Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_5/V13_535.TXT

Internet Message Format | 1991-06-28 | 19KB

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/oc=WLWW00WBw86fE4=>;
          Mon, 13 May 91 01:36:35 -0400 (EDT)
Message-ID: <oc=[e-mail]>
Precedence: junk
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Mon, 13 May 91 01:36:29 -0400 (EDT)
Subject: SPACE Digest V13 #535

SPACE Digest                                     Volume 13 : Issue 535

Today's Topics:
             Re: Laser launchers
Re: The Previous Eco-Venus Discussion (was Re: Ethics of Terraforming)
               Re: Saturn V and the ALS
                orbit23 works!
        Re: Alexander Abian wants to blow up the moon?
         Question about paint color for cars?
                 Scale models

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: 7 May 91 00:01:02 GMT
From: emory!wa4mei!ke4zv![e-mail]  (Gary Coffman)
Subject: Re: Laser launchers

In article <[e-mail]> [e-mail] (Nick Szabo) writes:
>In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>
>>Transmission,
>>control, and application of the electrical energy is, at best, 80%
>>efficient. And laser conversion is, at best, 10% efficient.
>
>8% better than the extra fuel needed to lift tank and
>fuel in rockets, due to the fuel being on board.

Sorry, but a laser launch system must carry "reaction mass" to be heated
by the laser beam. This *dead weight* produces no useful energy input.
It's mass and tankage mass must still be carried aloft by energy input
from the laser beam alone. Granted that at very low altitudes the
atmosphere itself may be used as a working fluid, but above roughly
5 km the atmosphere is not dense enough to carry the energy load and
internal reaction mass must be carried. It makes little sense to carry
*dead weight* when that same mass could release useful chemical energy.

>>That's
>>an overall efficiency of 3.2% right there.
>
>Which is better than chemical rockets (1-2% starting with a
>primary fuel like refined oil).

At least with a chemical rocket all the released energy is usable. With
the laser system most of the energy is expelled as waste heat on the
ground. Essentially all heat generated by a chem rocket is usable energy
that accelerates the reaction mass.

>>[more inefficiency from blooming]
>
>Eliminating blooming is a major problem that needs to be worked on
>by R&D.  In one regime -- using lasers to power suborbital regime
>payloads into orbit -- blooming is not a problem at all.  A
>paradigm shift needs to occur here for those stuck in the chem
>rocket paradigm -- an upper stage, especially one operating in
>vacuum, does not need to resemble in any way the lower stage.  It
>is quite possible, perhaps even probable, that we will have a suborbital
>regime consisting of chem rocket, laser (if blooming is solved), EML,
>gas gun, or airplane-slung tether, and a vacuum orbital regime consisting
>of laser or tethers.  The technologies we are discussing can be an imortant
>piece in a hybrid system, it is not necessary and perhaps not even
>desirable that they perform the entire task on their own.

Using a space based laser is even worse in some respects than using a
ground based laser. At least on the ground there is a large sink for
the waste heat produced in the process of generating the beam. At least
on the ground the massive tankage required for the laser reactants doesn't
have to be heaved into space. And you *still* have to carry reaction mass
on the payload for the laser beam to work against. So heaving your laser
launcher into space gains you only freedom from blooming, ie it might
work, but the mass required to be delivered to orbit to operate the
laser far exceeds the mass of fuel needed to deliver the payload directly
to orbit.

>The desirability of eliminating blooming and increasing laser efficiency
>is the big reason we are talking about government R&D funding here,
>not funding for an operational system which is the role of industry.

Blooming is the major killer for ground based laser systems and it is
worst at the lowest altitudes where the laser could possibly show a
slight advantage by not requiring the payload to have on board reaction
mass. Above 5 km, the required reaction mass on the payload means that
using that mass to supply the energy directly is going to always be more
efficient than beaming the energy up separately.

