Date: Wed,  9 Sep 92 05:03:58    
From: Space Digest maintainer <digests@isu.isunet.edu>
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Subject: Space Digest V15 #178
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Space Digest                Wed,  9 Sep 92       Volume 15 : Issue 178

Today's Topics:
            A personal report on the World Space Congress
             Climate cycles from Earth's orbital geometry
                     Clinton/Gore Space Position
         Is NASA really planning to Terraform Mars? (5 msgs)
                              Relativity
                            Space markets
                            Truax (2 msgs)
                            Venus orbiters

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Date: Tue, 8 Sep 92 21:45:16 GMT
From: "Andres C. Gaeris" <agae@elder.lle.rochester.edu>
Subject: A personal report on the World Space Congress
Newsgroups: sci.space

 
        As a vacation I went to the World Space Congress both to fulfill
my longed desire of attending an IAF Congress and at the same time knowing
the Empire's capital.
 
Considering I payed only $25 for my registration at the WSC (I am a graduate
student at UoR), that Washington is the American city that most looks like my
old own city (Buenos Aires), the Smithsonian Air & Space museum, the Space
Exhibition at the Convention Center, the Mars Rover rally and the receptions
to the participants, this vacations was not only enjoyable but a bargain!
 
        In the minus side I was appalled by the poor scientific level of the
papers presented in the sessions I was most interested. As a plasma physicist
that got into this subject after reading an article of Wolfgang Moeckel
(_The Next 25 years of Planetary Exploration_, A&A Nov71) on the future of
physical propulsion as the only way of going to deep space, I feel a profound
interest on any non-chemical propulsion method or technique (including
Astrodynamics and space power systems). Besides the dream of interstellar
flight is one of my most cherished ones so I went mainly to advanced propulsion
sessions of the IAF/WSC.
 
        The scientific/technological quality of the papers seemed to go
inversely proportional to the distance the authors pretend to reach or the
power/energy levels they pretend to obtain. Now let me describe what was
going on in the main three sessions I attended.
 
        The following text it is a very opinionated commentary of what I saw
at the WSC. Somebody could be offended/offuscated/upset about my views, but
I do not want to initiate any kind of flame war. So take it or leave it, but
please do not flame. Anyway, I am only a graduate student and I do not pretend
any expertise outside my field of study.
 
DISCLAIMER: THE OPINIONS, COMMENTARIES AND BAD JOKES APPEARING IN BOTH THE
PRECEDING AND FOLLOWING PARAGRAPHS ARE OF MY ENTIRE RESPONSIBILITY.
THE UNIVERSITY OF ROCHESTER, THE LABORATORY OF LASER ENERGETICS OR THE DOE
ARE NEITHER RELATED NOR AWARE OF THE CONTENTS OF THIS POSTING.

S.1 ADVANCED PROPULSION
There was very competent (and encouraging) papers describing current research
in plasma and ion thrusters from people at NASA Lewis, JPL, Stuttgart and
West Point. It seems that arc-jets and ion thrusters are a sufficient mature
technology to work but nobody wants to pay the penalties of being the first
non-experimental user of this gadgets.
 
Jordin Kare made a very exciting presentation about laser-heated rockets for
ground to orbit launch. I found Kare's work particularly atractive due my
current association to both very high power lasers and laser-produced plasmas.
 
A. Bolonkin (from the research lab of the AES<- somebody knows what AES stands
for?) presented a paper on the new fashion on sails-magnetic ones, but he was
so boring (he read the paper) and the trasparencies were so ininteligible
that I suffered a momentaneous brain disconnection and I cannot recall anything
about his work except the criticism done by Giovanni Vulpetti during the Q&A
time about the unworkability of magsails inside the Saturn's orbit due to the
formation of bow shocks between the solar wind and the sail's magnetic field
(I need some time to digest this comment, including to get a copy(es) of the
Zubrin/Andrews paper(s)). For the Argentinian slang speakers in the net I
cannot resist to add that Bolonkin's paper honored the author's surname 8-)
 
A pair of very enthusiastic researchers from Berkeley (Carpenter) and McDD
Space (Deveny) gave a really well researched talk on magnetic-mirror fusion appl
ied to propulsion with an eye to SEI missions.
Even when I am a little skeptic (mostly due to my plasma physics professors
telling me insistently that only tokamaks and laser-ICF work) about the
feasibility (even in the long-term) of this kind of magnetic fusion
configurations, it was noticeable the good level of detail and effort put by the
se guys, making this one of the highlights of this session and the other
physical propulsion presentations.
 
