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Subject: SPACE Digest V10 #184

SPACE Digest                                     Volume 10 : Issue 184

Today's Topics:
     Re: Trying to build a fluxgate magnetometer -- help!
     Re: Trying to build a fluxgate magnetometer -- help!
              Re: Wood in space
              Re: 'gator guards
              Re: Wood in space
      Payload Canister Investigation Update (Forwarded)
              Galileo Questions
              Re: Wood in space
     Re: Trying to build a fluxgate magnetometer -- help!
          Re: Threat to delay Shuttle launch
              Re: Wood in space
----------------------------------------------------------------------

Date: 29 Oct 89 19:30:01 GMT
From: cs.utexas.edu!mailrus!accuvax.nwu.edu!tank!ux1.cso.uiuc.edu!aries![e-mail]  (Jeff Forbes)
Subject: Re: Trying to build a fluxgate magnetometer -- help!


    NMR spectroscopists refer to their magnets in proton resonance
frequency as well as field in TESLA. A 500 MHz magnet is 11.7 T, a 60 MHz
magnet is 1.6 T, etc.

    Jeff Forbes

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

Date: 29 Oct 89 20:27:48 GMT
From: mcsun!sunic!bmc!kuling![e-mail]  (Bo Thide')
Subject: Re: Trying to build a fluxgate magnetometer -- help!

In article <[e-mail]> [e-mail] (Doug McDonald) writes:
>>>
>>>I would like to measure changes at least as small as
>>>10 gammas (.001 Gauss), and if possible, even smaller.
>>>
>>
>>?  You mean of course, nanotesla (nT), since 1954.  :-)
>
>I have been in the science business for over 20 years and have
>never heard anyone refer to magnetic fields in Tesla - everyone
>uses gauss.

I use Tesla (or, rather, nanoTesla) all the time.  But I have only
been in the science business for 17 years so I had a chance to
learn the SI system properly ... :->

Bo

   ^   Bo Thide'--------------------------------------------------------------
  | |       Swedish Institute of Space Physics, S-755 91 Uppsala, Sweden
  |I|    [In Swedish: Institutet f|r RymdFysik, Uppsalaavdelningen (IRFU)]
  |R|  Phone: [phone].  Telex: 76036 (IRFUPP S).  Fax: [phone]
 /|F|\        INTERNET: [e-mail]       UUCP: ...!uunet!sunic!irfu!bt
 ~~U~~ -----------------------------------------------------------------sm5dfw

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

Date: 26 Oct 89 14:25:52 GMT
From: cs.utexas.edu!mailrus!jarvis.csri.toronto.edu!db.toronto.edu![e-mail]  (John Hogg)
Subject: Re: Wood in space

In article <[e-mail]> [e-mail] (Will Martin) writes:
>Anyway, that started me thinking -- what
>would happen to wood exposed to space?  Consider the effects of vacuum,
>temperature, and radiation from the sun -- would wood dry up, crumble,
>and disintegrate in a matter of seconds or minutes, or would it remain
>strong enough to use for a reasonable length of time?
>
>Was any wood put on the LDEF? Maybe some of the instruments there should
>have had a nice Victorian-style mahogany housing... :-)
>
>Anyone have any ideas on this subject? Maybe we can have some nice teak
>space yachts at some future date...

I asked a similar question (``Where has wood been used on
spacecraft?'') some time ago, after reading in AW&ST that the Chinese
use oak heatshields on their return capsules.  That should answer part
of your question.  Shuttle SRBs have insulation that contains cork,
although you can debate whether it gets into ``space''.  I believe that
the Saturn V also used some cork insulation as well.

Nobody uses wood by itself in high-performance structures; various
adhesives and coatings are always applied.  A thick coat of epoxy
solves any drying problem immediately, although drying in itself is not
critically weakening.  It would also make the LEO oxidation problem
equivalent to that for any other epoxy-painted surface.  Dimensional
changes due to drying would probably be more annoying, so it might pay
to vacuum-dry the wood to zero moisture content at the very beginning.

Structurally, a wood composite can be quite respectable in most
respects, particularly in lightly-loaded situations.  (Denser materials
like aluminum can't be used effectively without an indecent amount of
cleverness, since buckling becomes the main limiting factor, and the
simple answer to buckling is to use a thicker piece.)  It has some nice
properties like strong damping as well; this matters if you don't want
your vehicle to ring like a bell each time you move something.

The main danger would seem to be decomposition due to excessive heat.
Wood will break down well before a comparable aluminum structure would
be damaged, although it might not be much worse than glass-epoxy.  (I'd
have to look that one up.)  This is compounded by the fact that wood is
a much poorer thermal conductor than aluminum.  In many cases, this is
a feature, but it does mean that close attention would have to be paid
to the design of continuously-exposed parts.

