Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V12_6/V12_704.TXT

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Subject: SPACE Digest V12 #704

SPACE Digest                                     Volume 12 : Issue 704

Today's Topics:
            Re: pressure-altitude relation
     Re: Air pressure questions (A human being in vacume)
             pressure-altitude correction
           Re: space news from Nov 19 AW&ST
           Could Iraq shoot down recon satellites?
               Re: Interstellar travel
             space news from Dec 3 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
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Date: 16 Dec 90 15:42:28 GMT
From: swrinde!zaphod.mps.ohio-state.edu!rpi!uwm.edu!ux1.cso.uiuc.edu!aries![e-mail]  (Doug McDonald)
Subject: Re: pressure-altitude relation

In article <[e-mail]> [e-mail] (Matthew T Velazquez) writes:
>
>In article 26774 of sci.space Dave Kinkley writes:
>
>^could somebody give me a pressure-altitude relation...
>
>
>    Depends on the atmospheric model you use. For the troposphere (valid
>up to circa 20 km):
>
>    P(sea level)/P(z) = [1-L/T(sea level)]^^gamma/(1-gamma)
>
That can't possible be right. It doesn't contain z.

Doug MCDonald

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Date: 16 Dec 90 15:38:02 GMT
From: prism![e-mail]  (Glenn R. Stone)
Organization: Dead Poets Society
Subject: Re: Air pressure questions (A human being in vacume)
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In <[e-mail]> [e-mail] (james d. Del Vecchio) writes:

>1)  Imagine a cabin door breaks, something causes the pressure to
>go way down.  Would it be better to try to hold your breath,
>or could that just cause more damage.


I'm with Spencer on this one.  Holding your breath would be a Bad Idea,
if not physically impossible....
>2)  If someone suddenly was exposed to 1/2 s.l. pressure
>What harm would be possible right away?  What about gradualy
>(over a few minutes or hours), like if he had extra oxygen?


Rapid decompression in and of itself is no big deal, if supplemental
oxygen is available.... Air Force and Navy pilots regularly go thru
decompression drills in hypobaric chambers as part of their flight
training.  (Classes involving these chambers are sometimes made
available to civillian pilots as well; I don't have details, though.)
You just have a nasty little gas problem for a few seconds, that's all.

>2.2)  What is the highest alt/lowest p. that people live at?
>Is it the pressure that limits them, or just cold and inaccesablility,
>no food, etc, that keeps them from going higher?

My best guess is 15,000 feet (agreeing with other posters); Federal
standards for supplemental oxygen in aircraft say that pilots
must have it at a rate of 1 liter/min/10kfeet for flights longer
than 30 minutes at cabin altitudes of more than 12,500 feet, and all
flights at cabin altitudes of more than 14,000 feet; passengers must
have O2 at more than 15,000 feet cabin altitude ("cabin altitude" being
the effective pressure INSIDE the cabin; with the advent of cabin
pressurization beginning in the mid-1940's, aircraft can fly much higher
without subjecting their occupants to either O2 masks or hypoxia....
currently up to 51,000 feet, depending on the aircraft.)  Federal standards
also mandate a maximum cabin altitude of 8,000 feet for all pressurized
aircraft on on flights for hire..... some people tend to suffer adverse
physiological effects at lower altitudes (10,000 to 11,500 feet),
usually in the form of a dull headache.  Smokers will, natch, suffer more
than non-smokers.... studies have indicated that one good puff on a
cigarette is good for an extra 5,000 feet of altitude.  <sigh>

>3)  If a person was breathing pure oxygen at 1/5 normal pressure,
>What do you think would happen?  What might be harmfull about it,
>under what conditions might it be safe?

To clarify what Henry said: it's not the total pressure of the air that
is critical to survival, it's the partial pressure of oxygen.  Since
O2 is about one-fifth our atmosphere, breathing pure O2 at 1/5 of the
standard atmospheric pressure should cause few detrimental effects in
and of itself... although I think there does need to be a certain (low)
CO2 partial pressure in there as well; there are some sublte problems
that can be caused by *not enough* CO2 available to the bloodstream...
Also, "medical oxygen" contains a certain amount of water vapor, so
that the patient's mouth, nose, and lung tissues don't dry out.... a
problem pilots experience, since "aviation oxygen" has NO water vapor
(since it will freeze in the supply lines).

