Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v15_0/v15no088.txt

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Date: Sun,  9 Aug 92 05:01:02
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #088
To: Space Digest Readers
Precedence: bulk


Space Digest                Sun,  9 Aug 92       Volume 15 : Issue 088

Today's Topics:
                A 12 mile tether that generates 5000v?
                           Atlas and Soyuz
                Energiya's role in Space Station assem
                           Fermi's Paradox
                        Fountains of Paradise
                Looking for information on OSC/Pegasus
                         mathematical models
                        Mir Radiation Exposure
    Modified Tether physics (was Re: Physics of shuttle & tether)
                More second-hand info on TSS (2 msgs)
                 Russian Comment on Soyuz vs Shuttle
                        Seeding Mars with life
         Soyuz as ACRV (Posting of previous discussion data)
             Spacecraft contamination from exhaust plumes
                         Whales and Dolphins

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

Date: 8 Aug 92 21:50:40 GMT
From: Henry Spencer <[e-mail]>
Subject: A 12 mile tether that generates 5000v?
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Andreas Windemuth) writes:
>What has been thought or done about rotating tethers? ...

Lots of thought.  The ideas you mention aren't new.  Distinct lack of
doing, so far.
--
There is nothing wrong with making      | Henry Spencer @ U of Toronto Zoology
mistakes, but... make *new* ones. -D.Sim|  [e-mail]  utzoo!henry

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

Date: 8 Aug 92 21:06:00 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Atlas and Soyuz
Newsgroups: sci.space

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

>  In defense of Allen's numbers, he hasn't been quoting numbers for
>the Atlas launcher...

Sorry. I was taking it as close but acheivable based on the numbers I
had (which you reporduce). I also believe there are several RL-10 and
Centaur upgrades in the pipe which would reducr risk.

>and any modifications desired to extend
>Soyuz life beyond the current 180 days.

None needed since we rotate vehicles every 90 days.

>Not to
>mention any other mods necessary to upgrade the unmanned Atlas to a
>"man-rated configuration" - with increased mass TBD.

No special steps are needed to man rate the Atlas. Its operational
record shows it to be as safe as anything.

>   In my opinion, those masses will probably put the total mass over
>the Atlas 7500 kg capability.
>    But it is close enough to be interesting.

Could be. In that case, we go to the backup and use Titan II or III. I
don't know if Titan II is up to the task but if it is, I don't think
it will add any cost. If we go with Titan III, it will add $300 million
per year but is still very worthwile since is will save billions.

BTW, using Titan III will give plenty of extra power to add whatever
is needed and still some.

   Allen
--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "If they can put a man on the Moon, why can't they     |
|  [e-mail]     |  put a man on the Moon?"                               |
+----------------------258 DAYS TO FIRST FLIGHT OF DCX----------------------+

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

Date: 8 Aug 92 21:08:50 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Energiya's role in Space Station assem
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Charles Frank Radley) writes:

>SSF is in 28.5 deg orbit because congress limited the number of
>Shuttle flights, and NASA wants to squeeze as much mass as it can
>into each Shuttle.

But if you use Energia, mass isn't a problem anymore. The internal NASA
report on using Energia has it up with four Energia and Shuttle flights;
that leaves plenty for whatever you want.

In addition, since you needn't worry nearly so much about mass, the cost and
risk of the entire program goes down quite a bit.

  Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "If they can put a man on the Moon, why can't they     |
|  [e-mail]     |  put a man on the Moon?"                               |
+----------------------258 DAYS TO FIRST FLIGHT OF DCX----------------------+

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

Date: 8 Aug 92 22:13:07 GMT
From: Henry Spencer <[e-mail]>
Subject: Fermi's Paradox
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Tom) writes:
> How fast do inter-stellar colonizers move? (No data)

No data... but reaching 10-15% of the speed of light doesn't look impossibly
hard.  We'll be able to do that ourselves within a century or two.  At that
speed, the galaxy is only a million years across.

> How soon did life-bearing conditions arrive, galaxy-wide? (Other galaxies?)

You can probably write off the first billion or two years of the galaxy's
life due to shortage of heavy elements.  After that, it should be okay in
the outer arms, where things aren't too noisy.  The center is probably a
fairly inhospitable place even today.

> What are life-bearing conditions?  (Water vs methane, C vs. Si, etc.)

