Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V16_0/V16NO068.TXT

Internet Message Format | 1993-07-13 | 33KB

Date: Thu, 21 Jan 93 05:12:52
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #068
To: Space Digest Readers
Precedence: bulk


Space Digest                Thu, 21 Jan 93       Volume 16 : Issue 068

Today's Topics:
              "Synchronous Orbits around other planets"
                       *** BUSSARD RAMSCOOP ***
               Adelaide Space Frontier Society Meetings
            A question about mercury and Gemini. (3 msgs)
                            averting doom
Earth's rotation rate may be due to early collisions [Release 93-12] (Forwarded) (2 msgs)
              Galileo Stuck Ribs / Remote Manipulator?
                       Goldin's future (2 msgs)
          Great stuff at NASA and D. WINGO is "why we now"
      Let's be more specific (was: Stupid Shut Cost arguements)
            Lunar Rotation (was: Earth's rotation rate...)
                        Shuttle safety margins
                    Territorial conquest? Pishaw!!

    Welcome to the Space Digest!!  Please send your messages to
    "[e-mail]", and (un)subscription requests of the form
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    (THENET), or [e-mail] (Internet).
----------------------------------------------------------------------

Date: Wed, 20 Jan 1993 21:01:17 GMT
From: Larry Wall <[e-mail]>
Subject: "Synchronous Orbits around other planets"
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:
: In article <[e-mail]> [e-mail] (Tom A Baker)
: writes:
: >Thousands of counterexamples exist if you are willing to consider SMALL
: >bodies.  You might find rocks, asteroids, that spin faster than their
: >surface's orbital velocity, and remain held together by cohesion.  A
: >synchronous orbit would be impossible, exactly as you are asking.
:
: Never say never.....  Simply tie the satellite to the body with a tether.

Somehow it seems to be cheating to use the term satellite for such an object:

    "Sorry, hon, I can't do the dishes tonight--I've got to shinny down to
    Oscar 2931 and change the batteries."

[I originally wrote "shinny up", but decided that was wrong...]

Larry Wall
[e-mail]

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

Date: 20 Jan 93 23:42:14 GMT
From: Lynne K Wahl <[e-mail]>
Subject: *** BUSSARD RAMSCOOP ***
Newsgroups: sci.space

[e-mail] (Jack Coyote) writes:

>In sci.space, [e-mail] (Henry Spencer) writes:
>>
[some really interesting stuff about fusion and radiation deleted]

>  More hazards/limits:
>  magnetic drag:  The large magnetic field will have a (admittedly smaller)
>                  interaction with the (unmapped) interstellar magnetic field.
>  dust:           Non-magnetic & relativistic (ouch)
>  Bok globules:   Blobs of cold dark gas. Rich in hydrogen, but the rapid rise
>                  in density is problematic to a ramscoop.
>  etc.
>  Sorry, few solutions, just more problems.
>  Note to flamers: I LIKE the idea, it just needs work.  The best way to solve
>                 the above requires that people know about them.  They haven't
>                 been mentioned (that I have seen), so I did.
>--
>"Pound for pound, lame puns are your best entertainment value." -- Gogo Dodo

Hmmm... This sounds like an interstellar probe is needed to collect
information before a *really* fast spacecraft is launched.  How about
a .01c speed probe with a small "sail" that would be primarily used to
collect interstellar H (for testing) and with magnetic sensors to check
on the magnetic medium as it goes.  How far from the sun would this
"Pathfinder" type of probe need to go before getting outside the sun's
environment?

As an exercise, how fast would, say a refueled shuttle ET, one SSME,
and a 30 ton probe go if launched in a "generic" solar escape orbit?
              ($)(0000000)<
  Probe=($)  Space Shuttle Main Engine= < External Tank=(0000000)

With a little money, and a Single Stage to Orbit shuttle (for refueling
the ET) this could be (launched? boosted?) by 1997.

