Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_0/V13_052.TXT

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Subject: SPACE Digest V13 #052

SPACE Digest                                      Volume 13 : Issue 52

Today's Topics:
Radiation belts and moons [Long](was Re: Humankind's Second Off-world
              Galileo Update - 01/14/91
      Re: Metrics (was Re: Rotating Joints for Habitat)
              Barium/Lithium altazimuths
            Note about gravitational pull
           Re: Rotating Joints for Habitat
           Re: Humankind's Second Off-world Colony

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

Date:     Sun, 13 Jan 91 08:47 CDT
From: Bill Higgins-- Beam Jockey <[e-mail]>
Subject:  Radiation belts and moons [Long](was Re: Humankind's Second Off-world
Apparently-To: <[e-mail]>

Colony)
To:       [e-mail]
Original_To:  SPACE,WRBANEK


One point has been overlooked in the discussion of colonies on Ganymede.
The radiation problem there-- even within the Jovian radiation belts--
may not be so bad.  The reason is that a satellite orbiting within a
Van Allen belt leaves a "hole" in its wake.

      (( o ))
         ^  ^
         |  |
Jupiter---  -----Radiation Belts

The radiation belts consist of charged particles (like protons and
electrons) trapped in the planet's dipole magnetic field.  Consider
one such particle. It is constantly moving back and forth along lines
roughly corresponding to the parentheses above.  It spirals around
such a "magnetic line of force," heading for the north pole.  Close to
the pole it encounters a high density of field lines, slows down, and
"bounces," moving southward along the line until it gets near the
south magnetic pole, where it rebounds again.   So it oscillates from
pole to pole.  (It may eventually lose enough energy to get tired and
leave the trap.  But another particle from the Sun or a cosmic ray
will soon come in to replace it.)

Now imagine that the space around Jupiter is filled with such
particles (it is, I assure you) zipping back and forth, roughly
north-to-south, throughout a doughnut-shaped volume.

Let's introduce a moon orbiting within the Van Allen belt, in the
plane of the planet's equator.  What happens to the radiation
particles?

The ones heading northward plow into the southern hemisphere of the
satellite.  The ones heading southward are stopped by the northern
hemisphere.  As the satellite moves along in its orbit, it absorbs
radiation.  Just behind it, then, is a zone where there are no trapped
particles.  Eventually, other particles will diffuse into the "vacuum"
and fill up the void.  But there is a region for some distance behind
the moon that is swept clean of radiation.  Your Geiger counter will
click very slowly there, compared to nearby regions of Jovian space
(say, just inside the moon's orbit, or just outside it).

If the time it takes to replenish the radiation is longer than the
moon's orbital period, a toroid of low-radiation space exists all
along its orbital path.  Just behind the satellite, space will be very
clean;   further behind, say halfway around the orbit, there will be
somewhat more radiation, since there has been time to "fill in" the
void.  Send a flyby spacecraft past the planet and its radiation
counter will produce a graph something like this:


          |
          |         -----   -----       -----   -----
Radiation |        -     \ /     \     /     | |     -
Intensity |       -       v       |   |      | |      -
          |     -                  | |       \ /        -
          |   -                    | |        V           -
          |                        | |
          |_________________________________________________
                          ^         ^         ^
                          |         |         |
Where the moon was        |      Where the    |    Where the moon
half an orbit ago   -------      planet is    ----- is now

In fact, on its Saturn flyby in 1979, Pioneer 11's radiation counters
actually discovered a satellite this way.  Furthermore, according to
my trusty copy of NASA TM-82501, "Space and Planetary Environment
Criteria Guidelines for Use in Space Vehicle Development, 1982
Revision," Volume II, Saturn's rings kill radiation counts
dramatically (at least a factor of 100), there is a definite depressed
region of proton flux due to absorption by Dione, Tethys, Enceladus,
and Mimas with about 100 times less flux between about 3 and 6 Saturn
radii, and particle flux at Jupiter has similar troughs due to
Amalthea, Io, and smaller satellites 1979J1, 1979J2, and 1971J3.

