Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_6/V13_657.TXT

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Subject: SPACE Digest V13 #657

SPACE Digest                                     Volume 13 : Issue 657

Today's Topics:
         Re: Self-sustaining infrastructures
               Re: satellite refuelling
               Re: Calculating delta-V
          Re: Extra Terrestrial Intelligence
               Re: Calculating delta-V
Re: Pregnancy in space (was Re: Rational next station design process)
           Re: Rational next station design process
                Re: Astrolabes
         Re: Moonbase movie *Plymouth* to air Sunday?
              Re: The Long Term
        Complete and utter nonsense from Nick

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

Date: 27 May 91 16:19:00 GMT
From: sun-barr!newstop!exodus!concertina.Eng.Sun.COM![e-mail]  (Steve Hix)
Subject: Re: Self-sustaining infrastructures

In article <[e-mail]> [e-mail] (Frank Crary) writes:
>>
>I think refueling would be easier to do, even if it might be a less effecient
>way to extend the lifetime of satellites. Replacing the station keeping
>system would invlove, at least, screwing in bolts. Refueling just requires
>connecting a hose. This would be easier to do teleroboticly, and may even
>be possible with a satellite not designed for refueling (or failing that,
>it would require very little re-design.)

Refueling doesn't address the previously-mentioned problems with hydrazine
catalysts.  (So use something besides hydrazine...)

There *are* other connectors besides bolts.  Special tools to deal even with
bolts reasonably in 0-g shouldn't be all *that* hard to come up with, though.

How are electric thrusters coming along?





--
------------
  The only drawback with morning is that it comes
    at such an inconvenient time of day.
------------

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

Date: 27 May 91 02:42:30 GMT
From: van-bc!rsoft!mindlink![e-mail]  (Bruce Dunn)
Subject: Re: satellite refuelling

> [e-mail] writes:
> Person: Fraering Philip
>
> Doesn't the design of some resistojets involve feeding the hydrazine
> itself into an arcjet, without prior decomposition?


     I don't know about this.  If you are going to dump a liquid into a
resistojet, you are better off from a specific impulse point of view to use
ammonia rather than hydrazine.  Ammonia can be stored in tanks under its own
pressure, eliminating the hardware associated with hydrazine tank
pressurization.
--
Bruce Dunn    Vancouver, Canada   [e-mail]

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

Date: 29 May 91 01:44:16 GMT
From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!caen!uflorida!mailer.cc.fsu.edu!prism![e-mail]  (Matthew DeLuca)
Subject: Re: Calculating delta-V

In article <[e-mail]> [e-mail] (Loren Petrich) writes:

>    In "English" units, there is a unit of mass called the "pound"
>and a unit of force called a "pound". Their ratio is the acceleration
>of gravity, about 9.8 m/s^2. In this type of system, the ratio of
>force to mass rate is measured in seconds, when it is really a
>velocity, the effective exhaust velocity (EEV).

Actually, the unit of mass in the English system is the slug.  At one
g, the weight of this unit is 32.2 pounds.
--
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: 28 May 91 22:12:40 GMT
From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!usc!nic.csu.net!csun.edu!corona![e-mail]  (Stephen Walton)
Subject: Re: Extra Terrestrial Intelligence

In article <[e-mail]> [e-mail]
(Fraering Philip) writes (in reference to advance warning of supernovae):

>Well, the combination of proximity given by interstellar travel and
>more advanced science will probably give the colony plenty of warning
>if the star is indeed about to blow up.

It won't.  The post-helium-burning stages of fusion in massive stars
(fusion of carbon, neon, oxygen, and silicon) last less than 1,000
years each, much less than the Kelvin-Helmholtz time scale for the
star's envelope.  The time from the start of iron production to
core collapse is less than 24 hours.  At most, they'd get a few hours
warning if they had neutrino detectors, because the neutrinos come
straight from the core while the explosion has to propagate through
the star's outer layers.

References:  "Supernovae" by Woosley and Weaver, _Annual Reviews of
     Astronomy and Astrophysics_, 1987 volume.
"Supernova 1987A" by Arnett, Bahcall, Kirshner, and Woosley, _ibid_ 1990.
--
Stephen Walton, Dept. of Physics & Astronomy, Cal State Univ. Northridge
    "Lately it occurs to me/What a long, strange trip it's been"

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

Date: 29 May 91 17:43:50 GMT
From: prism![e-mail]  (Matthew DeLuca)
Subject: Re: Calculating delta-V

In article <[e-mail]> [e-mail] (Perry G Ramsey) writes:
>In article <[e-mail]> [e-mail] (Matthew DeLuca) writes:

>>Actually, the unit of mass in the English system is the slug.  At one
>>g, the weight of this unit is 32.2 pounds.

>Well, sort of, but not really.  Nobody uses the slug.

Well, the only reason that I even know about the existence of the slug
is that I learned a bunch of equations in one of my aerospace classes
using slugs...the density of air was given in units of slugs per cubic
foot.  Gads.

