Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V09_5/V9_563.TXT

Internet Message Format | 1991-07-08 | 16KB

Return-path: <[e-mail]>
X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
Received: from corsica.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/0Yo2HLa00UkVA5yU5S>;
          Fri, 28 Jul 89 05:18:16 -0400 (EDT)
Message-ID: <[e-mail]>
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Fri, 28 Jul 89 05:18:08 -0400 (EDT)
Subject: SPACE Digest V9 #563

SPACE Digest                                      Volume 9 : Issue 563

Today's Topics:
               Re: Space Goals
              Re: Blackholes - evidence
         Re: Frequently asked SPACE questions
              Re: Freedom's logo
              Voyager Broadcasts
            Re: Lagrangian Points
    National Aero-Space Plane symposium slated (Forwarded)
              Re: Decaying Lunar Orbits
                 Re: Moonwalk
----------------------------------------------------------------------

Date: 9 Jul 89 23:17:00 GMT
From: [e-mail]  (Stainless Steel Gerbil [Joe Beckenbach])
Subject: Re: Space Goals


    My two cents:  those in JFK's world saw the Moon as "impossibly far",
but the goal of safely returning a man from the Moon's surface in under a
decade was accomplished.  How about one of three projects which are "impossibly
far and too soon" for the moment:

    1)  a full score of TAU craft [Thousand Astronomical Unit] to explore
        extra-solar space in all directions.  The vectors would be spread
        around to the vertices of a dodecahedron, centered on Sol.
        YEAR OF 20th CROSSING OF NEPTUNE "ORBIT": 2001.

    2)  exploratory craft scouting the two nearest stars to Sol.
        YEAR OF ENTRY TO BARNARD'S STAR INFLUENCE: 2015.
        YEAR OF ENTRY INTO ALPHA CENTAURI SYSTEM:  2030.

    3)  sustained human life outside Terra's atmospheric limits.
        YEAR OF THIRD GENERATION SPACE BIRTH:  2040.

--
Joe Beckenbach
339 S. Catalina #316     [e-mail]
Pasadena, CA 91125    [phone]

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

Date: 10 Jul 89 07:47:46 GMT
From: jarvis.csri.toronto.edu!utgpu!utzoo!censor![e-mail]  (Jeff Hunter)
Subject: Re: Blackholes - evidence



        There have been a number of good answers about black
holes, so I thought I'd look for some numbers. I've listed them to
two digits, but don't trust more than the exponent. (What's an
order of magnitude between theorists :-)

        The saying "black holes have no hair" means that a black
hole can be completely descibed by its mass, spin, and charge.
(This may remind you of an elementary particle. Coincidence?
I don't think so.)
        I'm taking the simple case of a neutral, spinless hole
viewed from a distance by a stationary observer (stationary to
the hole that is).
        The temperature is the Hawking Radiation of the hole. If
nearby matter is falling into the hole it can also generate amazing
heat.

                mass            radius          temp            lifetime
                (grams)         (meters)        (degrees        (years)
Cubic                                            Kelvin)
Kilometer
of water        e15             1.3e-15         1.1e11          1.2e11

Mount
Everest         e17             1.3e-13         1.1e9           1.9e17

Moon            7.3e25          9.7e-5          1.5             7.4e43

Earth           6e27            .008            .019            4.1e49

Sun             1.8e33          2400            6.2e-8          1.1e66

Galactic
Center          7e39            9.3e9           1.6e-14         6.5e85

Elliptic
Galaxy          9e42            1.2e13          1.2e-17         1.4e95

        (For those who shun metric, divide grams by 1e6 to get tons,
read meters as yards, and (Kelvin*2) + 300 = Fahrenheit)

        The "cubic kilometer of seawater" is a Gigatonne of
anything you have handy. It is in the range of the smallest hole
that could still have survived from the Big Bang. "Mount Everest"
may be a bit more massive than this. The "galactic center" is an
estimate of the mass of the suspected black hole at the center of
the Milky Way. "Elliptic galaxy" is the core of an energetic galaxy
that was probably a Quasar in its wild youth.

        The formulae I used are:
radius      = M / 7.5e29
temperature = 1.1e26 / M
lifetime    = 1.9e-34 (M**3)   <- Mass cubed
        (The mass loss of a black hole increases again when it drops
below e17 grams since it is then hot enough to radiate electrons and
positrons. (lifetime = 1.2e-34(M**3)) When it drops below 5e14 grams
the lifetime drops again, etc....)

        Some notes of interest (to me anyways :-)
A black hole of reasonable size (one meter) would be somewhat more
    massive than Saturn. It would be quite cold.
A hole of reasonable mass (100 Kg) would evaporate in much less than
    a second. This would be equivalent to about 2 Gigatonnes of TNT.
A hole at room temperature (~300K) would be about 1/200'th the mass
    of the moon (the mass of Ceres perhaps?), and would be too small
    to see.
The "elliptical galaxy" core is 1/200'th the density of water! Since
    the radius increases proportionally to mass the density of a huge
    hole can be arbitrarily low.
As Matt noted, any black hole with temperature less than ~3K (the
    background temperature of the Universe) will be stable until
    the universe expands enough to cool down some more.

