Date: Thu, 6 Aug 92 05:07:07 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V15 #078 To: Space Digest Readers Precedence: bulk Space Digest Thu, 6 Aug 92 Volume 15 : Issue 078 Today's Topics: Meteor Soaks Datona FL NASA Tools Whats wrong with this CIRCUIT (was: Tethered Satellites) (2 msgs) Welcome to the Space Digest!! Please send your messages to "space@isu.isunet.edu", and (un)subscription requests of the form "Subscribe Space " to one of these addresses: listserv@uga (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle (THENET), or space-REQUEST@isu.isunet.edu (Internet). ---------------------------------------------------------------------- Date: 6 Aug 92 01:20:43 GMT From: "James T. Green" Subject: Meteor Soaks Datona FL Newsgroups: sci.space In response to those who've asked for references: All I know is that KSBY-tv Channel 6 in San Luis Obispo reported it as their closing story that afternoon. They didn't cite any references, but I suppose they didn't make it up. The announcer did say that it had been thought to have been a landslide, but someone had determined it was a 1-meter meteor. If anyone hears any more on this, please post it. I suppose if it was thought to be a meteor, it'll show up somewhere else in the media. Perhaps someone in the Datona FL area might have heard it in their local media? Take if for what it's worth... :-) /~~~(-: James T. Green :-)~~~~(-: jgreen@eros.calpoly.edu :-)~~~\ | | | M y K a r m a r a n o v e r m y D o g m a ! | ------------------------------ Date: Thu, 6 Aug 1992 01:39:22 GMT From: Edmund Hack Subject: NASA Tools Newsgroups: sci.space In article <9208051253.AA16702@cmr.ncsl.nist.gov> roberts@CMR.NCSL.NIST.GOV (John Roberts) writes: > >-From: Bruce_Dunn@mindlink.bc.ca (Bruce Dunn) [munch]> >The Shuttle has all sorts of nifty tools stowed away, that they never take out >unless they really need them. I don't know if they have a sledgehammer, but >I'm sure they have a hammer of some kind. To the above tools, add pliers, >a couple of screwdrivers, an adjustable wrench, and some grey tape (duct tape), Actually, they have Gaffer's tape and not duct tape. Gaffer's tape is used in film production (hence its name) since it has the desireable quality of not leaving any adhesive residue behing when you remove it. It has the undesireable quality of costing a _lot_ more. (about $25 US in single rolls). My brother uses it by the yard when putting a light on the wall on location shoots. It is very nice stuff.... From a sign in my cubicle: "Duct Tape is The Force. It has a dark side and a light side, and it holds the universe together." -- | Edmund Hack - Lockheed Engineering & Sciences Co. - Houston, TX | hack@aio.jsc.nasa.gov SpokesPersonp(Me,or(NASA,LESC)) = NIL | **** Papoon for President! You Know He's Not Insane!! **** ------------------------------ Date: 6 Aug 92 00:34:32 GMT From: "John W. Cobb" Subject: Whats wrong with this CIRCUIT (was: Tethered Satellites) Newsgroups: sci.space,sci.physics In article , srobiner@pollux.usc.edu (Steven Robiner) writes: [PRevious poster] |>>|>Excuse me, but isn't something missing from this "Tethered Satellite" |>>|>experiment? The shuttle is at one end, and the satellite is at the |>>|>other, right? But that's an open circuit, so where's the load |>>|>joining the ends of this 'generator.'? |>>|> |> [COBB] |> [... stuff deleted ] |>>of electrons, it will shed them when its potential compared to the |>>local plasma is higher than the work function for the shuttle surfaces. |>>So now you have the "infused" electrons into the flux tube that contains |>>the shuttle. Eventually normal plasma-plasma and plasma-neutral interactions |>>will allow the electron to move back to its original flux tube. This however |>>may take some time. So the circuit is really completed in the same sense |>>that grounded circuits are completed, except here we don't have a good ground |> [Robiner] |>But in space, the plasma is not a great conductor, This is true when compared to completely ionized plasmas, but it is still a helluva lot better than styrofoam, or even water. Imagin what the resistivity is between two points located a few miles apart in water. It's not as large as you might expect because the current can take so many different paths. The real inhibitor is the magnetic field. It traps the particles in that it doesn't allow motion perpendicular to the field. |> and in fact, moving electrons |>should be repelled from moving against the magnetic field in a direction |>opposite from the induced current in the tether, right. No. electrons have trouble moving against an ELECTRIC field. charged particles spiral around magnetic fields until they drift away either collisionally or otherwise. Remember the geomtry. The shuttle's (and tether's) velocity is perpendicular to the magnetic field. The induced electric field is perpendicular to both. The current in the tether may be produced 1 of 2 ways (I'm not sure which it is. Either 1) It is a VXB effect. The tether is moving through space at a velocity V. In the frame of the copper string, the electric field is zero. transforming to the lab frame, you find an electric field across the leads. or 2) There exists a static potential drop across the flux tubes at the different altitudes. This potential drop is maintained by the flux of solar wind particles that fall into the polar regions and get mirror trapped in the magnetosphere. If the case is 1) then the EMF is caused by the motion, so after the tether passes, the electrons that are now higher do not see any static electric field preventing them from diffusing back to their original altitude. All they have to do is figure out how to move perpendicular to the magnetic field. This can occur from particle drifts or from diffusion. If the case is 2) then the electrons stay in the higher orbit. That is you are really tapping an energy source, the electrostatic energy stored in the magento-sphere. This is the ionospheric "Free lunch" principle equivalent to getting energy from thermal gradients in geothermal or OTEC (Ocean Thermal Energy Conversion) schemes. Except here you substitute Electrostatic potential for Temperature. |> I mean, just because |>the electrons aren't in a wire shouldn't mean that they aren't affected |> |>So how will the current manage to travel back up to the satellite? |> When I used to work with an experimentalist I asked him about a similar question. The problem had to do with fusion machines where high energy ion beams are injected into the vacuum vessel. I asked where do the neutralizing electrons come from. His answer was that in general electrons are so light and so loosely bound to metals that it was always easy to draw them off of the surface without any real thought. In fact sometimes it is too easy. That is why you can have problems with arcing and breakdown. So the electrons will just stream off of the shuttle rather easily. Now here's an interesting thought though. What about the effects of tether power supplies during docking exercise. You need to match up your potentials rather accurately or you will get NASA version of the "wool socks on the carpet" treatment john w. cobb jwc@fusion.ph.utexas.edu ------------------------------ Date: Thu, 6 Aug 1992 03:25:01 GMT From: Henry Spencer Subject: Whats wrong with this CIRCUIT (was: Tethered Satellites) Newsgroups: sci.space In article <77226@ut-emx.uucp> johncobb@ut-emx.cc.utexas.edu (John W. Cobb) writes: >... His answer was that in general electrons >are so light and so loosely bound to metals that it was always easy to >draw them off of the surface without any real thought... >So the electrons will just stream off of the shuttle rather easily. Except that the shuttle orbiter doesn't actually have very much exposed metal! This is why the TSS payload includes a set of electron guns that stay with the shuttle. Bear in mind, too, that this whole setup is strictly experimental, not optimized for any substantial power production. -- There is nothing wrong with making | Henry Spencer @ U of Toronto Zoology mistakes, but... make *new* ones. -D.Sim| henry@zoo.toronto.edu utzoo!henry ------------------------------ End of Space Digest Volume 15 : Issue 078 ------------------------------