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Subject: SPACE Digest V13 #486

SPACE Digest                                     Volume 13 : Issue 486

Today's Topics:
     Laser launchers &c. (was Re: SPACE Digest V13 #444)
              Re: Galileo works?
        Re: Terraforming Mars?  Why not Venus?
               Re: Saturn V blueprints
             Toward 2001 - 29 Apr

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Date: 30 Apr 91 22:47:01 GMT
From: agate!bionet!uwm.edu!caen!ox.com!fmsrl7![e-mail]  (Ron Carter)
Subject: Laser launchers &c. (was Re: SPACE Digest V13 #444)

The remainder of this article consists of elucidations, some of them
more than slightly condescending, a bit of flamage, and a pinch of
humor.  People who do not wish to waste their time, hit "N" now.

You were warned...

In article <[e-mail]> [e-mail] writes:
>So what?  Blooming is a function of energy-density, too.  7 watts/meter-squared
>is quite a bit less than what's required for propulsion from the surface!

A reader who did not wish to post a response informed me that he
personally worked with a 300 W/cm^2 (that's 3 MW/m^2) beam and
did not experience blooming problems.  That's roughly 6 orders
of magnitude higher than "7 watts/meter-squared".  Given 3 MW/m^2,
it would take only 333 m^2 of mirrors to handle a 1 GW beam.
That's a little over 100 2-meter mirrors, hardly difficult to make.

In my posting, I was picking at the "1000 to 1000000" attenuation
range which was so casually thrown around in the original.  You
have not given any information to support this either.

>>An optical system designed to avoid blooming will have many mirrors,
>About time!  I've been waiting for someone to point out the many-laser idea.

Perhaps people who think about the problem to any depth accept it as
a given.  It certainly is obvious.  However, Coffman ignored the issue.

>>>with terrible efficiency. While for a rocket, the longer it runs, the
>>>faster it goes since it's mass ratio is continually improving right
>>>up until burnout.
>>This statement ran my bogosity meter off the scale....
>I'm not sure what a 'bogosity meter' is, but I reckon it's a phrase you draw up
>whenever you don't have a real answer.
>Point being that what was said about rockets being more efficient in the later
>stages of a trip is neither 'ignorant' or 'careless', but rather; QUITE TRUE.
>No wonder you won't bother to 'pick it apart'.

Bogosity is a measure of how bogus something is, and you are wrong.

1.)    The quoted statement confuses acceleration and mass-ratio.
2.)    A rocket is most efficient (transforms fuel energy into
    final payload energy with the greatest efficiency) when it
    has a mass ratio of approximately 4.  Today's orbital
    boosters have much higher mass ratios.
3.)    The "mass ratio" is the fuelled mass divided by the empty
    mass, and cannot be meaningfully said to "improve" in flight.
4.)    While the acceleration can increase, the efficiency of a
    rocket is < 100% whenever its exhaust velocity is not exactly
    equal to its speed, otherwise it leaves its exhaust at non-zero
    speed relative to the point of origin.  This leaves wasted
    kinetic energy in the exhaust, which contributes nothing.
    Naive calculations of "efficiency" do not consider the
    kinetic energy of the fuel in the tanks before burning,
    which was paid for previously with more fuel.

Since a laser launcher can vary the exhaust velocity by changing
the pulse power and shape, it can be much more efficient than a
rocket.  One could even hit the magic mass-ratio exactly, if one
desired to save (cheap) energy at the expense of (costly) hardware.

>Sunlight does bloom, as does starlight, aurora light, light pollution, etc.
>Just ask the guys that paid for the hubble scope (since it was supposed to
>get, literally, above the blooming problem).

You prove that you don't know what thermal blooming is; you
have confused it with atmospheric turbulence.  Thermal blooming
is a phenomenon in which absorbtion of a light beam by the
medium (such as air) heats it, causing the index of refraction
to change locally and defocussing the beam.

>Also, questions which you seemed to have missed are;

Ask Coffman.  He must be the expert, since he is so certain
that it Cannot Be Done.  I just asked him to prove it.

>>[The] pitfalls experienced by the LF workers will not be applicable.
>
>Nonesense.  Of course it will.  Both need to transmit high amounts of energy
>via an electromagnetic beam which has been focused on a target of tiny angular
>size.  To claim otherwise is to prove the need for sanity checks yourself.

... with vastly different requirements in pulse width, *many* orders
of magnitude difference in power level at the target, huge differences
in the optics... need I go on?

