Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V10_2/V10_205.TXT

Internet Message Format | 1991-07-08 | 10KB

Return-path: <[e-mail]>
X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
Received: from beak.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/sZIegwe00VcJ0DnU5E>;
          Sat,  4 Nov 89 04:26:21 -0500 (EST)
Message-ID: <[e-mail]>
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Sat,  4 Nov 89 04:25:37 -0500 (EST)
Subject: SPACE Digest V10 #205

SPACE Digest                                     Volume 10 : Issue 205

Today's Topics:
              Re: Fragile Space Shuttle
           Radiation exposure for Apollo astronauts
             Re: PowerSat Options
             Re: PowerSat Options
            Re: Moon Colonies / Ant Tanks?
            Re: Moon Colonies / Ant Tanks?
              Re: Fragile Space Shuttle
----------------------------------------------------------------------

Date: 3 Nov 89 13:58:23 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: Fragile Space Shuttle

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>[I sez]
>>My prediction is that we will never be allowed to stop checking spacecraft
>>with a fine toothed comb...
>
>Until we start designing them not to need fine-toothed-comb checkout,
>this is trivially true.

Then my prediction AFTER THE SPENCER TRANSFORM, thank you very much, is
that it will never be practicable to design spacecraft that don't
require a fine toothed comb checkout.  The only way I'm wrong on this is
if we drag full scale war into space, since the military ethic is (or
used to be) to build things that could take a beating, at the cost of $$
and efficiency.   I would prefer not to be wrong for that reason. :-)
--
DEFINITION, n.  statement of precise   <\<   Tom Neff
meaning of word etc. [F f L (DEFINE)]   >\>  [e-mail]

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

Date:     Fri, 3 Nov 89 15:43 EST
From: <[e-mail]>
Subject:  Radiation exposure for Apollo astronauts

        So much talk has been flting by the last month about the effects of
radiation on astronauts on long trips.  To add to the mess, I have a couple
of questions.  First, what is the exact range of the van Allen belts, and
what shape are they?  How are they generated?  Second, how much exposure did
the Apollo astronauts receive (I assume the van Allen belts do not extend all
the way to the moon)?  Third, what are the chances of an astronaut on an
interplanetary journey from getting nailed by a cosmic ray of sufficient
energy to harm him/her?  Finally, how much are geosynchronous satellites
affected by cosmic rays/van Allen belts?

        With so much talk, and so few numbers, I have no idea what all the
hub-bub is about!

 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
|  Arnold Gill                          |
|  Queen's University at Kingston       |
|  BITNET:    gill@qucdnast             |
|  INTERNET:  [e-mail]  |
 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

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

Date: 3 Nov 89 15:53:00 GMT
From: munnari.oz.au!murtoa.cs.mu.oz.au![e-mail]  (John Keong-Jin Lim)
Subject: Re: PowerSat Options


Sigh!
It's been a few days since I posted my last message on this subject
but there are still people arguing about powersat beam weapons,
space laser batteries and the like.

As Paul Dietz has stated, the physical construction of the transmitting
array will not allow focusing of the beam to a smaller area than the
area of the transmitting array (about 1 km^2).
This (combined with the very low power density of the beam) should end
all speculation about SPS powered weapons.

As for lasers in space, why don't people look at why lasers were
abandoned for 'Star Wars' ????
The inefficiency of lasers requires vast amounts of coolant for lasers
of any great power to operate in space.(This applies to masers too)

The microwave generating device that has been the basis for realistic
SPS design study is the magnetron (as in your kitchen oven).
They are cheap (since we know how to churn out millions each year already),
sturdy, clean (in the RF sense) and highly efficient so that cooling can
be performed by reasonably sized radiators.

The frequency most suitable for power transmission is 2.45GHz which has
very low attenuation in all atmospheric conditions so we can forget about
all that 'altering the climate' crap.
(as for the guy proposing 50-60Hz transmission, hasn't he heard of all
the lobbying against overhead power lines ????)

What do you have to do to be read in this newsgroup, anyway?
 (Yanks and Canuks only, huh? ;->  )

    Greg Kaan (using anothers account).

    Support Cape York so I can work for the Space industry too!