--
--Lynn Wahl   [e-mail]           | The meek will inherit the
Kansas State University Student                | earth, the rest of us are
Soil Conservation Service Computer Specialist  | going to the stars. ----*

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

Date: 20 Jan 93 02:54:36 GMT
From: [e-mail]
Subject: Adelaide Space Frontier Society Meetings
Newsgroups: sci.space

The following meetings of the Adelaide Space Frontier Society (a Chapter of
the National Space Society of Australia) are scheduled on Wednesday's of each
month at 8:00 pm in

Tutorial Room 1-16
Signal Processing Research Institute
University of South Australia
The Levels  SA  5095

17 February    A talk from John Douglas on S.A. Government role in space.

17 March    A talk by John Dunkley on satellites.

21 April    A talk from Ian Tuohy from BAAe on Southern Launch Vehicle.

19 May        Paul Arthur to talk on GPS from Auspace Ltd.

16 June        A talk by Evan Semple on Single Stage to Orbit.

21 July        Jane Brooks to give a slide show on the Smithsonian Institution
        National Air and Space Museum.

18 August    Space videos.

15 September    Dean Hodgson to talk on Moon race.

20 October    Craig Robinson to talk on CNES, French Space Agency.

17 November    A talk by Mark Blair on AUSROC II-02.

 8 December    AGM and elections of ASFS officers.

--
Steven S. Pietrobon,  Australian Space Centre for Signal Processing
Signal Processing Research Institute, University of South Australia
The Levels, SA 5095, Australia.     [e-mail]

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

Date: 20 Jan 93 19:02:59 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: A question about mercury and Gemini.
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Pat) writes:
>
>During the mercury and gemini program, we had very little experience
>in the developement of rockets, capsules, engines, etc.  In fact
>mercury had a number of troubles with the main boosters.
>
>Now these systems had escape rocket towers for abort safety, but
>they would be jettisoned 1-2 minutes into flight.  My question,
>is if you have already paid the penalty, to carry the tower,
>why not keep it as an emergency retro-rocket, in case the main
>retro-roket failed?  granted the performance of the escape
>tower would have to be improved to match the main package,
>but were teh retros already fail-safe?   seems like they were
>awful sure.

Well, I can't say for certain, but consider the speed the vehicle was
moving when they jetison the tower as opposed to the speed it needed
to achieve.  I can imagine all sorts of possible aerodynamic problems
as the speed of the vehicle increased.

--
"Insisting on perfect safety is for people who don't have the balls to live
 in the real world."   -- Mary Shafer, NASA Ames Dryden
------------------------------------------------------------------------------
[e-mail] - I don't speak for others and they don't speak for me.

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

Date: 20 Jan 93 20:13:08 GMT
From: Steve Derry <[e-mail]>
Subject: A question about mercury and Gemini.
Newsgroups: sci.space

fred j mccall 575-3539 ([e-mail]) wrote:
: In article <[e-mail]> [e-mail] (Pat) writes:
: >
: >During the mercury and gemini program, we had very little experience
: >in the developement of rockets, capsules, engines, etc.  In fact
: >mercury had a number of troubles with the main boosters.
: >
: >Now these systems had escape rocket towers for abort safety, but
: >they would be jettisoned 1-2 minutes into flight.  My question,
: >is if you have already paid the penalty, to carry the tower,
: >why not keep it as an emergency retro-rocket, in case the main
: >retro-roket failed?  granted the performance of the escape
: >tower would have to be improved to match the main package,
: >but were teh retros already fail-safe?   seems like they were
: >awful sure.

: Well, I can't say for certain, but consider the speed the vehicle was
: moving when they jetison the tower as opposed to the speed it needed
: to achieve.  I can imagine all sorts of possible aerodynamic problems
: as the speed of the vehicle increased.

The sooner you can dispense with unneeded mass, the less fuel you expend
accelerating that mass.  The escape towers were undoubtedly jettisoned as
early as possible in the mission -- as soon as they were no longer needed
to escape a malfunctioning booster.  Carrying those towers the whole way
up to orbit would incur a substantially greater fuel penalty.

