Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_7/V13_705.TXT

Internet Message Format | 1991-06-25 | 19KB

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/McNifue00WBwIABU4Z>;
          Tue, 25 Jun 91 03:04:26 -0400 (EDT)
Message-ID: <YcNifmi00WBwMA=[e-mail]>
Precedence: junk
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Tue, 25 Jun 91 03:04:19 -0400 (EDT)
Subject: SPACE Digest V13 #705

SPACE Digest                                     Volume 13 : Issue 705

Today's Topics:
            Re: Beanstalk analysis reprise
              Re: Fermi Paradox
           Mars Observer Left without me !!
              Re: SPACE Digest V13 #602
               Aurora observed
            Freedom: I'm not dead!

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: 5 Jun 91 19:22:17 GMT
From: ssc-vax!bcsaic!hsvaic![e-mail]  (Dani Eder)
Subject: Re: Beanstalk analysis reprise

In article <[e-mail]> [e-mail] (Walter Dnes    ) writes:
>[e-mail] (Ron Carter) writes:
>
>     I get to play the devil's advocate again. I don't like to
>destroy people's dreams, but a reality check is in order here.
>Your calculations seem to be based on an airless earth, i.e a
>good vacuum. Don't forget that we have an atmosphere. I briefly
>considered cross-posting this followup to sci.geo.meteorology,
>but decided not to since it's all in support of a theoretical
>space discussion. Some questions to consider...
>     1) You've allowed for longitudinal forces. What about
>perpendicular forces ? What happens when the beanstalk gets hit
>by a 100 km/h (60 mph) wind ? How about a 250 km/h (150 mph)
>jetstream somewhere in the stratosphere ? Can you supply some
>typical "Asurf" values along with the taper as a function of
>height. I work in the Atmospheric Environment Service, (Canada's
>weather service) in a unit that calculates meteorological
>parameters for construction. Just down the hall from me, our
>industrial meteorologist does recommendations for CSA-S37, the
>design standard for antenna towers in Canada. I'd like to ask
>her to calculate the wind loading on the lowest (and thinnest)
>portion of the beanstalk.

To minimize the cost of a beanstalk, you would not design it
to hang all the way down to the ground.  There is a compromise
design which builds up from the ground using compressive structures
and down from GEO using tensile structures, having their tips
connected but not transmitting large forces across the connection.

I have done a conceptual design for a 10 km tower using existing
graphite/epoxy, with standard structural allowables and allowing
for a Mach 1 peak wind at 10km altitude (at jet stream altitude),
tapering down to 150 mph peak wind at ground level.  The numbers
come out not too bad.  Above 10 km, the lower pressure dominates
any conceivable wind speed (I assume no upper atmosphere winds
exceed Mach 1), and the 'scale height', the height over which
the cross sectional area of the structure changes by a factor
of e, increases towards the limit of the material, which is
10's of km for graphite/epoxy.  If we limit the area ratio of
the tower portion to 300, then we end up with a tower on the
order of 60 km tall (this may be off by as much as a factor of
2, since I have not gone and done a detailed structural analysis)

>     3) Surface temperatures at the equator can hit 40C to 50C.
>You can expect -40C to -50C up in the atmosphere, and some
>utterly farcical values (both hot and cold) in the vacuum of
>space. How will your materials react to this gradient ? How will
>the outer-space portion of the beanstalk react to extreme diurnal
>cycles (day/night) in a vacuum ?

The CTE of graphite is -0.5E-6/K.  So if the fiber goes from
200K (on the night side of the Earth you are still illuminated by
the IR of the Earth itself, to 350K (a blackbody will get to
390K maximum in space at 1 AU, use a coating that make it not
black), then you will expect a contraction of 75ppm, over a
distance of 35000 km, or 2.6 km contraction.  I suggest you
install a reel meachanism at the bottom end to take up the slack.

Note that the upper portion of the tether is thick enough to
carry multi-layer insulation, and would have thermal mass, and
that the entire tether does not go into shadow except at the
equinoxes, and even then, the tether will emerge from shadow over
a period of 45 minutes for the upper half (where the emergence
is fastest).  This means the typical excursions will be less than
a few km, and the peak contraction rates will be on the order
of 1 km/hr.