>>>  ....this tank and controlling this
>>>  tank through flight is a major part of chem rocket launch costs
>>>  and reliability problems.
>>
>>This is *the* advantage of the laser scheme.
>
>It is all the advantage it needs.  Storing massive amounts of
>volatile gas with the payload has produced unreliable transportation,
>from dirgibles to rockets.  Laser launch gets us out of that mode.

Laser launch means we carry reaction mass, the same reaction mass carried
by chem rockets, but the reaction mass of the chem supplies the necessary
energy input instead of relying on a separate, very inefficient, energy input.
Not all chems are cryogenically fueled, but a light molecule does have
advantages as a working fluid that even laser proponents must consider.
The higher exhaust velocity for a given heat input that light molecules
like H2 give you is extremely valuable in increasing performance.

>>I wasn't arguing that R&D engineering problems need to be solved so
>>much as I was arguing that fundamental physical laws prevent the system
>>from being a practical, efficient, alternative to rockets.
>
>What "fundamental law" says that blooming can't be solved?
>The solution may require adaptive optics on the launch site, to
>be sure.  In the end, it _may_ prove intractable.  Or it may not.
>The whole point of doing R&D is to find out for sure.  By just
>throwing our hands up we could throw away the best opportunity.
>We don't have too many good opportunities to throw away.

The blooming problem is more than just a defocusing of the beam that
can be solved by adaptive optics. At the beam power levels required,
the atmosphere is turned to a superheated plasma. This plasma is
optically opaque. It won't allow the beam energy to go further. It
just makes that spot in the atmosphere hotter and hotter until it
expands enough to cool below the plasma state. This expansion of
superheated plasma does defocus the fringes of the beam, but the
core of the beam is completely blocked until the plasma dissapates.
As the plasma dissapates, a partial vacuum forms that is immediately
refilled by the surrounding atmosphere starting the cycle all over
again. This "chugging" is very very rapid, even a short pulse laser
suffers from it. If the laser pulses are made submicrosecond, the
problem is minimized, but then the delivered power becomes very low
due to the small duty cycle of the beam. Remember that we are talking
gigawatts of power here to heave a payload into orbit.

>>Tethers need to exceed the theoretical strength of materials limits by
>>orders of magnitude to work.
>
>Kevlar can work today for most of the scenarios envisioned.
>The major problem is launch cost of the mass.  This can be brought
>way down by (a) manufacturing the tethers in space, (b) producing
>better tensile materials -- a very important and woefully underfunded
>field of R&D, (c) bootstrapping larger tethers into orbit with smaller
>tethers, or (d) a combination of the above.

A one square inch kelvar tether to geosync orbit would weigh 45.2 million
pounds. I don't have the handbook here at the terminal, but kelvar doesn't
approach 45 million pounds per square inch tensile strength by orders of
magnitude. It couldn't support itself, much less a usable payload.


>>Again, a fundamental scientific breakthrough,
>>not engineering R&D, needs to occur before tethers can become reality, if
>>ever.
>
>Materials strength is applied, not fundamental science.
>The other problems are engineering.  Your rhetoric is way out
>of whack with reality here.

Strength of materials ultimately depends on fundamental science. The bond
strength of elements and compounds *are* physical limits. Diamond rods
and certain graphite whiskers already approach physical limits quite
closely, and those limits are still orders of magnitude too low.

>>Science fiction is all well and good,
>>but the best way we know to go
>>up through the atmosphere is with wings and air breathing engines.
>
>So far, you haven't come out in favor of any kind of new ideas.
>Keep the rocket engineers at work, keep launch costs high, don't
>rock the rocket.  This sort of short-sightedness in the last thing
>needed in government R&D work, which by its very rationale is supposed
>to be working on promising but difficult problems that are too long
>term for private R&D.  In the twenties you could have, and perhaps would
>have, used these very same arguments against chem rockets.   "Goddard needs
>to take a refresher on elementary physics.  Everybody knows rockets can't
>operate in a vacuum" (paraphrase of New York Times...).