                        Have fun (I did) ...
--
    -- my opinions --    [e-mail]

    Keep track of the current path, and use it naturally.
        Glenn Reid (Postscript Language Program Design)

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

Date: 12 Jul 89 03:05:37 GMT
From: jarvis.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Frequently asked SPACE questions

In article <[e-mail]> [e-mail] (Tom Neff) writes:
>>1) What happen to Saturn V plans?
>>Underconstruction by Henry.
>
>Wow, so THAT'S where they went! ...
>PS I hope Toronto has adequate barge facilities...

We don't need no steenking barges.   ( Sorry, couldn't resist.  :-) )

Actually we will need some, as we plan to launch from the most worthless
area of land nearby:  downtown Buffalo...  :-) :-) :-)
--
$10 million equals 18 PM       |     Henry Spencer at U of Toronto Zoology
(Pentagon-Minutes). -Tom Neff  | uunet!attcan!utzoo!henry [e-mail]

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

Date: 13 Jul 89 19:20:43 GMT
From: aramis.rutgers.edu!klaatu.rutgers.edu![e-mail]  (J Storrs Hall)
Subject: Re: Freedom's logo

Thanks for that.  While we're on the subject:

Does anyone have a postscript version of the Pioneer plaque?

--JoSH

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

Date: 13 Jul 89 20:30:27 GMT
From: coplex![e-mail]  (Dannie Gregoire)
Subject: Voyager Broadcasts




I know this has already been posted but.....

Can someone please e-mail me the times and satelite channel(s)
that the Voyager pictures of Neptune can be Viewed.

                Thanx-a-head-a-time
                   dannie@coplex

   +--------------------------------------------------------------+
   | |\ /\   Yet Another Precise Exageration from......        \   / |
   | | | _                                -o o- |
   | |/.\/.        Dannie Gregoire  (dannie@coplex)  `Roof!'- U      |
   +--------------------------------------------------------------+

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

Date: 13 Jul 89 16:59:00 GMT
From: mcvax!ukc!strath-cs!nott-cs!piaggio![e-mail]  (Dr A. N. Walker)
Subject: Re: Lagrangian Points

In article <[e-mail]> [e-mail] (Henry
        ^^^^^^^^^^^^^^^^^^^^^ -- I see Henry is using C news! [:-)]
Spencer) writes:
>In article <[e-mail]> [e-mail] (Chandrasekhara
Sudhama) writes:
>>...Would someone please explain
>>(either on this network or in private email) the stability of the
>>equilibrium points in the Earth - Moon system? [...]
>
>I know of no intuitive explanation of why the "Trojan points" at 60 degrees
>are stable.  It is a non-trivial mathematical result.

    Somewhat agreed.  However, it's not *that* bad.

>Even worse is an explanation of why the Trojan points are stable against
>small perturbations, while the straight-line points are not.  Or of why
>the Trojan points stop being stable against perturbations if the mass
>of the primary is not at least N times that of the secondary (I forget
>the value of N but I think it's something like 30).

    It's fairly easy to see why the straight-line points are unstable.
First, you must use rotating co-ordinates, in which Earth and Moon are
stationary [ignoring perturbations from Sun, Jupiter, etc.] -- otherwise
there are no points of equilibrium at all.  In these co-ordinates, there
are four forces acting on a particle:

    gravity towards the Earth;
    gravity towards the Moon;
    centrifugal force away from the origin (centre of mass);
    Coriolis force.

Coriolis force is zero for stationary [in the rotating co-ordinates]
particles, so the Lagrange points occur where the other forces balance.
Take for example the straight line point "behind" the Moon.  This is
where the combined gravitational pulls towards the Earth and the Moon
exactly balance the centrifugal force away -- all forces acting along
the straight line.  Put a particle slightly further away -- bingo,
both gravities are weaker, centrifugal force is stronger, so the
particle is strongly pushed away, ergo unstable.  [This is an over-
simplified, intuitive, argument.]

    The triangular points are much less easy to analyse, but I
can offer some pointers.  Basically, they are *maxima* of the
modified potential energy [gravitational potential plus centrifugal
potential] (the straight-line points are saddle-points), and are thus
intrinsically unstable.  However, they are quite flat maxima, and if
the mass-ratio is large, as for the Earth-Moon system, it turns out
that before the particle gets far away from equilibrium, the Coriolis
force is sufficient to turn the particle back round.

    The critical mass-ratio is determined by whether

        27 m^2 - 27 m + 1

is positive (==> stable) or negative (==> unstable), where m is the mass
of the Moon in units of the total mass.  Thus, Henry's N is

        (27 + sqrt (27*23))^2 / 108 == 24.9599....

>As in other areas of celestial mechanics, there is just no substitute for
>mathematics in this.