I cannot say the same about the closing paper of the session, mainly because
the fusion scheme elected to analyze was the plasma focus, that had a moment
of popularity as a would-be fusion reactor configuration at the late 60's,
due to its compacteness and high power density, but it has been completely
discredited among the plasma community as a viable reactor since then because
the inherent MHD instabilities of the Z-pinch configuration in which it is
based. Without some experimental breaktrough giving some orders off magnitude
improvements on plasma stability, any plasma focus device is only a cheap
and compact gadget to study plasma physics and to generate high intensity
neutron pulses and not a serious way to fusion rockets.
 
F.1 EXPLORATION IN THE PLANETARY RANGE
F.2 EXPLORATION FROM PLANETARY TO COMETARY RANGES
Even with these titles it was pretty obvious from the names both of the papers'
contributors and the attendees to the sessions that these were the usual IAA
interstellar flight time slots. The most speculative and risky papers appear
here and I found myself very dissapointed of the pre-screening of the
presented papers. I believe that there are enough and respected contributors
to the field (R.L.Forward, R.W.Bussard, G.Vulpetti, L.R.Shepherd, A.R.Martin
among others usually publishing at Acta Astronautica and JBIS) to do a careful
refereeing and selection of papers and avoid some of the misleading and in
one case completely absurd contributions to these sesssions.
 
F.1
Matloff and Cassenti proposed a scheme to mine He3 using a pair of magnetic lens
es to focus the solar wind flow in a collector (other new fashion among
space industralization fans. Hey guys! How you pretend a D-He3-based fusion
economy when we are 10 years or more of demonstrating D-T fusion breakeven
scientifically and this milestone probably will be done with reactors
unworkable from the engineering standpoint? Any attempt to predict what will
go with fusion in the next 50 years is mostly technology-fiction and even
program insiders -both magnetic and ICF- acknowledge that with the current
levels of funding and technology commercial fusion reactors in the near future
is some kind of rainbow chase). Again G.Vulpetti commented about the
infeasibility of this magsail methods (see Bolonkin's paragraph). Cassenti
emphasized the possibilities of using this design for a toroidal uniform
magnetic lens as part of a Bussard-ramjet scoop.
 
The dynamic duo of interestellar flight, Martin and Bond made a competent but
unimaginative presentation about coupling an ion thruster currently manufactured
ky UKAEA Culham (were both of them work) to a state of the art but unbuilt
SP-100/Topaz-like nuclear reactor called Dragon, with interest to catch a
 
contract for the JPL's 1000 AU mission. I found this paper a little too
routine (not counting on the advertisement content for the UKAEA line of product
s) for two luminaries as Bond and Martin, who have me used to more
spectacular and always very good and comprehensive contributions.
 
A paper on a Martian Manned Excursion Module was given by R.J. Zhitz of
the Moscow Aviation Institute, but again the combination of monotonous
reading with poor transparencies send my brain to other realms of the mind
and my body to look for a cup of coffee, so I do not have any opinion on this
paper, except that Russian (and other East-Europeans) must improve their
presentation skills if they want to reach their audiences.
 
P.A.Hansson made an interesting and audacious presentation of the role
of miniaturization and nanotechnology on the future advance of space
instrumentation and probe design, but I am not knowledgeable in these
matters so my opinion is as good a anybody else's.
 
Finally for the F.1 session, V.J.Modi gave a very heavyweight talk on
attitude control and propulsion of space vehicles using solar radiation
pressure. Pretty interesting and really good technical stuff.
 
F.2
I lost the first one on Artificial jets as propulsion of cometary riders
because I was late. I catch a little of the last moments of it and the Q&A
part, but I do not have any elements for a responsible comment.
 
