Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V12_1/V12_150.TXT

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Date: Tue, 31 Jul 1990 01:29:47 -0400 (EDT)
Subject: SPACE Digest V12 #150

SPACE Digest                                     Volume 12 : Issue 150

Today's Topics:
                 Re: What if?
              RE: SPACE Digest V12 #143
             Info need on rovers
              Re: Space Junk velocities
           Re: Model Rockets become more space junk
            Re: Galileo Update - 07/27/90
              Re: HST testing (followup)
            Re: slowing the earth
            unusual sighting last evening
              Re: Omni magazine on Mars
          Re: space news from June 11 AW&ST

Administrivia:

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

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

Date: 30 Jul 90 19:44:16 GMT
From: sdd.hp.com!hp-pcd!hpcvia![e-mail]  (ken_scofield)
Subject: Re: What if?

From: [e-mail] (Perry G Ramsey)
Message-ID: <[e-mail]>

>To really accomplish what you want, you would have to send the angular
>momentum somewhere else.  Example:
>
>A big linear accelerator facing west.  Pick up some rocks and shoot them
>into space.  Chuck enough rocks out fast enough and you could make a dent.
>I'll get you some numbers.
>
>And here they are!
>Angular momentum of earth: 6.3 e33 kg m^2 s^-1
>Slowing to 25 hr rotation is 4% reduction, = 2.5e32
>If you chucked the rocks out at 15 km/s, you would need
>
>m =  delta angular momentum
>     ________________________   =  2.8 e21 kg of rock
>     radius of earth * velocity
>
>This amounts to a hole about 800 km on a side to quarry the rocks.

  This reminds me of a recurring thought I've had, to wit:  If a wayward
  asteroid struck the Earth with enough mass/energy to appreciably affect
  the rotation rate, would anybody survive to notice it?  I haven't checked
  your numbers above, but one might assume that "catching" an 800 km cube
  would have roughly the same effect as "throwing" the cube -- except that
  "catching" it all at once is obviously going to wreak havoc.  So, has
  anyone heard or read anything about what happens to us if this should
  occur?  (Again, I'm interested in the case where the Earth's rotation
  and/or orbit are affected to a significant degree.)  To a rough approx-
  imation, how big a "rock" would it take to do this?

                 Ken Scofield           C-9355  SSI #453890085
      ^          Hewlett-Packard, ICO   Phone:  [phone]
|----/-\----|    1020 NE Circle Blvd.   ([e-mail])
|   Gone    |    Corvallis, OR  97330   (ucbvax!hplabs!hp-pcd!kas)
| Divin' or |
|  Jumpin'  |     Cute Disclaimer:  Nobody ever listened to me before,
|-----------|                      so why start now?

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

Date: Mon, 30 Jul 90 09:56 EST
From: "ADMIRAL AQUILONE, GREAT ALLIANCE" <[e-mail]>
Subject: RE: SPACE Digest V12 #143

I have read your messages on this bulletin.  and I am wondering.  although
I think jet propolsion and stuff is fun is there any information or discussion
on aliens and the effects on us or the events, sightings and so forth?????

decnet  splava::aqui4156
bitnet  aqui4156@snyplava

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

Date: Mon, 30 Jul 90 18:09 CDT
From: Astronomers Do It At Night!! <[e-mail]>
Subject: Info need on rovers
X-Envelope-To: [e-mail]

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

Date: 31 Jul 90 02:44:51 GMT
From: usc!jarthur!nntp-server.caltech.edu!deimos.caltech.edu![e-mail]  (Karl Stapelfeldt)
Subject: Re: Space Junk velocities


  Two objects in a 28.5 degree inclination circular orbit CAN impact
each other with a relative velocity almost as large as the orbit
velocity.  Case in point: when the two orbits have a 180 degree
difference between the longitudes of their ascending nodes.  In this
case, the orbits have the same inclination to the Earth's equator
but their planes intersect at a 2*(28.5)= 57 degree angle.  The
relative velocity of two colliding particles in this case is
(17,500 mph)*sin(57)= 14,700 mph !!!  This represents the maximum
possible relative velocity; a typical collision will occur at
somewhat lower velocities.

   The equatorial bulge of the Earth perturbs low orbits in such
a way that the longitude of the ascending node is always changing
(`regressing').  This regression, combined with the constant influx
of new debris sources, essentially guarantees that there will be some
piece of junk in the a 28.5 orbit that can eventually realize the maximum
impact velocity with any given spacecraft.


   Remember :  Two orbits with the same inclination do not,
                  in general, lie in the same plane.

                                       Karl Stapelfeldt
                                       [e-mail]

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

Date: 30 Jul 90 20:17:11 GMT
From: talos![e-mail]  (Kyle Jones)
Subject: Re: Model Rockets become more space junk

David E. Jenkins writes:
 > Many people have been discussing a contest to put a model
 > rocket on the Moon.
 > [...]
 > At orbital velocities even the smallest fragment can cause potentially
 > fatal damage to equipment and/or crew members.  Do we really want to
 > contribute to this growing problem over a silly contest.