Water-carbon is the best bet.  Silicon is actually not a viable substitute
for carbon; it's just different enough that it does not form long chains.
Orthodox organic chemistry works fine in liquid ammonia, with only the
most minor changes.  Drastic variants of it might work in liquid methane.
You might be able to make a silicone (not silicon!) biochemistry work in
liquid sulfur or something on that order; silicones are pretty unreactive
at our temperatures, but get them seriously hot and they might be good
enough.  Quite possibly there are other possibilities we haven't noticed.
--
There is nothing wrong with making      | Henry Spencer @ U of Toronto Zoology
mistakes, but... make *new* ones. -D.Sim|  [e-mail]  utzoo!henry

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

Date: 8 Aug 92 23:06:47 GMT
From: John Roberts <[e-mail]>
Subject: Fountains of Paradise
Newsgroups: sci.space

-From: [e-mail] (Craig "Powderkeg" DeForest)
-Subject: Physics of shuttle & tether (LONG) (was: Re: Two questions about ...)
-Date: 7 Aug 92 20:40:29 GMT
-Organization: Stanford Center for Space Science and Astrophysics

-The result is that things in orbit about one another, tend to want to
-stretch along the axis between the things.  This is the effect that
-creates tides on the Earth (and Moon too!), aligns the LDEF experiment,
-and (in an extreme and hypothetical case) would hold up the Space
-Elevator[1].

-[1] as described in _The_Fountains_of_Paradise_, another one of Arthur
-Clarke's self-important novels.

-Craig DeForest:  [e-mail]  *or*  [e-mail]

During the in-orbit press conference yesterday, the Shuttle crew actually
pulled out a hardcover copy of Fountains of Paradise that they had brought
along, and waved it around. They related it to TSS, and commented that many
of Clarke's ideas end up being real technology (like geosynchronous
communications satellites).

John Roberts
[e-mail]

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

Date: 8 Aug 92 19:05:57 GMT
From: "Robert B. Sisk" <[e-mail]>
Subject: Looking for information on OSC/Pegasus
Newsgroups: sci.space,rec.models.rockets

In article <[e-mail]> [e-mail] (Brian Reynolds) writes:
>I would like to build a model of the OSC/Pegasus, but I have no scale
>information.  The sci.space FAQ doesn't really provide much
>information.  Can anyone give me the address or phone number for OSC
>so that I can request some information?  Does anyone know of a model
>of the Pegasus?  I recall that Monogram re-released their B-52 carrier
>aircraft / X-15 model substituting a Pegasus for the X-15, but I
>really don't want to build the B-52.  Did Monogram ever release the
>Pegasus as a separate kit the way they issued the desktop version of
>the X-15?
>
>Thanks in advance.
>
>--
>Brian Reynolds
>[e-mail]
>NAR# 54438
>IPMS# 30162

The new NCR Catalog list a scale model of the OSC Pegasus.  The lenght
of the model is 32", width 2.70", wingspan 14.25", and weight 16oz.
Recommended motors F25-6, F50-6, G40-7, and G80-7.

Bob
--
---------------------------------------------------------------------------
Robert B. Sisk  PhD            Internet: [e-mail]
NAR #53448                UUCP:     uunet!virginia!rbs
TRIPOLI #1583                           CIS:      [e-mail]

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

Date: 9 Aug 92 00:31:03 GMT
From: "R. Kym Horsell" <[e-mail]>
Subject: mathematical models
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (John Roberts) writes:
>-There are thus no ``mathematical formulas for evaluation of
>-the probability of a hypothesis''. Various statisticians will
>-give me an argument. But they are wrong. :)
>
>Predicting a future event is different from evaluating the degree of
>confidence that a given distribution model is correct. I don't know about
>you, but if I had a coin that came up heads a million times in a row, I'd
>be pretty dubious about the model that it's a fair coin. :-)

In my example of something happening n times out of n I asked ``what is
therefore the probability of that event happening again''. Very loose
talk for -- come up with its probability. As I said, there is no
formal method for doing so. (Or more exactly -- there are too many
of them :). Certain probabilities just must be taken on faith -- the rest are
calculated based on these.

I'm afraid the same problem applies to making tests on distributions -- i.e.
``evaluating [its] degree of confidence''.

