :-) )

3 - Either Scientific American was bought by Reader's Digest or the
editor was way past drunk.


Next, is a way to prove/disprove the theory:

Little experiment:

Get a porcupine, suspend it from the ceiling. (that's the asteroid)
Underneath it put a water-filled baloon. (that's earth)
On the surface of the baloon put any ammount of dinamite you choose.
(that's your atomic device)  (1)

Now, ignite the dinamite and release the porcupine at the same time (2).

The ballon busted, bad method.



Other experiment:

Get a porcupine, suspend it from the ceiling. (that's the asteroid)
Underneath it put a water-filled baloon. (that's earth)
Insert a charge of dinamite in the porcupine's mouth (that's your
atomic device).

Now, ignite the dinamite and release the porcupine at the same time.

The porcupine busted, but the baloon is intact, good method(3).



----
(1) - You are allowed to use five cray-months to choose the location
and ammount of explosive.

(2) - That's assuming that

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

Date: 28 May 91 15:08:49 GMT
From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!swrinde!elroy.jpl.nasa.gov!freedom!xanth![e-mail]  (Jonathan McDowell)
Subject: Re: Female Cosmonauts (Was Re: The Reasons for a Station? )

[e-mail] (Frank Crary) writes:

>The Soviet attitude torwards female cosmonauts is the result of their early
>experience, [...] Their first female cosmonaut,
>V. V. Tereshkova, [...] was the ONLY one of the Vostok cosmonauts
>to suffer from very serious space sickness (Space Adaptation Syndrome).

This is not true.  It is well known that German Stepanovich Titov, the
second male Soviet cosmonaut, also suffered from SAS, and possibly
others did as well.  They didnt make as much of a fuss about him being
sick though.  The Soviet attitude towards female cosmonauts is the
result of pervasive sexism in Soviet society.  This has been very
obvious to me in the few conversations I have had with Soviet space
program reps at exhibitions and so on, all of whom have been neolithic
in their expressed attitudes toward women, and in the presentation of
Soviet space films and of radio bulletins covering the flights of
Svetlana Savitskaya, which presented the fact that Savitskaya was able
to fly and do a spacewalk as evidence that Soviet space technology was
really advanced, as if you needed more advanced technology for a woman
to be able to do it. It should be clear to the Soviets from the US
experience that women do just fine in space, but of course lack of
data isn't the point.

Congratulations to Helen Sharman on her safe landing, the 15th woman to
make a spaceflight.


 - Jonathan McDowell

 .-----------------------------------------------------------------------------.
 |  Jonathan McDowell                 |  phone : [phone]                 |
 |  Huntsville NOW                    |                                        |
 '-----------------------------------------------------------------------------'

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Date: 28 May 91 18:46:00 GMT
From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!wuarchive!emory!ox.com!fmsrl7![e-mail]  (Ron Carter)
Subject: Beanstalk analysis reprise

[Gary Coffman, are you listening?  Here it is.]

I finally re-did the tether area calculations.  I found that
iron whisker is simply not strong enough for its density to
make a beanstalk (geosynchronous skyhook).  However, if there
is a sufficient source of carbon which can be used to mass
produce carbon whisker, this analysis indicates that the
strength is more than sufficient to support a beanstalk of
reasonable taper.  If silicon carbide whisker is the best
available material, a beanstalk is marginally feasible.  Any
material stronger than carbon whisker would make the construc-
tion of a beanstalk a piece of cake, relatively speaking.

Note:  This analysis is of the static case.  It ignores
tidal considerations which are important to objects in the
Earth-Moon-Sun system.  A working beanstalk will require
damping mechanisms to compensate for tidal forces.  Dynamic
momentum-transfer devices such as vertical Lofstrom loops
or space fountains could also transmit forces from far up
the tether back to the earth, reducing the tether's taper
and the amount of material required.

Constants:

Description            Symbol    Value

Mass of earth            Me    5.979e24 kg
Radius of earth at equator    Req    6.380e6 m
Gravitational constant        G    6.673e-11 N*m^2/kg^2
(Source:  CRC Handbook of Chemistry and Physics, 55th ed.)
Earth's rotational speed    omega    7.29246e-5 radians/sec
(2*pi/23 hrs 56 min sidereal period)

Conventions:

    r = Radius from center of earth
    Rgeo = Geosynchronous orbit radius from center of earth
    dm = differential of tether mass
    a = local acceleration due to gravity and centrifugal force
    A = local tether area
    rho = tether density, material dependent
    T = local tether tension, force
    Tw = Tether working tension, force/area

Materials:
    C whisker
        Density = 1.7 = 1.7e3 kg/m^3
        Tensile strength = 3e6 psi = 20.7 GPa

    SiC whisker
        Density = 3.2 = 3.2e3 kg/m^3
        Tensile strength = 3e6 psi = 20.7 GPa

Note:  I am assuming the tensile strength figures are more accurate
than may be warranted.  You have been warned.

(Source:  Handbook of tables for Applied Engineering Science, 2nd ed, CRC Press)

First, we must calculate the geosynchronous orbit radius.
This is necessary to set the endpoint of our integration later.

