Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_5/V13_533.TXT

Internet Message Format | 1991-06-28 | 17KB

Return-path: <[e-mail]>
X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
Received: from hogtown.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/[e-mail] (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests)
          ID </afs/andrew.cmu.edu/usr1/ota/Mailbox/Mc=C3vm00WBwI5s04G>;
          Sun, 12 May 91 02:30:23 -0400 (EDT)
Message-ID: <wc=[e-mail]>
Precedence: junk
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Sun, 12 May 91 02:30:12 -0400 (EDT)
Subject: SPACE Digest V13 #533

SPACE Digest                                     Volume 13 : Issue 533

Today's Topics:
              Re: Why the space station?
             Re: Why the space station?y
              Re: SPACE Digest V13 #499
       Re: Ethics of Terraforming (was Re: Terraforming Venus)
              Re: SPACE Digest V13 #486
       Re: Ethics of Terraforming (was Re: Terraforming Venus)

Administrivia:

    Submissions to the SPACE Digest/sci.space should be mailed to
  [e-mail].  Other mail, esp. [un]subscription requests,
  should be sent to [e-mail], or, if urgent, to
             [e-mail]

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

Date: 8 May 91 17:56:44 GMT
From: sdd.hp.com!caen![e-mail]  (Ken Sheppardson)
Subject: Re: Why the space station?

[e-mail] (Frank Crary) writes:
>[e-mail] (Ken Sheppardson) writes:
>>[e-mail] (Brian Yamauchi) writes:
>>>Is it really less expensive to build an orbital microgravity + life
>>>sciences lab than an orbital assembly platform?
>>
>>  Actually, it is -- if you can only build one station.
>>
>If I understand the rest you what you are saying, you mean a microgravity +
>life sciences  facility is less expensive than an orbital construction +
>life sciences platform. While this may be true, A purely construction
>station (e.g. NO or almost NO science.) would be very cheap.

   Agreed. In fact, I think I said that.

>
>>  Given the station we have today, there's not a whole lot of extra
>>  capability that you could cut if you were to decide that SSF was going to
>>  be dedicated to the support of lunar and planetary exploration. You still
>>  need to habitation space, the power generation capability, and the limited
>>  lab space of the current design. I can't think of any system in the MTC/PMC
>>  design that could be eliminated or any system capability which could be
>>  reduced if all you planned to do was to support the Space Exploration
>>  Initiative (i.e. lunar/mars exploration) PMC is pretty much the minimum
>>  viable permanently manned station one can come up with...
>>

   What I said, which you replaced with '...', was

   "PMC is pretty much the minimum viable permanently manned station one
    can come up with given the constraints imposed by launch vehicle, the
    current program structure, contracts already awarded, consideration of
    sunk cost, and politics."

>This not the case at all.

    Yes, it is. The agency spent the past six months demonstrating that.
    If you send me your FAX number I'd be more than happy to send you the
    tons of paperwork documenting my (unabridged) statement.

>The current soviet station, Mir, is able to
>support limited orbital construction (they have done numerous test
>EVAs practicing orbital construction techniques.). Mir consists of
>2 science modules (Kvant and Kristal), 1 EVA/life support module (Kvant 2),
>and one core/habitation module. If the science modules were replaced
>with EVA support and extra living space, Mir would be as capable as
>Freedom's PTC for orbital construction (E.g. 4-man, w/ suits for all of
>them.) This "consturction" Mir would consist of 5 20-ton modules.

  If you're as "capable as Freedom's [PMC]" you can't construct diddly.
  The requirements for carrying out the sort of vehicle processing
  tasks we're talking about are on the order of 14 crew and 150 kW.
  You also need a place to put the vehicles while you're working on them
  (e.g. to provide debris protection in LEO).

>A 5 Titan-launched-size modules is MUCH cheaper than Freedom.

  Excuse me?

>
>>  Indeed. One of the advantages of the old 'sticks and balls' erectable truss
>>  concept was the fact that there was all sorts of open space for the
>>  addition of growth structure to support vehicle processing facilities
>>  (hangars) and growth systems and utility lines.
>
>The problem with a design with lots of open space is DOCKING. A failed
>docking attempt will put the space shuttle flying past the station. If
>the station has trusses sticking out in many directions, the chance of
>a colission is much greater.

  Sure. Are you saying we should never build space structures larger than
  some specific dimension? What do you propose as that limit?

  One benefit of a design with lots of open space is that you have lots
  of open space. Something you need when you want to attach all sorts
  of payloads and vehicles.

>Note that a lunar base could be supported with a construction-only station,
>while a interplanetary mission would need life-sciences research to address
>long duration zero-gravity issues.

  Right.