Which also leads into the (in)famous ``inversion of the implication'' often
performed in statistics: we know that ``if a then b'' does not imply
``if b then a'' although this is common (just watch TV)!

Traditional statistics does somewhat the same ``if X has distribution D then
parameter THETA will be Y'' does not mean ``if parameter THETA has value Y
then X has distribution D''.

As I understand it Jones sorted most of this out for QP.

-kym

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

Date: 8 Aug 92 17:04:51 GMT
From: Dennis Newkirk <[e-mail]>
Subject: Mir Radiation Exposure
Newsgroups: sci.space

Recently, there were questions about radiation exposure on Mir.
Here's some numbers I've run across for radiation exposure on long
duration missions on Salyut 7 and Mir.  This kind of data is usually
found translated in the periodical NASA CR-3922.

Soyuz T-9    long duration mission / 149 days - Salyut 7
Launched : June 27, 1983, 1:12 P.M.
Crew : Vladimir Lyakhov & Aleksandr Aleksandrov
Reported were exposed to 1755 mrad radiation.

Soyuz TM-4     Long Duration / 12 months - 3rd Main Mir Expedition
Launched : Dec. 21, 1987, 2:18 P.M.
Crew : Vladimir Titov & Musa Manarov
The radiation environment over the entire flight was rated as calm. The total
radiation exposure amounted to 12.2-14.0 rems or 7.6-8.7 rads.

Soyuz TM-8   Long Duration / 5th Main Mir Expedition
Launched : Sept. 8, 1989  1:38 AM
Crew : Aleksandr Victorenko & Aleksandr Serebrov
Between Sept. 29 and Oct. 24, four major solar flares.  Mir's orbit, then at 387 *
407 km. and 51.6 inclination, is protected somewhat by the Earths magnetic field.
On Sept. 29, during the worst of the flares, the cosmonauts experienced 600 mrem
compared to the normal 15 to 40 mrem per day.  Dangerous levels to health were
considered to be 50 rem per day.  If high levels of radiation were detected in orbit,
the cosmonauts were told to enter the Kvant module for added protection which could
lower exposure by about 2 to 3 times.  The cosmonauts did go into Kvant as a
precaution when Mir passed over the South Atlantic Anomaly where the Earths
magnetic field weakens to allow increased radiation to penetrate to lower altitudes.
This lasted from 6 to 12 minutes typicially.  The Moscow Institute for Biomedical
Problems has a Space Radiation Group or Radiation Safety Service checks solar
activity and the threat to cosmonauts in space.  It started service for the ASTP flight
in 1976 and has operated ever since.

Dennis Newkirk ([e-mail])
Motorola Inc, Land Mobile Product Sector
Schaumburg, IL

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

Date: 8 Aug 92 19:03:00 GMT
From: [e-mail]
Subject: Modified Tether physics (was Re: Physics of shuttle & tether)
Newsgroups: sci.space,sci.space.shuttle

In article <[e-mail]>, [e-mail] (Craig "Powderkeg" DeForest) writes...
>[e-mail] (Alan Kilian) writes:

Craig I don't mean this to flame, just explain tether dynamics from the folks
who did the experiments.

>   1) The shuttle is at one end of a conductive wire. The satellite is at
>      the other. If the wire moves through a magnetic field you can generate
>      an electric potential. Now how do you measure the potential?
>      They were hoping for 5000 Volts on a 12 Mile tether but got 40 Volts
>      on a 750 Feet tether.

This is from the Tethers in Space Second Edition

3.4 Electrodynamics

3.4.1 General

    Electrodynamic tether systems can be designed to produce several useful
effects by interacting with magnetic fields. They can be designed to produce
either electrical power or thrust (either a propulsive thrust or a drag).
 They can also be designed to alternately produce electrical power and thrust.
In addition, they can be designed to produce ULF/ELF/VLF electromagnetic signals
in the upper atmosphere, and shape-stability for orbiting satellite
constellations.