Crossposted to rec.aviation, since it might be of interest;
Followup to ME.

-- Glenn R. Stone
[e-mail]

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Date: 16 Dec 90 21:05:16 GMT
From: snorkelwacker.mit.edu!bloom-picayune.mit.edu![e-mail]  (Matthew T Velazquez)
Organization: Massachusetts Institute of Technology
Subject: pressure-altitude correction
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Whoops, I goofed!!!

The correct equation should read:

    P(sea)/P(z) = [1-L*z/T(sea)]^^gamma/1-gamma

    Sorry, guys, I was busy trying to think of a letter to call the linear
lapse rate (L). That's the right version Doug. I promise.

                -T

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Date: 16 Dec 90 21:26:58 GMT
From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Organization: U of Toronto Zoology
Subject: Re: space news from Nov 19 AW&ST
References: <[e-mail]>, <[e-mail]>
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In article <[e-mail]> [e-mail] (Steven Bellovin) writes:
>> a solar-storm-warning satellite to help protect power-distribution networks
>> against high solar activity.
>
>It's nice to be warned, I suppose, but what could be done with the warning?

There are various things that can be done to reduce vulnerability and
prepare for trouble, such as shifting loads and starting backup generators
to minimize reliance on long transmission lines (where trouble tends to
strike).  But there are enough extra costs involved that such things are
not done without fairly strong assurance that trouble is imminent.
--
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| [e-mail]   utzoo!henry

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Date:     Sun, 16 Dec 90 22:45 CST
From: Bill Higgins-- Beam Jockey <[e-mail]>
Subject:  Could Iraq shoot down recon satellites?
To: [e-mail]
Original_To:  SPACE

[I tried posting this once, but it doesn't seem to have made it to the net in
the last few days.  I could be wrong.  Please forgive me if it pops up twice.]

Iraq is under the watchful eyes of a number of superpower
reconnaissance satellites in low orbit.  It's not a *large* number.

Iraq has built its own ballistic missiles, variations on the Soviet
"Scud."

Suppose you're an Iraqi missile engineer. Suppose Saddam Hussein
called you and your colleaques in and said, "Boys, I want you to turn
those missiles into anti-satellite weapons as soon as you can." Could
you do it?  [Note that I am supposing you are a boy, too, a reasonable
conjecture in the Iraqi defense establishment. (-:]

--Delivery vehicles which can reach range R ought, in a naive
analysis, to be able to reach an altitude of .7071R (that is,
[sqrt(2)/2]R, assuming a 45-degree launch angle gets you the maximum
range).   R was about 500 km last I looked.

--This should be enough to get you to orbital altitude, but not
orbital speed.  Then you put an essentially stationary payload in the
path of a fast-moving satellite.  This is more or less the method
employed by the (defunct) American air-launched ASAT missile.

--You don't need a precision-guided homing vehicle to damage your
target satellite.  Arrive at a point on the satellite's orbit just as
the satellite is arriving there too.  Fill some volume of space with
small metal pellets.  Oldest trick in the book.  (The book is *The
Exploration of Space*, Arthur C. Clarke, 1950.)

--Hence the problem hinges on making the cloud of pellets (volume
which has pellets above some density with high kill probablilty)
larger than the probable error of the delivery vehicle.   This is
probably very tough.  I know the Iraqi IRBMs are not very accurate.  I
should do some numbers.  Guess I'll do a follow-up posting soon.

--Tracking your targets is quite do-able.  Are they listed in the
Two-Line Elements?  Could Iraq get these from Kelso's BBS in Ohio?  If
not, optical or radar tracking could be kluged up.  It's be nice to
have observations.

--Recon sats can manuver.  If you attack one, the allies will move all
the others.  And they will keep jinking if necessary (how often? Once
a day?) I presume the Iraqis would be hard pressed to keep up with
this. Therefore:

--A surprise attack, taking out all adversary satellites in a short
time, is called for.  This is a one-shot deal, so you'd better play
this card it until it's militarily useful.  It could be used to cover
preparations for a sudden attack.

--If you are fully successful,  the other guys will be blind until
more low-orbit satellites can be launched.  I am fairly sure the
Soviets could have one up in a week or two.   I am fairly sure the
USAF will take several months.

--If you are partly successful, you may at least create a gap in photo
coverage, a recurring period of time when you may safely move your
forces around without being observed optically.

