Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_6/V13_611.TXT

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Subject: SPACE Digest V13 #611

SPACE Digest                                     Volume 13 : Issue 611

Today's Topics:
             Re: Gravity vs. Mass
         LOW LATITUDE AURORAL ACTIVITY WATCH
Re: S.E.T.I.Who can give me any reasons why there would not be at least
             Re: Gravity vs. Mass
           Re: Keck (was Re: Privatization)
       Re: Request For Discussion: sci.space.moderated
              Re: Budget Numbers Wanted
        Re: Hypersonics ... paritcularly Hotol
          Saenger, Ferri, Sloop BOOKS WANTED
                Other Planets
                 Houston Pork
             Re: Gravity vs. Mass

Administrivia:

    Submissions to the SPACE Digest/sci.space should be mailed to
  [e-mail].  Other mail, esp. [un]subscription requests,
  should be sent to [e-mail], or, if urgent, to
             [e-mail]

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

Date: 21 May 91 15:48:58 GMT
From: eru!hagbard!sunic!lth.se![e-mail]  (Magnus Olsson)
Subject: Re: Gravity vs. Mass

In article <[e-mail]> [e-mail] (Isildur) writes:
>I was having a debate with one of my friends over this one... You somehow
>dug a hole clean through the earth in a diameter through the core and it was
>completely insulated from the heat changes running through the planet.  When
>you climbed into the tunnel (fall into the the tunnel...) and reach the
>center of the planet, would your weight be incredibly multiplied because of
>your new relative location to the center of the earth (using the
>mass/gravitational constant formula) or would you have zero-weight because
>you were surrounded by virtually identical mass (and also assuming that the
>tunnel closes up outside your immediate location)?

You'd be weightless. It's relatively easy to show that if you're inside a
spherically symmetric body, at a distance R from its centre, the gravitational
forces from the parts of the body at distances greater than R from the centre
will all cancel. The result is that as long as you're outside the body, the
gravitational force is proportional to 1/R^2. Assuming that the body is
homogenous, the force when you're inside the body is proportional to R, falling
off to zero at the centre. If the body isn't homogenous, the dependence on
R is more complicated, but the cancellation mentioned above still occurs,
and you become weightless at the centre.

The proof is done using Gauss' theorem; see any textbook on vector caclulus.

Historical note: The proof is elementary with today's mathemematics, but it
is said that it held up the publication of Newton's Principia for twenty
years!

Magnus Olsson                   | \e+      /_
Dept. of Theoretical Physics    |  \  Z   / q
University of Lund, Sweden      |   >----<
Internet: [e-mail]     |  /      \===== g
Bitnet: THEPMO@SELDC52          | /e-      \q

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

Date: Thu, 23 May 91 02:17:58 MDT
From: oler <@BITNET.CC.CMU.EDU:[e-mail]> (CARY OLER)
Subject: LOW LATITUDE AURORAL ACTIVITY WATCH
X-St-Vmsmail-To: st%"[e-mail]"

                /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

                     LOW LATITUDE AURORAL ACTIVITY WATCH

                            ISSUED: 23 MAY, 1991
                             VALID: 25 - 27 MAY

                /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\


ATTENTION:

     A Low Latitude Auroral Activity Watch has been issued for the southerly
middle and low latitude regions.  A geomagnetic and auroral storm caused by
a well placed coronal hole is expected to occur between 25 and 27 May.
Activity is expected to peak on 26 May (+/- approximately one day).  The
probability for geomagnetic and auroral storming is fairly high.  Whether the
intensity of the auroral activity will be sufficient become visible over the
lower latitudes is not known.  However, judging by the most recent data,
there is reason to suggest this might become possible.

     Lunar phase will interfere with attempts to view auroral activity.  The
best observing period will occur after (and as) the Moon sets in the early
morning hours.

     If conditions intensify sufficiently, a warning may be issued for low
latitude auroral activity. Conditions are expected to calm down after 28 May.


**  End of Watch  **

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

Date: 23 May 91 12:34:24 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: S.E.T.I.Who can give me any reasons why there would not be at least

In article <[e-mail]>, [e-mail] (Lydick, Carl) writes:

            ......................

> Perhaps we could, if we started NOW.  However, how long will it take before
> overpopulation and resource depletion render us incapable of bootstrapping
> ourselves into space?  And if something were to devastate our techonlogical
> infrastructure in the near future (suppose, for example, that the cold war had
> turned hot enough that we reverted to 18th century levels), would the survivors
> be able, with the resources left to them, to achieve the technological level
> necessary for a permanent presence in space?