3.4.2 Electric Power Generators

    The discussion of electric power generation by tether systems will
begin with electrodyncmic systems in LEO.  Consider a vertical, gravity-
gradient stabilized, insulated, conducting tether, which is terminated at
both ends by plasma contactors.  As the system orbits the Earth, it cuts

ACROSS the geomagnetic field from west to east at about 8 km/s. An
electromotive force (emf) is induced across the length of the tether.
This emf is given by the equation:

V = [integral sign] (v x B)[dot product] dl

where

V = induced emf across the tether length (volts).

v = tether velocity relative to the geomagnetic field [vector quantity] (m/s)

B = magnetic field strength (webers/m2), [vector quantity]

dl = differential element of tether length-a vector pointing in the direction
of positive current flow (m)

For the special case where the tether is straight and perpendicular to the
magnetic field lines everwhere along its length, the equation for the emf
simplifies to:

V = (v x B) dot product L;

where L = tether length- a vector pointing in the directionof positive current
flow (m)

The equation for the induced emf across the tether in this special case can also
be written as:

V = L v B sin theta; where theta is the angle betwee v and B

(from these equations it can be seen that equatorial and low-inclination
orbits will produce the largest emfs, since the maximum emf is produced when
the tether  velocity and the magnetic field are PERPENDICULAR TO EACH OTHER).

    The emf acts to crate a potential difference across the tether by
making the upper end of the tether positive with respect to the lower end.
In order to produce a current from this potential difference, the
tether ends must make electrical contact with the Earth's Plasma environment
Plasma contactors a the tether ends proved this contact, establishing a current
loop (a so called "phantom loop") through through the tether, external plasma,
and ionosphere.  Although processes in the plasma and ionosphere are not
clearly understood at this time, it is believed that the current path is like
that shown in figure 3.19.

>   2) Why does the ball (It's easier than satellite) keep moving away from
>      the shuttle as you unwind the tehter?
>
>This is a pretty cool effect, and it can be explained in two equivalent
>ways.
>
>First, one can say that the ball, being at a different altitude than the
>shuttle, `wants' to orbit with a different period, so will pull `ahead'
>(if, as on this flight, it's lower than the shuttle), or `behind' of the
>shuttle.  The tether pulls it back against this tendency, so is kept taut.

On TSS 1 the tether was deployed upward at an angle of 22 degrees from the
vertical,  The end mass is in a higher orbit than the shuttle so its velocity
(but not orbital momentum) is lower than the shuttle. Since it is a two body
system, the tether is constrained to the orbit of the shuttle and therefore
the composite orbit of the system is at the center of mass of the system. This
means that the Shuttle is orbiting in a slightly lower orbit than it should
be and the endmass is orbiting in a much higher orbit than it should be
based upon the actual orbital momentum of the objects taken individually.  This
ratio is exactly equal to the ratio of masses, which in this case is about
185/1.  That means that for every 185 meters of deployment, the center of
mass of the system shifts one meter AWAY from the CG of the orbiter.  This is
the primary source of the tension of the tethered system.

>Alternatively (and perhaps better), the space around the shuttle is
>subjected to a gravitational gradient.  That is to say, the gravitational
>field (due to the Earth) in the vicinity of the shuttle, changes with
>altitude above the Earth.  The ball, being closer (farther) to (from) the
>earth than is the shuttle, is pulled more strongly (weakly) by the earth
>than is the shuttle.
>
>The result is that things in orbit about one another, tend to want to
>stretch along the axis between the things.  This is the effect that
>creates tides on the Earth (and Moon too!), aligns the LDEF experiment,
>and (in an extreme and hypothetical case) would hold up the Space
>Elevator[1].
>
This gravity gradient force differential is on the order of magnitude of
1 X 10-7 g wheras the gradient due to the center of mass shift and momentum
transfer is on the order of 1 X 10-5 g, a much greater force.

[craigs stuff deleted]

>There's one more effect we need to describe.  That's the reason why the
>conductive loop was *really* *large*, instead of just (more-or-less)
>shuttle-sized.
>
>When a charged particle moves at right angles to a magnetic field, it
>`feels' a force at right angles to the motion and to the field.  The result
>is that its motion (if there's no electric field) is circular.  But *any*
>motion can be resolved into a component at right angles to the field, and
>one along the field.  So any charged particle travelling through a magnetic
>field (in the absence of collisions and electric field) will spiral around
>the field lines themselves.
>
>If you stand far back and squint (ie you care only about really long
>distances), this means that electrons travel *only* along magnetic field
>lines.  The only ways to conduct across the field lines involve a high
>electric field, or collisions between charge carriers. So it's really easy
>to conduct electricity along magnetic field lines and hard to conduct it
>across them.  The magnetic field lines act almost like wires!
>
>The conductive loop in the tether experiment consists of (a) the tether
>between the shuttle and the ball; (b) the (REALLY LONG!) field line
>extending from the shuttle to the nearest magnetic pole of the Earth; (c)
>some small resistive elements between nearby field lines (which get really
>close as you get closer to the poles); and (d) the field line extending
>back to the ball from the magnetic pole.
>
>The ball is, well, a conductive ball, so it has a lot of surface area to
>collect electrons from the surrounding space.
>