--This trick will not work on high-altitude satellites. I believe
geosynchronous orbit is used mostly for signals-intelligence and
missile-warning spacecraft, not high-resolution photoreconnaissance.
So the allied capability will be somewhat crippled, but there will
still be some intelligence flowing from space.

--In particular, the ICBM-warning birds will probably see your
launches, so your adversaries will know exactly what you're up to.
(Hmm... can we make them look like gas-well fires?  (-:  I guess not.)

--The usefulness of this idea is dubious in the current context of
Iraqi military operations.  It's still an interesting excercise.   It
may apply to some other IRBM-packing nation in some future conflict.

     O~~*           /_) ' / /   /_/ '  ,   ,  ' ,_  _           \|/
   - ~ -~~~~~~~~~~~/_) / / /   / / / (_) (_) / / / _\~~~~~~~~~~~zap!
 /       \                          (_) (_)                    / | \
 |       |                      Bill Higgins
 \       /                      Fermi National Accelerator Laboratory
   -   -                        Bitnet:                [e-mail]
     ~                          Internet:             [e-mail]
                                SPAN/Hepnet/Physnet:         43011::HIGGINS

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Date: 16 Dec 90 18:19:03 GMT
From: [e-mail]  (Alan M. Carroll)
Organization: Technophiles Inc. - Engineers with Attitude
Subject: Re: Interstellar travel
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In article <[e-mail]>, [e-mail] (/dev/null) writes:

> I believe the Orion was discarded due to technical difficulties - it relied
> upon the continuous detonation of atomic bombs in a reaction chamber to supply
> the thrust - not much even on the forefront in the way of materials that can
> withstand a direct nuclear explosion with no appreciable damage.
>

That's not what Freeman Dyson, one of the project members, claims. In
fact, I've seen a statement that Orion is in fact the most efficient
drive achievable with current technology. As for material technology,
carbon coated steel apparently can withstand nuclear detonation at
close ranges (~100 meters), and this was known during the design phase
of Orion. Dyson claims that it was the cessation of above-ground
nuclear testing that did in Orion. While it was under consideration,
calculations indicated that it would contribute only a fraction of the
fallout that testing at the time was generating.

--
Alan M. Carroll                "It's psychosomatic. You need a lobotomy.
Epoch Development Team          I'll get a saw."
CS Grad / U of Ill @ Urbana    ...{ucbvax,pur-ee,convex}!cs.uiuc.edu!carroll

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

Date: 17 Dec 90 00:48:25 GMT
From: news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: space news from Dec 3 AW&ST

[This is the last AW&ST summary for the next 2-3 weeks, as I will be on
vacation.  The good news, though, is that I'm actually caught up even
so, since I consider a month behind to be normal.]

Hydrogen turbopump of Pratt&Whitney's alternate SSME pump assembly runs
successfully at 100% power.  P&W has a contract to demonstrate an alternative
to the current (Rocketdyne) pumps, up to and including flight certification
in 1993.  [There are, however, no specific plans to actually fly the new
pumps, or to convert the shuttle fleet to use them, even if they work well.]
P&W is about to deliver its first pump set to Stennis for tests.

The X-30 overall color scheme will be white for first flight, but once the
program starts on higher Mach numbers, it will probably revert to the natural
surface colors.  No current paints are considered capable of surviving on the
hotter sections.

Pictures of the first Titan 4 version of the Centaur -- essentially the
Centaur G-prime originally meant for the shuttle -- about to be shipped
to the Cape in preparation for use on a military payload next year.  GD
has a $1.3G contract for 15 over the next five years.  The new version is
fatter than the old Centaurs and carries about 50% more fuel.  Further
improvements are being pursued.  Modernized electronics will be more
reliable and will cut electronics parts count and weight by about 50%.
GD is also scheming a single-engine Centaur to reduce overall weight
substantially, since the Titan application does not need the higher
thrust of the current pair of engines.

[Aha, I told you so!]  NASA wants to postpone the Spacelab J shuttle mission
to 1992, giving other [US!] payloads the last one or two slots in the reduced
shuttle manifest for 1991.  Japan, naturally, wants to fly its mission as
planned.