>                                   Frank Crary
>                                   UC Berkeley

===============================================================================
 Ken Sheppardson                                  Email: [e-mail]
 Space Station Freedom Advanced Programs Office   Phone: [phone]
 NASA Langley Research Center, Hampton VA         FAX:   [phone]
===============================================================================

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

Date: 8 May 91 19:22:02 GMT
From: aio!vf.jsc.nasa.gov![e-mail]
Subject: Re: Why the space station?y

In article <[e-mail]>, [e-mail] (Frank Crary) writes:
>
> The problem with a design with lots of open space is DOCKING. A failed
> docking attempt will put the space shuttle flying past the station. If
> the station has trusses sticking out in many directions, the chance of
> a colission is much greater.
>

They docking method planned for the space station and the orbiter is not a
"slam-em together scheme."  It involves using the shuttles RMS arm to pull the
shuttle in gently.


>
>                    Frank Crary
>                    UC Berkeley

--

Mike Kent -      Lockheed Engineering and Sciences Company at NASA JSC
        2400 NASA Rd One, Houston, TX 77058 [phone]
        [e-mail]

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

Date: 8 May 91 18:30:22 GMT
From: psuvm![e-mail]
Subject: Re: SPACE Digest V13 #499

MATHCOUNTS is a Math test/contest for children I in the grades he a
qq

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

Date: 8 May 91 21:38:18 GMT
From: zaphod.mps.ohio-state.edu!rpi![e-mail]  (Jim Kasprzak)
Subject: Re: Ethics of Terraforming (was Re: Terraforming Venus)

In article <[e-mail]> [e-mail] (Lon Stowell) writes:
>  Life continuance and even quality doesn't depend on
>  terraforming.
>
>  Halfdome is just a lifeless rock.  Fisher Towers are just
>  lifeless rocks.
>
>  Has anyone considered making a "planetary park" out of Mars to
>  preserve Mt. Olympus and some of the other formations?  Just
>  cause it is lifeless doesn't mean it is without beauty...and
>  worth preserving.

 The point is, even if we manage to terraform Mars, I'm sure it will
still have its areas of "lifeless rock" and desert. And even in the
green areas, with that much land opening up at first, we can afford
to be generous in designating planetary parks, recreation areas,
wildlife refuges and the like. If it were up to me, I'd designate
Olympus Mons and the other Tharsis volcanoes as permanent wilderness
areas, along with most of Valles Marineris. That's a pretty big
chunk of the planet, but it still leaves a lot for human habitation.

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

Date: 8 May 91 23:20:23 GMT
From: mintaka!olivea!samsung!caen!ox.com!fmsrl7![e-mail]  (Ron Carter)
Subject: Re: SPACE Digest V13 #486

In article <[e-mail]>
 [e-mail] (someone who hides his name behind
 a gateway) apologizes for Coffman's errors:

>I think it's pretty clear that he meant....

So why isn't that what he wrote?

>He wasn't referring to absolute mass-ratio but the change in mass-ratio....

In point 3, I showed that "change in mass-ratio" is a meaningless
concept.  Not only does Coffman not know what he's talking about,
neither do you.

>You know damn well what he meant.

Again, why didn't he write what he meant?  Further, how do YOU
know what he meant, given that he didn't write it?  Do you read
minds?  (I don't, and don't pretend to.)

> Quit screwing around.  The rocket's fuel
>is used less on other fuel and more on actual payload at later times in the
>flight.  Just admit that he knew what he was talking about!

He'd have failed an essay test of knowledge.  He uses terms
and concepts wrong.  This betrays ignorance.

>I'm reaching into some very dark memeories at this point, but if I remember
>correctly, efficiency is <100% whenever the exhaust velocity is < c, and the
>mass conversion is less than 100% in the fule system.  So what was your point?

You are suddenly re-defining "efficiency".  (Also mis-spelling "fuel".)
Here is the definition again, for your edification:

    eff = energy_output/energy_input

In the case of a rocket, the output is the final kinetic energy of
the payload, and the input is the energy in the fuel (chemical
energy in the case of chemical fuels).

Mr. Tommie Mac, your knowledge does not impress me in the slightest.

>Sorry, I had assumed that blooming not only meant
>the ionization of material, but also the refraction.

You missed it *twice*.  Thermal blooming refers to the *refraction*,
but only that refraction caused by absorbed energy.  Turbulence and
other sources of variant refractive index are not "thermal blooming".
Ionization is not required to cause heating; ionization is a rather
extreme case.  Exercise for the student:  list 2 different physical
phenomena by which an electromagnetic field can ionize a gas.

>Yes.  Again the problem is the dissipative effects.  The problem, as I under-
>stand it, is that at certain power levels, the atmosphere blocks the beam.

Define "power level" in the sense you are using it, such
as peak, average, RMS, etc.  Also whether this is absolute
power, power per unit area, etc.  You use terms as sloppily
as Coffman does, and I refuse to re-write your posting to
my taste (you might not agree with my re-write).

>Since you've about ignored the idea of using different parts of the spectrum, I
>will assume ( since you know so much more than me ) that it is impossible to
>use ,say, radio or microwave to avoid the dissipative effects.

