Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V15_4/V15NO415.TXT

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

Date: Thu, 12 Nov 92 05:10:46
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #415
To: Space Digest Readers
Precedence: bulk


Space Digest                Thu, 12 Nov 92       Volume 15 : Issue 415

Today's Topics:
                           Hubble's mirror
                   IS SWIFT-TUTTLE THE REAL THREAT?
                  Japanese X-ray satellite: Astro_D
              Jimmy Carter and Gerald Ford TV Commercial
                     Lunar "colony" reality check
                Mars Simulation in Antarctica (3 msgs)
                        NASA Coverup (2 msgs)
                       Positioning Satellites?
             Study says: Space research spinoffs marginal
                Swift-Tuttle Comet a threat to earth?
       The story on Oxygen Was Re: Lunar "colony" reality check
              What kind of computers are in the shuttle?

    Welcome to the Space Digest!!  Please send your messages to
    "[e-mail]", and (un)subscription requests of the form
    "Subscribe Space <your name>" to one of these addresses: listserv@uga
    (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle
    (THENET), or [e-mail] (Internet).
----------------------------------------------------------------------

Date: 11 Nov 92 14:52:35 GMT
From: "William H. Jefferys" <[e-mail]>
Subject: Hubble's mirror
Newsgroups: sci.astro,sci.space

In article <[e-mail]> [e-mail] (Gary Coffman) writes:
#
#According to the NASA investigation of the Hubble mirror problem, there
#was nothing wrong with the specs. The backup mirror built to the same
#specs by Kodak is *perfect*. The problem was that Perkin-Elmer bollixed
#up the testing of the figure of the mirror and ignored the results of
#a Foucault test that showed the mirror to have spherical abberations
#because their primary test was supposed to give more accurate results.
#Unfortunately, they installed a fixture backwards when making the
#primary measurements and got the *wrong* result.

I'm pretty sure there was never a Foucault test; that
there hadn't been one became an issue after the mistake
was discovered. This was brought up at NASA reviews I
attended. After all, the interferometric test was supposed
to be so accurate that a crude test such as the Foucault
test wouldn't tell you anything you didn't already know
(or so they thought).

The "fixture" that was used backwards was the Invar rod;
It was indeed used backwards, but that was not the chief
reason for the mis-manufactured null corrector. This was,
as I posted earlier, the laser return from the end cap,
which had had a fleck of black paint scraped off.

Bill

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

Date: Thu, 12 Nov 1992 02:23:55 GMT
From: Paul A Daniels <[e-mail]>
Subject: IS SWIFT-TUTTLE THE REAL THREAT?
Newsgroups: sci.astro,sci.space

In <[e-mail]> [e-mail] writes:




>=========================================================================

>The Comet Swift-Tuttle saga : an addendum  - Duncan Steel, 1992 November 6th


>One thing that no-one has picked up on so far, it seems, is that it is more
>likely that an asteroid or comet big enough to wipe out mankind will hit
>the Earth before P/ST may perchance clobber us on 2126 August 14th than
>the probability of that comet itself doing the job.  That was a mouthful,
>but think about it: what I am saying is that even IF P/ST does hit the
>Earth on that date there is a chance that we may have already been hit by
>some other as-yet undiscovered object.

>A very crude estimate of the chance of P/ST hitting, a priori (that is at
>this stage without the observations to be made over the next decade) is
>about 1 in 10,000.  That is, the perihelion date is uncertain by about
>25 days, and if it does come back so as to pass its node on 2126 August 14th
>then since it takes about 3.5 minutes to cross the Earth's path and
>24 hours = 400 x 3.5 minutes, more-or-less, the probability is about 1 in
>25 x 400 = 10,000.

>However, if there are about 3,000 Earth-crossing asteroids larger than 1 km
>in size (that is about the size limit for a global catastrophe, depending upon
>mass and impact speed) and these have a mean collision probability with our
>planet of about 6 x 10^(-9) per year (see Steel & Baggaley, MNRAS, 212, 817,
>1985) then one expects one impact by such an object every ~50,000 years.
>[See also the discussion in the Spaceguard Survey report, ed. D. Morrison].
>That figure may be a little on the high (frequent) side, but I would plump
>for one per 100,000 years as being in the right ball park.