This explanation is wrong for the reasons stated in the equations above. The
max emf is generated when you are traveling at right angles to the magnetic
field in question not along it.  The best orbit is one that is equatorial and
very low to increase  both v and B to their max values.

>
>[1] as described in _The_Fountains_of_Paradise_, another one of Arthur
>Clarke's self-important novels.

Reference here is the Tethers in Space Handbook -Second Edition-
National Aeronautics and Space Administration Office of Advanced Program
Development, NASA HQ Code MD (now code DD) Washington, DC 20546
[Book produced under NASA contract # NASW-4341. Edward J Brazill, NASA HQ
contract monitor.

Also see NASA Conference Publication 2422 Applications of Tether in Space
Workshop Proceedings Vols 1 and 2.
[Proceedings of a workshop held in Venice, Italy, Octover 15-17, 1985]

>Craig DeForest:  [e-mail]  *or*  [e-mail]

Hope this helps to clear the confusion up on tether power generation and this
also gets me off the hook with Henry and Allan for the references I promised
you guys about six months ago!

Dennis, University of Alabama in Huntsville

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

Date: 8 Aug 92 22:00:49 GMT
From: Henry Spencer <[e-mail]>
Subject: More second-hand info on TSS
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Chuck Shotton) writes:
>Running 12 miles of cable off a spool doesn't seem to be a particularly
>difficult task, even in zero G. Why is it that we have another
>over-engineered solution that has apparently failed? Is this really any
>more difficult to engineer that an elaborate fishing reel? ...

The first fishing reels didn't work very well either.

The problem with a project like this is not solving any particular
engineering problem, but *understanding which problems must be solved*.
There really is no substitute for trying the thing out and finding out
what breaks.

The reason the solutions are over-engineered, at colossal cost, is all
the people who cry "incompetents!" when something being tried for the
very first time doesn't work.  The natural response is to put more money
and effort into trying to avoid failures.  This cripples projects even
when ample funding is available.  Worse, it doesn't really help much.

Progress requires setbacks.
--
There is nothing wrong with making      | Henry Spencer @ U of Toronto Zoology
mistakes, but... make *new* ones. -D.Sim|  [e-mail]  utzoo!henry

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

Date: 8 Aug 92 23:43:43 GMT
From: "J. D. McDonald" <[e-mail]>
Subject: More second-hand info on TSS
Newsgroups: sci.space

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

>In article <[e-mail]> [e-mail] (Chuck Shotton) writes:
>>Running 12 miles of cable off a spool doesn't seem to be a particularly
>>difficult task, even in zero G. Why is it that we have another
>>over-engineered solution that has apparently failed? Is this really any
>>more difficult to engineer that an elaborate fishing reel? ...

>The first fishing reels didn't work very well either.

>The problem with a project like this is not solving any particular
>engineering problem, but *understanding which problems must be solved*.
>There really is no substitute for trying the thing out and finding out
>what breaks.

>The reason the solutions are over-engineered, at colossal cost, is all
>the people who cry "incompetents!" when something being tried for the
>very first time doesn't work.  The natural response is to put more money
>and effort into trying to avoid failures.  This cripples projects even
>when ample funding is available.  Worse, it doesn't really help much.

>Progress requires setbacks.
>--
>There is nothing wrong with making      | Henry Spencer @ U of Toronto Zoology
>mistakes, but... make *new* ones. -D.Sim|  [e-mail]  utzoo!henry

But how hard would it be to carry several spooling systems, and try
them all?

Doug McDonald

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

Date: Sat, 8 Aug 1992 21:16:04 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Russian Comment on Soyuz vs Shuttle
Newsgroups: sci.space

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

>    According to the trade press, cosmonaut Anatoly Artsebarsky
>stated at a press conference in Chicago last Tuesday, regarding the
>Buran:

>    "We need it (Buran) to bring back (to Earth) materials and
>experiments from the station... When using the Soyuz spaceship, we
>have to abandon some experiments and materials due to its limited
>(return) capability."

