Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT_ZIP/spacedig/V13_5/V13_557.ZIP/V13_557

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/QcAVqam00WBw5A405p>;
          Thu, 16 May 91 01:50:34 -0400 (EDT)
Message-ID: <[e-mail]>
Precedence: junk
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Thu, 16 May 91 01:50:25 -0400 (EDT)
Subject: SPACE Digest V13 #557

SPACE Digest                                     Volume 13 : Issue 557

Today's Topics:
              Re: SPACE Digest V13 #485
              Re: Honking at cyclists...
               Re: Saturn V and the ALS
        Tethers (was Re: Gas Guns and Tethers
               Re: Saturn V and the ALS
              Re: Honking at cyclists...
              Re: Why the space station?

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: 14 May 91 20:30:39 GMT
From: usenet.ins.cwru.edu!ncoast!fmsrl7![e-mail]  (Ron Carter)
Subject: Re: SPACE Digest V13 #485

In article <[e-mail]> [e-mail] (Walter Dnes) writes:
>     This is starting to get interesting. I assume that we're not
>*REALLY* "borrowing" energy from the future. I believe that the
>correspondent is trying to say that a departing crew would exit at
>the same time as a fresh crew arrives. Thus the centre-of-mass of
>the main-space-station-plus-one-shuttle would be preserved.

Perhaps that's what he meant, but that is certainly not required.

>     I wonder how often several thousand miles of tether can be reeled
>in and out without stress failure. We haven't even begun to consider
>the longterm effects of micrometeorite bombardment on the structural
>integrity of the tether.

The tether studies I've read assume that a non-redundant tether
would be severed by an impact from meteoroids or (more likely)
space junk.  The cross-sectional area of the tether is such that
these events have a rather high probability of happening every
few years.  So, you plan for it.  As for reeling a hundred
miles of tether in and out, I've not seen anyone consider it
a problem.  (Note:  This would be a LEO to LEO tether.  Nobody
is considering going from LEO to GEO with today's technology.)

>     Whoa... you can *CONVERT ORBITAL ENERGY TO ELECTRICAL ENERGY*.
>If you've got humungous solar panels you could conceivably generate
>lots of electricity and *CONVERT ELECTRICAL ENERGY TO ORBITAL ENERGY*.
>The solar panels could only operate half of the time. They should
>double  as "solar sails" from "satellite noon" to "satellite midnight".
>From "satellite midnight" to "satellite noon" the space station is
>heading into the solar wind. During that time, the panels should be
>oriented to present a minimal profile to the sun.

Sorry, you're wrong.  The thrust from I*l x B vastly exceeds the
drag from 2 * E * c, for reasonable values of l, so the panels
should be oriented for full power all the time.  As a matter of
fact, a space station's orbital motion makes a better battery than
the station can carry.

>     Given that 99% of the mass of the space station would consist of
>several ... tether, drums ... electrical motors ... solar panels....

You are greatly exaggerating the masses involved here, unless you
are assuming a space station designed to do nothing but tether work.
Consider a station keeping a 250 mile orbit, massing 500 Klbm, and
able to drop a 200 Klbm Shuttle orbiter to 100 miles on a tether.
Compute its orbital rise, the max extension of the tether, the
max static tension on the tether, the required cross-sectional
area (for, say, Kevlar) with a 3x safety factor, and the mass
and volume.  Do those amount to even 10% of a 500 Klbm station?

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

Date: 14 May 91 14:58:44 GMT
From: psuvm!esoc![e-mail]  (Rupert Williams)
Subject: Re: Honking at cyclists...

In article <[e-mail]>, [e-mail] (Mark
SOKOLOWSKI) says:
>
>Given all the flames that my article has, I want to simply add this:
>
>My point is that we'll have to expand our energy consumption and our
>vital space NO MATTER WHAT goes on. Of course we can improve
>our efficiency to use this or that source of energy and matter, but
>sonner or later we'll have to use the minerals of Antarctica, the
>deuterium in the Earth's oceans, and go to the moon in order to
>build a plateform there for Mars, Marcury and the asteroids.
>Our ever increasing population will need more and more, and each individual
>will need more and more of everything. And sooner or later even the
>entire solar system won't be sufficient, so we'll have the rest of the        .
>galaxy..
>
>Mark

   What has all this rubbish got to do with rec.autos??! Post it to the
appropriate group will you - rec.space, rec.environment etc...

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

Date: 14 May 91 20:47:01 GMT
From: iggy.GW.Vitalink.COM!widener!hela![e-mail]  (Allen W. Sherzer)
Subject: Re: Saturn V and the ALS

In article <[e-mail]> [e-mail] (Brad Mears) writes:

>|> Why would they lowball for a fixed price contract? They would lose
>|> a lot of money that way.

>One _possible_ reason to lowball on a fixed-price contract is to bet on future
>contracts for maintenance, training, updating, etc.  The original builder will
>have an edge in those efforts.

I don't think that would be possible. We are talking about one to twenty
launches all bought for a fixed fee. There is no firm expectation of
buisness beyond that.

