Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_6/V13_604.TXT

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Subject: SPACE Digest V13 #604

SPACE Digest                                     Volume 13 : Issue 604

Today's Topics:
        Re: Tethers (was Re: Laser launchers)
             Re: Building Infrastructure
               Building Infrastructure
               Re: Saturn V and the ALS
       Re: Request For Discussion: sci.space.moderated
            Re: Fred vs. Exploration XXXIV
           Re: Rational next station design process
          Re: SPACE STATION FREEDOM WOUNDED

Administrivia:

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

Date: 20 May 91 03:03:34 GMT
From: snorkelwacker.mit.edu!think.com!sdd.hp.com!usc!jarthur!nntp-server.caltech.edu![e-mail]  (Earl A. Hubbell)
Subject: Re: Tethers (was Re: Laser launchers)

[e-mail] (Walter Dnes    ) writes:


>[e-mail] (Christopher Neufeld) writes:

>> In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>> >
>> >Let's look at a typical strawman tether launch. Let's propose a 1000 km
>> >tether whose center of mass is in a 700 km orbit. To hook on to the
>> >
>>    No, that's not right. If the tether is rotating, resembling the spoke
>> of an invisible wheel rolling around the surface of the Earth, then the
>> velocity of the tip drops to zero briefly. A person standing on the
>> ground would see the tether come in from a high angle, straightening out
>> until it was coming straight down, stop, then take off in the upward
>>
>     "If the tether is rotating..." W-H-O-A !!!!!!!!!!!!!!!!!!

>     ( w = omega, MS-DOS can handle it but other character sets
>are different. ) Let's see... orbital velocity is approximately
>7 km/sec at that altitude. Assuming that the tether is as above,
>you've got 500 km of tether rotating with the end moving at
>7 km/sec.
>                 wr = v

>                      v    7
>                  w = - = --- = 0.014 radians/sec
>                      r   500

>    A small section length dr will have mass kdr where k is the
>linear density. a = v * v / r = w * w * r at any radius r.

    And here you have just discovered the reason for exponentially
tapered cables - if you taper the cable's cross section (thicker at
the middle, thinnest at the ends) the argument falls apart - say you
replace your mass function with k*exp(-fr)dr - f chosen for some reasonable
taper (10:1, whatever), your integrals work out >very< differently (a simple
exercise in integration by parts) to yield that your effective 'weight'
of your cable is decreased by a factor roughly proportional to your taper.
(using your terminology - I'd use 'self supporting length' and say that
it increases, but to each...)


>     Let's assume a cable of material X (neutronium ?) The 500 km
>section would have a centrifugal/centripital tug of...

>                /~ 500 km      /~ 500 km
>Ascii           |              |          k(wr)^2   evaluated at
>integral   F =  | ma    = kw^2 | r dr  =  -------   r = 500 km
>sign           _/             _/             2
>                 0 km           0 km

>     But we started off with wr = 7 km/sec, so we're looking at


>     k(wr)^2   k(7km/sec)^2   k(49000000m^2)   k(24500000)m^2
>     ------- = ------------ = -------------- = --------------
>        2           2             2sec^2           sec^2

>                                               k(500000m)*49m
>                                             = ---------------
>                                                   sec^2
>     but 500000m = 500km
>     since k is the linear density
>     k(500000)m = mass of the 500km section of tether
>     49m/sec^2 = approx 5 g's
>     This is one half of the tether. Newton's 3rd law implies that
>the other portion has identical force *IN THE OTHER DIRECTION*.
>Also 5 times the earth-surface weight of the tether. And we were
>worrying about whether the tether would hold up under its own weight.
>At this point gravitational force becomes a secondary mechanism in
>the process of tearing the structure apart. Back to the drawing
>board...

    See previous comment - this argument demonstrates nicely
why no-one considers linear cross section cables.  Note that you
do pay a price for exponential taper - the total mass of your
cable system goes up >very< fast - a severe consideration for space work.

>Walter Dnes
>--------------------------------------------------------------------------
>[e-mail]             [e-mail]
>...hybrid!torag!w-dnes!waltdnes  [e-mail]
--
Earl Hubbell -- [e-mail] -- Opinions expressed: mine
"There's a whole new breed of scientist out there today:  They drink,
smoke, fool around with women, but they won't answer one simple
question:  How do you destroy Washington, D.C.?" -villian, Matt Helm flick

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

Date: 20 May 91 04:12:04 GMT
From: haven.umd.edu!socrates.umd.edu!socrates![e-mail]  (Raul Rockwell)
Subject: Re: Building Infrastructure

Allen W. Sherzer:
   >>No large infrastructure project has ever been done without major
   >>government involvement.
   Well, here is what happened with oil rigs: some company decided
   that an oil rig was needed. To design it a bunch of engineers got
   up and rode on government supplied roads to their jobs.  They
   talked over phone lines belonging to a government chartered ...

oil rigs predate this.