>This means that in the next century there is about a 1 in ~1,000 chance of
>a 1 km asteroid dropping in to play (havoc).  This is 10 times our current
>estimate that mankind will be stuffed by P/ST in 2126.  Note that no comets
>(either SP or LP) have been included in my sum, and these may comprise
>about 25% of the total risk (i.e. asteroids 75% of the hazard).

    Does that mean that we have a close flyby by one of these potential
killers every 10 years? I would say that there is a good case for a fair bit
of funding then..

Paul.

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

Date: Thu, 12 Nov 1992 04:09:21 GMT
From: Robert W Murphree <[e-mail]>
Subject: Japanese X-ray satellite: Astro_D
Newsgroups: sci.astro,sci.space

[e-mail] (John A. Nousek) writes:

>The instruments consist of four conical foil X-ray telescopes
>built by Pete Serlimitsos of Goddard Space Flight Center, two
>X-ray CCD cameras built by George Ricker of MIT (with Penn State
>Co-I's) and two gas scintillation proportional counters built
>by Prof. Makashima of Tokyo University.  The four telescopes
>are coaligned and will simultaneously point at the observing
>target, allowing both CCD cameras and both GIS counters to
>collect data.  Each mirror detector system has an effective
>area around 400 cm^2, giving a total effective area greater
>than Einstein, ROSAT or AXAF over most of the energy range.
>Moreover the graze angle is smaller for these mirrors so they
>retain large effective area up to 12 keV!  (For reference
>the Einstein mirrors dropped off at 3-4 keV, ROSAT at 2 keV
>and AXAF at 9 keV).

>The major limitation of these mirrors is that they are not
>true imagers (i.e. they are right cone segments and not para-
>boloid-hyperboloid pairs).  This limits the spatial resolving
>power to 1.3 arc min half power radius [although there is
>a sharp core to the PSF which has been demonstrated to resolve
>point source 36 arc sec apart.]  The spectral resolution
>of the detectors is quite good.  The GIS has 8% energy resolution
>at 5.9 keV, and CCDs have 120 eV resolution at 5.9 keV.  The
>energy band pass runs from 0.4 keV up to 12 keV.


I gather that Astro-D is a superlative x-ray spectrometer.
Is it "the first x-ray spectrometer" or only the first wiht
with this wide and bandwidth, resolution, and apeture?
Is the 1 arc minute resolution a significant handicap for
many objects?  What new capacities for doing science will
it result in?  Is this a "major" observatory like ROSAT
and/or AXAF.  I'm not the one to say, but for spectrometry
it seems it may be a "major"  observatory.  Of course,
it doesn't have to be a "major" observatory to do good
science, and the fact that the japansese have launched 3-4
small missions in the x-ray band in 10 years may actually
be much more significant in terms of science than a behemoth
like AXAF that gets launched every 10-15 years or not at all.
The US hasn't launched any free-flyers in the X-ray since
HEAO or Eistein 10 years ago, have they? A few detectors on
other people's satellites of course, but nothing big since
Einstein.
`

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

Date: Thu, 12 Nov 1992 03:15:35 GMT
From: Wesley D Scott <[e-mail]>
Subject: Jimmy Carter and Gerald Ford TV Commercial
Newsgroups: talk.politics.space,sci.space

I saw a commercial with Jimmy Carter and Gerald Ford advertising
the National Space Foundation last weekend.  Does anyone have
any more information?

[e-mail]

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

Date: Thu, 12 Nov 1992 03:05:13 GMT
From: "J. Lewis" <[e-mail]>
Subject: Lunar "colony" reality check
Newsgroups: sci.space,alt.sci.planetary

In article <[e-mail]> [e-mail] (steve hix) writes:
>In article <[e-mail]> [e-mail] writes:
>> ... Yes, nitrogen has narcotic effects at high pressure, but so does
>>oxygen.
>
>I think it's worse than that for O2: above two atmospheres or so, it's very
>toxic.

I don't have references to hand, but, from memory: above 2 atm or so, O2 is
an acute and chronic neurotoxin; toxic, but in a different way than N2.
Remember that O2, unlike N2, has some of the chemical properties of a free
radical.
Below *about* 2 atm, nearly all of the oxygen in the blood is complexed as
oxyhemoglobin; above about 2 atm, the hemoglobin is saturated with oxygen,
and O2 is present dissolved in the blood plasma.  It is apparently this
dissolved O2 that does the damage.