Magellan images, in quantity.  The geologists are jumping up and down.
The current big mystery is that crater counts make the surface relatively
young, about 400Myr, while it is clear that there is very little erosion,
with successive features superimposed on each other with all details
preserved.  (Earth's land surface averages 1Gyr.)  The current guess is
that the resurfacing is due to lava flows, which are quite prominent.
It is not clear whether vulcanism is still occurring, although Magellan
images may eventually resolve this.  Another surprise is that the impact
craters seem to be mostly the same age, while the Moon and other bodies
show a wide range of ages.

Minor problems for Magellan on the horizon:  around April, thermal stresses
will be at their peak, when the electronics sections are getting more or less
continuous sunlight rather than being shaded by the antenna.  This is an
issue because Magellan's ability to reject heat is not up to spec, perhaps
due to problems with its thermal blankets.  Engineers are studying ways to
reduce heat load, possibly by shortening the hot data-playback phase of
each orbit -- this would limit mapping, but the hoped-for extended mission
could cover missed areas.

Hubble mirror board reports, blaming faulty test equipment, lack of proper
management supervision, and inadequate expertise at and oversight by NASA.
The board says NASA is half to blame, a view that "some high NASA officials"
are not at all happy about.  A possible contributing factor is that the
project was being overseen by Marshall, during its worst pre-Challenger
phase of discouraging reports of problems.  The PE optical division
successfully held off attempts to get either contractor or NASA personnel
in to assess mirror fabrication operations.

The ultimate problem was a fabrication error in the reflective null
corrector, used in mirror testing.  PE planned to certify the RNC with
great care and avoid any need for independent testing of the mirror...
but the board could not find any documentation that the RNC *was*
properly certified, and criticizes PE for not planning independent tests.

The probable problem in the RNC was that a measurement was done on the
wrong part.  It was supposed to be done on the end of a rod, visible
through a hole in an end cap, but in fact a small piece of nonreflective
coating had broken off the cap, and it seems likely that the measurement
was actually done on the shiny spot on the cap instead.  The board says
that PE missed at least three chances to catch the problem.  First,
spacing washers had to be added to the rod to make it line up; "that
in itself should have alerted people that something was different than
designers had intended".  Then, two other devices -- an inverse null
corrector and a refractive null corrector -- were also used to check
the mirror, and both indicated problems.  However, PE engineers decided
that the RNC was a certified test device and the inherently lower
precision of the two other devices invalidated their results.  A later
request from an advisory body for an independent test for gross flaws
was rejected because PE was confident that the earlier tests were right.

Adding to the problem were managerial flaws.  PE's own management did
not supervise the Optical Operations Division properly.  NASA project
management lacked the expertise to evaluate the optical work.  PE's
best people were not involved in the Hubble mirror at all.  NASA did
not take the initiative to examine the fabrication process.  And the
NASA/USgovt review and QA process was adequate for issues like safety
and handling but inadequate for optical quality.

The Hubble backup mirror by Kodak, currently in storage, is essentially
perfect.

Hubble board, requested by NASA to review the Hughes Danbury (nee Perkin-
Elmer) work on the mirrors for AXAF, gives it a clean bill of health.
Communications with management have improved greatly, and QA and review
people involved are on the ball this time.

Hubble image of Saturn, showing the huge white storm in the planet's
equatorial region, now planetwide.  Despite the mirror problems, the
Hubble image is 3-10 times better than Earth-based ones, and at least
400 images of the storm are planned.

Soviets launch Gorizont comsat for internal use... not by the whole USSR,
but on contract to the Russian Soviet Federated Republic, a first.

Tenth operational Navstar launched by a new Delta version.  This Delta
has new lightweight strap-ons from Hercules, replacing the old Thiokol
ones, and a higher-expansion nozzle on the main engine.

Letter from Cathleen S. Lewis of the National Air and Space Museum,
questioning AW&ST's calculations of the size of the Soviet space budget.
She says that the ruble-dollar exchange rate AW&ST assumed -- 0.56R/$ --
is no longer even the USSR official rate.  The official rate is now
1.80R/$ for commercial use and 5.90R/$ for tourism [!], and the black-
market rate, which economists consider by far the most realistic, is
20-40R/$.  At the lowest black-market rate, the annual operating budget
of the Soviet space program is circa $325M, about the budget of the
Smithsonian!
--
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| [e-mail]   utzoo!henry

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End of SPACE Digest V12 #704
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