Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V10_1/V10_189.TXT

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Subject: SPACE Digest V10 #189

SPACE Digest                                     Volume 10 : Issue 189

Today's Topics:
              Re: Wood in space
               News of the Week, Oct 26
             Re: PowerSat Options
             Asteroid Collisions
    Administrator Truly gives boost to reading program (Forwarded)
         Re: Mach - what does it really mean?
         Re: Mach - what does it really mean?
              Re: Wood in space
              Re: Computer Virus
----------------------------------------------------------------------

Date: 26 Oct 89 16:51:34 GMT
From: swrinde!cs.utexas.edu!mailrus!jarvis.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Wood in space

In article <[e-mail]> [e-mail] (Will Martin) writes:
>...Anyway, one of the features of the equipment hung on
>the spacesuits' belts are a number of wood-handled tools...... 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?

It will definitely last for at least a modest length of time.  The Chinese
use wooden heatshields (thick oak) on their recoverable capsules.  (They
say it works just as well as sexy aerospace materials and is much cheaper
and easier to work with.)

Eventually you'd run into trouble with cracking due to dehydration, I'd
expect.  Overall, though, wood is fairly tough stuff.

>Was any wood put on the LDEF? ...

Not that I know of.  Pity.
--
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry [e-mail]

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

Date: 26 Oct 89 18:23:07 GMT
From: frooz!cfa250![e-mail]  (Jonathan McDowell)
Subject: News of the Week, Oct 26

Jonathan's Space Report

Oct 25,1989 (no.28)
Pressure of various kinds of work means that I will be behind on
analysing data for these reports for the next few weeks...
---------------------------------------------------------------------

Atlantis/STS-34 was launched on Oct 18 and landed on Oct 23. It deployed
the Galileo probe into a Venus transfer orbit.

Viktorenko and Serebrov continue to work on the Soyuz TM-8/Mir/Progress M
complex. The D module launch has been delayed.

The fourth Block II Navstar GPS satellite was launched by Delta 6925 from
Canaveral on Oct 21.

The Czechoslovak Magion-2 satellite was released from the IK-24 magnetospheric
research satellite on Oct 3.

Kosmos-2047, launched on Oct 3, and Kosmos-2048, launched Oct 17, are
GRU photo reconnaissance satellites.

The Uosat-1 amateur radio satellite reentered on Oct 13.

(c) 1989 Jonathan McDowell

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

Date: 27 Oct 89 01:46:49 GMT
From: crash!orbit!pnet51![e-mail]  (S Schaper)
Subject: Re: PowerSat Options

Because the energy density is so low, aht is why they have to have large
antenna farms to collect the energy, I don't think that there is any danger to
birds flying through.  I probably wouldn't want to build a house  at that
location, though. But that doesn't mean that it might not be safe. SPS has
three main problems that I know of. 1) Politics - lack of vision, 2)Getting
them built, we know how, but then we know how to build shuttles, too. 3), and
in my mind most important :-) , a constellation of solar power sats is said to
seriously degrade `seeing' for professional and amatuer astronomers.

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

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

Date: 27 Oct 89 15:48:45 GMT
From: frooz![e-mail]  (Steve Willner)
Subject: Asteroid Collisions

As part of an excellent article <[e-mail]> on possible uses and
dangers of Earth-approaching asteroids, [e-mail] (Nick Szabo)
asks:
>  Question: if two asteroids collide at high speed, do they shatter,
>  vaporize, or remain for the most part intact?

There is a partial observational answer.  The IRAS satellite discovered
several "dust belts" above and below the ecliptic.  These are attributed
to dust generated by asteroid collisions.

This observation doesn't give the whole answer, though.  First of all,
it applies only to main belt asteroids, and the Earth-approachers may
be different.  Second, the shattering may happen only for some, not
all, collisions and/or some, not all, asteroid types.  (In particular,
I would not expect metallic asteroids to shatter.  I don't think the
composition of the dust belts is known, though.)  And third, even where
shattering occurs, it may not affect all of the original mass.  (I.e.,
largely intact chunks could go flying off as well as the dust.)  Or
finally, of course, the explanation for the observed dust belts might
simply be wrong (though it certainly seems plausible enough to me).

In spite of these cautions (and maybe others I haven't thought of), it
seems fair to say that at least some of the time, collisions must result
in substantial shattering.
-------------------------------------------------------------------------
Steve Willner            Phone [phone]         Bitnet:   willner@cfa
60 Garden St.            FTS:      830-7123           UUCP:   willner@cfa
Cambridge, MA 02138 USA                 Internet: [e-mail]

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

Date: 27 Oct 89 21:00:12 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: Administrator Truly gives boost to reading program (Forwarded)

[Not strictly space, just your space agency working on the broader picture.-PEY]

Jeff Vincent
Headquarters, Washington, D.C.                   October 27, 1989


RELEASE:  89-166

ADMINISTRATOR TRULY GIVES BOOST TO READING PROGRAM


     NASA Administrator Richard H. Truly took his launch skills
to an elementary school today and personally helped a new reading
program get off the ground.  It was a successful mission.