By the way, Mercury and Apollo used escape towers; Gemini had ejection
seats.
--
Steve Derry
<[e-mail]>

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

Date: 20 Jan 93 23:09:57 GMT
From: Bob Pendleton <[e-mail]>
Subject: A question about mercury and Gemini.
Newsgroups: sci.space

 In article <[e-mail]> [e-mail] (Pat) writes:
>
>During the mercury and gemini program, we had very little experience
>in the developement of rockets, capsules, engines, etc.  In fact
>mercury had a number of troubles with the main boosters.
>
>Now these systems had escape rocket towers for abort safety, but
>they would be jettisoned 1-2 minutes into flight.  My question,
>is if you have already paid the penalty, to carry the tower,
>why not keep it as an emergency retro-rocket, in case the main
>retro-roket failed?  granted the performance of the escape
>tower would have to be improved to match the main package,
>but were teh retros already fail-safe?   seems like they were
>awful sure.

Gemini had an escape rocket tower? I was only a kid but I don't
remember seeing one. The models I built of Gemini didn't have one.

Mercury had an escape tower. Gemini may have been able to use its
retro rockets to boost the capsule away from the booster. But I'm
pretty sure it didn't have an escape rocket tower.

                Bob P.

--
Bob Pendleton             | As an engineer I hate to hear:
[e-mail]              |   1) You've earned an "I told you so."
Speaking only for myself. |   2) Our customers don't do that.
                   <<< Odin, after the well of Mimir. >>>

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

Date: 20 Jan 93 22:14:26 GMT
From: Michael Robert Williams <[e-mail]>
Subject: averting doom
Newsgroups: sci.astro,sci.space,sci.physics,sci.environment

In article <[e-mail]> [e-mail] (Nobody of Importance) writes:
>In article <[e-mail]> [e-mail] (Joshua Bell) writes:
>]In article <[e-mail]> [e-mail] (Patricia C. Vener-Saavedra) writes:
>]>Hi there. As I recall, in about a billion years the sun will have
>]>about twice the luminosity it presently has. The average surface of
>]>Earth will be about 100 degrees C. Some lakes and rivers will have
>]>begun to boil. It will not be pleasant for homo sapiens.:-)
>]
>]I would say that if Homo sapiens is still on Earth in a billion
>]years, it deserves it. :)
>

Actually, for solar-sail proponents like myself, that's prime sailing
weather! Twice the luminosity=twice the thrust. I think by then we
should have a way to make 30nm thick aluminum sails with embedded
control structures (unless, of course transportation has evolved to
the *poof! You're there stage).

In Real Life:Mike Williams     | Perpetual Grad Student
e-mail      :[e-mail]|   - It's not just a job, it's an indenture
---------------------------------------------------------------------------
"If you ever have a world of your own, plan ahead- don't eat it." ST:TNG

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

Date: 20 Jan 93 19:44:26 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: Earth's rotation rate may be due to early collisions [Release 93-12] (Forwarded)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Ray Davis) writes:
>>     "A popular theory holds that the collision of a Mars-sized planetary body
>> with the Earth threw considerable debris into orbit, which then came together
>> to form the moon," Dones said.  "Thus, the same impact which gave Earth its
>> spin, could also have formed the moon."
>
>How does this popular theory account for the moon having zero spin?

I don't think it has to.  Tidal locking would would work independently
of how the moon got where it is now, or so it seems to me.

--
"Insisting on perfect safety is for people who don't have the balls to live
 in the real world."   -- Mary Shafer, NASA Ames Dryden
------------------------------------------------------------------------------
[e-mail] - I don't speak for others and they don't speak for me.

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

Date: 20 Jan 93 20:46:54 GMT
From: Larry Wall <[e-mail]>
Subject: Earth's rotation rate may be due to early collisions [Release 93-12] (Forwarded)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Bruce Watson) writes:
: In article <[e-mail]| [e-mail] (Ray Davis) writes:
: ||     "A popular theory holds that the collision of a Mars-sized planetary
: || body with the Earth threw considerable debris into orbit, which then came
: || together to form the moon," Dones said.  "Thus, the same impact which gave
: || Earth its spin, could also have formed the moon."
: |
: |How does this popular theory account for the moon having zero spin?
: |
: The moon rotates once a month, otherwise it wouldn't keep the same
: face to the earth.
:
: The "lock" occurred due to tidal friction and took a long time to happen.