Ob space:

Does anyone know of a reasonably compact database/model of the solar
system for playing around with orbital trajectories?  For instance,
something no larger than half a megabyte (uncompressed) of equations,
documentation and coordinates?  [For that matter, is there anything
close to a standard coordinate system for such purposes?]

Thanks

Raul Rockwell,
who somehow never took any astronomy classes.

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

Date: 19 May 91 05:55:07 GMT
From: ogicse!sequent!muncher.sequent.com![e-mail]
Subject: Building Infrastructure

In article <[e-mail]> [e-mail] (Allen W. Sherzer) writes:

>No large infrastructure project has ever been done without major
>government involvement.

Where did the thousands of billions of dollars worth -- over 1,000
times more $$$ than available to NASA -- of oil rigs, oil pipelines,
communications satellites, auto factories, steel factories, IC fabs,
railroads, ocean-going ships, airplanes, skyscrapers, shopping malls,
apartment buildings, power plants, etc. etc. etc. on this planet come
from?

In only a few of these cases does a free-market-economy government
have any significant influence in the type and scale of operations.
And even in the cases of utilities and real estate zoning, the
most successful outcomes occur when the needs of a diverse
marketplace, rather than central planning, determine the technological
details.


>This is the approach we need to take. If we want to reduce launch
>costs, let's gurantee a large market at 75% of current prices and
>reduce that price periodically. We need to take similar steps for
>other industry as well.

Fine, but don't dictate the size of rocket or satellite, the "best"
or "paradigmatic" orbits, or the best payloads to launch.  These
decisions best made by the industries serving the marketplace.

And be careful that "prizes" don't end up making industry design
something inappropriate to the actual needs of the commercial market.



--
Nick Szabo                [e-mail]
"If you understand something the first time you see it, you probably
knew it already.  The more bewildered you are, the more successful
the mission was." -- Ed Stone, Voyager space explorer

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

Date: 20 May 91 15:36:11 GMT
From: mojo![e-mail]  (Doug Mohney)
Subject: Re: Saturn V and the ALS

In article <[e-mail]>, [e-mail] (Allen W. Sherzer) writes:
>
>>>Even as we speak the DoE is doing work using a Soviet military reactor.
>
>>The DoE has bought a soviet "Topaz 2" space nuclear reactor. They did NOT
>>buy it for use.
>
>Correct. The original poster was claiming that it would be impossible
>to buy ANY space hardware. I agree it would be a bigger step to buy
>a Soyuz to acutally use but it could be done.

NO, I did not claim that, you are implying it. I am stating as fact that you
will not be able to purchase any tin cans to send up men. If you wish to buy
heavy lift, or unmanned vehicles, you have better than a snowball's chance in
Haiti. Don't put words into my mouth, Alan.

>>How will the experiment module get to the station? Unless you have an
>>OMV (Which is worth having, but not trivial to build, fly and operate)
>
>As I said, with a portion of the second or third years savings from
>the Shuttle we could build an OMV.
>
>>Also, from where will the module get power during the time it is
>>in transit to the station? This will take at least a few hours and many
>>payloads CANNOT be turned of in filght.
>
>This would be a problem. I guess you are correct we would need to
>send them up using the HLV; a Titan wouldn't do. Fortunatly, we
>built two with about a third of the first years savings.

I'm sorry, you just shot the hell out of your budget. Let's see, you need one
launch for the OMV, at least one or two for the gas-bag spacestation, one or
two to get crews in orbit (remember, you can only get 2-3 men in the tin can),
and gee...but you are taking those savings and building all those HLVs.

I'm still waiting on your magic tricks as to how you defeat the "Astronaut
Mafia," the Air Force, Lockheed, and Rockwell International. Plus the
additional stunts you need to pull in order to fix Hubble, GRO, and Solar Max
with tin cans and OMVs and a bigger station than the LLNL gasbag.

It might be easy enough for you to ignore the Air Force, NRO, and other people
who use National Means of Technical Verification, but you won't be able to
service spy sats with Soviet tin-cans :-)


     Signature envy: quality of some people to put 24+ lines in their .sigs
  -- >                  [e-mail]                        < --

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

Date: 20 May 91 15:59:36 GMT
From: mojo![e-mail]  (Doug Mohney)
Subject: Re: Request For Discussion: sci.space.moderated

In article <[e-mail]>, [e-mail] (Frank Crary) writes:
>In article <[e-mail]> [e-mail] (Mary Shafer) writes:
>>I'm inclined to leave it like it is.  In general, moderated groups
>>work best for factual issues and it's obvious that much of sci.space
>>would not qualify.  I think the group would wither and die.
>>
>You may be right. However, might a sci.space.news, for factual postings
>only (e.g. the flare warnings, shuttle and interplanetary probe status
>reports, etc.) be a good idea?