The Zubrin paper was superb from the presentation point of view (this guy
really knows how to catch the attention of his audience) but I found it
flawed in approach. It discuss the use of unknown ultra-dense stellar objects
(white/brown/black dwarves, neutron stars, black holes) in the near-solar
neighborhood for perigee-kick gravity assists for interstellar missions.
The paper is interesting, the ideas are relevant but the methods are poor.
Calculating orbits near high gravitational fields using classical mechanics
or special relativity is at best inaccurate and as the last case (black hole)
analyzed by Zubrin can be completely wrong (v-infinity speeds greater than c
are predicted for some orbits!). As my GTR knowledge is today non-existant
(but it will be some at the end of this semester) and besides I could not
afford a copy of the paper, I can not be more explicit about where is the
mistake in Zubrin's calculation, but obviously he is using the wrong model
for this problem.
 
H.D. Froning spoke about the neccesity of launching an Interstellar Exploration
Initiative, now! ;-) Any further comment from me would be insulting for
the author of otherwise a very enjoyable presentation that esentially was not
more than an exercise of wishful thinking (but anytime some guy
come speaking about field propulsion, hyperspaces and quantum vacuum energy
ramjets and the necessitiy of funding research of this my stomach revolves,
I get a cold fever and I must see the current NSF/DOE/NASA budget to recover
myself with a reality shock).
 
I am being insulting now because I felt insulted when hearing this nonsense.
C. Poher from CNES/Aerospatiale at Cannes-La-Bocca, France (probably affected
for the excess of sunlight at the Cote-Azur) presented a paper(well...)
with the title _Universons, a possible key to interstellar exploration_
This guy invented a theory of gravitation of his own, which contradicts any
current experimental evidence from both GTR and Quantum Mechanics. Again
G.Vulpetti came to the rescue and clobbered the guy with a  set of very good
questions and counterexamples. It is a shame that this kind of crap appears
in this conference, because my colleagues in Physics and Astronomy use this
comtemptible examples of crankpottery to discredite the scientific value of
these sessions in particular and of the IAF Congresses in general. Does
somebody suggest a way to comunicate to the IAF or IAA committees relevant
to these sessions the damage that papers like this one do to the
credibility of these organizations?
 
After that A. Ewing refreshed the air with a short nice competent work on
solar sail parametrization.
 
Finally G.Vulpetti introduced the concept of staged propulsion (that is a
generalization of the usual fuel staging), and then provided us with a
bunch of colorful (literally) examples of missions using combinations of
solar sails/NEP for missions to the heliopause and beyond. Really good
stuff, with good scientific and technical fundaments.
 
At the end of each presentation there was a Q&A period, usually used by
L.R.Sheperd to do some interesting and appropiate comment, by Vulpetti to
argue (with great authority) about some weak point of the past paper and
for a annoying crank to illuminate us with some irrelevant and inane comment
of his own.
 
One thing I notice after enduring both F.1 and F.2 in their entire duration
was that the audience was thinning more and more with time, going from ~25
people at the beginning to no more than a dozen at the end. Was the
audience voting with their feet?
 
I attended only two other IAF sessions(Nuclear power applications and space in
cinema and photography) but I would not comment on them.
 
As friend of one of the leading SETI researchers in Argentina I was in some
way an informal member of the Argentinian delegation to the SETI session
organized by the IAA/COSPAR/IAF/NASA/AIAA. Of course I was introduced to all
the SETI-set (and I got a photograph with George Mueller, who opened the
session, thing that  had me smiling two days but considered irrelevant to my
astronomer friends) and I was witness of a lot of the behind the curtains
talks. The feeling I got from all this is that now SETI is fashionable for
some sectors of the radioastronaomical community and a lot of guys that five
years ago would not have paid any attention to the search programs now are
trying to jump into the SETI bandwagon (and catch the research grants!).
Considering that the field is mostly hot air (and it reflects in the low
quality of the papers presented -again the French are talking nonsense,
introducing numerology into a fact-poor subject) I can not understand the
hype that SETI produces, unless you want to see it as an exercise on
publicity and marketing for certain brands/names of this self-advertised
community of scientists.
 