     Meeting with about 340 students at the Rock Creek Forest
Elementary School, Montgomery County, Md., Admiral Truly helped
initiate the "Launch into a Good Book" program, which is designed
to encourage reading among elementary school children.  The
program features audio cassettes with prominent people reading
book passages.  The students can read along and practice their
skills.

     Admiral Truly presented the students with an audio tape on
which he read a passage from "Album of Spaceflight" by Tom
McGowen.  He also spoke briefly with them about the importance of
reading and how it is an essential skill for achieving their
goals, including those who aspire to space travel.

     Just yesterday, at a speech to the National Press Club,
Admiral Truly said:  "There is a new determination across our
land to improve our educational system."  He said there are
certain themes that are particularly effective in reaching
children.  "Ghosts can do it, dinosaurs can do it, and space can
do it.  I predict that no other benefit from our future space
endeavors will loom so large."

     The NASA Administrator also participated in the President's
recent education summit with the nation's governors in
Charlottesville, Va.

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

Date: 26 Oct 89 16:14:49 GMT
From: skipper![e-mail]  (Mary Shafer)
Subject: Re: Mach - what does it really mean?

In article <[e-mail]> [e-mail] (Kenneth Van Wyk) writes:

   In article Mach - what does it really mean? of 25 Oct 89 19:49:22 GMT
   [e-mail] (Chris Jones) writes:

   > Mach 1 is the speed of sound (under ambient conditions,
   > I would guess).  I understand the usefulness of saying that something
   > is going more or less than the speed of sound, since aerodynamic
   > characteristics change passing through that speed, but hearing that
   > the shuttle enters the atmosphere at, say, Mach 24 is so much hooey in
   > my opinion.  What does it mean when I hear some NASA spokesperson say
   > that?

   Well, it's been a few years since I took Thermodynamics (my degree is
   in M.E.), but...  "Mach 1" indeed means the speed of sound and yes,
   the speed of sound varies with temperature, pressure, etc.  However,
   it's not impossible that "they" are referring to N times the speed of
   sound at Standard Atmospheric Conditions.  In other words, if the
   speed of sound is 700 mph at standard atmosphere, and the shuttle is
                                ^^^^^^^^
I think you mean sea level

   doing 7000 mph, then they might (incorrectly) refer to this as "Mach
   7".

We're smarter than that.  :-)

   Of course, this wouldn't be as accurate as saying N m/sec or some
   other speed relative to the earth's surface, since it wouldn't count
   for the fact that the speed of sound is *significantly* different at
   these very high altitudes.

We've noticed.

   But, then, perhaps they actually mean
   "Mach N" literally, in which case they should be supplying local
   atmospheric conditions along with "Mach N" so that viewers can take
   out their HP calculators and figure out the speed of sound under those
   conditions...  :-)

The Standard Atmosphere takes care of this problem.  If you know the
altitude (pressure altitude, corrected for temperature) then you know
density, speed of sound, etc.  The Shuttle air data is all Standard
Atmosphere.  So instead of your HP you get out your bright yellow 1966
Standard Atmosphere and discover that at 373,685 ft at 60 deg North in
January, for example, the speed of sound is 1165.2 ft/sec.

The Standard Atmosphere is really quite accurate.  The tapeline
altitude (from radar) and the pressure altitude agree quite well
during the Shuttle flights.

The Standard Atmosphere is so standard (sorry!) that it probably
doesn't get explained.  The theory is probably that if you don't know
about it, you don't care, and if you do know about it, you don't need
an explanation.



Extra information because I don't have nearly enough lines for this
to get sent follows:

The Mach number is really about 24 when it first enters the
atmosphere.  The stability and control derivatives, particularly
lateral-directional, are functions of Mach number, for example.
Actually the longitudinal derivatives are usually functions of angle
of attack, but angle of attack ties into Mach through the lift
coefficient, although it's not linear.  I can't remember if this is
true for the high Mach numbers for the Shuttle and I can't find the
papers right now.  If you can't live without knowing, let me know and
I'll keep searching to give you a citation.

Another document of interest is NASA Reference Publication 1046,
"Measurement of Aircraft Speed and Altitude" by William Gracey, 1980.
However the Standard Atmosphere tables in this only go up to 100,000 ft.

--
Mary Shafer   [e-mail]  ames!elxsi.dfrf.nasa.gov!shafer
         NASA Ames-Dryden Flight Research Facility, Edwards, CA
                    Of course I don't speak for NASA







--
Mary Shafer   [e-mail]  ames!elxsi.dfrf.nasa.gov!shafer
         NASA Ames-Dryden Flight Research Facility, Edwards, CA
                    Of course I don't speak for NASA

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

Date: 26 Oct 89 16:53:12 GMT
From: agate!sag4.ssl.berkeley.edu![e-mail]  (David Ray)
Subject: Re: Mach - what does it really mean?