But at what cost? The Shuttle is killing the entire program. We can't
design a replacement because Shuttle operations costs are so high that
is uses all the money which might go to a replacement. We won't go
anywhere so long as we have this millstone around our necks.

I think what he  ment was that they needed the ability to return larger
payloads. That doesn't mean it MUST be Buran.

  Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "If they can put a man on the Moon, why can't they     |
|  [e-mail]     |  put a man on the Moon?"                               |
+----------------------258 DAYS TO FIRST FLIGHT OF DCX----------------------+

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

Date: 8 Aug 92 23:26:59 GMT
From: Kenneth Tolman <[e-mail]>
Subject: Seeding Mars with life
Newsgroups: sci.space

 It appears that with today's technology an attempt to begin terraforming
Mars could begin now.

  Terraforming Mars could be begun by flying in a landing craft which
carried on board a diverse spectrum of biological entities.  The biological
entities would include:
  Bacteria which currently lives in the ice pack
  Genetically engineered bacteria for the conditions which exist on Mars
  Bacteria which lives in extreme conditions currently, such as from thermal
    vents, deep in rock strata

 The landing craft would not have to be too terribly sophisticated, but
presumably would have some sort of MIRV like entry for multiple dispersion
over a wide area (perhaps targeting specific temperate regions).
  The colonization bacteria would have ZERO competition for resources,
and if any of it survived it would begin mutation and development.
Presumably, aneorobic bacteria would be best to start, with plenty of
photosynthesizers going along.  At the very worst, this project would fail
to implant life.  At the worst of the best, life would exist elsewhere in
our solar system even if it took billions of years to evolve further, and
at the best of the best life could begin to raise the temperature and free
up oxygen for eventual multi species colonization.

 What do you think?

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

Date: 8 Aug 92 23:01:27 GMT
From: "Paul J. Gravestock" <[e-mail]>
Subject: Soyuz as ACRV (Posting of previous discussion data)
Newsgroups: sci.space

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


>In other words he's a REAL engineer?  Personally, I'd need to do the
>shopping in at least a Busy Beaver DIY store in a major american
>city... :-) :-)

Either that or he's a member of the A-Team.

B-)

------------------------------------------------------------------------------
Paul J. Gravestock                  | email: [e-mail]
Hertfordshire                       |        [e-mail]
England                             |
------------------------------------------------------------------------------

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

Date: 9 Aug 92 00:43:14 GMT
From: Bruce Dunn <[e-mail]>
Subject: Spacecraft contamination from exhaust plumes
Newsgroups: sci.space

> Henry Spencer writes:
> Sorry, Dennis, that exhaust velocity is an *average*.  There is always
> some small fraction which emerges at much lower velocity.  Hence the
> well-known problems with plume contamination of things that are far away
> from the exhaust nozzles.


        One of the nicest propellants for an ion engine is mercury - the ion
mass is high and the energy needed for ionization is low.  Unfortunately, a
mercury ion engine ends up contaminating the space craft on which it is
mounted.  Mercury therefore is not used in most ion engine designs, which use
xenon (very good, but very expensive) or argon (not so good, but not
expensive).
--
Bruce Dunn    Vancouver, Canada   [e-mail]

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

Date: 8 Aug 92 19:35:56 GMT
From: John Roberts <[e-mail]>
Subject: Whales and Dolphins
Newsgroups: sci.space

-From: [e-mail] (Edward V. Wright)
-Subject: Re: Whales and Dolphins
-Date: 6 Aug 92 20:47:31 GMT
-Organization: Engineering, CONVEX Computer Corp., Richardson, Tx., USA

-In <[e-mail]> [e-mail] (John Roberts) writes:
->Human search parties won't go out to rescue one person if the expected
->outcome is that several people *will* die in the attempt. (Unless it's
->the President or something.)

-Nonsense.  Look at the motto of the USAF pararescue: "That others
-may live."  How many times have you seen firefighters go into a burning
-building on the evening news?
-...Humans are
-not rational animals, they are rationalizing animals.