Now, now. I'm not anti-progress. I just don't see laser launchers or tethers
as the solution for sound technical reasons. I want a cheap way to orbit
as much as anyone, but I don't have any brilliant new scheme that is orders
of magnitude better than the chemical rocket. The best scheme that I can
envision is using wings and air breathing engines on a carrier craft to
get the rocket the critical first 5 km above the atmosphere. Pegasus is
a small scale forerunner of this concept. It's way too expensive, but
prototypes usually are. The third or fourth generation system should be
much easier to use and much cheaper with much greater payload capacity.

Gary

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

Date: 8 May 91 16:38:56 GMT
From: sdd.hp.com!caen![e-mail]  (Ken Sheppardson)
Subject: Re: The Previous Eco-Venus Discussion (was Re: Ethics of Terraforming)

[e-mail] (Paul A. Estin) writes:
>[e-mail] (Heidi Hammel) writes:
>
>>>[e-mail] (Ken Sheppardson) writes:
>>>>
>>>>  Is there anyone else out there who questions the ethics of tampering
>>>>  with other planets (with or without the presence of life) to make them
>>>>  more 'earthlike'? ...
>
>>Anybody else out there getting this strange feeling of deja vu?
>> ...
>>Didn't anybody out there save all the
>>discussion of the ethics of terraforming from last time around?   Seems
>>pointless to rehash all this when we just did it a few weeks ago .....
>
>I don't have all of it, but I did save some key bits (OK, so I'm a
>net.packrat with too much disk space on my hands).  Here goes...

   Thank you for reposting the articles.

   Apparently this was one of the two dozen or so threads I didn't
   follow the first time around. I haven't read the articles yet,
   but I look forward to seeing what you'all concluded. I won't waste
   anymore bandwidth until I've done so.

   I'm always impressed by the professionalism in sci.space, as opposed
   to other groups where I'm sure I would've been deluged by "We already
   talked about that. Go away." :)

===============================================================================
 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 15:35:15 GMT
From: csus.edu!wuarchive!cs.utexas.edu!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Saturn V and the ALS

In article <[e-mail]> [e-mail] writes:
>> What everyone else is saying is "The Shuttle was going to be a pick-em-up
>> truck.  Why is ALS different?"  The only answer I've seen you give to date
>> is "NASA says so."
>
>There is one reason to believe that ALS will be close to what it is
>claimed to be: The Air Force says so.

They are possibly the only people in the world with a worse record in
high-tech procurement than NASA.

>There is some big general somewhere, along with a few little generals,
>a bunch of colonels, majors, captains, ... Whose next promotion
>depends on ALS being exactly what they say it will be. The Air Force
>works on an "up or out" system...

Ha ha ha.  It also works on a "ticket puncher" system.  The people who
get things started will be long gone to some other job before the excrement
hits the revolving blades.  Unless ALS is being run in a very non-standard
way (like the Navy's long-range missiles), no senior USAF personnel are
committed to stay with it from start to finish.  When the time comes to
fix the blame, there will be nobody home.

>The U.S Air Force are the people who brought you the Atlas and Titan
>boosters, the Minute Man I, II, and III, and the Peacekeeper missiles.

Those people are long retired, for the most part; except for the very last,
those programs were 20+ years ago.  Some of them also had some small problems
with budgets, schedules, performance, and reliability...
--
And the bean-counter replied,           | Henry Spencer @ U of Toronto Zoology
"beans are more important".             |  [e-mail]  utzoo!henry

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

Date: 8 May 91 22:02:21 GMT
From: caen!zaphod.mps.ohio-state.edu!magnus.acs.ohio-state.edu![e-mail]  (Earl W Phillips)
Subject: orbit23 works!