As I say, from memory.  I distinctly  remember, though, seeing a paper
about 20 years ago on chick embryos in hyperbaric O2, perhaps 20 atm;  the
effects of the O2 were comparable to those from high doses of gamma
radiation.

O2 is nasty, dangerous stuff;  should be banned.

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

Date: Wed, 11 Nov 1992 22:45:44 -0500
From: Samuel John Kass <[e-mail]>
Subject: Mars Simulation in Antarctica
Newsgroups: sci.space

   "The Tartan", our school newspaper, has reported that the problem
"can be fixed easily, but until it is, the project cannot be approved.
Consequently, the date of departure for California en route to
Antarctica will continue to be pushed back."
    Basically, Dante looks like a big, purple bug.  It's transport
counterpart, "Virgil" (which was dropped from the Antarctica mission due
to manpower and time constraints) looked like a high-tech purple dune
buggy with lots of extra wheels.
    The project was concieved of a year ago, and has already completed
most final testing.  It has some pretty neat features, including the
ability to repel down steep slopes, and look around with a laser
scanner.  It's being worked on as a joint project with NASA and the NSF,
who are interested in Mt. Erebus' analog to alien landscapes.
    If our newspaper reports anything new and exciting, I'll be sure to
post again.
    --Sam

-- Disclaimer:  Everything is true. - [e-mail]               --
-- A Math/CS major at Carnegie Mellon University --  Beward the fnords.  --

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

Date: Wed, 11 Nov 1992 23:24:24 -0500
From: Lawrence Curcio <[e-mail]>
Subject: Mars Simulation in Antarctica
Newsgroups: sci.space

Is this rover the same robot we at CMU call, AMBLER? Big red sucker?
Legs arranged like eggbeaters?

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

Date: Thu, 12 Nov 1992 02:05:15 GMT
From: Frank Crary <[e-mail]>
Subject: Mars Simulation in Antarctica
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Kevin W. Plaxco) writes:
>>    Later this season, NASA plans to send an eight-legged robot into the
>>crater of Antarctica's Mount Erebus, the world's only easily-reached volcano
>>with a permanent lava lake.

>This is obviously some new definition of the phrase "easily-reached".

How about, "within 25(?) miles of a United States Navy base?" Mt.
Erebus is right next to MacMurdo station, which is a fairly
sizeable establishment providing all the logistical support for
American research stations in the Antarctic.

                                          Frank Crary
                                          CU Boulder

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

Date: Thu, 12 Nov 92 04:13:41 GMT
From: [e-mail]
Subject: Nasa Coverup

>      However,evidence gathered by the Apollo  missions  indicates  that  the
>    moon  and  earth  differ  greatly in composition.  Scientists now tend to
>    lean toward the third theory -  that  the  moon  was  "captured"  by  the
>    Earth's  gravitational  field  and  locked into orbit ages ago. There are
>


Not true. Current theory is based on supercomputer simulation that shows a final
Mars sized planetisimal collision with earth created the Moon. Don't argue that
here, go to the literature. There is loads of stuff on it.

>    planets  in  the  solar  system , is known to harbor life and a satellite
>    with this peculiar quality . The theory that the moon was placed here  by
>    intelligent  being(s) as a sort of "planet marker " , is only a  theory .
>    As we all  know  ,  theories  are  not  necessarily  the  same  thing  as
>    "Science."
>


True. There is no such theory and never has been.

>      99 percent of moon rocks brought back turned out upon  analysis  to  be
>    older than 90 percent of the oldest rocks that can be found on earth . If
>    we  assume  that the moon came from a different area of the solar system,
>    where the component material might have been different  ,this  assumption
>    would  still  not  account  for  the  disparity in the average age of the
>    matter composing the two bodies.
>


True, the rocks are older. The moon does not have plate tectonics. Very little
of it's crust has been turned over since the late bombardment period. The Earth
turns over oceanic crust in 100MY or so; other crust is bent, twisted, turned
over, scraped along continental margins, uplifted, downlifted, sedimented,
covered with lava, eroded by wind and water...

Other than some central canadian; Australian; Greenland and central CSR(?)
areas, very little old crust is available at the Earth's surface.