If they hold prices down, there is a good chance for more buisness since
they are reducing costs by a factor of three. If they don't then there
will be no buisness. Either way, it will be hard to recover  a lot of
money if they run over.

>Additionally, the cynic in me believes that even on a fixed-price contract,
>cost-overruns will be passed to the taxpayer.  I know that isn't the way its
>*supposed* to happen, but Congress+Lobbyists = Trouble.

Even if that ever happens, it would be rare. Not the sort of thing you would
gamble hundreds of millions of $$ on.

  Allen
--
+---------------------------------------------------------------------------+
|Allen W. Sherzer |        Allen's tactics are too tricky to deal with      |
|   [e-mail]   |             -- Harel Barzilai                           |
+---------------------------------------------------------------------------+

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

Date: 14 May 91 21:19:36 GMT
From: agate!usenet.ins.cwru.edu!ncoast!fmsrl7![e-mail]  (Ron Carter)
Subject: Tethers (was Re: Gas Guns and Tethers

In article <[e-mail]> [e-mail] (Walter Dnes) writes:
>[e-mail] (Ron Carter) writes:
>
>> In article <[e-mail]> [e-mail] writes:
>> [regarding capturing sub-orbital payloads with a tether]
>> >Theoretical problem 1) The centre-of-mass of the combined structure has
>> >instantaneously dropped... The result should be a lower orbit.
>> This is not a problem.
>     Note that the orbit has dropped. It will drop *EACH TIME THAT
>YOU REEL IN A SHUTTLE*.

True.  TANSTAAFL.  But it rises every time you un-reel a Shuttle.

This thread began with the idea of capturing sub-orbital payloads
using a tether, and bringing them up to orbit this way.  The Shuttle
is not designed for such rapid maneuvering.  The Shuttle's OMS and
RCS capability really can't handle this job, so talking about
capturing and reeling Shuttles in (as opposed to payloads
designed to do this) is not realistic.

Another problem not addressed in this thread is that reeling in
a tether amplifies every vibration mode and adds energy to them.
This makes it difficult to do.  Reeling things out is much easier.
This is what we would do at first.

>     In another reply on this thread, I made a glaring error that
>would seem to allow this scheme to work. I assumed that a shuttle
>could be "reeled out". ( Silly me, I'll never graduate to sci.skeptic
>this way. ) If the shuttle detaches and the main station unreels
>several thousand miles of tether... you'll merely end up with an
>atrocious "crowsnest" like no fisherman has ever seen before. The
>shuttle will tend to remain in the same orbit as the station, *UNLESS
>IT FIRES ITS ROCKET ENGINES TO DE-ORBIT*. That's what the shuttle has
>to do right now.

You have two mistaken ideas here.

1.)    You have assumed that the center of mass of the Shuttle
    orbiter and space station could be in the same place, so
    that the tidal forces between them would disappear.  This
    is naive.

2.)    You have assumed that it would take a rocket burn equivalent
    to an OMS de-orbit burn to get adequate separation to tension
    a tether.  This is not true.  The tidal and centrifugal
    acceleration in LEO is roughly .004 m/sec^2/km for a vertical
    separation.  Assuming that 10 N is required to hold the tether
    straight, a 100,000 kg mass must be offset only
    10 N / (1e5 kg * .004 m/sec^2/km) = 10 N / (400 N/km )
    = >>>25 meters<<< from the center of mass to tension the
    tether.  A Shuttle can easily back off a kilometer or more
    using the RCS jets.

Because capturing a Shuttle on the end of a tether would be next to
impossible, the only real possibilities involve having one rendevous
with the station and be attached there.  It would then be reeled out
(and, maybe, back in again).  If it is reeled out in the downward
direction and then released, three things are accomplished:

1.)    Considerable work is done on the tether reel, which can
    be used to charge batteries.  (Reeling one out 150 km
    in LEO would yield roughly 4.5 GJ of work, or 1,250 KWH.)

2.)    The space station is placed in a higher orbit, without any
    consumption of fuel.  (Orbit-raising fuel is expensive.)

3.)    The Shuttle is placed in a lower orbit, also without any
    fuel used.  This orbit could be a re-entry orbit if desired.

I can't think of any missions which would require a Shuttle orbiter
to be reeled out and then back in, can you?

>     ... raising the shuttle from LEO to
>GEO, and then dropping from GEO to LEO.

Where did you get the idea that anyone would put a space station at
GEO and try to send a Shuttle to it?  You might as well have a Model
T handle freight for the Condorde.  By the time we are ready to build
space stations at GEO, all remaining Shuttles will be in museums.

It is no wonder you're getting results saying "impossible".  You
are looking at the wrong problem.

>I think
>that you've run afoul of the 2nd law of thermodynamics (entropy) with
>something resembling Maxwell's demons that could filter cold and hot
>molecules in a gas.

I think you are not sufficiently clear on what tethers *are* and
*do* to be able to distinguish them from snake oil.  That's all
right, just keep your mind open and keep asking questions.

