Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_5/V13_501.TXT

Internet Message Format | 1991-06-28 | 10KB

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/wc9slSO00WBwA57k4R>;
          Wed,  8 May 91 01:27:58 -0400 (EDT)
Message-ID: <[e-mail]>
Precedence: junk
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Wed,  8 May 91 01:27:51 -0400 (EDT)
Subject: SPACE Digest V13 #501

SPACE Digest                                     Volume 13 : Issue 501

Today's Topics:
                   tether's
                 Re: tether's
              Re: Why the space station?
              Saturn V computers
               Re: Saturn V blueprints
                  GREAT IDEA

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: 4 May 91 20:45:25 GMT
From: mcsun!ukc!slxsys!ibmpcug!demon![e-mail]  (Ian Stirling)
Subject: tether's

In article <[e-mail]>
[e-mail]
(F026) writes:
\  Nick Szabo's explanation of tethers in space misses the *really*
/interesting part for LEO users: if you have a longish (>1000m) tether
 orbiting within a >magnetic field, eg LEO, an electrical potential is
\induced (at the cost of >orbital velocity)....[use orbital energy as
/battery for use inside shadow]

\I don't know about the *really* part, :-), but you point out
/another interesting and quite promising use of tethers that I had
 failed to mention.  I was bound to miss some of 'em.  For this
\application,
/as well as EML, magsails, etc., increased R&D on superconducting
 materials
\is very important, as well as R&D on high tensile strength materials
/for
 tethers in general.
\
/Paul Dietz and I have worked on his proposal for tapping the large
 kinetic
\energy of Jupiter's inner moons, via Jupiter's strong magnetic
/field,

\Using a similar scheme.  The energy available, and readily
/extractable, is at minimum millions of megawatts for over a thousand
 years. I have also proposed a scientific "astronomy flashlight"
\mission that could take advantage of the magnetic flux with a small
/probe in the near term.

\While this is not directly related to launch costs, a large
/inexpensive source of energy could become very important for
 second-generation space industry and colonization. Work on launch
\tethers could, in addition to reducing launch costs, very well "spin
/off" to the kinds of technology we are discussing here.


Perhaps I'm missing something incredibly obvious but how can a tether
generate any power?
A tether moving in a magnetic feild will have a voltage between the
two ends,but how can you get a current to flow?For a current to flow
you would need a return cable,and that would have the same voltage as
the primary cable induced in it,so how can any currrent flow?
Mail to either                            |PLEASE do not send large
[e-mail]|(>20K)mail messages as
[e-mail]                   |I get charged for them.
[e-mail]                           |
one of these may work                     |

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

Date: 5 May 91 00:11:17 GMT
From: news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: tether's

In article <[e-mail]> Ian Stirling <[e-mail]> writes:
>A tether moving in a magnetic feild will have a voltage between the
>two ends,but how can you get a current to flow?For a current to flow
>you would need a return cable,and that would have the same voltage as
>the primary cable induced in it,so how can any currrent flow?

The simplest way is to have each end of the cable in good electrical
contact -- details left to the student :-) -- with the surrounding plasma.
Then you get current because the plasma is not moving at the same speed
with respect to the field as you are.
--
And the bean-counter replied,           | Henry Spencer @ U of Toronto Zoology
"beans are more important".             |  [e-mail]  utzoo!henry

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

Date: 5 May 91 21:01:06 GMT
From: usc!rpi![e-mail]  (Michael V. Kent)
Subject: Re: Why the space station?

In article <[e-mail]> [e-mail] (Frank Crary) writes:
>From these conclusions, NASA went to Congress and President Nixon. Neither
>wanted to pay for the whole package... So NASA thought "Well, the first
>thing we will need is the reusable Earth-to-orbit transport. Lets get
>that done first." So NASA focused on the Space Shuttle (without really
>remembering why they needed it). They got Congress to pay for it,
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

You were doing pretty good, until you got to this point.  NASA has always said
the main purpose of a space shuttle is space station support.  Don't blame
NASA for the Vietnam-era politics in which it found itself.