The first point is, frankly, the one which worries me.  It will never be
the case that the majority of mankind, or even the majority of the US
population, will be able to immediately and directly benefit from a large
manned presence in space.  I am not convinced that without the Cold War we
would have even gotten to the stage of the first satellites by now through
governmental actions.

As to the last point, I believe the answer is yes.  Even if most of the
details are lost, the basic knowledge needed to rebuild will most likely
remain.  We will know how to build electric generators and internal
combustion engines, etc.  We will know how to build radios and computers.
There still will be accessible hydropower, fuels, and metals.  Quite
possibly, even nuclear reactors can be recommissioned and reactivated.
--
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: 21 May 91 23:53:39 GMT
From: agate!stanford.edu!unixhub!slacvm![e-mail]  (Jon J Thaler)
Subject: Re: Gravity vs. Mass

In article <[e-mail]>, [e-mail]
(Sandy Antunes) says:
>
>Easy physics here...
>>(most of message deleted) When you climbed into the tunnel...
>> and reach the center of the planet, would your weight be incredibly
>> multiplied or zero?
>
>The mass/gravitational constant formula assumed point masses.  If
>you were in the center of the Earth, there is technically no central
>mass attracting you.  The gravitational force is due to the entire
>mass surrounding you, and a simple integral (simple?) solves the
>problem... zero weight.

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

Date: 22 May 91 01:34:36 GMT
From: [e-mail]  (Jonathan Leech)
Subject: Re: Keck (was Re: Privatization)

In article <[e-mail]> [e-mail] (Paul Dietz) writes:
>In article <[e-mail]> [e-mail] (Jonathan Leech) writes:
>>pain.  Further, no planetary mission will return as much science in
>>its brief lifetime as the Keck will over decades, and the risk factor
>>is very high.
>
>One wonders, then, why we should spend multiple billions on planetary
>science when the scientific return on the dollar is so much greater
>from ground-based telescopes (and, last I heard, telescope time
>worldwide is oversubscribed by at least 4 to 1).  Sure, there are
>questions that can only be answered on-site, but the questions the
>telescopes are trying to address (the fate and nature of the universe
>as a whole) seem more fundamental.
>
>The question "why spend money on planetary probes" is at least as
>problematic as "why spend money on manned spaceflight".

    I've brought this up a few times before to be roundly ignored, but
perhaps some discussion will happen this time.    My feeling is that
space science, particularly planetary science, is grossly overfunded
in proportion to its science return.  (For those who think not: would
you be willing to have the $2G NASA science budget transferred to NSF
and subjected to the same peer review process as other NSF funded
research?  If not, why not?)

    This doesn't mean I think we shouldn't be doing space science - by
no means!  - but that additional justifications must be drawn up as
they must for manned spaceflight.
--
    Jon Leech ([e-mail])
    __@/

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

Date: 22 May 91 00:52:22 GMT
From: amdcad!brahms![e-mail]  (Phil Ngai)
Subject: Re: Request For Discussion: sci.space.moderated

[e-mail] (Frank Crary) writes:
>I was not aware that sci.space HAD a moderator. I certainly agree that
>sci.space would benifit from one (or a more active/visible one). It is
>worth noting that on sci.military, untill about a month ago, there was
>apparently no moderator. When one appeared (Actually I think he had beed
>out of town or something...) the time I spent reading that newsgroup
>decreased by about 50%, without the quality or level or information
>really changing.

But it didn't change the fact that you didn't/don't have a clue as to
what was going on.

--
For the Welfare system to flourish, its clients must not.
Conflict of interest?

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

Date: 23 May 91 22:46:29 GMT
From: csus.edu!beach.csulb.edu!nic.csu.net!csun.edu!corona![e-mail]  (Stephen Walton)
Subject: Re: Budget Numbers Wanted

In article <[e-mail]>
[e-mail] (Frank Crary) writes:
>As can be seen from Stephen Walton's post, most programs did not recieve
>"the money taken away from Freedom" the following items are the only ones
>to recieve more money without Freedom as opposed to with Freedom:
>
> [3 lines deleted]
>
>The following did not LOOSE money, as a result of the deletion of Freedom:
>
> [11 lines deleted]
>
>There were a large number of items which lost LESS money as a result of
>Freedom being removed, but were still cut back.

It is also worth noting that the total NASA budget is several hundred
million less without Fred than with.  That said, I confess to being
someone who wrote a letter supporting space science to the committee,
which may have led to the result cited---though I certainly did not
expect this.

My understanding of the situation as of early May was this:  Congress
wanted a $700M cut from the Administration NASA budget.  Since Freedom
had already been scaled back, Truly was taking the position that the
entire $700M should come from space science---which would have
resulted, according to my NASA sources, in the cancellation of every
space science mission not already flying as well as significant cuts in
NASA support of ground-based astronomy.