        You will be asking what I found positive about WSC?
- The International Space Exhibition
- The talks with the participants outside the sessions.
- Washington DC
- The Smithsonian museums
- The atmosphere of comradeship and collaboration for the most exciting
goal you can imagine: THE CONQUEST OF SPACE.
 
Even with the shortcomings about the sessions contents I found myself
mesmerized with the WSC and I will attend again anytime this events repeat
near my workplace or I could afford to go.
Andres C. Gaeris
agae@lle.rochester.edu
 

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

Date: 8 Sep 92 21:48:46 GMT
From: Joe Cain <cain@geomag.gly.fsu.edu>
Subject: Climate cycles from Earth's orbital geometry
Newsgroups: sci.geo.geology,sci.astro,sci.space,sci.geo.meteorology

	We were just going over some sedimentary cycles in a class
today which related to an article in EOS.* I would
like to find some material which discusses the Milankovitch-type
forcing functions which lead to climate cycles. i.e. 
 
precesssion of the equinoxes  19, 23 K years
obliquity of Earth's axis     41, 54 K years
eccentricity of orbit         95, 123, 413, and 2035 K years

I am looking for something about the level of Scientific American with
some pretty pictures that discusses the geologic findings in this
area.  This is for a beginning planetary geology class for
non-scientists. Has anyone seen anything recently?


*Olsen, P. E. and D. K. Kent, Continental coring of the Newark Rift,
EOS April 10, 1990, pp 385,394.
Joseph Cain		cain@geomag.gly.fsu.edu
cain@fsu.bitnet		scri::cain

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

Date: 8 Sep 92 23:48:35 GMT
From: Mike Van Pelt <mvp@hsv3.lsil.com>
Subject: Clinton/Gore Space Position
Newsgroups: sci.space

In article <3SEP199210570592@ariel.lerc.nasa.gov> aavso@ariel.lerc.nasa.gov (Tom Quesinberry) writes:
>Senator Al Gore chairs the Senate Subcommittee on Science,
>Technology, and Space...

How has he voted on the various attemts to scuttle DCX?
-- 
Mike Van Pelt                          Here lies a Technophobe,
LSI Logic/Headland Products               No whimper, no blast.
sun!indetech!hsv3!mvp                  His life's goal accomplished,
mvp@hsv3.lsil.com                         Zero risk at last.

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

Date: 8 Sep 92 20:20:48 GMT
From: "Thomas H. Kunich" <tomk@netcom.com>
Subject: Is NASA really planning to Terraform Mars?
Newsgroups: sci.space

In article <14941@mindlink.bc.ca> Nick_Janow@mindlink.bc.ca (Nick Janow) writes:
>knapp@spot.Colorado.EDU (David Knapp) enquires:
>
>> Thomas, would you expound on which bacteria or fungi can exist in a hot
>> sulfuric acid/sulfur dioxide environment [Venus' upper atmosphere]?
>
>I don't know if there are any microorganisms that can survive those conditions
>(I don't know that there aren't, either).  However, Perhaps advances in

Back when the Viking lander was on Mars and they began saying that there
were 'life-like' processes occuring in the on-board bio-lab I said that
that was probably proof positive that life didn't exist on Mars.

My line of thinking was the following: Life probably evolved from
a chemical process. These chemical processes would, no doubt, have
first used up all of the cheap energy gradients, so simple chemical
processes releasing energy are rare on earth while they may be plentiful
on any planet where life never existed.

It has been stated that there are more organisms still to be discovered
right here on earth than have been catagorized yet. So not knowing
any specific organism isn't necessarily an inhibiting factor.

It was scant years ago when the idea of living organisms existing in
volcano vents would have brought on derision of the first water. Now
there are several sciences (PCR for one) founded upon this discovery.