Me thinks Frank has the right idea. Peter Yee and the other Official
NASA folks (ooops, can't remember the other one) who bring us daily updates,
GIFs, plus the orbital stuff should go into one group.

This would leave sci.space open for the political lobbying which it was not
intended for....

     Signature envy: quality of some people to put 24+ lines in their .sigs
  -- >                  [e-mail]                        < --

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

Date: 21 May 91 00:33:08 GMT
From: hub.ucsb.edu!ucsbuxa![e-mail]  (Charles Frank Radley)
Subject: Re: Fred vs. Exploration XXXIV



OK, you asked for it........planetary probes produce nothing
but pretty pictures and instruments readings whihc interest nobody
except the Principle Investigators.
   Who needs them.

Super cynical, because I enjoy the pretty pictures...I have
a vast collection of them....and I have worked on Galileo and
Magellan myself.   But really, why do the scientist think what
they are doing is more important than manned spaceflight ?
  If I had my way we would have them both.....but with Hubble
we can plenty of pretty pictures, why do we need probes ?
  We have already visited a comet and Saturn, they can wait if
necessary, but I hope it won't come to that.

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

Date: 21 May 91 00:20:15 GMT
From: agate!bionet!uwm.edu!ogicse!sequent!muncher.sequent.com![e-mail]
Subject: Re: Rational next station design process

In article <[e-mail]> [e-mail] (George William Herbert) writes:

>A rational approach (as far as I know, _the_ rational design approach) to
>aerospace design is to follow the following steps in designing a vehicle:
>
>1. Mission
>
>Mission:
>    What can we do with a manned space station?

I am sorry to say, this design approach is not at all rational.

Instead of _assuming_ a design concept "space station", start with the
question: "what do space users need?"  The major space users being
defense, commerce (mostly communications), and exploration.

If we start out with the question "what can we do with a manned
space station", then of course we can make up some justifications
for it.  If we start out with the question "what do space users need",
then we can design the most useful infrastructure to extend our reach into
space.  It may or may not have anything to do with a "space station" --
we must examine many alternatives and be prepared to change or
preconceived notions.

Unless we take this step farther back in the thinking process, we are
just fooling ourselves into believing we are making something useful.


>    * Human Biological Research
>    * Human Psychological ""
>    * general Bio Res.
>    * Space Infrastructure Field Testing
>    * some Microgravity work
>    * some Astronomy/Astrophysics work
>    * some Materials Processing (for profit?)
>    * Space Vehicle Refurbishing/Repair (field study on practicality)
>    * ... (fill in blanks.  I think that mostly covers the field)

Other points to consider:

* What _else_ needs to be done, besides the above tasks (opportunity costs).
* How can the above tasks be done most efficiently (examine alternatives:
  sounding rockets, animal experiments in a variety of orbits, ...)



--
Nick Szabo                [e-mail]
"If you understand something the first time you see it, you probably
knew it already.  The more bewildered you are, the more successful
the mission was." -- Ed Stone, Voyager space explorer

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

Date: 18 May 91 07:16:31 GMT
From: ogicse!sequent!muncher.sequent.com![e-mail]
Subject: Re: SPACE STATION FREEDOM WOUNDED

In article <[e-mail]> [e-mail] (Allen W. Sherzer) writes:

>There is a middle ground between our current socialistic approach and
>total government non-involvement (nither of which will work IMHO).

We've never tried a totally non-government approach, actually, so
it is hard to say how it would turn out.  The steps required are
so numerous and radical (cancelling Shuttle, creating an open
market for radio frequency, creating a pay-for-exploration-data system
as proposed by Jim Bowery, etc. etc. etc.) that this approach is
for now politically impractical.

Doing at least the latter two wouldn't hurt, though.


>That
>is to have the government provide infrastructure to seed commercial
>development. This is what happened with railroads, airports, the
>highway system, and others.

In the succesful cases the government followed the lead of industry
regarding the type and scale of the technology, rather than dictating
a central plan bearing little relation to the current market.

NASA's space development efforts need to follow the lead of commercial
space industry -- which for now most especially means assisting our
largest and fastest growing primary space industry, communications --
rather than trying to set its own economically fantastic, centrally
planned direction.



--
Nick Szabo                [e-mail]
"If you understand something the first time you see it, you probably
knew it already.  The more bewildered you are, the more successful
the mission was." -- Ed Stone, Voyager space explorer

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

End of SPACE Digest V13 #604
*******************