In article Mach - what does it really mean? of 25 Oct 89 19:49:22 GMT
[e-mail] (Chris Jones) writes:
>
> Mach 1 is the speed of sound (under ambient conditions,
> I would guess).  I understand the usefulness of saying that something
> is going more or less than the speed of sound, since aerodynamic
> characteristics change passing through that speed, but hearing that
> the shuttle enters the atmosphere at, say, Mach 24 is so much hooey in
> my opinion.  What does it mean when I hear some NASA spokesperson say
> that?

Good question, in other words, why talk about speed in terms of Mach
numbers instead of actual distance/second?

My guess is that the Mach number tells the propulsion experts what kind
of mathematical model to use when calculating maneuvers. The effects of
atmospheric drag, lift, etc., are profoundly affected by Mach number more
than distance per second, and as a result different models and calculations
are used for atmospheric/orbital maneuvers.

-Dave

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

Date: 26 Oct 89 21:41:10 GMT
From: swrinde!gem.mps.ohio-state.edu!ginosko!shadooby!mailrus!jarvis.csri.toronto.edu!db.toronto.edu![e-mail]  (John Hogg)
Subject: Re: Wood in space

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>>what would happen to wood exposed to space?
>
>It will definitely last for at least a modest length of time.  The Chinese
>use wooden heatshields (thick oak) on their recoverable capsules.  (They
>say it works just as well as sexy aerospace materials and is much cheaper
>and easier to work with.)
>
>Eventually you'd run into trouble with cracking due to dehydration, I'd
>expect.  Overall, though, wood is fairly tough stuff.

This shouldn't be a problem if proper construction techniques are used.
First, use small pieces of wood.  (In fact, almost any reasonable
application will involve laminated veneers.)  Radial cracks appear in
drying wood due to tangential contraction being greater than radial
contraction.  This is minimized if the dimensions are small.  Secondly,
dry it right out to begin with, and don't let it reabsorb moisture
before launch.  (I.e., coat it with the same epoxy used in lamination.)

A lot of furniture cracking is not due so much to low humidity as to
cyclic humidity.  When the wood absorbs moisture, it swells, comes up
against some restraining limit, and crushes slightly.  This sets it up
for a crack the next time that the humidity drops again, and it
shrinks.  (And this, incidentally, is the main reason that hammer heads
loosen over time:  the handle has been exposed to moisture or high
humidity, and has been crushed by the head.)

Leaving aside the protective coating, a piece of wood in space is
absolutely, positively guaranteed not to absorb moisture.  If it starts
out dry, it will stay that way.  Cracking will not be an issue.  And
finally, in many applications, minor cracking along the grain is not
particularly serious anyway, although it may let in undesirable things
(like bugs, moisture, or monatomic oxygen.)  Take a close look at the
next large wooden mast you see.  If it's not built up, it's cracked.

Another problem that might arise, though, is outgassing of adhesives.
Again, epoxy is *probably* OK, once thoroughly cured.  But don't build
your imperial battlecruiser out of lumberyard plywood---the
formaldehyde adhesive will not agree with the space cadets living
inside.

Wood is nice stuff.  Don't underrate it.
--
John Hogg            [e-mail]
Department of Computer Science, University of Toronto

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

Date: 26 Oct 89 17:40:49 GMT
From: lightsabre![e-mail]  (Rick Kwan)
Subject: Re: Computer Virus

In article <[e-mail]> [e-mail] (Ron Baalke) writes:
>
>
>I just hope the new computer that they are replacing on the Space Shuttle
>is not infected with the "Friday the 13th" computer virus......

When I first read this, I was infected by a simultaneous giggle and
a shudder.

As I recall, the Command and Data Systems (CDS) computer(s) on Magellan
and Galileo are rad-hard, CMOS RCA 1802 chips.  There was talk at the
time (about 4 years ago) about moving to 8086-type processors
manufactured by Harris (again, rad-hard requirements).

Of course, this would make it really easy to use IBM PCs, running
MS-DOS, to do development.  Given larger memories coming, and standard
tools to play with, one could imagine writing routines in "C" and doing
final unit testing of the code on the PC, taking the resulting
binaries, and integrating it into the spacecraft computer.

Now, of course, we couldn't possibly expect a virus to show up in a
future interplanetary/interstellar CDS, and go forth to infect the
universe... could we?  I mean... the thought of such contamination...

A more serious question:  what will be used for computing power on such
probes in the near future?  Is it Harris or what?

    Rick Kwan (aka Obi-Kwan Kenobi)
    Sun Microsystems - Intercontinental Operations
    [e-mail] or [e-mail]

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

End of SPACE Digest V10 #189
*******************