My letter did not bash Fred.  I mentioned no other government programs,
merely wrote a short letter stating my support for the Augustine
Commission recommendations: space science support at 20% of NASA budget
total and implementation of the OSSA Strategic Plan, neither of which
would have been possible if the $700M cut had gone through.  I suspect
a number of other astronomers and space scientists did likewise.
--
Stephen Walton, Dept. of Physics & Astronomy, Cal State Univ. Northridge
    "Lately it occurs to me/What a long, strange trip it's been"

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

Date: 24 May 91 03:09:36 GMT
From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Hypersonics ... paritcularly Hotol

I wrote:
>>There was talk about a Hotol derivative using conventional rockets launched
>>from the back of an Antonov Mriya...
>Rumor (via email) hath it that aerodynamic problems killed the idea, but
>I have no details.

And of course, no sooner do I post that, than I come across a piece about
it in the May 6 Space News.  This item reports that BAe and the Soviets
have concluded that the idea *will* work.  The next stage is to try to
get somebody -- hoped to be ESA plus the USSR -- interested in funding
detail work.
--
And the bean-counter replied,           | Henry Spencer @ U of Toronto Zoology
"beans are more important".             |  [e-mail]  utzoo!henry

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

Date: 22 May 91 22:49:50 GMT
From: zephyr.ens.tek.com!tektronix!reed!intelhf!ichips![e-mail]  (Larry Smith)
Subject: Saenger, Ferri, Sloop BOOKS WANTED


Does anyone have any of the following books in their
collections for sale:

ANY of the reprints of:
"Rocket Drive For Long Range Bombers"
by:  E. Saenger and J. Bredt

Elements of Aerodynamics of Supersonic Flows
by: Antonio (Tony) Ferri
Macmillan, New York, 1949

Liquid Hydrogen as a Propulsive Fuel
by: John Sloop
NASA SP 4404

Please contact me if you have any of these.

If anyone has access to the Saenger/Bredt book, maybe they
could tell me how many pages it has.

Larry Smith

[e-mail]

503-696-4465

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

Date: 21 May 91 21:24:35 GMT
From: mcsun!ukc!edcastle!hwcs![e-mail]  (Stewart Fleming)
Subject: Other Planets

I was looking through an old (1980 edition) Guinness Book of World Records
over the weekend [OK, so I couldn't sleep...]  In the section
'Universe and Space', it has an entry for "STELLAR PLANETS" : planets in
remote systems which have a mass of less than 7% of the parent star.

The existence of the following planets has been postulated :

61 Cygni (1942)
Lalande 21185 (1960)
Kruger 60,
Ci 2354,
BD + 20 2465,
One of the two components of 70 Ophiuchi.

Also :

Epsilon Eridani and Barnard's Star - last two reported by Peter van de Kamp.

Has there been any evidence presented since 1980 which either refutes,
confirms, or supports these claims ?  Indeed, what evidence led to these claims
in the first place ?

Thanks,
STF
--
[e-mail]                        ...ukc!cs.hw.ac.uk!sfleming
"Wow ! A flying mouse !"  "Eeek ! A flying cat !"

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

Date: 20 May 91 19:39:27 GMT
From: van-bc!rsoft!mindlink![e-mail]  (Bruce Dunn)
Subject: Houston Pork

> [e-mail] writes:
> Person: Fraering Philip
>
> You are dreaming if you think the congresscritters are really
> considering things in that fashion, instead of maybe using Fred as a
> bargining chip to get more pork money for their own districts, or are
> even thinking of a long-term plan for space exploration.
>


     I was in Houston for a conference at the time that Fred got cut.  The
local newspapers treated the cut not as a disaster for space , but as a
disaster for the local economy (Houston of course being the home of the Johnson
space center).  They blamed the cut on a committee of "northerners" who were
trying in effect to grab money from Houston's pork barrel (space) and put it in
their own (urban renewal etc.).
--
Bruce Dunn    Vancouver, Canada   [e-mail]

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

Date: 21 May 91 20:14:49 GMT
From: eru!hagbard!sunic!news.funet.fi!funic!nntp.hut.fi!cs.hut.fi![e-mail]  (Harri Pasanen)
Subject: Re: Gravity vs. Mass

In article <[e-mail]> [e-mail] (Sandy Antunes) writes:

   <stuff deleted>

   As a side comment, if the general point-mass assumption used in the
   simple form of the grav const. formula were true, there would be no
   tides... tides are due to the fact that things really aren't point masses.
                         sandy

I thought tides were created by the moon?

Harri

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

End of SPACE Digest V13 #611
*******************