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

Date: Tue, 8 Sep 1992 21:03:13 GMT
From: Frank Crary <fcrary@ucsu.Colorado.EDU>
Subject: Is NASA really planning to Terraform Mars?
Newsgroups: sci.space

In article <jvrnh5#.tomk@netcom.com> tomk@netcom.com (Thomas H. Kunich) writes:
>Without references it is difficult to remember, but isn't there
>water, water vapor and possible liquid water along the interface of
>the Martian north pole? 

Not that we know of, just water ice and permafrost. There is some,
distant theoretical possibility of sub-surface water (liquid). But 
the evidence for this isn't too substantial...

                                                 Frank Crary
                                                 CU Boulder

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

Date: 8 Sep 92 22:42:56 GMT
From: "Thomas H. Kunich" <tomk@netcom.com>
Subject: Is NASA really planning to Terraform Mars?
Newsgroups: sci.space

In article <1992Sep8.210313.4979@ucsu.Colorado.EDU> fcrary@ucsu.Colorado.EDU (Frank Crary) writes:
>
>Not that we know of, just water ice and permafrost. There is some,
>distant theoretical possibility of sub-surface water (liquid). But 
>the evidence for this isn't too substantial...

Frank, I seem to remember clouds at the atmospheric boundary
on Olympus Monds (sp?). Certainly that indicates that there is
some water vapor there.

I also recall that there was speculation that the most verdent
growth on earth during the ice ages was directly in the narrow
band adjacent to the advancing glaciers. This was because most of
the water was tied up in the ice and there was little free water in
the atmosphere. Humidity was extremely low. 

During warm spells the ice would melt enough to water the surrounding
narrow band and this drew large numbers of animals. When the wind changed
and blew _off_ of the glaciers it would often kill the animals with
cold and so we find so many animals frozen in glacier ice.

If such things happen here it would give _some_ hope that such
conditions might exist on Mars.

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

Date: Wed, 9 Sep 1992 00:13:26 GMT
From: David Knapp <knapp@spot.Colorado.EDU>
Subject: Is NASA really planning to Terraform Mars?
Newsgroups: sci.space

In article <samw.715971213@bucket> samw@bucket.rain.com (Sam Warden) writes:
>Re Venus: We seem to know more about the Venusian atmosphere than I
>knew we knew.  :-)  Since when are the _upper_ clouds H2SO4? 

The uppermost are not.

> And,
>do we really know what the overall composition of the crust and
>atmosphere is, to say that there is somehow an "excess" of oxygen?

yes.

>Were Venus ever to cool off, I would expect ferocious amounts of
>oxidation/carbonation weathering to occur, for example.

I wouldn't hold my breath for Venus to cool off. It is locked in a stable 
greenhouse mode.


>Re Mars: I'm impressed with the Gaia approach, to this negative
>extent: the lack of a fixed atmosphere on Mars seems like strong
>evidence that life is not active there now, or it would exhale
>one.  I'm not convinced that `seeding' Mars would be impossible,
>but it would have to be not isolated spores but a complete
>ecosystem capable of maintaining its own microenvironment.  A
>blob with a crust, so to speak.  Things like the Dead Sea plankton 
>that secrete glycerol come to mind.  This is pretty dependent
>on whether the Martian crust is a pre-biotic permafrost as 
>has been speculated, but I'm uncomfortable with dismissing the
>possibility out of hand.

There is a reason why Mars doesn't have an atmosphere. Evidence seems to 
support that if we somehow put one there, it wouldn't stay.

>As for the morality of this sort of thing, I don't share the
>comfortable expectation that we as a civilization _have_
>future centuries at our disposal for a conservative planetary
>exploration.  The spread of terrestrial life to other 
>now lifeless environments seems _very_ moral to me, even a
>moral imperative, given a possibly limited window of ability
>to do so.  My opinion; others of course are free to differ.  ;-)

If you think so, make sure you consult your congressman about funding
Nasa better.

>
-- 
> 
>samw@bucket.rain.com (Sam Warden) -- and not a mere Device.
> 


-- 
David Knapp                                      University of Colorado, Boulder
Perpetual Student                                   knapp@spot.colorado.edu

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

Date: 9 Sep 92 00:05:29 GMT
From: Frank Crary <fcrary@ucsu.Colorado.EDU>
Subject: Is NASA really planning to Terraform Mars?
Newsgroups: sci.space

In article <1992Sep8.192140.21365@cs.rochester.edu> dietz@cs.rochester.edu (Paul Dietz) writes:
>The "excess" of oxygen is that if the CO2 is converted to biomass
>and oxygen, we now have 100x more oxygen that in Earth's atmosphere.