Summing up, there is no reason that an entire spacecraft structure
could not be cold-moulded from wood.  The structural performance would
in most cases be somewhat worse than that of a comparable aluminum
vehicle, and considerably worse than if exotic composites were used.
Note that exotics haven't been flown much either.

Why don't you try selling this one to SDIO?  The secret is to pitch it
properly.  Use the following buzzphrases: anisotropic cellulose-epoxy
composite laminates; proven aerospace track record; high Q-factor
(damping); low radar observables.  Perhaps Jordin Kare could help you
by pushing wood capsules for laser launching.  Then you'd also have the
environmentalists on your side; after all, who could fault a launch
system based on wood and water?
--
John Hogg            [e-mail]
Department of Computer Science, University of Toronto

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

Date: 27 Oct 89 18:25:11 GMT
From: crash!orbit!pnet51![e-mail]  (S Schaper)
Subject: Re: 'gator guards

The alligator density at the launch site was enough to put the KSC landing
strip for the shuttle out of commission (although there were other reasons as
well).

UUCP: {amdahl!bungia, uunet!rosevax, chinet, killer}!orbit!pnet51!schaper
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INET: [e-mail]

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

Date: 26 Oct 89 16:37:38 GMT
From: zephyr.ens.tek.com!tekgen!tekred![e-mail]  (Tony Ozrelic)
Subject: Re: Wood in space

It seems to me that I read (in Fine Woodworking?) that the Chinese use white
oak as an ablative heat shield on their nose cones....

tony "weekend woodbutcher" o.

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

Date: 26 Oct 89 22:51:20 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: Payload Canister Investigation Update (Forwarded)


          October 26, 1989

          Payload Canister Investigation Board:
          Statement of Activity


               Witness interviews began late Tuesday afternoon and
          concluded late Wednesday.

               Damage to the payload canister has been found to be to
          panels of the canister's lower interior starboard wall, the
          underlying internal electrical, environmental, and pneumatic
          systems, the port side canister door, and two retention fittings
          on which the test weight rested.  The canister is expected to be
          out of service a maximum of two months.  There is no apparent
          damage to the payload transporter which moves the canister.
          There is minimal damage to the test weight.

               This afternoon, in High Bay 4 of the Vehicle Assembly
          Building, the payload canister doors were individually cycled
          closed.  They closed smoothly with no unusual sounds during the
          operation.  There are no apparent warps or other defamations of
          the doors.

               Tomorrow, the canister will be transported to the KSC
          Industrial Area.   A detailed assessment of the cost to repair
          the canister will be undertaken by NASA and by McDonnell Douglas,
          the Payload Ground Operations contractor.  The repairs will be
          performed at KSC by McDonnell Douglas.

               Today, the board constructed guidelines for developing a
          test procedure to attempt to recreate the operation of the crane
          at the time of the mishap.  At this time the test is planned for
          Friday.  The board also did a status of the assigned action
          items, and discussed what format the board's final report should
          take.  The discussion among the members about findings is
          expected to begin early next week.


          George H. Diller
          Public Affairs Board Representative

          Approved for release by William G. Mahoney,
          Board Chairman

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

Date:     Thu, 26 Oct 89 15:38:31 CDT
From: Will Martin <[e-mail]>
Subject:  Galileo Questions

Thanks to Peter Yee for the posting of the STS-34 Press Kit. There's a
lot of good info in there and it answered most of my questions about
Galileo right at the start!

I do have a few minor queries:

1) I seem to recall some traffic on the SPACE Digest some months or even
years back about litium batteries in space-rated hardware. As I recall
the discussion, it seemed to be that lithium batteries were not allowed
in payloads going up in the Space Shuttle, due to the risks of their
exploding or outgassing or doing something else nasty. The Galileo probe,
however, is powered by lithium batteries. I assume nothing else would
give the long 5-year dormancy followed by a brief 75-minute spasm of glory
as the probe executes its brief mission. :-)

Am I recalling the earlier discussion correctly? If so, was the restriction
on lithium batteries only on *commercial* versions? I am assuming these probe
batteries are not "stock" off-the-shelf items but instead specially
constructed custom components designed for this mission, and thus may be made
far safer than ordinary versions. Is this the case?  If so, can anyone
describe briefly how these differ from commercial versions? Are we likely to
see a spinoff from this for very-high-reliability commercial batteries, or
very-safe versions for use in explosive atmospheres or other critical
applications?

2) This is actually much more general than just Galileo-related: the
"T-minus" countdown chart included in the press kit listed a number of
"built-in holds", such as the one at T-27 hours and so forth. Why is the
countdown constructed this way? Why build in a "hold" of 8 hours instead
of just lengthening the countdown period by 8 hours and scheduling the
actions that take place during this hold at the same relative time?
It would appear on the surface that a "hold" should always be an
exceptional condition -- something caused by a problem -- as opposed to
a regular scheduled event expected to occur at some scheduled time.
There must be a good reason for these built-in holds, but I can't figure
it out. I'd appreciate enlightenment on the subject.