For most satellites of Jupiter and Saturn, only a modest dip in the
flux seems to occur. I presume this is because the void behind the
satellite fills up pretty fast with particles.  Perhaps a
space-physics guru could comment further.  What factors govern this
filling time? (Dale Greer?  Pat Reiff?  You reading this?)

The ultimate question is this: For a chosen satellite, does the
absorption effect reduce Van Allen radiation to safe levels for
operating a habitat there?

If the moon is tide-locked, there will be a trailing hemisphere which
will see a minimum of radiation, and would be a good site for a base.
On the other hand, I would expect that prudent construction would
include using native regolith for shielding the base, just as lunar
and Martian bases would do.  On the other other hand, there is the
problem-- already discussed-- of combining cryogenic solids with
relatively hot imported equipment.  Not impossible, but certainly
eased if you need less shielding in the first place.

I still wouldn't want to operate a base deep in Jupiter's or Saturn's
radiation belts.  I'd have to overcome the radiation hazards to
spacecraft traveling to and from the base.  Bad for people and robots
alike.  And I'd be inside some mighty deep gravity wells, so delta-vee
costs would be high.  Seems to me that bases on an outer moon would be
preferred if you had to go there at all.

                        ///        Bill Higgins
   E                   ///
  |8D:O:          occc))))<))      Fermi National Accelerator Laboratory
   E                 ///
                    ///            Bitnet: [e-mail]

Bumper sticker seen on a Soyuz:    SPAN/Hepnet/Physnet: 43011::HIGGINS

    VISIT SCENIC MIR--             Internet: [e-mail]
YOUR VACATION SPOT AMONG THE STARS

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

Date: 14 Jan 91 17:44:38 GMT
From: snorkelwacker.mit.edu!usc!elroy.jpl.nasa.gov!jato!mars.jpl.nasa.gov![e-mail]  (Ron Baalke)
Subject: Galileo Update - 01/14/91


                         GALILEO STATUS REPORT
                           January 14, 1991

     The health of the Galileo spacecraft continues to be excellent.  The
spacecraft status is as follows:

     o System Power Margin - 43 watts
     o Spin Configuration - Dual Spin - cruise mode
     o Spin Rate/Sensor - 3.15 rpm/star scanner
     o Spacecraft Attitude Sun Point Angle - 2.8 degrees
       plus or minus 0.3 degree (leading)
     o Downlink telemetry rate/antenna - 1200 bps
        (uncoded)/LGA-2 (Low Gain Antenna 2)
     o General Thermal Control - all temperatures within acceptable range
     o RPM (Retro Propulsion Module) Tank Pressures - all within acceptable
       range
     o Orbiter Science- all powered off except HIC (Heavy Ion Counter), DDS
       (Dust Detector), MAG (Magnetometer), EUV (Extreme Ultraviolet
       Spectrometer) and UVS (Ultraviolet Spectrometer)
     o Probe/RRH (Radio Relay Hardware) - powered off, temperatures nominal
     o Command Loss Timer Setting - 240 hours

Today, spacecraft planned activities include:

     o Cruise science memory readouts for the EUV, MAG and DDS instruments.
     o Continued collection of UVS data.
     o A SITURN to lead the sun.
     o A downlink data rate change from 1200 bps to 40 bps
       (uncoded) consistent with link performance predictions.

No spacecraft activities are planned for tomorrow, January 15.

      ___    _____     ___
     /_ /|  /____/ \  /_ /|
     | | | |  __ \ /| | | |      Ron Baalke         | [e-mail]
  ___| | | | |__) |/  | | |___   Jet Propulsion Lab | [e-mail]
 /___| | | |  ___/    | |/__ /|  M/S 301-355        |
 |_____|/  |_|/       |_____|/   Pasadena, CA 91109 |

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

Date: 14 Jan 91 17:40:26 GMT
From: att!watmath!watserv1!utgpu!cunews!bnrgate!bwdls61.bnr.ca!bwdls58!bwdlh490![e-mail]  (Henry Troup)
Subject: Re: Metrics (was Re: Rotating Joints for Habitat)

Well, there are two separate pronunciation problems:

a) North Americans tend to the keel-o-gram rather than correct kill-o-gram
   pronunciation

b) but tend to inconsistently pronounce the road distance unit as
   k'l'o'meter - with antepenultimate stress (love that phrase!)