>     The dark areas on the moon are known as "maria" ,some of which form  the
>    familiar  "man  in  the  moon". Maria are significantly absent on the far
>    side of the moon. The ones on the near side area consist mainly of  lunar
>    soil and smaller rocks.  Astronauts found it extremely difficult to drill
>

>


Gravitational focusing is certainly one reason. There are other dynamical
reasons as well. I'll let some astronomers explain it more accurately than I
can.

>     Samples  brought  back to earth by both Soviet and American Space Probes
>    contain particles of pure iron. The  Soviets  announced  that  pure  iron
>    particles  brought back by the remote controlled lunar probe Zond 20 have
>    not oxidized even after several years on earth. Pure iron particles  that
>


Ah, yes. Stainless steel. Iron and Nickel. That's what some asteroids are made
of. You can buy pieces from the Barringer crater that are considerably older
than that and are not rusted. I've held one in my hand. About 40KY old isn't it?

>     When  the  Apollo  15  astronauts  used  thermal  equipment  to  measure
>    temperatures  below the surface , they got unusually high readings, which
>    indicated high subsurface temperatures near the  Apennine  mountains.  It
>    was  speculated  that  ,  since  the  presumed  density of the moon would
>    preclude the possibility of lava flows, magma and the like (volcanism has
>    never been observed  on  the  moon)  that  the  high  readings  could  be
>    explained   by  highly  radioactive  elements  just  under  the  surface.
>    Actually, the amount of radioactive materials on the SURFACE of the  moon
>    is  "embarrassingly  high"  .   Where  did  all  of this hot ,radioactive
>    material ( uranium and thorium ) come from ? And  if  it  came  from  the
>    interior  of  the  moon  (very  unlikely)  ,how  did it get to the moon's
>    surface?
>


I know nothing about this, but if you are right, maybe I'll get rich before Nick
Szabo :-) Nothing like fissionables for power and active magmatics for creating
useable veins of minerals.


>      The few lunar excursions indicate that the moon is a  very  dry  world.
>    One  Lunar  expert  said that the moon was "a million times as dry as the
>    Gobi Desert" .  The early Apollo missions did not even find the slightest
>    trace of water. But after Apollo 15, NASA experts  were  stunned  when  a
>    cloud  of  water vapor more than 100 square miles in size was detected on
>    the  moon's  surface.  NASA  officials  suggested  that  two  tiny tanks,
>


The lunar materials brought back are indeed hyperdry. There is no reason to
believe that volatiles do not exist in permanently dark craters at the lunar
poles. This has been a subject of debate on this digest for years. We all hope
to see results from a lunar orbitting gamma ray spectrometer to settle it once
and for all.

As to clouds: there is an amateur astronomy group that studies Transient Lunar
Phenomena. There could be lunar volcanic activities, venting and such. It is not
the prevalent idea, but it does not break anyones models too badly if TLI prove
to be real. That is the caveat. They might be venting or they might be lighting
effects. We probably won't really know until we get "ground truth" from some of
the areas where they are most commonly seen. It really is neither spectacular
nor embarrassing. Again, if true, it would be damned useful.

>      Lunar  explorations  have  revealed  that  much of the lunar surface is
>    covered with a glassy glaze , which indicates that the moon's surface has
>    been scorched by an unknown source of intense heat .   Expert's  analysis
>    shows  that  this  did not result from massive meteorite impactings . One
>    explanation forwarded  was  that  an  intense  solar  flare,  of  awesome
>    proportions  ,  scorched  the moon some 30,000 years ago. Scientists have
>    remarked that the glaze is similar to the glaze created by atomic weapons
>    on earth soil.
>


I have heard no such thing. I have seen many pictures and have seen no such
thing. The surface is grey dust that has been gardened by micrometeorite impacts
for aeons. Again, the literature on this is wide and deep and has been much
discussed here over the years because it is relevant to lunar resource
extraction. I would suggest you start with the proceedings from the first Lunar
Base Symposium.