>Doesn't all this just make you want to puke?

Hear hear. :)
--
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: 29 May 91 18:51:43 GMT
From: news-server.csri.toronto.edu!utzoo![e-mail]  (Kieran A. Carroll)
Subject: Re: Pregnancy in space (was Re: Rational next station design process)

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (S. J. Okay) writes:
>>... I would think that given the the fetus is already
>>floating weightless inthe amniotic sac during its development, the absence of
>>gravity wouldn't be that much of a problem (but then, I'm no MD either).
>
>Floating in fluid produces only approximate weightlessness.  For example,
>bones are still heavier than soft tissues, and have some small tendency
>to try to sink.  For that matter, the whole fetus probably doesn't exactly
>match the average density of the amniotic fluid, and consequently will
>feel some gravity.  Whether any of this matters to development, nobody knows.

An additional factor to consider crops up during labour and delivery.
The presence of gravity is a perhaps-crucial factor involved in
an about-to-be-born baby becoming "engaged" --- that is, the baby's
head dropping down into the mother's pelvic cavity. Once this happens,
the baby's head puts pressure against the mother's cervix. I was
told in pre-natal class that this pressure is instrumental in
triggering hormonal releases in the mother, that result in
"effacement" (thinning) of the cervix, and eventually the beginning
of cervical dilation (i.e. labour). Thus, gravity is instrumental in
bringing on labour. This is a strong enough effect that particular
postures and exercises are recommended for women whose babies don't
become engaged naturally. If engagement doesn't occur properly, the
result is usually a very long, hard labour, and/or a Ceasarian-section delivery.
--

     Kieran A. Carroll @ U of Toronto Aerospace Institute
     uunet!attcan!utzoo!kcarroll [e-mail]

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

Date: 29 May 91 23:39:16 GMT
From: agate!lightning.Berkeley.EDU![e-mail]  (Frank Crary)
Subject: Re: Rational next station design process

In article <[e-mail]> [e-mail] writes:
>Well, there were a load of alternate designs looked into prior to signing
>on to the original dual-keel, balanced (in terms of solar arrays), multi-
>purpose, multi-module configuration.  And that has been mentioned here
>before.  Most notably by Mr. Sheppardson, who will no doubt accuse me of
>spreading misinformation again.

I was unaware of these configurations. How funadmentally different from
the final (or current) design were they? Were they all, for example,
launched and supported/supplied by the space shuttle, used long sections
of truss structure, etc?

> ...And, if you want detailed design studies of all
>proposed alternative concepts, the database would be *huge*.
>
While I agree agree that such a database would be too large to compile or
use, this does not mean that it cannot be comprehensive. If, for example
20 possible designs, and thier estimated preformances/costs/etc..., were
to be considered a reasonable sized database to work with, then these 20
designs should be as different as possible. If they are all permutations
of the same basic concept (as for example, the "different" mission concepts
in NASA's 90-study of manned Mars missions were,) then the full range of
studied designs is too small for a good trade-off study.

>...And keep in mind, although this is only my harmless
>opinion, Lewis Research Center has gone a long way toward delivering a
>working electrical power system for Fred: working end-to-end test beds,
>a design selected for actuation of solar arrays, etc.  The arrays themselves
>have been designed and re-designed, and could be built - but proximity
>operations considerations will delay this process for some time.

To what extent are the Lewis solar pannels/power supply tied down to the
specific design of Freedom? Would it be possible to use them, with only
slight modifications, on totally different space systems?

                         Frank Crary

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

Date: 30 May 91 00:39:50 GMT
From: agate!lightning.Berkeley.EDU![e-mail]  (Frank Crary)
Subject: Re: Astrolabes

In article <[e-mail]> [e-mail] (Doug Brownell) writes:
>I was just introduced to a reproduction of a 13th century astrolabe
>(I think that's what it's called), and was mightily impressed when it
>accurately predicted the hour (to within +/- 5 minutes) based upon a
>sighting of the sun (at ~3:30 pm) and knowledge of the date.  Does
>anyone know where such marvels can be purchased for less than a small
>fortune?  The one I saw was nearly $300 (gold electroplated), but the
>design is so simple that there's got to be one for under $100, and
>maybe even $50.  I'd really apprecieat any leads as to where I might
>search for one.

As well as predicting the hour of the day, an astrolabe can do many other
things: Calculate the time and azimuth of sunrise and sunset.
    Calculate the phase of the moon on any given date.
    Find the location of any star (but, unfortunatly not planets) marked
       on it, at any given time.
        Etc.
The accuracy of the device depends on its size and quality. From your
discription of the one you saw, I would guess that it was about 20cm in
diameter. Astrolabes exist (or did once exist...) of up to 5 METERS in
diameter, these were accurate to on the order of 10 min. of arc.