    True, but the mathematics is within the scope of a competent first-
year university undergraduate -- needs vectors, "normal modes", and a
little mechanics.  A complete expose [of the equilibrium and its stability]
occupies [riffle, riffle] two sides of A4 in my lecture notes.

--
Andy Walker, Maths Dept., Nott'm Univ., UK.
[e-mail]

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

Date: 15 Jul 89 06:59:27 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: National Aero-Space Plane symposium slated (Forwarded)

Mary Sandy
Headquarters, Washington, D.C.                      July 14, 1989


N89-53
EDITORS NOTE:  NATIONAL AERO-SPACE PLANE SYMPOSIUM SLATED


     Media representatives are invited to attend the first open
symposium on the National Aero-Space Plane (NASP), sponsored by
the NASP Joint Program Office and the American Institute of
Aeronautics and Astronautics.  The symposium is being held in
conjunction with the Dayton Air and Trade Show, July 20-21, at
the Dayton, Ohio Convention Center.

     The symposium will include presentations on the status of
the NASP program and status of foreign aerospace plane
projects.  In addition, progress in the areas of propulsion,
materials, computational fluid dynamics and other technology
areas will be discussed, as will potential commercial and
civilian spin-offs from the NASP.

     Designed to achieve single-stage-to-orbit flight, NASP is a
joint Department of Defense and National Aeronautics and Space
Administration program involving the development of technologies
leading to an experimental vehicle, the X-30.  The vehicle also
will be capable of sustained hypersonic flight within the
atmosphere.

     To help explain program goals and progress, members of the
NASP Joint Program Office at Wright-Patterson AFB will man a
unique information display at the air show.  Central to that
display will be a 75-foot, half-scale mock-up of the X-30.  It
will be located in Trade Structure "B" and will be open to the
public during trade show hours -- from 9 a.m. to 5 p.m. each of
the four days.

     Media representatives are invited to a reception which will
be held for symposium participants on the evening of the 20th,
from 7 p.m. to 9 p.m. in the Trade Structures at the air show.

     If you are interested in seeing the NASP display at the air
show or attending the symposium, please contact JoAnne Rumple at
the Joint Program Office at XXX/YYY-ZZZZ for further details.

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

Date: 15 Jul 89 21:34:05 GMT
From: jarvis.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Decaying Lunar Orbits

In article <[e-mail]> [e-mail] (Henry Melton) writes:
>... upper portion of the LEM was abandoned in lunar orbit and then
>later decayed to crash on the Lunar surface.  How fast is this orbital
>decay, considering that there is no atmosphere to speak of?  Is there
>some other mechanism that can cause such a fast decay?

Even the Earth is not gravitationally a perfect sphere, although you can
model it moderately well as a sphere with an equatorial bulge.  The Moon
is a very different story; gravitationally, it's just plain lumpy.  This
makes it difficult for any low orbit to be stable for long periods, as I
understand it.  Eventually it gets perturbed enough to hit the surface.

Also, the later LM ascent stages were crashed deliberately, to provide
artificial moonquakes for the benefit of the seismometers left on the
surface.
--
$10 million equals 18 PM       |     Henry Spencer at U of Toronto Zoology
(Pentagon-Minutes). -Tom Neff  | uunet!attcan!utzoo!henry [e-mail]

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

Date: 17 Jul 89 19:07:15 GMT
From: att!chinet![e-mail]  (John Mundt)
Subject: Re: Moonwalk

In article <[e-mail]> [e-mail] (Marc Siskin) writes:
>In article <[e-mail]> [e-mail] (Doug Krause) writes:
>>Also, how did the camera that was left behind on the Moon track the
>>top of the Eagle taking off?  and how did they get THAT reel of film back?
>I am not sure how long the Apollo astronauts were on the moon, but I do

I believe a max of three days on the moon by the Apollo 17 astronauts and
the last flight.

>know that teh shot of the LM launching was not from Apollo 11 but from a
>later flight.  It wasn't filmed either but was a live video shot from the
>Lunar Rover's camera.  It was exciting watching the liftoff live (so to
>speak) when it occured.

I don't have cable so I don't get the liftoff to splashdown coverage of
A&E, but only the networks truncated coverage.

I am disturbed that no one felt the need to explain that most of the pretty
color pictures were from the lunar rover's cameras on later flights.  It
seems that Americans are such bozos that they would not notice that the
11 astronauts landed in a purposely plain, flat area, whereas the pictures
of later flights have sizeables hills and craters.

Also, CBS's coverage spent most of its time showing the trivial things
being done at the same time as Apollo 11, rather than mission activities.
If I'd have wanted to see a horse being broken, I'd have checked out a
John Wayne movie!
--
---------------------
John Mundt   Teachers' Aide, Inc.  P.O. Box 1666  Highland Park, IL
[e-mail]
[phone] (Day voice) || -432-8860 (Answer Mach) && -432-5386 Modem

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

End of SPACE Digest V9 #563
*******************