Well finally, I got Orbit23 working on my old CP/M system,
got the right paramaters for my city, and ran off an orbit
for SoyuzTM-11 last nite, and it performed flawlessly! Right
at the designated spot at the designated time, the satellite
sailed across the sky, making a nice arc from the west to the
north. I got about 1/2 dozen shots, hope they come out!

*****************************************************************
*                                    | ====@====      ///////// *
* [e-mail]|     ``________//         *
*                                    |       `------'           *
*                 -JR-               | Space;........the final  *
*                                    | frontier...............  *
*****************************************************************

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

Date: 29 Apr 91 22:36:31 GMT
From: bu.edu!buast5![e-mail]  (Alan Lohof)
Subject: Re: Alexander Abian wants to blow up the moon?

In article <[e-mail]> [e-mail] (Lloyd E Vancil) writes:
>In article <[e-mail]> [e-mail] (Robert Duff) writes:
>>
>>If the Earth were tilted to 0 degrees and the Moon obliterated,
>> what would be the impact on
>>life on Earth?  Sure, it would be Springtime all
>> year round
>>devestating for plant life whose life cycles are base
>> on the seasons.  Also, no more tides!
>>
>>Could life continue without the moon?
>>
>Yes say good by to Apples.. and many other fruits.
>Not to mention,
>     What does this guy propose to mitigate the effects of this one impact?
>Does he suppose that this thing will splash down like a tennis ball in a bath-
>tub?



YO!!!  did everyone forget something called conservation of momentum????
If the moon blew up, all the little pieces would stay in the original
orbit.  some parts would (after time) start to spread out in the orbit
and form a nice ring about the earth.  everyone remember jupiters rings??
notice the similarities??  how about the asteroid belts around the sun??
same thing.

Someone mentioned that  all the crops would die because its always Spring?
recall that seasons are due to the tilt of the earth with respect to the
Sun. the north pole points to Polaris.  loss of the moons mass all at
one point would have virtually no effect on the earths tilt. angular
momentum must be conserved.  there would be a minor change in the
precession of the earths axis when the moons mass spread into a even ring,
but that wouldn't change the tilt by much and it would take A VERY long
time.

Tides: yes these would be gone. but the loss would be as gradual as the
        spreading of the moons mass.

Earth - moon fragment collisions:  remember that all previous collisions
that we know of were from meteors, asteroid stuff.  the moon fragments
would come in as decaying orbits, spiraling in, like the space shuttle.
lots of time spent burning in the atmosphere. and it would take a very
large chunk to make it thru the atmosphere and hit surface.

Comments??

alan
[e-mail]

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

Date: 7 May 91 18:36:00 GMT
From: bonnie.concordia.ca!ccu.umanitoba.ca!arda![e-mail]  (Cyrus Shafai)
Subject: Question about paint color for cars?

What paint color lasts the longest on cars?
I have heard that red paint doesn't last too long, and that metallic paint doesn't
do too well in the sun.

Cyrus Shafai
--
Cyrus Shafai            <[e-mail]>
The Scanning Tunneling Microscopy Laboratory
Electrical and Computer Engineering, U of Manitoba
Winnipeg Manitoba

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

Date: 9 May 91 16:28:48 GMT
From: van-bc!ubc-cs!alberta!cpsc.ucalgary.ca![e-mail]  (Gaston Groisman)
Subject: Scale models

I am wondering about the existance of scale models of the Hubble Space
Telescope and the Voyager space craft.  Has anybody seen these in any
hobby shop?

                   Thanks,

 Gaston Groisman          +-------------------------------------+
 Computer Science Dep.    |      [e-mail]        |
 University of Calgary    |      [e-mail]       |
 Alberta, CANADA          +-------------------------------------+
--
 Gaston Groisman          +-------------------------------------+
 Computer Science Dep.    |      [e-mail]        |
 University of Calgary    |      [e-mail]       |
 Alberta, CANADA          +-------------------------------------+

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

End of SPACE Digest V13 #535
*******************