Are these little bits of metal and whatnot a serious danger to
LEO spacecraft?  I would think that all the garbage and
spacecraft would be orbiting in the same direction and at roughly
the same speed, so the collisions wouldn't be as bad as if the
garbage was in (say) retrograde orbit.

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

Date: 30 Jul 90 13:03:27 GMT
From: cs.utexas.edu!sdd.hp.com!uakari.primate.wisc.edu!aplcen![e-mail]  (Ray Sterner)
Subject: Re: Galileo Update - 07/27/90

In article <[e-mail]> [e-mail] (Ron Baalke) writes:
>
>                     GALILEO MISSION STATUS
>                          July 27, 1990
>  . . .
>     The flight team is now planning the remaining maneuvers and
>cruise sequences, together with the Earth science activities for
>the early December Earth gravity-assist flyby.

 Are there any concerns about Galileo's high speed dive so deep
 into the cloud of space debris around the earth?

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

Date: Mon, 30 Jul 90 18:12:03 EDT
From: John Roberts <[e-mail]>
Disclaimer: Opinions expressed are those of the sender
    and do not reflect NIST policy or agreement.
Subject: Re: HST testing (followup)


>From: zaphod.mps.ohio-state.edu!uwm.edu!ux1.cso.uiuc.edu!aries![e-mail]  (Doug McDonald)
>Subject: Re: HST testing (followup)

>In article <[e-mail]> [e-mail] (John Roberts) writes:
[deleted]

>This is a long quote. Sorry. I'll give it because the retort is so
>simple: there was another mirror made.

Thanks to Henry Spencer for pointing out that the second mirror was not
completed, with most of the time and dollars still not put in. There have been
conflicting reports in the media. Last week, CNN made some airhead comment
about bringing HST back to earth and switching mirrors.

>IF a real test had been done,
>it is unlikely that the second mirror woudl have had a serious error.

That's assuming NASA provided the correct specifications. They're pretty sure
they did, but the investigation is not completed, so it's really not possible
to make a definite statement now.

>IF it did, of course, then money (not necessarily the taxpayer's)
>would have been needed for fixing it. BUT if the second one was OK -
>no more cost. AND we would have KNOWN about Perkin-Elmer's
>incompetence earlier.

You're forgetting the second (expensive) test, which almost certainly would
have been demanded at that point.

Component testing comes to be of decreasing utility as fabrication nears
completion. At the time of completion of the mirrors, the expected cost to
detect and fix an error apparently would not be dramatically less than the
expected cost to fix it now. A reasonable conclusion is that the flaw *should*
have been detected much earlier, when it would have been much cheaper to
correct, and that's where the big mistake was made, not in the decision not
to test upon completion.

Two major areas of the current investigation are how the error was introduced
in the first place, and why the testing didn't pick it up. For the second
question, it could be an error in the testing methodology, or in the application
of the tests, or a combination of the two. NASA and Perkin Elmer apparently
both came up with portions of the test methodology, so either could be at
fault. If the error was in the application of the tests, it is likely that
PE would receive the bulk of the blame, since NASA has maintained that they
were not able to have as much direct oversight as they would have liked.

By the way, in reference to your comment that the testing could have been
performed before coating, thus avoiding risk to the coating:
the encyclopedia states that the thickness of a reflective coating (aluminum)
should be at least 0.12 um for maximum reflectance. With a coating ~ 1/4 wave
thick, and a tolerance of ~ 1/50 wave, unless they could be absolutely sure
that the coating would be completely uniform, the definitive final testing
(integrated or otherwise) would have to be performed after the coating
process had been completed.

Additional HST information (mostly from recollection of the HST telephone
conference a few weeks ago):
 - Researchers are becoming increasingly confident that the error is fully in
    the primary mirror. That would be good, because it's the easiest type to
    correct.

 - If the error is purely a spherical aberration in the primary, then the
    blurring of star images should be fairly symmetric. If there is an error
    in the secondary, it is likely to produce coma (off-center blurring, i.e.
    comet-like tails on the stars), which will be more pronounced in
    instruments which are off the main optical axis of the telescope.

 - The wide field/planetary camera (WF/PC) is pretty much on the main optical
    axis. The faint object camera (FOC) is more off the axis. By comparing
    images from these two cameras, researchers can determine whether coma is
    present at the best focus, and thus deduce the nature of the aberration.

 - The people who are trying to find a fix for the problem are confident that
    they can deduce and compensate for at least 95% of the aberration based
    purely on images from space. (Would that be enough to put the optics fully
    within spec?) Nevertheless, determining the exact source and nature of
    the error by ground-based investigation (i.e. looking at the test equipment)
    would be a valuable check, and might improve the accuracy of the correction.

 - The magnitude of the error appears to be about four wavelengths of visible
    light. (Is 500nm the reference?)

 - With no further corrections or computer enhancement, image resolution is
    about as good as the best ground-based optical telescopes, or maybe a
    little better. Being above most of the atmosphere, HST is still very
    useful as an ultraviolet telescope before any fixes are made. Many of the
    other instruments are also usable.