>      In 1968 ,tracking data of lunar orbiters first indicated  that  massive
>    concentrations  (mascons) existed under the surface of the circular lunar
>    maria.  NASA  even reported that the gravitational pull caused by themwas
>    so  pronounced  that  the  spacecraft  overhead   dipped   slightly   and
>    accellerated  when  flitting  by  the  lunar  plain  , thus revealing the
>    existence of these hidden structures,  whatever  they  are.  Calculations
>    show that they are enormous concentrations of dense heavy matter centered
>    like a bull's eye under the  lunar  maria.  NASA  has  never  offered  an
>    explanation of their existence.
>


You haven't been reading very much then. There is discussion of it in a number
of texts I have read. I think "The New Solar System" was one with an excellent
technical summary of lunar geology.

Besides which, as was pointed out, the Earth has MASCONS too. There are gravity
anomalies anywhere the crust is a bit thicker. Central mare are the impact sites
of some rather large objects and were thereafter the site of massive flood
basalts. Read that as: a great thickening of the crust.



>   10. Is there anything "funny" about the moon?

Yes. We should have bases there by now.

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

Date: Thu, 12 Nov 1992 00:25:35 GMT
From: "Gregory N. Bond" <[e-mail]>
Subject: NASA Coverup
Newsgroups: sci.space,alt.conspiracy

>>>>> On Sat, 7 Nov 1992 23:42:20 GMT, [e-mail] (Josh 'K' Hopkins) said:

Josh> Did you know that fully _half_ of all babies are born within one
Josh> week of a full Moon!  No kidding.

And what is worse, half of those babies born within a week of a full
moon have below-average intelligence!

Obviously, the radiation from the alien artifact that is holding the
moon up is affecting them.
--
Gregory Bond <[e-mail]> Burdett Buckeridge & Young Ltd Melbourne Australia
``There is Faith, Hope and Charity.  But greater than these is Banking.'' - 1492

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

Date: 12 Nov 92 04:49:13 GMT
From: Rich Kolker <[e-mail]>
Subject: Positioning Satellites?
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Chris Allen) writes:
>
>Can anybody help me? (perhaps by telling me which group this *should* be in :)
>
>I have heard people mention a satellite or satellites whose signal enables
>you to find your position wherever you happen to be.
>
>Can anybody tell me more - or point me to papers or references?
>
>many thanks,
>
>
>chris allen.
>
>--
>
> * Meeeow ! Call Spuddy on [phone]/682331 for FREE mail & Usenet access *

The Global positioning system will do just that.  You can buy a receiver at
any nautical supply or aviation supply house.  I'm sure others will fill
you in on the theory.

++rich
-------------------------------------------------------------------
   rich kolker       [e-mail]
                          It's been a long, long time
--------------------------------------------------------------------

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

Date: 12 Nov 92 04:48:04 GMT
From: Gregory Aharonian <[e-mail]>
Subject: Study says: Space research spinoffs marginal
Newsgroups: sci.space,sci.econ

    Chance spin-offs are not a good enough reason for investing in space
research, reports Germany's Fraunhofer Institute for Systems and Innovation
Research, the ISI, in Karlsruhe.  The ISI's analysis of patent citations
concludes that space research produces no more - and perhaps fewer - advances
in earth-bound technology than other areas of research.
    "Politicians have used spin-offs to justify funding for manned space
flight", says Ulrich Schmoch, who led the project.  "But the study's results
mean they must now rely more heavily on direct, scientific arguments for space
flight, like its usefulness in observing the Earth or repairing satellites".
    ISI researchers identified 3000 patents for advances in space technology
filed since 1988, and then looked for patents that cited one or more of the
source patents.  Those that were for spin-offs into other fields numbered
between 20 and 30 per cent of the original 3000.  "It's difficult to express
in percentages because the definition of a spin-off is subjective", says
Smooch.
    The researchers used patent citation analysis because they thought it
would be less biased than other methods, such as asking companies if they use
space research.  "The officials issuing the patents didn't know we were going
to do a study", says Schmoch. When the ISI used the same method to investigate
transfers from research on sensors for robots, it found three times as many
spin-offs.
    According to the report, some space research, such as fittings for
remote-controlled telescopic arms, heat-resistant materials and control
technologies, did find other uses. Gas turbines, for example, can now operate
at higher temperatures because the surface of the blades is treated by a
process developed for space flight.  The air-cooled motorcycle helment is an
even more down-to-earth example, says Schmoch.
    The project was commissioned by the Federal Ministry of Research and
Technology, but in 1990 responsibility for it was transferred to the German
Space Agency, DARA.  Although the study was completed in April, it remained
under wraps until this month.  Franz-Peter Spaunhost of DARA says the delay
had nothing to do with the agency.  "This is not a DARA study", he says.
"It is something we inherited from the federal ministry".
    "In 1988, Germany didn't have the budgetary problems it does today",
Schmoch says.  "That's a recent addition to the discussion on whether to stop
funding space flight".
[New Scientist 10/31/92, 6]