3) This is purely speculative -- I've been trying to figure out some
in-flight use for the many pounds of ablative heat shield that burns off
the probe during Jupiter-atmosphere entry. The problem is that it can't
be anything consumable, like maneuvering-thruster fuel, which would be
used during the flight, because that mass has to be there to be burned
off as heat shielding when the probe enters. Also, it has to be dense
and massive and approachng homogeneous, so it will function adequately
as ablative material. So far, the only thing I've been able to think of
is densely-packed electronics embedded in some potting compound. Or
perhaps some really futuristic crystalline mass of computing circuits
based on nanotechnology? (How about an AI that takes measurements
during the flight but then dies a fiery death during the probe entry?
Shades of HAL -- what a motivation to sabotage the mission! :-)

Maybe some sort of entirely-solid-state scanning mechanism to take
detailed star-chart type images during those long lonely years of travel
between slingshot points? Any other ideas?

(I'm sure better minds than I had spent many long hours trying to come
up with some sort of productive use for that otherwise-inert and
extremely-expensive-to-ship weight; anyone from NASA care to post any
notes on what might have been proposed, if anything?

Regards, Will Martin

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

Date: 27 Oct 89 01:46:57 GMT
From: crash!orbit!pnet51![e-mail]  (S Schaper)
Subject: Re: Wood in space

Hmm, this might create yet another profitable revenue for terrestrial-class
planets to compete with O'Neal colonies and Belters.  :-)

The Volgons are coming! The Volgons are coming!

      January White sale now at K-mart...

Steve Schaper

UUCP: {amdahl!bungia, uunet!rosevax, chinet, killer}!orbit!pnet51!schaper
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INET: [e-mail]

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

Date: 29 Oct 89 17:46:31 GMT
From: cs.utexas.edu!uwm.edu!ux1.cso.uiuc.edu!aries![e-mail]  (Doug McDonald)
Subject: Re: Trying to build a fluxgate magnetometer -- help!

>>
>>I would like to measure changes at least as small as
>>10 gammas (.001 Gauss), and if possible, even smaller.
>>
>
>?  You mean of course, nanotesla (nT), since 1954.  :-)

I have been in the science business for over 20 years and have
never heard anyone refer to magnetic fields in Tesla - everyone
uses gauss. It is true that people know that someone somewhere
created a unit of magnetic field called a Tesla, but no one
remembers how many gauss are in one Tesla, and no one uses it.
Sometimes it might appear in a textbook (usually directed at
freshmen or sophmores - more advanced books use gauss).

There are lots of names of units out there that are simply not used.

(Also, I might add, a lot of people refer to actual physical
magnets, though not the fields they create, in megahertz - as
in "it's a 500 MHz magnet" meaning, of course, that the NMR
resonance frequency of protons in it would be 500 MHz." Even the
people who do this snicker a bit while doing it, however.)

Doug McDonald

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

Date: 28 Oct 89 02:03:26 GMT
From: umigw!mthvax.cs.miami.edu![e-mail]  (David Lesher)
Subject: Re: Threat to delay Shuttle launch

# Since I've never even been to Florida, I'm not sure how much of a threat
# 'gators really are, but it was an interesting point.

I remember a 'hold', maybe in the Gemini series, while they
chased a gator off the concrete flame spill chute or what ever
it is called. Boy that would have spoiled HIS day!
--
A host is a host & from coast to [e-mail]
no one will talk to a host that's close..............(305) 255-RTFM
Unless the host (that isn't close)......................pob 570-335
is busy, hung or dead....................................33257-0335

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

Date: 26 Oct 89 16:37:00 GMT
From: agate!sag4.ssl.berkeley.edu![e-mail]  (David Ray)
Subject: Re: Wood in space

In article <[e-mail]> [e-mail] (Will Martin) writes:
>  etc..
>What would happen to wood exposed to space?  Consider the effects of vacuum,
>temperature, and radiation from the sun -- would wood dry up, crumble,
>and disintegrate in a matter of seconds or minutes, or would it remain
>strong enough to use for a reasonable length of time?

   At a recent spacecraft design seminar, I leaned that a Chinese space
probe used a oak wood heat baffle for re-entry. The wood was treated
(soaked in some kind of solution) to prevent it from combusting. Wood
is actually a very good "composite fiber".
   Maybe they'll solve the shuttle tile problem by replacing them with
treated oak. Would look nice, too.
   -Dave

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

End of SPACE Digest V10 #184
*******************