Henry Troup - BNR owns but does not share my opinions | The .signature is the
P.O. Box 3511, Stn. C. Ottawa, Ontario, Canada K1Y 4H7| lowest form of humour
uunet!bnrgate!hwt%bwdlh490 [e-mail] [phone] |

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

Date: 14 Jan 91 18:40:06 GMT
From: agate!bionet!uwm.edu!rpi!dali.cs.montana.edu!uakari.primate.wisc.edu!aplcen!warper.jhuapl.edu![e-mail]  (Ray Sterner)
Subject: Barium/Lithium altazimuths


      CRRES 15 Jan 1991 (UT) first of two releases.
      This is to be a small barium cloud.  Tables for two alternate
      times are given below.  From hotline information as of 1:08 pm EST.

   -------------------------  Primary release time  ----------------------

       Combined Release and Radiation Effects Satellite (CRRES)
       Marshall Space Flight Center hotline: [phone].

       Values are for a spherical earth with no atmospheric refraction.
       Distances in km, angles in degrees.  Universal time is given.

           Small barium release at 04:11:00 15 Jan 1991 UT.
           Satellite altitude = 15063.
           Sub-satellite lat, long (deg) =  17.90    97.40

          *****************************************************
          * An alternate time is 05:31:59 15 Jan 1991 UT.     *
          * Table below does NOT apply to the alternate time! *
          *****************************************************

                         City                Satellite
           City      Lat     Long      Azi      Alt     Dist

      Anchorage     61.2    149.8    115.6     16.8    18714
        Atlanta     33.8     84.4    219.6     62.4    15583
        Bermuda     32.3     65.8    250.8     46.2    16377
        Chicago     41.8     87.6    202.2     54.8    15912
       Columbus     40.0     83.0    213.5     54.8    15913
         Dallas     32.8     96.8    182.2     69.0    15363
         Denver     39.7    105.0    161.1     58.2    15756
       Edmonton     53.5    113.5    154.5     38.8    16858
        El Paso     31.8    106.4    147.4     67.3    15415
       Honolulu     21.3    157.8     82.0     16.8    18713
         London     51.5      0.0    286.9     -7.7    21341
    Los Angeles     34.0    118.3    125.6     55.7    15866
          Miami     25.8     80.2    247.3     65.0    15490
       Montreal     45.5     73.6    223.5     43.6    16539
       New York     40.7     74.0    228.4     48.2    16263
          Paris     48.8      2.3    285.7     -7.0    21265
        Phoenix     33.5    112.0    136.4     61.5    15619
    Puerto Rico     18.5     66.2    273.9     49.1    16207
 Salt Lake City     40.8    111.9    147.2     53.9    15956
  San Francisco     37.8    122.3    125.4     49.3    16197
        Seattle     47.6    122.3    137.0     41.0    16708
      St. Louis     38.7     90.3    198.7     59.7    15691
 Washington, DC     38.8     77.0    226.0     52.0    16051
       Winnipeg     50.6     96.3    181.9     45.1    16442

---------------------  Alternate release time  --------------------

       Combined Release and Radiation Effects Satellite (CRRES)
       Marshall Space Flight Center hotline: [phone].

       Values are for a spherical earth with no atmospheric refraction.
       Distances in km, angles in degrees.  Universal time is given.

           Small barium release at 05:31:59 15 Jan 1991 UT.
           Satellite altitude = 26605.
           Sub-satellite lat, long (deg) =  14.30    91.50

          *****************************************************
          * An alternate time is 04:11:00 15 Jan 1991 UT.     *
          * Table below does NOT apply to the alternate time! *
          *****************************************************

                         City                Satellite
           City      Lat     Long      Azi      Alt     Dist