 - The wide field / planetary camera is about the size of a telephone booth
    (younger readers can see old Superman episodes for reference :-). It
    contains eight tertiary reflectors, each about the size of a US 5 cent
    piece. Changing the curvature of these small mirrors can compensate for
    errors in the primary/secondary pair, as long as the big mirrors are
    sufficiently "smooth", which appears to be the case.
        John Roberts
        [e-mail]

"We get 20 agents to memorize the book. That way, if something happens to 19
of them, we still have the information." - Maxwell Smart, Control Agent 86
                                           (paraphrased)

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

Date: 30 Jul 90 16:50:28 GMT
From: cs.utexas.edu!ut-emx![e-mail]  (Srinivas Bettadpur)
Subject: Re: slowing the earth

In article <[e-mail]> [e-mail] (John Roberts) writes:
>
>>From: usc!samsung!noose.ecn.purdue.edu!mentor.cc.purdue.edu!mace.cc.purdue.edu![e-mail]  (Perry G Ramsey)
>
>
>>To really accomplish what you want, you would have to send the angular
>>momentum somewhere else.  Example:
>

The nice thing about rigid body mechanics in 3-D is that you dont have
to "send angular momentum" anywhere in order to change the angular
velocity of the body, you can accomplish the same thing by a
re-distribution of mass (due to the change in the Moments of Inertia).
How about simply shifting the entire population of the earth to the
equator so that the polar moment of inertia of the earth rises ?
That should result in a drop in the spin rate  about the Z axis
to keep the net angular momentum in the Z direction constant.
                         Corrections are welcomed.
                                            Srinivas Bettadpur
                                        ( aoab314 @ utchpc
                                          aoab314 @ emx.cc.utexas.edu )

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

Date: 30 Jul 90 16:23:18 GMT
From: usc!jarthur!nntp-server.caltech.edu![e-mail]  (Horowitz, Irwin Kenneth)
Subject: unusual sighting last evening

I was wondering if the folks who read these newsgroups can help identify
something that I saw last evening.  At 7 p.m. I observed an object that
appeared to be a very high flying aircraft (at first I thought it might
have been an extremely bright star, and my curiousity was aroused by the
fact that it was still an hour till sunset!).  The unusual aspect of this
object was that it was moving at an extremely slow rate, and I was able
to follow it for nearly 30 minutes.  Most normal aircraft, even flying that
high, would move out of range in a matter of minutes.

The object appeared due north at first, at an altitude between 70 and 80
degrees (ie-near the zenith), and was moving on a heading of around
300-310 degrees (towards the northwest).  I looked at it through my
binoculars, but was only able to discern that it wasn't point-like in
appearance.  Unfortunately, by the time that I set up my telescope, it had
already moved out of visual range, and I couldn't recover it (this was around
7:40 p.m.).

If anyone out there has a reasonable explanation to describe this object, I
would appreciate hearing it.  For readers of sci.aeronautics, I am cross
posting this to your newsgroup, but I don't read sci.aeronautics, so please
e-mail any responses that you have.
-------------------------------------------------------------------------------
Irwin Horowitz                        |"Suppose they went nowhere?"-McCoy
Astronomy Department                  |"Then this will be your big chance
California Institute of Technology    | to get away from it all!"-Kirk
[e-mail]               |       from STII:TWOK
[e-mail]                 |
-------------------------------------------------------------------------------

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

Date: 30 Jul 90 13:59:07 GMT
From: crdgw1!gecrdvm1![e-mail]
Subject: Re: Omni magazine on Mars

In article <[e-mail]>, [e-mail] (Peter R. Cook)
says:
>
>        The July issue of Omni is dedicated to Mars, exploration, etc...
>        I found it very good reading.
>
>        FYI
>
>        /prc
>
Hmmm...I guess the reading was ok, but I'm still trying to figure out
why the spacecraft on the cover has wings.
For some truly informative reading, legible to the average joe, check
out the July issue of "Aerospace America". The issue is dedicated to
propulsion technology and is jammed with articles on stuff like ion
thrusters, solar sails, laser propulsion, solid fuel rockets etc. It
even addressed associated environmental concerns.
fyi
Pete G.

>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>~
>  Peter R. Cook                         -Don't DEC for my opinions.
>  Digital Equipment Corp.
>  Marlboro, MA. (MR01-3/SL1)
>  508-467-6936                     "1984 has past forget about Big Brother,
>                                   welcome to the 90's where the government's
>                                   your mother!" - Scatterbrain
>  Call your rep about HR 4079!

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

Date: 30 Jul 90 17:22:12 GMT
From: mojo![e-mail]  (Doug Mohney)
Subject: Re: space news from June 11 AW&ST

In article <manning.649117127@arrester>, [e-mail] (Evan Marshall Manning) writes:
>
>But a full production run will most likely not be made.  I'm betting
>no production craft will be made, giving us a divide by zero error
>in calculations of unit cost.  Comparable to the cost of a successful
>Phobos, I guess ;-)

Ahh, but 13 aircraft are already funded and paid for, regardless of what
happens in the future. I'm not sure, but I think even the test article
planes (1 & 2) will be able to take megatons to Moscow.

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

End of SPACE Digest V12 #150
*******************