>     5) What about charged particles in the van Allen belts
>"doping" the crystalline structure of the beanstalk ?
>     Questions 4 an 5 are important because you need the great
>strength of a pure "whisker". Chemical impurities and crystal
>irregularities will decrease the strength to the breaking point.

A structure that large will absorb the van Allen belts.  There
is only on the order of 1 kg of stuff in the Van allen belts.

A beanstalk has enough cross section that the material in the
van-allen belts will be absorbed.  Because of meteoroid and
debris hazards, you will design the beanstalk with multiple
strands crosslinked periodically, so that if a particular
strand is cut for any reason you can stand the loss, then go
in and replace the section of missing strand.  A recommended
cross-link interval is 10 km, and a minimal design should have
6 strands spaced more than the width of the largest piece of
orbital hardware, so that in the worst case (for a hexagonal
arrangement of strands) , no more than 2 strands get cut.  If
a 100 m space station is the largets object, then space the
strands at least that far apart.

Modular beanstalk design also allows incremental upgrading
as better materials become available.  With today's materials,
about half a beanstalk could be built with a tolerable taper
factor.  As stronger materials get developed, or simply for
scheduled replacement if aging is a worry, you go through and
replace one strand section at a time.

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

Date: 31 May 91 18:34:51 GMT
From: ssc-vax!bcsaic!hsvaic![e-mail]  (Dani Eder)
Subject: Re: Fermi Paradox

In article <[e-mail]> [e-mail] (Frank Crary) writes:
>My second objection is the speed at which a civilization is assumed to expand.
>While the actual exploration crafts could have spread all over the galaxy, even
>at 0.001c and in only 500 million years, what the colonies would do is a
>totally different issue. At the speed I guessed at, travel between stars would
>take roughly 5000 years (at approximately 5 light years between stars.) But
>how long would it take a new colony to settle an entire new world, grow to the
>point where people want to leave it (and form a new colony) and have developed
>the industrial base to support an interstellar colonization effort? Even if
>they worked as hard as they could at it, I suspect it would take at least a
>few thousand years. In fact, however, these colonists might easily get
>distracted. If they suffered a civil war/interstellar war/collapse of
>government the above process could be set back a great deal. In short, I feel

This is much too slow, because it is thinking bounded by the rocket
propulsion paradigm.  Let us consider an alternate approach:

INTERSTELLAR FAX MACHINES

(following are logical steps in an argument, not the order of
steps in carrying out the mission)

Step 1: Send a small (order of a ton) robotic probe to another star
(alpha Centauri will serve as an example).  Using nuclear-electric
propulsion at a specific impulse of 20,000 s (exhaust velocity of
200 km/s), a mass ratio of 5, one stage to boost and one stage to
de-boost at the destination, you get an acceleration time of 1 year,
final speed of 321 km/s (0.001c), coast time of 4000 years, and
deceleration time of 1 year.

Step 2: The robotic probe using local asteroidal material builds
copies of itself, which eventually build (a) a receiving array, and
(b) an atom-placing machine based on scanning-tunneling microscope
and related technologies

The receiving array is located about 1000 AU behind the star, and
uses the gravity of the star to focus incoming signals.  The star
then acts as a gravitational lens.

Step 3: Set up a transmitting array somewhere near the Sun (within
a few hundred AU.  The transmitting array consists of a 10^6 x 10^6
array of emitters spaced 10m apart, emitting in the optical at a
total rate of 10^12 Hz per emitter, for a total data rate of 10^24
bits/sec.  The receive array needs detectors spaced 5 cm apart, giving
a receive array size of 50 km square.  If the array areal thickness is
1 m (allowing for power supply, etc.), then the total mass of the
receiver is 2.5E9 tons at a density of 1000 kg/m^3.  If the
robot doubling time is 1 year, then the time to get the array
built at the receiver end is 32 years.

Step 4: Take a human and read out atom by atom the configuration
(using STM techniques).  Allowing 10 bits per atom to specify
element, isotope, and bonding state, this requires around 10E29 bits
(with no data compression).  At the aforementioned data rate,
it would take a day to send the specification for a person.

