Return-path: 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/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Wed, 16 Jan 91 20:47:06 -0500 (EST) Message-ID: Precedence: junk Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Wed, 16 Jan 91 20:47:01 -0500 (EST) 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 Administrivia: Submissions to the SPACE Digest/sci.space should be mailed to space+@andrew.cmu.edu. Other mail, esp. [un]subscription requests, should be sent to space-request+@andrew.cmu.edu, or, if urgent, to tm2b+@andrew.cmu.edu ---------------------------------------------------------------------- Date: Sun, 13 Jan 91 08:47 CDT From: Bill Higgins-- Beam Jockey Subject: Radiation belts and moons [Long](was Re: Humankind's Second Off-world Apparently-To: Colony) To: SPACE+@ANDREW.CMU.EDU 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: HIGGINS@FNALB.BITNET Bumper sticker seen on a Soyuz: SPAN/Hepnet/Physnet: 43011::HIGGINS VISIT SCENIC MIR-- Internet: HIGGINS@FNALB.FNAL.GOV 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!baalke@bloom-beacon.mit.edu (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 | baalke@mars.jpl.nasa.gov ___| | | | |__) |/ | | |___ Jet Propulsion Lab | baalke@jems.jpl.nasa.gov /___| | | | ___/ | |/__ /| 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!hwt@ucbvax.Berkeley.EDU (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 HWT@BNR.CA +1 613-765-2337 | ------------------------------ 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!sterner@ucbvax.Berkeley.EDU (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: 205-544-5356. 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: 205-544-5356. 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 sterner%str.decnet@warper.jhuapl.edu 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!news@ucbvax.Berkeley.EDU (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!gd@ucbvax.Berkeley.EDU (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 gdeinstadt@geovision.UUCP ------------------------------ 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!jdnicoll@apple.com (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 *******************