Nevertheless, I don't know of any evidence that Moon ever did have much
of a spin (relative to the "lock").  The fact that the back side of the
Moon is so different from the front side would tend to argue against it.

But to answer what I believe to be the original question, the apparent
inconsistency of a collision giving spin to the Earth but not to the
Moon is resolved easily.  The Earth and the Collider were already
formed at the time.  Since they were both sizeable, it's statistically
likely (but not certain) that after the collision the Earth would be
left with a significant spin, just as football player getting tackled
is likely to have his attitude adjusted, so to speak.

Now here's the key to the conundrum.  The Collider, according to
theory, *pulverized* both itself and a bunch of the Earth's crust and
mantle, throwing lots of little rocks into orbit around Earth, but no
Really Big Ones.  These eventually accreted into the Moon.  Since
there's lots of little rocks coming from every which a way, however,
it's statistically unlikely that the Moon would end up with a large
residual spin, just as a football player doesn't expect to be suddenly
upset by the air molecules that are pounding him constantly from every
direction (in the absence of tornadoes).

Now, in actual fact, I expect that there might be some small residual
spin, perhaps because most of the rocks are going the same direction
around the Earth, and the inner ones are going faster than the outer
ones, making a sort of "wind" of rocks.  Even football players have to
take the wind into account upon occasion.  But the general principle
still holds to the first approximation.  Statistics only works well
with large samples.  You're much more likely to be knocked down by a
snowball than by an equivalent number of snowflakes.

Larry Wall
[e-mail]

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

Date: Wed, 20 Jan 1993 18:25:15 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: Galileo Stuck Ribs / Remote Manipulator?
Newsgroups: sci.space,sci.astro,alt.sci.planetary

In article <[e-mail]> (Walt Sellers) writes:
>In article <[e-mail]>, [e-mail] (Alec Habig) writes:
>>
>..
>> >would it be to incorporate a robotic arm manipulator into these designs,
>> >articulated so that it could reach everything on the probe/satellite?
>>
>> I think the big problem would be that this arm would be just as likely to get
>> broken as any part that it might be able to fix.
>>
>If anything did break that the arm *could* fix, then it would be more than
>sensible to bring it along, wouldn't it?

Sure, but figure all the odds and then figure the opportunity cost of
hauling along the weight of the arm on those occassions when nothing
it could fix broke (instead of filling that space/weight with more
instruments).

Hey, I know.  We could only include the arm on vehicles where we knew
something it could fix was going ot break!  ;-)

--
"Insisting on perfect safety is for people who don't have the balls to live
 in the real world."   -- Mary Shafer, NASA Ames Dryden
------------------------------------------------------------------------------

[e-mail] - I don't speak for others and they don't speak for me.

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

Date: 20 Jan 93 18:40:39 GMT
From: Anita Cochran <[e-mail]>
Subject: Goldin's future
Newsgroups: sci.space,talk.politics.space

In article <[e-mail]>, [e-mail] (Pat) writes:
> >In article <[e-mail]> [e-mail] (Jeffrey David Hagen) writes:
> >>Besides, catch a clue about JPL. It is widely considered to be the single most
> >>bloated, pig-headed, and inefficient part of NASA among industry folks I have
> I am here in Washington DC, and mostly deal with NASA HQ and GOddard people.
> The senior Scientist I met who was heavily involved in funding Planetary
> Science programs (Name withheld due to confidence) Blamed JPL for the
> cancellation of Magellans Cycle 4-5 imaging.  His comments were that
> JPL can't do mission support for under 50 million/year.
>

I couldn't let this pass, especially since you are ascribing it to someone
anonymous.  I have been involved the past few years with a National
Research Council committee which evaluates current missions and works
on future strategies.  We are, technically, independent from NASA but
do interact a great deal.  We have discussed Magellan a great deal
in this committee.

First, last year when it was decided to terminate Magellan after cycle 4,
Wes Huntress (then head of the Solar System Exploration Division) stated
that he and Len Fisk made the decision since the mission had been
baselined as a 1 cycle mission and it had accomplished more and the money
was needed elsewhere.  I am not privy to why exactly that money was needed
but I trust Wes.  He did make sure that cycle 4 was able to do the
gravity mapping (including lowering the orbit some).