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

Gregory Aharonian
Source Translation & Optimization
--
**************************************************************************
Greg Aharonian
Source Translation & Optimiztion
P.O. Box 404, Belmont, MA 02178

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

Date: Thu, 12 Nov 1992 02:11:07 GMT
From: Paul A Daniels <[e-mail]>
Subject: Swift-Tuttle Comet a threat to earth?
Newsgroups: sci.astro,sci.space

    If a comet like ST did strike the earth, what would the after effects
be geologically? Would you end up with a large area of vulcanism?
Would you end up with a hot spot?
    What would the the result of say a 5km dia. hole in the mantle?

Paul.

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

Date: Thu, 12 Nov 1992 01:16:47 GMT
From: David Knapp <[e-mail]>
Subject: The story on Oxygen Was Re: Lunar "colony" reality check
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Steve Linton) writes:
>In article <[e-mail]>, [e-mail] (John D. Boggs) writes:
>|> From article <[e-mail]>, by jenkins@fritz (Steve Jenkins):
>|> >
>|> > Oxygen, like many gases, has narcotic effects at very high pressures,
>|> > such as in deep-sea diving.  It can cause blindness in newborns
>|> >
>|>
>|> Yes to blindness in newborns, but it is the *nitrogen* that has the narcotic
>|> effect in deep sea diving -- hence the use of helium for the really really
>|> deep dives.
>
>Oxygen causes drunkenness-like symptoms above around 2atm. Any inert gas (except
>helium, which I'll come back to) causes narcosis (anaesthesia) at sufficient
>partial pressure. Roughly, the larger the molecule, the lower the pressure
>needed. For nitrogen it's about 10atm, for ether or chloroform, less than 1.
>Helium, presumably because of its very small molecule, causes the opposite effect
>at very high pressure (> 50atm), causing trembling and over-excitation  of the
>nerves. Hence divers at great depths breathe  mostly helium, with a few %
>nitrogen to balance the effect of the helium, and less than 1% oxygen. Hydrogen
>is also used, but I'm not sure of the details.


Oxygen Poisoning:

Oxygen is essential for life, so it may seem surprising that it can have
poisonous effects; but this is important for divers to understand. The normal
partial pressure of oxygen in air is 0.21 atm, equivalent to 21 percent oxygen
at sea level.  Above about 1/2 atmosphere (e.g., 50% oxygen at surface
or 25% oxygen at 33ft), lung damage will develp within hours or days depending
on the oxygen "dose".  This is a recognized problem in treating hospital
patients who need extra oxygen, but it seldom affects divers except in
prolonged periods at depth in saturation diving or in extended recompression
with oxygen breathing.

More important for most divers is the fact that oxygen can cause convulsions,
like th efits or seizures of grand mal epilepsy. Drowning is the usual result
of an underwater convulsion, but the risk of convulsion selfom arises unless
the partial pressure of oxygen approaches 2 atmospheres. Such a dose is
reached with pure oxygen at 33 ft, 50% at 99ft, 20 % at 297 ft, etc.
Convulsions may occur at lower pressures with excess carbon  dioxide either
inhaled or retained.

There shoud be no possibility of oxygen poisoning in the use of open-circuit
scugba unless charged with something other than compressed air. In most
closed-circuit scuba, only pure oxygen can be used; and the depth of safe
diving is severely limited. Special closed- and semiclosed- ciruit
apparatus designed for gas mixtures must be used with great care to avoid
oxygen poinsonin. The severity of the limits is illustrated by U.S. Nave
rules which normally restrict the use of 100 % oxygen for working dives
to no more that *25 ft* (the emphasis mine), with a 75
minute time limit at that depth. Limits permitted for unusual circumstances
extend to 40 ft, where only 10 minutes are allowed.

Taken from  The New Science of Skin and Scuba Diving, by the Council
for National Cooperation in Aquatics, New Century Publishers, 1980.