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

Date: 14 May 91 21:07:18 GMT
From: prism![e-mail]  (Matthew DeLuca)
Subject: Re: Saturn V and the ALS

In article <[e-mail]> [e-mail] (Doug Mohney) writes:

>Duh, huhhhh? We're going to build *TWO* new, improved lift vehicles, buy and
>Americanize a Soyuz and mount it on top of a U.S. booster (either? Both? You
>don't say up there) OR rebuild a CSM and certify it atop New, Improved
>boosters (two separate steps there), and then put up an Econo-lodge space
>"station" for the low-low-low price of one year's Shuttle costs?

>To use the Henri Spencer (TM) Phrase:

>            "Numbers, Please"


Oh, *no*.

More of those numbers...

"90% less..."

"Two years from 'go'..."

"We'll save $2 billion..."

"Martin Marietta says it will cost..."

Sorta reminds me of the periodic SR-71/A-12 threads that pop up...around
the world, you can hear a collective "not *again*!"


--
Matthew DeLuca
Georgia Institute of Technology      "I'd hire the Dorsai, if I knew their
Office of Information Technology      P.O. box."  - Zebadiah Carter,
Internet: [e-mail]    _The Number of the Beast_

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

Date: 14 May 91 22:11:12 GMT
From: snorkelwacker.mit.edu!usc!sdd.hp.com!news.cs.indiana.edu!noose.ecn.purdue.edu!en.ecn.purdue.edu![e-mail]  (/dev/null)
Subject: Re: Honking at cyclists...

In article <[e-mail]>, [e-mail] (James Davis Nicoll) writes:
>
>     Granted, C is the important limit on how fast we could grow (and
> I did say at one point 'ignoring C' when I was talking about Eating The
> Universe) but all that means is that we run out of resources to continue
> our current growth rates sooner rather than later. I was disagreeing with the
> thesis 'Human wants will grow unbounded, and so will our use of resources'.

I agree with you, but the one resource left out of the equation is the human
mind and ingenuity.

If we only could renew the "non-renewables" :)

>
>     Anyway, if there are 5x10**9 humans at 50 kg each, and they grow
> at 3% a year, and the universe masses 100x10**9 (Number of stars) x 100x10**9
> (number of galaxies)x1000 (Fudge factor in case there's *lots* of dark matter)
> x 2x10**33 kg (mass of a sol-type star), it still only takes ~3700 years
> (Given no speed limit) for the mass of all humans to equal the mass of the
> universe. Since we can't ignore the C limit, our rate of increase of demand
> will *have* to decrease before AD 5700.

Change 'increase of demand' to 'increase of demand of raw materials per capita'
and we agree.

>
>     Note I am *not* saying the standard of living of all humanity couldn't
> be indefinitely maintained at a higher level than today. I just saying it
> won't grow forever.
>
>     Are we agreeing yet?

Yes, except that it may be possible to indefinitely increase living standards
without consumption of more materials.  Cars have gotten much better in the
last 10 years.  They are also consuming less in their operation and their
construction.  If it were possible to salvage all of the car after it is
"used up" then you can re-use the materials to make more cars that work
better.  Now this is a very specific example, if similar measures were
applied to other areas, we might find that increasing ones standard of living
has only a small correlation to the amount of resources available.
(Doing more with less.... :)

I *do* agree that the population is likely to "MAX-OUT" in the next few
millenia.

If we find FTL, however, all bets are off! :)


--
+-----------------------------------------------------------------------+
| Society of Philosophers, Luminaries,           | Brent L. Irvine       |
| and Other Professional Thinking People.....   | Only my own ramblings |
+-----------------------------------------------------------------------+

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

Date: 14 May 91 19:03:31 GMT
From: att!emory!wa4mei!ke4zv![e-mail]  (Gary Coffman)
Subject: Re: Why the space station?

In article <[e-mail]> [e-mail] writes:
>In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>
>>The smaller probes definitely don't need assembly.  The bigger ones really
>>could use it.  Just look at some of the elaborate schemes people have put
>>together trying to do a Mars sample return using existing launchers with
>>no in-space assembly.  Those plans are far riskier and far more exotic than
>>putting the mission together in orbit.
>
>Care to expand on this?  I fail to see how in-orbit assembly makes
>a sample return, from Mars or other places, any easier.
>
>Note that both the Soviet Union and the U.S. did extensive sample
>return from the Moon without in-orbit assembly.

I wouldn't call the Soviet sample return activity extensive. I'm not
even sure I'd want to call the Apollo missions extensive sampling.
In any case they had an HLV that no longer exists and the Moon is
a lot closer than Mars. Not necessarily in energy terms mind you,
but there are other considerations for long duration flights. A
manned mission would require so much life support as to be positively
huge. A more doable super Viking would still likely be much larger
to support a rover and the return vehicle. Without that HLV, putting
the thing together in orbit makes sense. Spending the multiple billions
that a sample return mission would cost without returning a good
statistical sampling would be an enormous waste. A Soviet style
land, grab the first thing at hand, and blast off for home is
hardly of enormous scientific value. You would want a system that
could rove around and take representative samples from many locations.
This phase could take months, probably over a year. Then you'd need
a return craft capable of returning all those samples. We're talking
lots of mass out and back. Without HLV we must assemble in space or
forego the mission.

Gary

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

End of SPACE Digest V13 #557
*******************