I'm not sure the terraforming ideas for Venus involve such a conversion:
I remember one paper (in JBIPS about two years ago) that suggested
(somehow) cooling the atmosphere enough to precipitate water. This
would (according to the paper) remove the sulphuric acid (quickly) and 
the carbon dioxide (slowly) by disolving them in water. 

If surface water were to be established (somehow) carbon dioxide
removal would occur the same way it did in the early Earth's 
atmosphere: Disolving on carbon dioxide into the water, which then
reacts with calcium (also disolved in the water, assuming a
salt water sea, or similar) to form insoluable calcium carbonate
(sedimentary rock).

                                            Frank Crary
                                            CU Boulder

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

Date: 8 Sep 92 21:51:46 GMT
From: John Roberts <roberts@CMR.NCSL.NIST.GOV>
Subject: Relativity
Newsgroups: sci.space

-From: Alan_Barclay@mindlink.bc.ca (Alan Barclay)
-Subject: Re: Relativity
-Date: 7 Sep 92 04:40:24 GMT
-Organization: MIND LINK! - British Columbia, Canada

-#4300029 from John Roberts

-I always thought I had a good handle on the basics of relativity.
-Can you have a look at this for me, and tell me what you think?

-A Thought experiment:

-Star A is four light years from star B.  A spaceship leaves earth
-and accelerates to .9 C and ceases acceleration when it passes
-Star A.  An observer inside the moving frame notes the length of
-subjective time passing.  When the ship passes star B, the observer
-inside the frame has only experienced 1.95 subjective years.  For him,
-he traversed four light years in only 1.95 years.  A subjective speed
-of 2.05 C.

-          ---->---->---->---->---->.9C
-              *A             *B

-                                                   __
-                 T = d/v     ->   T = 4ly/0.9C = 4.44 yrs
                                     ________________
-                 Tsubjective = T x \/ (1-(v*v/c*c))

-                              = 4.44 yrs x 0.44
-                              = 1.95 yrs

-                 Vsubj = d/Tsubj = 4ly/1.95yrs
-                                 = 2.05 ly/yr


-However, if he were to use instruments to determine his velocity
-relative to the frame of reference, his velocity would remain .9 C.

The astronaut knows from previous experience that the distance from A to B
in the frame of reference of A and B is 4 light years, so only in that sense 
he can say that the "effective" speed was greater than that of light. However,
by any measure he can make while traveling, the distance from A to B is less
than 4 light years, so it still works out to .9 c.

-From: davidme@qdpii.comp.qdpi.oz.au (David Meiklejohn)
-Date: 7 Sep 92 12:53:50 GMT
-Organization: Qld Dept Primary Industries

-No, his time measured is 1.95 years, as you say.  What you're missing is that
-there is no favoured frame of reference, given that he's not accelerating.
-Therefore, as far as our astronaut is concerned, he's stationary, and the
-universe is rushing by at 0.9 c.  Now, when you move, the only relatavistic
-effect isn't time dilation.  You gain mass, and your metrics contract in the
-direction of motion.  This last effect means that the observer measures the
-distance between the stars as 2.17 ly.  As far as he's concerned, he's taken
-1.95 years to travel between two objects 2.17 ly apart, so he's measured his
-speed as 0.9 c.

You divided by .9 instead of multiplying by it. The correct measured distance
is 1.74 light years. Otherwise, I agree.

-From: sk4i+@andrew.cmu.edu (Samuel John Kass)
-Subject: Re: Relativity
-Date: 7 Sep 92 15:15:49 GMT
-Organization: Sophomore, Math/Computer Science, Carnegie Mellon, Pittsburgh, PA

->>A recent SF book used relativistic mass to produce black holes.
->>i.e. accelerate a spaceship until it's massive enough to collapse
->>into a singularity.  Something seems missing in this equation.
->>Could it happen?
->I don't see why not.  To continue to accelerate, the spaceship needs energy.