I saw Wes again at one of these meetings last week.  Wes is now head
of Mission from Planet Earth (half of the Office of Space Science and
Applications).  Over dinner, I asked him about Magellan.  He said that
the transmitter on Magellan had gotten so balky that they were thrilled
to get most everything they did manage to get at the end of cycle 3.
He stated that it would have been impossible to get much imaging in
cycle 4 due to this equipment problem.  It is not the radar but the transmitter.
He is one of the people who is pushing that there be an aerobraking
experiment at the end of cycle 4 and, since he controls the purse strings,
he is the one who can make this happen.

Magellan is a great mission but apparently it does indeed have some problem
which limits the radar now (anyone from the Magellan office care to
comment).  Wes feels badly the plug had to be pulled.

Now, lets push for future missions.  And yes, the political reality is
that they have to be smaller than Cassini.  There is still a lot to do.

--
 Anita Cochran  uucp:  !utastro!anita
                arpa:  [e-mail]
                snail: Astronomy Dept., The Univ. of Texas, Austin, TX, 78712
                at&t:  [phone]

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

Date: 20 Jan 93 17:52:25 GMT
From: Steinn Sigurdsson <[e-mail]>
Subject: Goldin's future
Newsgroups: sci.space,talk.politics.space

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


   >In article <[e-mail]> [e-mail] (Jeffrey David Hagen) writes:
   >>Besides, catch a clue about JPL. It is widely considered to be the single most
   >>bloated, pig-headed, and inefficient part of NASA among industry folks I have

...
   In fact,  the big push on now is to design probes that bypass
   NASA infrastructure.  NO TDRSS, No SHuttle, NO JPL.  direct comms
   back to the PI's.

Does that mean a lot of Universities can look forward to 70m class
radiotelescopes on their campuses or are they going to stick very
large high power antennas on future probes that go beyond Earth orbit.
(I'll grant you easy 9600 baud cellular links to Earth orbit probes
via Iridium or other system of your choice!).

Just think, the grad students could watch HBO most of the night
and then retarget for a high speed download from the Pluto orbiter
during the comedy hour...

|  Steinn Sigurdsson    |I saw two shooting stars last night        |
|  Lick Observatory    |I wished on them but they were only satellites    |
| [e-mail] |Is it wrong to wish on space hardware?        |
| "standard disclaimer"    |I wish, I wish, I wish you'd care - B.B. 1983    |

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

Date: Wed, 20 Jan 1993 21:40:30 GMT
From: [e-mail]
Subject: Great stuff at NASA and D. WINGO is "why we now"
Newsgroups: sci.space

 In article <[e-mail]>, [e-mail] (Bill Higgins-- Beam Jockey) writes:
> In article <[e-mail]>, [e-mail] (Brian Stuart Thorn) writes:
> [responding to Allen Sherzer's question:]
>>>This is not the case. There is lots of great stuff going on at NASA. I
>>>criticize the unproductive things NASA does so that we can have more of
>>>the good stuff. Why does that bother you so much?
>>
>>      Because very seldom does anyone ever mention the great stuff
>>      going on at NASA.
>
> Emphatically *not* true.  That's why God made Dennis Wingo.

THAT IS HISTERICAL!!!  not that I am disagreeing with you but this^ was
a very funny quip.  Curiosity?  How many people got it?  I know Dennis Wingo
(I am from Huntsville) but is he known everywhere?   Hopefull not like "Dr."
Wayne Matson.  Oh well, couldn't resist this post...thanks for the chance to
chortle.