As far as buying one, I do not know about the prices. But there are a few
things to look for: The circles on the tympan (the part you hold in your
hand) that mark lines of elevation above the horizon should NOT have a
common center. The center of the 0 or 10 degree elevation line should be
well above the center of the 70 or 80 degree elevation line. This is the
easist way to see if the astrolabe was correctly constructed. If all these
circles have a common center, then the maker did not know what he was doing.
Also, the on the rete (the part that turns) there is a inner circle, with
the dates of the year marked on it. The lengths of the months on this circle
should NOT be of equal size (the ANGLES from the center of the astrolabe
, not the center of the cricle, should be equal.)

Good astrolabes are hard to find (at a good price espacially) these days. If
you are into function as opposed to appearance, it is usually easier to
construct your own using drafting tools and stiff cardstock.

The following may be helpfull:

      Chaucer, Geoffrey (father of the poet) _A Treatise on the Astrolabe_
      Ed. Walter W. Skeat, Oxford, 1872. Reprinted 1968.

      Gunther, Robert T., _Astrolabes of the World_ Oxford, 1932

      North, John D., "The Astrolabe" Scientific American, January
      1974 (96-106).


                        Frank Crary

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

Date: 30 May 91 21:48:29 GMT
From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!usc!jarthur!petunia!zeus![e-mail]  (James T. Green)
Subject: Re: Moonbase movie *Plymouth* to air Sunday?

One piece of non-reality about "Plymouth" was the fact that so
many people with absolutely no relevant background were sent
to the Moon.

It seemed that Plymouth was the only moonbase, or perhaps one
of a few.  With so many people here on Earth so willing to
go into space, and dedicating their lives and careers to
that goal, I find it extremely unbelieveable that a bunch
of hicks would be sent.

I was very annoyed by all the "was it right to come here"
BS dialog that was being bantered about by some of the
characters.  I don't believe anyone who wasn't absolutely
positive about the rightness of going would be *ALLOWED* to
go (at least anytime in the next century).

However, there was one character (the kid with the super
moon buggy) who said that he "couldn't be pried (sp) out of here...
every time an airlock opens, you're making history."  I would
have like a lot more of that kind of positive attitude throughout.

Technically, it seemed OK.  We could probably do it within
20 years (or less) if it could only get funded :-(
--------------------------------------------------------
James T. Green, Innocent Bystander
[e-mail]

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

Date: 31 May 91 14:37:14 GMT
From: usc!cs.utexas.edu!cse!texas!csl.dl.nec.com![e-mail]  (Larry Baker)
Subject: Re: The Long Term


 [e-mail] (Henry Spencer) writes:
|> In article <[e-mail]> [e-mail] (Kevin S. Van Horn) writes:
|> But what do you call it when a group of
|> >venture capitalists finances a startup (like the one I'm working for -- MasPar)
|> >with the expectation that they'll have to wait maybe five years to see a
|> >return on their money?
|>
|> Medium term at best.  Ask the Japanese.

The 5-year plan is the "near-term" plan in our company.  They don't openly
discuss the mid-term or long term plans with us peons, but they exist.

Someone once asked Mr. Morita, the CEO of Sony corp. how far in advance
they (at Sony) plan.  His answer was: "200 years."
--
Larry Baker
NEC America C&C Software Laboratories, Irving (near Dallas), TX
[e-mail]  cs.utexas.edu!necssd!baker

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

Date: 1 Jun 91 04:09:58 GMT
From: usc!wuarchive!rex!rouge!pc.usl.edu![e-mail]  (Phil Fraering)
Subject: Complete and utter nonsense from Nick

In article <[e-mail]> [e-mail] rants:

>* The best cost estimate for a four-man station is $120,000 million
>(GAO). It is unknown what Mir costs.  A two man station requires the same
>life support, refuelling, etc. equipment R&D and would not, I think,
>cost significantly less than a 4-man job.

Nick, a two man station will cost less than Skylab, which
cost a lot less than 120 Billion. And our technology has
*improved* since then.

For those of you who don't remember the ancient history,
Skylab was a three-man station. I remember reading all about
it in the late seventies in _National Geographic_ (you know,
that invertebrate "astronautist" rag?). The NG article was from
the early seventies, but

You are taking the life-cycle cost of a twelve-man station over
thirty years with the most expensive booster possible (you mentioned
900 million per launch) needed four times a year for resupply as the
startup cost of its four-man "construction phase" initial operations
capability.

And that for what many consider to be an extremely expensive and bad
example of a space station.

I think you know all this already, but blanket statements like "120,000
million for a four-man station... and a two-man station will cost just
as much..." (not exact quotes, I know, but I can't stand to read the
thing twice) sort of make you feel superior, don't they?

Phil Fraering || Usenet (?):[e-mail] || YellNet: 318/365-5418
Standard disclaimer, whatever a disclaimer is, applies.
''It hardly mattered now; it was, in fact, a fine and enviable
madness, this delusion that all questions have answers, and nothing is
beyond the reach of a strong left arm.`` - Larry Niven and Jerry
Pournelle, _The Mote in God's Eye_

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

End of SPACE Digest V13 #657
*******************