-Could it?  I'm no expert either, but I thought that to get collapse,
-parts of the object had to be pulling against each other.  Since the
-ENTIRE spaceship is accelerating, from the frame of reference of the
-spaceship, wouldn't it be 'normal' mass?  Of course, from the frame of
-reference of a 'stationary' observer, the spaceship will have sqashed
-itself so flat that it should have fused anyway.  Since, by general
-relativity, there is no preferred frame of reference, why would the
-Earth, then, not collapse into a black hole, just because such a thing
-is possible.  (ie. Compared to the frame of reference of something else,
-the Earth has enough mass to collapse.)  For example, there may be an
-object in the universe travelling at such speeds that, to it, the Earth
-should have collapsed into a black hole.  But we're not a black hole. (I
-don't think.)

I think that's about right. The spaceship doesn't think that it's become
more massive. I don't know about interstellar gas and dust that the
spacecraft may encounter along its path - from its viewpoint, the
spacecraft should be perceived as more massive. Also, I don't know whether
increased mass/gravity would be perceived by an observer to the side.
I strongly suspect that to include gravitational effects, even with objects
of constant relative velocity, we have to go to general relativity, which 
makes things much harder for the amateur to figure out.

Another "paradox": suppose you run a train station, and a train of known
(rest) length is approaching the station at relativistic speed. You decide
that it would be a good prank to fire two paintballs at the train, a yellow 
one at the engine, and a blue one at the caboose. You want to fire the two 
paintballs at exactly the same time, so you set up the two paintball guns 
the (previously known) length of the train apart along the station, minus 
a smidgen, and use a calculation of the arrival time of the engine at the
yellow paintball gun to control both paintball guns. (You can put a high-speed
camera with a wide-angle lens midway between the two guns to verify that they
fire simultaneously.) (Note that accurately calculating the arrival time of
the engine isn't as easy as it looks, but it can be done.) Now the train 
zooms past the station and you fire the paintball guns. As the train speeds
away, you go to a telescope and look at the train for paint splotches
(compensating for the redshift, of course, so there's no confusion about
the colors). By the principles of special relativity, you find that you have 
hit the engine (yellow), but missed the caboose. Since the guns were fired at
exactly the same time, you conclude that the train was actually shorter
than you had been led to believe from its description. So far, so good, but
that's not all there is to the story.

Now suppose that the engineer on the train has a powerful telescope, and he
sees the paintball guns at the station, and figures out what you're up to,
so he decides that turnabout is fair play. He mounts two paintball guns on
the train, a green one at the front of the engine, and a red one at the
back of the caboose. Using techniques similar to your own, he calculates
exactly when the engine will pass the yellow paintball gun at the station,
and rigs a control halfway along the train to fire both of the train's
guns at that instant. The station whizzes by, and the guns fire. Looking
back, the engineer sees that the yellow paintball gun has been hit with the
green paint - a good shot. However, the red paintball has missed its target -
it hit way behind the blue paintball gun (i.e. further from the yellow
paintball gun than is the blue paintball gun). The engineer can draw the
logical conclusion that the train station was shorter than he thought is
was. 

Now it begins to look more confusing: from the viewpoint of the train, the
station is shorter, but from the viewpoint of the station, the train is
shorter, and both had their shots go wide (by the same amount, incidentally).
It seems like these two event would be mutually inconsistent. Fortunately,
the paradox can be resolved by an adjustment of the concept of simultaneity.
>From the viewpoint of the train engineer, his two shots were simultaneous,
meaning that an observer in the middle car of the train would see the flash
(or EMP, or whatever) of the two guns at exactly the same time. Similarly,
an observer standing on the platform at the station midway between the
two paintball guns there would see them fire at the same time. However, from
the viewpoint of the train, the station did *not* fire its guns simultaneously,
and vice versa. To the train engineer, it looks like the yellow gun fired
first, then the blue gun. From the viewpoint of the station, the red gun
fired first, then the green gun. Thus, nobody sees any inconsistencies. 
That's part of what I meant when I said in an earlier post that between
different frames of reference, simultaneity has no meaning (though you might
set up a single reference point at locations in the two frames that are
temporarily coincident in space).