Paul Shanley



>
> Bill Higgins                         | Favorite carol around Higgins house:
> Fermi National Accelerator Laboratory| Glooooooooooooooria
> Internet:  [e-mail]     | In excelsis Deo
> Bitnet:     [e-mail]      | Deo
> SPAN/Hepnet: 43011::HIGGINS          | Daylight come and me wanna go home

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

Date: 20 Jan 93 18:59:28 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: Let's be more specific (was: Stupid Shut Cost arguements)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Pat) writes:
>In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>>
>>are a preferred solution. Honeycomb composite structures are another good
>>solution, but remain very expensive to fabricate.
>>
>
>
>Too the best of my understanding, the chinese use Bamboo heat shields
>on their rocket capsules.  The bamboo carbonizes, and becomes an almost
>perfect insulator.  A friend of mine watched a thermite lance get halted
>by a piece of plywood.  the carbon just sucked up the heat.

I believe that what the Chinese are reported to be using is oak, not
bamboo.  they are also reported to produce a lot of their space
hardware in a refrigerator factory, or soemthing like that.  So much
for Western requirements for Level 100 cleanrooms.

--
"Insisting on perfect safety is for people who don't have the balls to live
 in the real world."   -- Mary Shafer, NASA Ames Dryden
------------------------------------------------------------------------------
[e-mail] - I don't speak for others and they don't speak for me.

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

Date: 20 Jan 93 23:29:31 GMT
From: Del Cotter <[e-mail]>
Subject: Lunar Rotation (was: Earth's rotation rate...)
Newsgroups: sci.space

In article <[e-mail]> "UTADNX::UTDSSA::GREER"@utspan.span.nasa.gov writes:
>The moon does spin.  Its rotational period is equal to its orbital period
>about the Earth, so it always presents the same face to the Earth.  This
>happened because the distribution of the Moon's mass is not perfectly
>spherical; it's a little lumpy.  Originally, the Moon was spinning more
>quickly than today, but over time, tidal forces working on the lumps in the
>Moon slowed it down until the lump with the greatest angular moment became
>"locked" into place, so that it always points toward the Earth.  The
>technical term for this is Gravity Gradient Stabilization.

>Dale M. Greer

You're right that the lumps determine *which* side of the Moon finally
wound up facing us, but it would have slowed down even if it had been a
homogeneous fluid mass.  The tidal forces deformed the spinning satellite, so
that it became an ellipsoid.  The satellite swept round, deforming all the
while, so that kinetic energy of rotation was dissipated as heat.  Incidentally,
the angular momentum of rotation was conserved by increasing the angular
momentum of revolution (ie. the Earth-Moon distance).

The same story can be told a completely different way, using torque on the
lagging bulge of the ellipsoid, with no mention of energy.  The two
descriptions are equivalent, with friction/viscosity the key factor in both.
A body made of an *inviscid* fluid would keep spinning forever.

BTW, I heard that the Moon is actually *bistable*.  Aren't we lucky we
got the pretty face?
--
 ',' ' ',','  |                                                  |  ',' ' ',','
   ', ,','    |       Del Cotter       [e-mail]      |    ', ,','
     ','      |                                                  |      ','

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

Date: 20 Jan 93 17:49:34 GMT
From: Pat <[e-mail]>
Subject: Shuttle safety margins
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (John Roberts) writes:
>
>This is in part a reply to a comment by Pat several weeks ago. Pat was
>concerned by mechanical safety margins, and felt that the Shuttle operates
>within 5% of destruction for its major mechanical and structural systems.
>It's difficult to find anything authoritative on this subject, but there
>was mention of one safety factor in the STS-54 post-flight press conference
>Wednesday morning.
>

John

    Please be very careful of what NASA pulicizes as to their
    expected margins versus real margins.

>It turns out that with the measured wind patterns, if one of the SSMEs had
>failed (it didn't) right when the Shuttle was passing Mach 1.55, three of
>the struts in the structure would have had a safety factor of 1.36 (36%),
>while the target safety factor under those conditions is a minimum of
>1.4 (40%). Analysis of the situation and of the particular orbiter indicated
>that this safety factor was acceptable, so permission was granted to proceed
>with the launch.
>

    NOTE:  The phrase measuered wind patterns.  In higher strength
    winds, the vehicle would have lower margins.  Post challenger,
    NASA tightened up the Launch criteria giving a larger margin,
    not improving the design by 35%.

>It should be noted that under normal flight conditions (all three engines
>working, which was the case) the safety factor would be greater.
>

    Under normal flight conditions you dont launch in freezing weather.