>He may be talking through his hat, but as far as material strengths are
>concerned, there is no practical tether material (for lifting from the surface)
>His lack of thourough research does not change the fundamental problem.

You show your own ignorance.  If "the surface" includes anything
an airplane can reach, a rotating tether is feasible with today's
materials.  (Not easy, or cheap, but feasible.)  Further, tethers
can be operated outside the atmosphere and lift payloads launched
on sub-orbital trajectories to orbit, or beyond.  Keith Henson
has done studies on catapulting small payloads into space using
tethers anchored on *airplanes* (crack-the-whip maneuvers).  You
really do need to study more than just simplest cases.

>Rather than pointing out what was incorrect, or providing information to the
>other party, you seem to feel it's ok to (try to) insult/belittle someone for
>making a factual error or expressing an idea you don't like / disagree with.

The information has been repeated in this newsgroups many times.
For Coffman (or you) to ignore it without first refuting it is
dishonest.  For Coffman to claim that all cases of X are
impossible after:
a.)    Pulling a bogus number out of the air to "prove" it, or
b.)    Considering only the naive case
is ridiculous.  So I ridiculed him.  He should know better.

>It's especially worthy of ridicule when you are doing exactly what you are
>flaming someone else for doing!

When Coffman quotes numbers like "1000 to 1000000 times", I want to
know where he gets them and why he doesn't agree with the people who
appear to be more experienced than he.  Since he has not posted a
rebuttal, my suspicion that his figures are bogus is reinforced.

>For example, claiming someone is ignorant while being quite ignorant yourself.

I have not claimed expertise in anything, save rocket mass ratios
and energy requirements.  If you want a demonstration of my expertise
in that, you may attempt to confirm my energetically optimum mass ratio
number above.  If you want to compute tether stresses and mass
requirements for different designs and materials, go ahead.  I'll
listen to any analysis which includes computations I can check.

>Or saying they should read up on something that you're talking through your hat
>about, too.

Would you care to check my bookshelf for references?  BTW, the
proceedings of the first AIAA conference on tethers in space
are most interesting and enlightening.  Lay your hands on a copy.

>Or calling for sanity checks while invoking irellevant facts.

Show me where I cited an irrelevant fact.  And spell it right next time. ;-)

>P.S. maybe I'm wasting space, but I feel that keeping the flak and not-so-
>     friendly sparring to a minimum is important.  Especially since, by the
>     nature of my abrasive personality, I find it so easy to join in.

Had I known you existed, I would not have tempted you.  Perhaps,
after being put back in your place, you are now feeling so small
that I can once again consider you non-existent for the purpose
of responding to net postings.  ;-)

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

Date: 1 May 91 01:39:46 GMT
From: hub.ucsb.edu!ucsbuxa![e-mail]  (Charles Frank Radley)
Subject: Re: Galileo works?



why do they not simply point the high gain antenna to Earth, turn on the transmitter, and
observe the signal strength.
This will establish the bottom line of whether there is
enough gain to transmit TV and data.

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

Date: 1 May 91 03:53:40 GMT
From: waikato.ac.nz![e-mail]
Subject: Re: Terraforming Mars?  Why not Venus?

In article <[e-mail]>, [e-mail] (Katani) writes:
>
>    If you were really set on the terraformation of Venus, and you had some
> pretty hot technology, you could calculate the interference caused by the
> sun and the  magnetic flow caused by the planets spin and SLOW DOWN THE
> PLANET to the required level. [about that of earth] and the
> vulcanism/earthquakes would slow  and probably drop to a more manageable
> level after a while [while defined as a  minimum period of a few
> centuries!!]. Well, that's my eight cents worth.
>

    An idea I had (and probably a lot of other people) is to change venus
orbit so that it passed originally closer to the sun (boil off the atmosphere)
and then bring it out to earth's orbit. This would cool it down to earth like
temperarures (and maybe reduce the vulcanism?).

    I can see various problems with this proposal, method of orbit change
(mass driver, collision) and how it's orbit would effect earths (maybe put it
60' forward or back, 180'?). Also how significant would be the changes to it's
climate.