Step 5: If we have developed human-intelligence level computers,
it sould take on the order of 1E16 bits to specify the equivalent
of the synapse connection stengths of a human brain.  At the 1E24
Hz data rate, the equivalent of the world's population can be
sent in one minute.

Step 6: If we use data compression, it should be possible to reduce
the time to specify a human to 1/100 of a day.  For example, water
molecules make up 70% of the body, and they would probably not have
to be specified at all beyond providing the right number density
in a particular region of a cell.  The bones have calcium carbonate
crystals which can be described by the size, position, and orientation
of the crystal rather than listing the atoms.  At this rate you
can send 36,000 people per year through the fax machine.

Step 7: The human-assemblers should not be any less efficient than
human themselves are in assembling themselves.  A human consumes on
the order of 20 tons of food to age 18.  36000 people would then require
720,000 tons of atom-placing machines, which is negligible compared
to the receive array mass.

Step 8: There is enough room to easily place 1000 transmit arrays
in solar vicinity (if spaced in a ring 150 AU in radius, they would
be 1 AU apart.  Each array is about the diameter of the Earth.  The
total mass of the transmit arrays would be about that of a large
asteroid (400 km diamteter), so there is plenty of mass to use to
build such a thing.  With 1000 transmit arrays, 36,000,000 people can
be sent per year, or the entire population of the Earth in 150
years.

Step 9: Thus, given the ability to manipulate matter at the atomic
scale, using refinements of the STM technology at hand, and given
propulsion no better than nuclear-electric that is within 20 years
of today's technology, we can move the entire population of the
Earth to alpha centauri in 1.5 centuries, which is suely sufficient
to then propagate to the next star.

Step 10: Given a high-speed robotic probe (3%c), and assuming that
a human crew of 1 million is sufficient to manage the construction
of the next generation of probe, the cycle time is

    Probe travel time        150 years
    Replication/build receiver    32 years
    Send 1E6 people            28 years
    Build probe             4 years
    -----------------------------------------
    Total cycle time        214 years

    Distance        4.3 light years

    Average velocity    =0.02c

Time to fill galaxy from Earth (max=70,000 LY) = 3.5 million years

Conclusion: The Fermi Paradox is very much with us.

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

Date: 6 Jun 91 18:15:21 GMT
From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!sdd.hp.com!elroy.jpl.nasa.gov!jpl-devvax!beowulf![e-mail]  (Carlos Carrion)
Subject: Mars Observer Left without me !!

[e-mail] (Steve Jenkins) writes:
>[e-mail] (Don Allen) writes:
>>...taken  by Viking 1 in 1976.  Hoagland believes the Mars  observer
>>spacecraft  was  deployed  by the  Space  Shuttle  "Atlantis"  on
>>mission STS-38.
>
>Wow!  I guess we better get busy with the Mars Observer telemetry
>system.  It's not scheduled for ground testing until later this year.
>
    Wait Up!!  I've only just released the Mars Orbit Insertion Sequence
to the Flight Team, and MO has been launched already (and by the Shuttle!) ??
Quick, start up the VTL!!


carlos.

Ever feel like the whole world is a tuxedo and you're a pair of brown shoes?
      ...ames!elroy!jpl-devvax!{beowulf|pituco}!carlos

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

Date:         Thu, 06 Jun 91 17:47:46 EDT
From: Tom McWilliams <[e-mail]>
Subject:      Re: SPACE Digest V13 #602

Re: Aurora

Did anyone else see the incredible aurora display the night of June 4/5?

Wow!!!!! About 80-90% of our sky was covered for at least 4 hours (I had to
go to bed).  At one point the birds started waking up, apparently since
it was about as bright as early dawn-light.

I had gone out to a large field near my house to scope Sag. and Scor.
since we get few nights of very good seeing.  This night was really clear,
to the point of actually seeing the Milky Way (unusual 5 miles from Lansing)
(Lat. about 45%)

Good thing I chose southern constellations, as that was all I could see
after about 1:30a.m.