      Anchorage     61.2    149.8    111.6     16.8    30566
        Atlanta     33.8     84.4    200.1     64.8    27100
        Bermuda     32.3     65.8    238.5     53.9    27616
        Chicago     41.8     87.6    188.1     56.1    27497
       Columbus     40.0     83.0    198.6     57.2    27438
         Dallas     32.8     96.8    164.1     66.5    27035
         Denver     39.7    105.0    151.3     55.7    27517
       Edmonton     53.5    113.5    147.8     38.4    28641
        El Paso     31.8    106.4    138.6     62.7    27184
       Honolulu     21.3    157.8     84.3     16.2    30631
         London     51.5      0.0    280.2     -0.9    32463
    Los Angeles     34.0    118.3    122.6     52.0    27724
          Miami     25.8     80.2    225.0     70.7    26895
       Montreal     45.5     73.6    211.6     47.9    27973
       New York     40.7     74.0    215.1     52.8    27676
          Paris     48.8      2.3    278.9      0.1    32348
        Phoenix     33.5    112.0    131.0     57.3    27436
    Puerto Rico     18.5     66.2    264.0     59.8    27315
 Salt Lake City     40.8    111.9    140.3     51.2    27770
  San Francisco     37.8    122.3    122.3     46.3    28074
        Seattle     47.6    122.3    132.0     39.4    28561
      St. Louis     38.7     90.3    182.9     60.1    27300
 Washington, DC     38.8     77.0    211.5     56.2    27493
       Winnipeg     50.6     96.3    172.1     45.7    28116


  Ray Sterner                     [e-mail]
  Johns Hopkins University        North latitude 39.16 degrees.
  Applied Physics Laboratory      West longitude 76.90 degrees.
  Laurel, MD 20723-6099

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

Date: 14 Jan 91 16:50:56 GMT
From: eagle![e-mail]  (Ronald E. Graham)
Subject: Note about gravitational pull

[This note appeared in the Cleveland Plain Dealer, 01/13/91.  It was pulled
 from wire reports.  - RG]

Measurements made in Finland during a total solar eclipse last year suggest
that the intermediate presence of one body, like the Moon, cannot partly
shadow the gravitational pull of a more distant object, like the Sun, as it
does light from such a body.

An Italian physicist, Quirino Majorana, predicted such an effect shortly
after Albert Einstein applied his relativity theory in 1916.

Majorana reported that laboratory experiments seemed to support his hypo-
thesis.  But space observations and other tests have failed to support the
idea, and it has never gained much support.

If it were proved true, however, it would have basic consequences for physics.
It has generally been believed that when two objects are aligned, gravity
from each of them combines, with no shadowing effect.

Because the Sun was low in the horizon during the Finland eclipse, its grav-
itational pull, as opposed to that of the Earth, was almost horizontal, which
was ideal for the test.

The measurements were made at three sites, using falling bodies, a water tube
580 feet long (to record changes in tilt), a borehole tiltmeter, and a highly
sensitive gravimeter.

The Finns now report that no observable effect could be seen to within
1.0e-09 parts of the force of gravity.

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

Date: 12 Jan 91 03:38:52 GMT
From: agate!bionet!uwm.edu!cs.utexas.edu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!ists!yunexus!lethe!tvcent!comspec!censor!utzoo!utgpu!cunews!cognos!geovision![e-mail]  (Gord Deinstadt)
Subject: Re: Rotating Joints for Habitat

I wonder about separating the structural function from the gas-containment
function.  In other words, erect a rigid structure with
some rotating sections, none of it airtight - then put a bag around the
whole thing.

I've been wondering about this for some time.  Has anybody studied it?
--
Gord Deinstadt  [e-mail]

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

Date: 13 Jan 91 18:58:21 GMT
From: usc!elroy.jpl.nasa.gov!sdd.hp.com!spool2.mu.edu!news.cs.indiana.edu!maytag!watmath!watdragon!watyew![e-mail]  (James Davis Nicoll)
Subject: Re: Humankind's Second Off-world Colony


    Here's an idea to handle the 'buildings warmer than the melting
point of the surface beneath them' problem: treat the surface as if it
were a fluid and design accordingly. Put floatation units on it to
keep most of the building above the surface (and it's probably a real
bad idea to put anything you really like or need in the subsurface
basement if the fluid around the subsurface rooms is water and there's
a chance of a freeze sometime). Think of the fluid as a moat :)

    If the fluid water evaporates, you might find yourself tunneling
your way to the core, though. For that matter, heated water ice on Ganymede
probably sublimes, doesn't it? Oh, well.

                            James Nicoll

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

End of SPACE Digest V13 #052
*******************