>One of the questions during the press conference was "what if something
>additional had happened, and the stress was increased another 36%, so that
>zero safety margin was passed?". The spokesman (Brewster Shaw, Deputy
>Director of the Space Shuttle Program) replied that the safety margin
>stated is not to the point of destruction - you'd get local yielding,
>and the load would be redistributed to the surrounding members. (Of course,
>orbiter repairs would be needed afterward.)
>
Local yielding maybe.  I'd be worried by such a blithe answer.
If local yielding is 1",  how much gap does that entail at the
ET/ORbiter Feed flange?  How much fuel spill will now be observed
from this flange?   If local yielding increases a moment of torque, will
that overstress another member?
The mechanical complexity of the Shuttle system is very high, and i doubt
NASA still knows it's exact behavior.



JOHN

    my problem with the shuttle is that they used Military safety amrgins.
    Now when one flys a 747, one does not usually put the vehicle
    past 1.25 G.  The vehicle is rated for 4 Gs.  The failure limit
    is around 6 Gs.   99% of the time you will be below 1.25 Gs.
    an emergency manuever may require you to pull 4 Gs,  everytthing
    is sized for this.  if something unusual occurs you can exceed
    the limit.  Hence 747's have ridden out hurricanes and supersonic
    dives.

    Now an F-15  is rated for 9 Gs.  THe pilots will routinely
    pull 9 Gs.  but at 10 Gs, structural damage is assumed
    and the vehicle is overhauled.  Now F-15 pilots will
    pull these high G forces in Training,  in operations,
    in Combat and in emergencies.

    Which is the Safer airplane?  That is engineering judgement.
    Now the 747 is less likely to break up in an emergency,
    but on the other hand  the 747 is pate to a IR Missile.

    Just because NASA has now gone and said,  we wont launch
    in heavy weather,  doesn't mean that the vehicle may still
    find itself in extreme conditions.

    Probably in the post challenger re-design,  the struts were
    improved,  having been criticized as weak points,  but
    there are still numerous weak points.

    Engineering judgement is a funny one.  There was a bridge
    down south, that was hit by a speeding camaro.  The bridge
    collapsed and the state sued the driver.  He argued, that a bridge
    should expect car accidents.  THe state won on a negligence issue.
    but nevertheless, the original point is correct.  Certain things
    must expect certain conditions.  Now i dont expect a bridge
    to withstand the North AMerican Fat ladies precision Hop SCotch
    squad :-)  but i do expect it to withstand 3 cement trucks
    in close order.  Same thing with aircraft.  i dont expect
    nuclear detonations,  but i do expect the occasional hurricane.

    in short, i think NASA has underestimated the expected
    envelope of shuttle performance areas.  Do i have many facts
    to back it up.  not really, just gut feel and the occasional
    article.

pat

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

Date: 20 Jan 93 22:04:20 GMT
From: [e-mail]
Subject: Territorial conquest? Pishaw!!
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Ed Faught) writes:
> In article <[e-mail]> [e-mail] (Tom) writes:
>>
>>>>>The urge to colonize the universe seems to come from an urge for
>>>>>territorial conquest that has been with us for a long time.  It is
>>>>>interesting how old themes are constantly repeated in the present.
>>
> IMHO, territorial conquest was the politcal reason used to obtain funding.

Yes, much like the authors employers and supporting politicians conquest for
large chunks of land in Texas to bury huge tubes to accelerate small things
to very fast rates in order to see what happens.  Nothing wrong with the
premise, learn to learn (plus spin-offs) but cost to learn might have been a
worthy consideration.  :]   Also, the urge to colonize the universe is
doubtfully conquestial (word?) in impetus.  If it is, it hasn't worked.  Seventeen
Billion dollars ain't much in the scheme of theings, especially when a small
percentage of it is actually for exploring this solar system much less the
universe.

Just a thought or two, no flame intended.

Paul S. Shanley
Auburn University

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> Ed Faught  WA9WDM  [e-mail]
>  Superconducting Super Collider Laboratory

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End of Space Digest Volume 16 : Issue 068
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