It started around midnight, with a strange glow across the northern sky,
about 10 degrees above the horizon.  I looked later, and it had split in two,
the lower one with changing rays and uneven edges.  Later the rays had
extended up to U. Major (about zenith at that time), and covered about 100
degrees of the horizon.  Within another hour, the rays were coming from all
directions and converging in an area about 10 degrees south of zenith.
As I watched, different areas would suddenly increase in brightness relative
to the other areas.  The best description that I can think of is a giant
plasma ball (you know, those things in spencers gifts).  It seemed like
the whole sky was intermittently pulsating, but it was easiest to see
where it all converged.  Sometimes the pulsations seemed to move vertically
along the rays.  And sometimes it seemed like really strong heat-lightning.
Sure wish I'd had a camera.

The center areas of the convegence point kept changing shape, too.  At this
point, the entire north side of the sky was a sheet of light.  No stars were
visible, and there were scintillating bands that seemed to flicker like a
distant Drive-in movie screen.  It was mostly greenish-white, but the
brightenings in the center were a deeper green,
and my boss saw some red light, about 20 miles further from the city.

At about 2:30 I got cold and tired and headed for home.  My house-mates
had things like "uh" to say when I asked if they wanted to see it. (losers)

Just before I went to bed, around 3:00, it had changed from greenish-white to
bluish-white, and instead of a wall of light in all directions, there were
3 or 4 big twisty rays that still converged near Zenith.  If you watched the
convergence point, all the rays would suddenly drift to to east, making
the illusion of clouds very strong, except for Vega shining through!  As they
drifted east, the east-most areas would fade, and other places on the western
side would increase in brightness, until the whole thing had changed shape,
and it would start again.

I've never seen anything even close to this!  No -one at the Physics-
Astronomy Dept. where I work had seen it like this, either, except for
Debbie, when she lived in Alaska.

On of my co-workers, who had been doing solar observations for a while,
reported a particularly large sunspot that formed recently, and very
strong magnetic events associated with it are probably the cause of said
aurora.  I'll repost if I hear anything interesting.

Since I saw lights to OUR south, I'm assuming they were quite widespread.

Anyone else see this the night of June 4/5, Tue/Wed?
June 5/6 had a few rays, very transitory (that I saw), but maybe you saw
more?

Tommy Mac
Acknowledge-To: <18084TM@MSU>

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

Date: 6 Jun 91 22:13:58 GMT
From: cis.ohio-state.edu!magnus.acs.ohio-state.edu![e-mail]  (Earl W Phillips)
Subject: Aurora observed



Right here in Columbus, Oh. (Lat:40.1178, Long:83.0838). Last night,
UT 6/6/91. The show lasted roughly 45 minutes. It began as a line
along the horizon, stretching about 15 degrees either direction E/W,
with rays climbing up about 20 degrees from it. There were brilliant
reds, oranges, and less bright bluish/greens. At times, white rays
were observed almost as bright as an auto-dealer's searchlight! The
curtain would at times seem solid, then break up into rays, then
almost disappear, then come back with a vengeance w/many colors. A
beautiful display !! Of course, I did not bring my camera !! You can
bet I will tonite !! Since I have reports from a couple of my
students that they some some "shimmering colors" for about 5 minutes
in the northern sky night before last, chances are good they'll be
around again tonite, especially in light of the recently reported
new major flare. I'll keep ya posted !!

*****************************************************************
*                                    | ====@====      ///////// *
* [e-mail]|     ``________//         *
*                                    |       `------'           *
*                 -JR-               | Space;........the final  *
*                                    | frontier...............  *
*****************************************************************

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

Date: 6 Jun 91 23:30:16 GMT
From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!mips!pacbell.com!iggy.GW.Vitalink.COM!widener!hela![e-mail]  (Allen W. Sherzer)
Subject: Freedom: I'm not dead!


The House just voted 240 to 173 to adopt the Chapman amendment to freeze
NASA funding and restore funding to Space Station Freedom.

  Allen

--
+---------------------------------------------------------------------------+
|Allen W. Sherzer |   DETROIT: Where the weak are killed and eaten.         |
|   [e-mail]   |                                                         |
+---------------------------------------------------------------------------+

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

End of SPACE Digest V13 #705
*******************