Equate centrifugal force and gravitational attraction:

(1)    omega^2*Rgeo = G*Me/Rgeo^2

Combine like terms:

(2)    Rgeo^3 = G*Me/omega^2 = 7.503e22 m^3

(3)    Rgeo = 4.218e7 m


Derive downward acceleration as a function of radius, r:

(4)    a = G*Me/r^2 - omega^2 * r


Calculate tension as a function of radius:

(5)    dT = a*dm = a*rho*A*dr

Assume tether stress is constant, at T/A = Tw for all r.
Given this, we derive

(6)    dA = rho*A*a/Tw dr  =  rho*A/Tw*(G*Me/r^2 - omega^2*r) dr

Combining like terms,

(7)    dA/A = rho/Tw*(G*Me/r^2 - omega^2*r) dr

Integrate.

(8)    ln A = rho/Tw*(-G*Me/r - .5*omega^2*r^2) + C

Use (8) to find the ratio between the area of the tether at
the surface of the earth and the area at geosync as a function
of the tether material properties:
                              |4.218e7 m
    ln(Ageo/Asurf) = rho/Tw*(-G*Me/r - .5*omega^2*r^2)|
                              |6.380e6 m
    = rho/Tw*(-1.419e7m^2/sec^2 + 6.265e7 m^2/sec^2)

(9)    = rho/Tw*4.846e7 m^2/sec^2

(10)    Ageo/Asurf = e^(rho/Tw*4.846e7 m^2/sec^2)

The dimensional analysis is left as an exercise for the reader.

Compute the area ratio for actual materials.  Assume a working
strength of 2/3 the ultimate tensile strength of the material.

For carbon whisker:
        rho = 1.7 = 1.7e3 kg/m^3
        Tensile strength = 3e6 psi = 20.7 GPa
        Tw = 13.8 GPa

    Ageo/Asurf = e^(1.7e3/1.38e10*4.846e7)
           = e^5.969
           = 391

A carbon-whisker beanstalk appears to be practical.

For silicon carbide whisker:
        rho = 3.2 = 3.2e3 kg/m^3
        Tensile strength = 3e6 psi = 20.7 GPa
        Tw = 13.8 GPa

    Ageo/Asurf = e^(3.2e3/1.38e10*4.846e7)
           = e^10.87
           = 52400

A silicon-carbide whisker beanstalk appears to be marginal.

This posting is copyright (c) 1991 by Ron Carter.  All rights
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------------------------------

Date: 29 May 91 02:03:06 GMT
From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!mips!spool.mu.edu!news.nd.edu!mentor.cc.purdue.edu!pop.stat.purdue.edu![e-mail]  (Herman Rubin)
Subject: Re: Fred vs. Exploration: head-to-head competition

In article <[e-mail]>, [e-mail] (Doug Mohney) writes:
> In article <[e-mail]>, [e-mail] (Herman Rubin) writes:

> >We need diversity, and not direction by bureaucrats or ignorant Congress-
> >people.  The funding should not come from taxes, but from those who wish
> >to invest or donate to the cause.  There will be cooperation between the
> >various groups, as there is now, and there will not be the problem of
> >trying to get majority support, or even convince politicians.

> Thanks, but I'd prefer not to add space zeleots <sp> to the other junk mail and
> phone calls I get.

Well, I am opposed to any solicitation by phone for anything.  And I doubt
that you would get as much mail solicitation from space zealots as from
sweepstakes.  I can remember when the largest part of good higher education
in the US was in private schools, and research was not supported from
government grants.  These schools were supported by private donations.

There are tens of millions of Americans alone who believe that man belongs
out there on a permanent basis.  There are others in the rest of the world.
There are firms which will invest, and there are other firms which will donate
for public relations and to encourage research, which private industry used
to consider of importance.  Anyone who understands research knows that most
of it will run into blind alleys and obstacles.

> The system we have now ain't perfect, but it, in a fashion, works. And I can't
> see any private set of individuals gathering up $1 billion for two
> Voyager-class probes, nor maintaining infrastructure for 15+ years to collect
> all the data.

What about all the optical telescopes?  I see absolutely no problem with a long
ongoing project.  As for the collecting the data from such probes, I can see no
shortage of funding for it.  Possibly they would have given up trying to get the
probes to produce data now, but most of the collecting is automated.

> Some projects are going to need governmental support and funding, and the
> knowledge which results should go into the public domain. I think it would be
> unseemly to have Corporation XYZ putting out bids for the TV rights to the
> landing of the <privately financed> Mars Rover. Access to the data? Sure.
> Can your University come up with the $50,000 access fees?

Almost all of the pure research done in this country before WWII, the great
bulk of it privately funded, went into the public domain.  BTW, it WAS suggested
that those TV stations showing the lunar landings should have paid NASA for the
rights, and there is no reason why it should not outsell the Olympics.  The
idea of access fees for data seems to be a product of the computer age, with,
for the first time, commercially developed instructions, which cannot be used
without permission.

Is the Manned Space Development Society, or the Planetary Research Society,
going to keep its data from university researchers?  Even Spacecraft, Inc.
is unlikely to do that.
--
Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907-1399
Phone: [phone]
[e-mail] (Internet, bitnet)   {purdue,pur-ee}!l.cc!hrubin(UUCP)

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

Date: 28 May 91 23:37:57 GMT
From: argosy![e-mail]  (Kevin S. Van Horn)
Subject: The Long Term

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>>One year is long term? ...
>
>Well, in the US it is...

Give me a break.  I'm always hearing about how American business doesn't look
past the next quarter's profits.  But what do you call it when a group of
venture capitalists finances a startup (like the one I'm working for -- MasPar)
with the expectation that they'll have to wait maybe five years to see a
return on their money?

------------------------------------------------------------------------------
Kevin S. Van Horn | The means determine the ends.
[e-mail]  |

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End of SPACE Digest V13 #677
*******************