I have not ignored it.  I have not yet addressed it.  However,
radio and microwave transmission can be ruled out immediately
on optical considerations; their longer wavelength means that
they cannot be focussed precisely enough to put most of their
power on a small (~1 meter) target using antennae of reasonable
size, nor is the skin depth small enough to allow heating of
thin layers of the target without melting lower layers.  Both
of these are required for laser-launch type operations.

>Pulse-width doesn't change the power level (Energy per second), nor do the
>optics on the ground.

True.  I am frankly amazed that you understand this, given that
you spend so many bytes defending someone who does not.

> Breaking up the beam or using different wavelengths
>seem promising, but you seem to be pushing single, large power, visible light
>lasers (They would look impressive on the news!).

Where did I say that?  You are reading a great deal, including
much which I never wrote.  This is intellectually dishonest of you.
I said that I did not dismiss the concept because I thought beyond
the naive case, while you are accusing me of doing just that.

>So, since you are such a wealth of useful info;  spread it around!
>HOW DO IT WORK?

Since you insist, I'll give you a thumbnail sketch of what has
already been posted to this group many times:

A payload is placed on top of a block of ice (propellant).  It
is blown out of an air cannon (to get it moving); as it rises
into the air, the mirrors for an array of drive lasers track it.
They deliver precisely shaped pulses of light to the propellant,
which vaporizes a thin layer off the back and then flashes it
into plasma with a high-power burst.  The plasma expands and
propels the payload.  When the plasma has dissipated enough to
permit laser light to penetrate once more, the process is repeated.
One does this until the payload has achieved orbit.

Note:  this is a THUMBNAIL SKETCH.  It is not intended to be a
reference work, nor address all the physical and engineering
problems of laser-launch systems.  If you demand that I do,
I will politely tell you to get lost.

>So.  Maybe the guy is new to this group.

Coffman is very old here.  I've been reading him for a long,
long time.  He should know better.

>If that kind of behavior is expected, I'm getting off this group right now!

Given the quality of your scholarship, I wish you'd done so before
posting the quoted material.

>(You're kind of new to this group, aren't you?)

<<chuckle>>

>Pointing it out is one thing (Which is done quite a bit), but blasting people
>for it shows, not ignorance, but plain old lameness and immaturity.

Or exasperation with willful ignorance.  You show ability to learn,
but lack of tact, scholarship, and reading ability.  You could be
educated easily, had I the patience.  I doubt Coffman can be, not
because he is unable, but because he is UNWILLING.

>And you blasted Coffman for making a true statement about them.

Hogwash.  The statement was nonsense as written.  Your
excuses for his shoddiness (quoted above) prove it, and
that you know it.  Pathetic.

>Claiming that the most efficient mass-ratio has some effect on whether or not
>one mass-ratio is better than another is a good start.

I left the proof as an exercise for you, the student.  Now, I
shall spell it out in somewhat more detail:

Terminology:    Vexh = Exhaust velocity
        Vfin = Final payload velocity

Assume:        Payload mass = 1 (units irrelevant).
        Efficiency of conversion of energy to
        propellant exhaust energy is 1.

    Mass_ratio = loaded_mass / payload_mass = e^(Vfin/Vexh)
    Fuel mass = payload * (Mass_ratio - 1) = e^(Vfin/Vexh) - 1

    Total energy required     = (energy/unit_fuel) * (fuel_mass)
(1)                 = 1/2 (Vexh)^2 * (e^(Vfin/Vexh) - 1)

From formula 1 above, show that the mass-ratio which results in
the least energy required to achieve a given Vfin is approximately 4.
(You are not getting any points for ignoring the question the first time.
You get 2 points if you read this far.  You get MUCHO points if you
actually work the problem and learn something.)

>Jeez, you missed not only the point, but the joke, too.  What a rube!

I cannot believe that I can put smiley-faces on my counter-joke, and
it is still missed completely.  Your are either denser than neutronium,
or unable to respond to wit with wit.

>Please, don't follow up.  I don't give a rat's ass what you have to say.

How incredibly nice for me.  Perhaps you will decide to educate yourself
by doing some calculations and looking at the answers, rather than
reflexively flaming on the net as you did last time.

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

Date: 9 May 91 04:06:46 GMT
From: sun-barr!ccut!wnoc-tyo-news!astemgw!kuis!rins![e-mail]  (will)
Subject: Re: Ethics of Terraforming (was Re: Terraforming Venus)

In article <[e-mail]>, [e-mail] (Henry Spencer) writes:
>
>I assume, then, you oppose the terraforming of Los Angeles?  After all,
>it's fine the way it is, with smog and asphalt everywhere; why introduce
>foreign phenomena like trees and clean air to make it more "earthlike"?
>

    Give up on terraforming places like Los Angeles, Miami and N.Y.. These
    are lost causes with no solutions.  Even with Trillions of $$ you would
    never acomplish it.  The only way to terraforming places like this is
    by terraforming the population.

                            Will....

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

End of SPACE Digest V13 #533
*******************