Note that this is just a thought experiment - it's not entirely realistic,
and some of the details have been glossed over. For instance, having four
different colors of paintballs would be too expensive, and I bet green ones
are hard to get since they don't show up well on camouflage. There would
also be a few complications with the physics. :-)

For additional amusement, what do the wheels of the train look like:
 - from the viewpoint of a person at the station?
 - from the viewpoint of a person on the train?
 - from a camera mounted on a wheel?

John Roberts
roberts@cmr.ncsl.nist.gov

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

Date: Tue, 8 Sep 1992 18:52:00 +0000
From: Anthony Frost <vulch@cix.clink.co.uk>
Subject: Space markets
Newsgroups: sci.space

 
  > In the commercial world not one manager of of a program will
  > dare to use any technology that has not been "proven" by the
  > military or NASA on government sponsored space flights.  The
  > solar arrays, batteries, power systems and upper stages were
  > all proven as a military or NASA program previous to their 

 
Mind you, you can get unproven technology very cheap. UoSAT-1, the first
satellite built by the University of Surrey, got its solar cells more or
less free as a donation from the manufacturer. (I think it was a case of
"Here, give us fifty pence for them" [made up number though!]) For UoSAT-2
they went back to the same manufacturer as the panels had been nicely
reliable and were quoted telephone numbers for the purchase price. "Why the
increase?", "Oh, they are space qualified now thanks to you!"
 
          Anthony

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

Date: Wed, 02 Sep 92 22:47:28 CST
From: Haus Der Luge <al@sys6626.bison.mb.ca>
Subject: Truax
Newsgroups: sci.space

 
Is there anybody using this sub-board who is at all familair with the 
work of one Bob Truax ???
 
From what I've heard, he's quite the "space ranger".
 
HausDerLuge
 
PS:  On the subject of Truax ... are there any L-5 types around here ???


;--- (Haus Der Luge) a user of sys6626, running waffle 1.64
;E-mail: al@sys6626.bison.mb.ca
;system 6626: 63 point west drive, winnipeg manitoba canada R3T 5G8

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

Date: Tue, 8 Sep 1992 22:20:36 GMT
From: "Phil G. Fraering" <pgf@srl07.cacs.usl.edu>
Subject: Truax
Newsgroups: sci.space

al@sys6626.bison.mb.ca (Haus Der Luge) writes:


>PS:  On the subject of Truax ... are there any L-5 types around here ???

Yah, but we're outnumbered by the local friendly "Just lie back
and NASA will fix everything with Freedom and NLS" crowd.

--
Phil Fraering pgf@srl0x.cacs.usl.edu where the x is a number from 1-5.
Phone: 318/365-5418 SnailMail: 2408 Blue Haven Dr., New Iberia, La. 70560
If seven maids with seven brooms swept for half a year,
do you think, the Walrus asked, that they could make it clear?
I doubt it, said the Carpenter, and shed a bitter tear.
---------
"NOAH!"                        \           \ Lewis Carrol
"Yes lord?"                     > Bill Cosby, The Story of Noah
"HOW LONG CAN YOU TREAD WATER?"/

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

Date: 8 Sep 92 23:57:36 GMT
From: Steinn Sigurdsson <steinly@topaz.ucsc.edu>
Subject: Venus orbiters
Newsgroups: sci.space

In article <1992Sep6.185946.22912@access.digex.com> prb@access.digex.com (Pat) writes:

   also word is that small light probes are hot for funding in the near future.
   cheap fast missions are being experimented with to avoid cost problems
   with  heavy big birds.

AO arrived today - they plan on 1/year 3years from conception to
launch, instrumentation to be ready in 2 years, total cost for
launch, excluding operations and analysis are to be less than
$35 million, 1/2 for development! Baseline launch vehicle is
Pegasus!

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

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End of Space Digest Volume 15 : Issue 178
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