Oxygen Poisoning:

...an excess of oxygen is just as bad as too little. If you breathe an excess
of oxygen for an extended period of time, the outcome can be harmful. Excess
oxygen can injure lung tissues and can adversely affect the central
nervous system.

Parial Pressures:

How much oxygen is too much? This depends on three things: the amount, its
pressure, and the exposure time. Ordinarily, we breathe a mixture of 78%
nitrogen and 21 %g oxygen at atmospheric pressure (14.7 psi). Dalton's
Law states that the total presssure of a gas mixture equals the sum of the
partial pressures that make up the mixture. In other words, the sea level
partial pressure of nitrogen equals 78 % of 14.7 psi, or 11.6 psi. The
parital pressure of oxygen is 21 % of 14.7 psi or 3.09 psi.

Now, oxygen poisoning can occur when the partial pressure of pure oxygen
equals two atmospheres absolute, or 29.4 psi (two times 14.7 psi). This
could happen if you were breathing pure oxygen (not air) at a depth of
33 feet. It could also happen by breathing ordinary air at a depth of 297
feet (this is where He-Ox mixes are used, with lower partial pressures
of oxygen -d.k.), or 10 atmosphere (10 time 3.09 psi).

Taken from Open Water Certification Sport Diver Manual by Jeppeson Co
(used by PADI diver training)

The bottome line is that we don't dive much beyond 100 ft on air. If
we're going to go deeper, we get life insurance and use a helium oxygen
mix with much lower fraction of oxygen. Helium is used as a buffer
because it is not chemically reactive when it dissolves in the blood.

I'm not sure if it dissolves less into blood than N2 but I know that
decompression is still an issue using heliox mixes.

Note that at Steve's upper limit of 50 atm, most people would have
been long dead if they were using pure oxygen, so there's no need to worry
about convulsions.



All spelling errors are mine.





--
David Knapp                                   University of Colorado, Boulder
Perpetual Student                                 [e-mail]
Looks like hate *is* a family value after all and Colorado families are for it.

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

Date: 12 Nov 92 00:10:47 GMT
From: Rich Kolker <[e-mail]>
Subject: What kind of computers are in the shuttle?
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (I am a terminator.) writes:
>The computers used to control the shuttle use very complex programs
>that people don't want to rewrite for newer computers. Has any
>upgrades been done or are the computers still the same old beasts?
>
>Henry Choy
>[e-mail]

The shuttle computers have been upgraded.  The joke around is that 1960's technology h
has been replaced with 1980's technology, but they are a giant step forward.

Now, if we can just get the money for the glass cockpit...

++rich
:
-------------------------------------------------------------------
   rich kolker       [e-mail]
                          It's been a long, long time
--------------------------------------------------------------------

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


          id aa02875; 11 Nov 92 22:57:57 EST
To: [e-mail]
Xref: crabapple.srv.cs.cmu.edu sci.space:51202 alt.sci.planetary:300
Path: crabapple.srv.cs.cmu.edu!cantaloupe.srv.cs.cmu.edu!drycas.club.cc.cmu.edu!pitt.edu!zaphod.mps.ohio-state.edu!caen!uvaarpa!murdoch!fermi.clas.Virginia.EDU!gsh7w
Newsgroups: sci.space,alt.sci.planetary
Subject: Re: Lunar "colony" reality check
Message-Id: <[e-mail]>
From: Greg Hennessy <[e-mail]>
Date: 11 Nov 92 00:22:43 GMT
Sender: [e-mail]
References: <[e-mail]> <[e-mail]> <[e-mail]>
Organization: University of Virginia
Lines: 14
Source-Info:  Sender is really [e-mail]
Source-Info:  Sender is really [e-mail]

Henry Spencer writes:
#Even so, nobody would have been rash enough to *predict* ice there.
#Recent radar-mapping work shows strong echos from Mercury's poles which are
#very difficult to explain as anything but ice deposits.

The late Axel Firsoff has predicted ice on the caps of Mercury.

However, Firsoff was known to have some "non-mainstream" ideas also.

--
-Greg Hennessy, University of Virginia
 USPS Mail:     Astronomy Department, Charlottesville, VA 22903-2475 USA
 Internet:      [e-mail]
 UUCP:        ...!uunet!virginia!gsh7w

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

End of Space Digest Volume 15 : Issue 415
------------------------------