Pete Smith
Waikato NZ

(PS: keep the flame throwers on low, I singe easy)

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

Date: 30 Apr 91 18:35:33 GMT
From: snorkelwacker.mit.edu!think.com!samsung!umich!sharkey!fmsrl7![e-mail]  (Ron Carter)
Subject: Re: Saturn V blueprints

In article <[e-mail]> [e-mail] (Michael V. Kent) writes:
>We (the govt.) could issue a contract for more Saturn V's, but we would have
>to make sure there are approriate safety measures in place.  After all, what
>good are a few Saturn V's if half of our aerospace industry goes backrupt to
>produce them?

There appears to be little risk of that.  Tankage is something
we bend metal for regularly, and we have extensive knowledge of
liquid-fuelled engines going back to Von Braun at Peenemunde.

Given the numbers quoted for costs to re-develop the F-1, the
risk of a company going belly-up is minuscule.  It seems almost
as if a couple manufacturing engineers and metallurgists could
swing it.  The only requirement right now is a customer or two.

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

Date: 29 Apr 91 04:05:22 GMT
From: elroy.jpl.nasa.gov!sdd.hp.com!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!pitt!nss![e-mail]  (Bev Freed)
Subject: Toward 2001 - 29 Apr


                            ***********
                            TOWARD 2001
                            ***********
                       Week of 29 April 1991
                 A Weekly Feature of SPACE CALENDAR
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This information is reproduced by permission of the Space Age
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1991.  Reproduction in any form without written permission violates
federal statute with penalty of up to $50,000.  SPACE CALENDAR is
edited and published on the Big `Space' Island of Hawaii.
====================================================================
                           * * * * * * *
# Gamma Ray Observatory
Earth Orbit

Scientists at the Payload Operations Control Center at NASA Goddard
continue to check out the systems and instrumentation of the
recently deployed spacecraft.
                           * * * * * * *
+ Instrumentation Technology Associates
Exton PA

A total of 42 separate experiments processing 182 samples are
undergoing analysis following successful completion during the STS
37 Atlantis mission. ITA spokeswoman Valerie Cassanto reports the
MDA `Minilab' is proving to be a dependable technology for micro-g
users.
                           * * * * * * *
o Glavkosmos
Moscow USSR

A number of defense industry enterprises will attempt to market
satellites through a new international communications corporation
called Koskom, Glavkosmos said recently. Plans call for Koskom to
launch 28 satellites over the next three years.
                           * * * * * * *
o ESA / Hungary Agreement
Venice, Italy

In its strongest step yet toward eastern European, ESA will
cooperate with Hungary in the fields of space science, earth
observation (particularly environmental protection), and
"fundamental research" in microgravity and telecommunications.
Director general Jean-Marie Luton and Hungary's research and
technology minister Erno Pungor.
                           * * * * * * *
+ Delta GEM Contract
Huntington Beach CA

Hercules Aerospace will continue production of graphite epoxy solid
rocket motors (GEMs) for the Delta 2 rocket through a recently
awarded contract with McDonnell Douglas. Hercules is to build 117
motors -- 13 flight sets -- beginning in 1993.
                           * * * * * * *
+ Space Telescope Science Institute
Baltimore MD

Will support a limited number of visiting scientists who wish to
spend 3 to 12 months doing research at STScI. Requests for support
for the 1991 academic year should be sent to Visiting Scientist
Program, c/o Tim Heckman, STScI, 3700 San Martin Dr, Baltimore MD
21218, USA. Deadline is 1 May.
                           * * * * * * *
+ Hawaii In Space Panel
Honolulu HI

Adm Thomas Hayward, advisor to the governor on space, will chair a
panel of 8 distinguished academic and government figures at the 17th
Pacific Science Congress on 31 May. The panel will focus on Hawaii
space-related activities, including astronomy, space education, and
prospects for a commercial space launch program.
                           * * * * * * *
o Takasaki Astro Park
Tokyo, Japan

Young Astronauts Club Japan is sponsoring an international
competition to design 60-hectare `Martian city 10,000 years in the
future'. Info Takasaki Astro Park Development Committee, Young
Astronauts Club Japan, Keiko Takemoto, Nishishinbashi Aiko Bldg 6F,
1-6-15 Nishishinbashi, Minato-ku, Tokyo 105 Japan.
                           * * * * * * *
+ Lunar Footnote (Statistic)

6,710 Days since Moon last visited by humans.
                           * * * * * * *
o International Space Year 1992 (Quotation)

      The most important policy objective of the ISY . . . is
 to instill a new Space Age frame of reference in the thoughts and
              actions of governments and individuals."
                 -- The late U S Senator Spark M Matsunaga, Hawaii
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End of SPACE Digest V13 #486
*******************