>but the final product is not well suited for its origional purpose:
>building and supporting a space station.

Supporting, yes, but the shuttle was not meant to build the space station.
That was to be done with the Saturn V.  It was only after NASA was forced to
make the choice between the Space Shuttle and the Saturn V that they decided
to build the space station with the Shuttle.

>Now, having the shuttle, NASA wants to proceed with their origional plan:
>The "Next Logical Step" is a space station. So NASA, again forgeting WHY

No, NASA knows very well why they want a space station.  But the space station
they want must be built incrementally, like the pieces of their overall plan.
Freedom will be expanded into an orbital base as soon as NASA is given the
money to do so.

Mike

--
Michael Kent                                   [e-mail]
McDonnell Douglas                              Rensselaer Polytechnic Institute
All facts in this post are based on publicly available information.  All
opinions expressed are solely those of the author. Official positions may vary.

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

Date: 1 May 91 17:44:19 GMT
From: stanford.edu!snorkelwacker.mit.edu!think.com!rpi!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Saturn V computers

In article <[e-mail]> [e-mail] (Tommy Mac) writes:
>The computer that was used on the original Apollo Landings had only 64K of core
>memory.
>It's teeny sure, but they did it with tubes back then...

Uh, no, sorry, you have your paleoastronautical eras confused. :-)  The
Saturn V electronics were pretty well entirely solid-state.

Also note that back then, "core" meant *core*, magnetic core memory, not
tubes or transistors for every bit.
--
And the bean-counter replied,           | Henry Spencer @ U of Toronto Zoology
"beans are more important".             |  [e-mail]  utzoo!henry

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

Date: 2 May 91 01:55:07 GMT
From: world![e-mail]  (unicorn)
Subject: Re: Saturn V blueprints

Just a couple of ideas about this thread.

1. If we space enthusists argue about what should be done, Congress will
   never give us money to do anything.

2. Fighter aircraft are often upgraded (radically) to extend their life
   span ( manufacturing life span that is ).  They are NOT fantastic top
   notch planes, but they are relatively cheap and reliable.

3. In software design ( my speciality ) there is the concept of High Level
   Design, Low Level Design and Implementation.  Software written in Fortran
   can *usually* be ported to C ( a much better language ) by just changing
   the implementation.  Usually, you want to change the Low Level Design as
   well to take advantage of features of C that make it more effecient.
   ( For instance, using registers instead of saving temp data in RAM )
   It is usually not necessary, and not a good idea to change the High Level
   Design at all.  This is why you are porting it instead of rewriting it.
   So look at the Blueprint of the Saturn V, take its basic design and figure
   out how you would do the same thing today.

The Wizard of AHs

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

Date: 2 May 91 12:50:40 GMT
From: agate!bionet!uwm.edu!caen!uakari.primate.wisc.edu!crdgw1!gecrdvm1![e-mail]
Subject: GREAT IDEA

Seems like the consensus of this group is that we need a dumb,cheap
booster. Some want it big, some want it new, some want it an extension
of existing boosters, but most want it. So what happens if we get it?
what if company X gives us a booster that will launch for low bucks per
pound?  Does the entire payload community sign up (once the test flights
are out of the way and it looks like it's reliable)? what happens to the
rest of the launch companies, especially if company X decides not to
share the technology?  Now you have all your eggs in one basket (sounds
like the early shuttle days) and along comes some disaster and company X
is out of business along with our entire launch capacity.  Sound plausible?
Only if company X is very powerful to begin with (politically and economically)
since if there ever was a real chance of such a booster coming into existence
all the established big launch companies along with any political power they
might command would be trying mighty hard to shut down Company X.  Maybe
this is why none of those small startup companies with promising ideas
never get anywhere. shades of early automotive competition.

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

End of SPACE Digest V13 #501
*******************