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

Date: 4 Nov 89 00:01:15 GMT
From: rochester![e-mail]  (Paul Dietz)
Subject: Re: PowerSat Options

In article <[e-mail]> [e-mail] (John Keong-Jin Lim) writes:

>As Paul Dietz has stated, the physical construction of the transmitting
>array will not allow focusing of the beam to a smaller area than the
>area of the transmitting array (about 1 km^2).

Actually, I said that diffraction would prevent the microwave beam
from being less than several km across at the Earth's surface.  It
could be focused to much smaller size (smaller than the transmitting
antenna) at points much closer to the transmitter.

    Paul F. Dietz
    [e-mail]

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

Date: 4 Nov 89 02:55:38 GMT
From: munnari.oz.au!bruce!monu1!vaxc![e-mail]
Subject: Re: Moon Colonies / Ant Tanks?

In article <[e-mail]>, [e-mail] (Lance Franklin) writes:
> In article <[e-mail]> [e-mail] (Tom Neff) writes:
>>Oh by the way, if you have to burrow underground to survive in a
>>Moon colony, why bother to go?  Why not just build underground
>>colonies here?  Sure is easier to ship stuff here.  If you have
>>to spend your whole life in the basement, how much does it matter
>>which basement?
>
>
> How deep would you have to dig to get 1/6th earth gravity?  :-)
>
>
>
> Lance
>
>
> --
> +-------------------------+ +------------------------------------------+
> | Lance T Franklin        | | "And all who heard should see them there,
> | [e-mail] | |  And all should cry, Beware!  Beware!
> +-------------------------+ +  His flashing eyes, his floating hair!"

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

Date: 4 Nov 89 07:18:06 GMT
From: swrinde!cs.utexas.edu!wuarchive!mailrus!jarvis.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Moon Colonies / Ant Tanks?

In article <[e-mail]> [e-mail] writes:
>From what I learnt from school, I recall that the gravitational force
>is inversely proportional to the distance between the center of masses. Hence
>the gravitational force will increase as you go towards the center of the earth.

Sorry, you have missed a key assumption in that force law:  "assuming all
masses are point masses".  A spherical homogenous object, or a spherical
object made of spherical homogeneous shells, behaves like a point mass...
so long as you don't start digging down inside it.  It turns out that if
you continue to assume spherical homogeneous shells, the shells above
you have no effect whatsoever, and it's only the mass below you that
counts.

(Note, by the way, that when things get non-spherical or non-homogeneous,
all bets are off and the simplifications no longer apply.  The Earth is
*not* spherical, although for the purposes of this sort of calculation
it's probably close enough.  Don't forget that its density is not uniform,
though -- the core is denser for several reasons.)
--
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry [e-mail]

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

Date: 4 Nov 89 07:12:58 GMT
From: swrinde!cs.utexas.edu!wuarchive!mailrus!jarvis.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Fragile Space Shuttle

In article <[e-mail]> [e-mail] (Tom Neff) writes:
>Then my prediction AFTER THE SPENCER TRANSFORM, thank you very much, is
>that it will never be practicable to design spacecraft that don't
>require a fine toothed comb checkout...

Actually, there are two relevant questions here.

First, will NASA ever find it practicable to do so?  I think we both
agree that the answer is no, although perhaps for different reasons. :-)

Second, will *anybody* ever find it practicable to do so?  Here, Tom,
I'm afraid I have to continue to disagree.  While I respect your opinions
on a number of things, when you say "no" and Max Hunter says "yes", I'm
afraid I believe him, not you.  (For those who don't know who Hunter is,
the Delta launcher is a slightly souped-up Thor missile, and Hunter
designed the Thor... taking it from contract signing to operational
service in 3.5 years.)

If you want a sample of what Hunter is saying lately...  The shuttle
system manages 6-8 launches a year, with hopes for somewhat more, at
a manpower level of 9000+ for three orbiters.  Arguably airlines are
an unfair comparison, so let's compare to the SR-71:  it too is an
advanced, kludgey, quirky beast that requires a lot of babying and
arguably has never really been "operational" in the normal sense.
"Any engineer who examines the situation would agree that very high
performance aircraft are every bit as high tech, tricky and complex
as space launchers, and likely more so.  Fighting high-speed aerodynamic
forces in the atmosphere is *not* for the faint-of-heart.  Space
publicists (and apologists), of course, would disagree..."

About 8 SR-71s fly over 400 flights per year with a total support
staff of 385 people.
--
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry [e-mail]

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

End of SPACE Digest V10 #205
*******************