Reread what I posted. Humans take calculated risks, and sometimes there
are mistakes in the calculations. Individuals are prone to miscalculation
in the heat of the moment, which is why a rescue *party* (as I specified)
really should have some form of organization or leadership, to make as
accurate an assessment as possible with the available data, and to decide
when the rescue should be abandoned because the danger is too great (in
other words, the expected loss is greater than the expected gain).

Those firemen don't go into the building expecting to die - they know they're
taking a risk, but the risk is managed so that generally they survive. Whales
that beach themselves entirely seldom if ever survive (though on the "R-rated
Gory Animal Videos" series commercials on television, they show a killer
whale getting its head out on the beach to chomp a sea lion). If whales have
anything akin to human intelligence, and if they have a community that
communicates and passes down lore, then they must realize that if they
beach themselves, they're going to die, and they're not going to be able to
do anything to help the one that's already stranded.

If what the whales do is deliberate suicide, it's even less akin to normal
human behavior. There are cases of extended human families all committing
suicide because of the grief following the death of a family member, but
that's extremely rare, while mass beachings appear to be comparatively common
among some species of whales.

Tell you what - find me some specific examples where a group of rescuers
deliberately sacrificed themselves to save a much smaller group of people
of no particular merit. ("We lost five firefighters, and the abandoned
corset factory burned to the ground," the fire chief told the press, "but
we rescued the wino who set the fire, and we're glad - we'd do it again
in a minute. We're just lucky we didn't lose ten firefighters, like we had
expected to before we went in.") That would fit in with your theory of
rationalization, since it's in their interest to claim they made the best
possible decision.

-If you want further proof, look at the
-amount of money NASA is planning to spend on a lifeboat, which probably
-won't ever be used, for Space Station Freedom, and think about how
-many lives that money could save if spent in other ways.

A good point, in the general case. It's politically popular to maintain
the illusion that there are infinite amounts of money and resources available
to save people, and that money and resources mean nothing in comparison to
human lives, but in fact if that were the case, society could not function.
Money and resources are a result of human lifetimes of effort, and if you
treat them as valueless, then you're still throwing away human lives, but
in a more subtle fashion. People realize this in general, but they don't like
to think or talk about it. This is what lawsuit lawyers thrive on - they
maintain that even the slightest injury or inconvenience to one person is
grounds for claims of many millions of dollars against anyone even peripherally
connected to the injury or inconvenience. There's a tendency to think of these
as isolated events, but the cumulative effect is to distort the US economy
by hundreds of billions of dollars, to the general detriment of most of the
public.

I think the valuation that has been shown to be workable over the long run
is something like $1-2 million dollars per human life put at risk. It might
be argued that the level might be higher for humans who are highly selected
and trained, and who are in a uniquely valuable position. So perhaps one
might justify $10-20 million dollars per astronaut for rescue expenses,
or an even larger amount for the publicity value of rescuing the astronauts.

To be fair, throwing money at safety issues has some merits. Americans pay
a lot of taxes for sophisticated military equipment, but they're also fairly
unlikely to be drafted or to be killed in battle. But that's only thousands
of dollars per person, not millions.

->Anyway, the discussion was whether whales have *intellect* comparable to
->humans, not *emotion*.

-To be precise, the question was whether the fact that whales engage
-in mass beachings proves they are not intelligent.  (Somewhat analogous
-to the question of whether the fact that millions of Americans smoke
-cigarettes proves that they are not intelligent.)

You've forgotten the subject of my earlier post. The initial discussion
had been on indications of the intelligence of whales, then I introduced
the topic of mass beachings as part of a specualtion on whether whales
show emotion to a degree that it overrides whatever intellect to a
degree greater than that typically shown by humans.

->Humans often have the intellectual capability to realize that the
->action most strongly prompted by emotion would defeat its own purpose
->if carried out.

-If so, they very seldom use it.  (At least, I seldom noticed it during
-the two years I worked as an ambulance attendent. ;-)

So - in keeping with your philosophy, when rushing to the aid of a person
about to expire, was your ambulance invariably driven with the accelerator
shoved to the floor, without regard to road or traffic conditions? And each of
the first ten times the ambulance was wrecked, did the boss call the crew in,
and say "you totalled your vehicle, injured yourselves, and the patient
died before we could get another ambulance there, though he probably would
have lived if you'd driven a little more slowly and carefully, but you did
the human thing, and I'm proud of you"? :-)

John Roberts
[e-mail]

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End of Space Digest Volume 15 : Issue 088
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